Darkside Motorcycle Setup

darksideHave you ever heard of the darkside setup for motorcycles? The picture on the left here sort of explains it all, except for the why and I’ll handle that. Basically it’s an automobile tire on the rear of a motorcycle. On the surface it looks pretty stupid to do but Darksiders are adamant that their setup is the best. Why would it be the best?


A rear tire for my motorcycle runs pretty close to 300 dollars retail although it can be had for about 220 bucks at discount houses. A car tire with the same rating would be around a hundred bucks or a bit more. So that’s a savings right off. The motorcycle tire for my bike (it’s a big heavy one) wears out at about 6000-7000 miles. The car tire is going to last 3 or 4 times as long I’ve been told.


So how do they handle? My bike is a Kawasaki Vulcan VN2000 or it’s also know as the V2K. It’s the largest production V-twin made. About 500cc’s larger t.an the “big” Harley. It’s a cruiser and cruisers aren’t known for their ability to carve turns but since I’ve been riding bikes since the early 60’s and I’ve never stopped riding so I’m fairly experienced and I can get my V2K to carve pretty good, for a cruiser. The Darksiders insist that their bike’s handling is not negatively affected. Some go so far as to insist that their bike handles even better with a car tire back there. Now on a kawi forum when someone logs on and says their bike isn’t handling better they talk about which car tire would have worked better OR what pressure the tire should be run at.


So a buddy of mine has the same exact bike as I do. He went darkside and of course having drunk the kool-aid of darkside mania he’s convinced his bike handles much better than it used to handle and of course much better than my bike. So I suggested we switch bikes for a few turns so I can get an idea of what it’s all about.

Test ride

So off I go up Highway 140 in Oregon out of White City towards Klamath Falls. I get into my first sweeper and honestly it was ok. I was pretty certain that once I rolled over towards the sidewalls that I’d be heading for a guardrail. That wasn’t the case. OK, let’s see what this baby can do so I upped the pace and took it into a highspeed sweeper at about 85mph.


That baby went into a wobble that pretty much scared me to death. I rolled off slowly and the wobble went away. Well there were some switchbacks ahead, let’s see what happens there. The transitions were horrible. Both left to right and right to left were anything but smooth. So up towards the top of the hill is where we were turning off to head back towards Butte Falls down Fish Lake Road. I pulled off and shut her down as did my buddy on my bike.


I gave him my opinion which was I did not like how it handled and that at speed it seemed pretty dangerous. Now I know he doesn’t ride at the same pace I usually do when I’m alone but his first excuse was that I was riding too fast. He said if I chilled I would notice the transitions. That there wouldn’t be a wobble. OK so in other words if I rode as though I was afraid to crash all would be ok. I can’t argue that and so we switched back to our own bikes and went for a leisurely ride down Fish Lake Road.

So when I get home I log onto the forum and post my opinion. Now trust me talking to Darksiders in a way that isn’t giving them a verbal blowjob only brings out the worst in them. The excuses at first piled up. Wrong tire pressure, wrong tire, worn out headset, worn out suspension. It’s a new fucking bike for crying out loud. Trying to reason with a darksider is like trying to reason with a religious fanatic or even worse with a liberal who’s lips are dripping with Obama juice. I told them that an experienced rider would not enjoy the darkside unless they were slow. That anyone who rode the bike close to it’s limits would notice the poor handling.

Naw, they blasted me and blasted me to the extent that the forum moderators had to delete the entire thread. The forum is run by a Kawasaki dealer so I get why they’d delete the thread. I don’t understand why they allow these morons to continue to push a modification that Kawasaki itself is against. As a matter of fact every manufacturer of motorcycles AND tires are against this mod. So far the darksiders have only their “word” to take for it. No magazine will even do a road test to demonstrate the difference and even if that were done and it proved that darkside hurt handling and that decreased safetly were a result they’d argue the point. There hasn’t even been a tire or motorcycle engineer support their silly claims.

So why do they push for this modification?

Money and the need to justify being a cheapskate.


30 Responses to “Darkside Motorcycle Setup”

  1. Eric Says:

    Thanks for the alternate viewpoint. I appreciate the objectivity. I’ve been looking into the idea of a car tire on my rig (2005 Road King with Dnepr sidecar) and wanted to get some unvarnished input. What I take from your report is that so long as I run this as a 3-wheel rig, a car tire might be a reasonable thing to do for economic and PERHAPS handling reasons, but not to plan on unhooking the rig and expecting it to handle as well as a stock machine. For the record, I’m 58 and have been riding since I was 14.

  2. Vance and Hines Exhaust Says:

    If you are motorbike enthusiast and fun for modification, it’s true.. it’s a waste of money and time. However, it will get you a creative one and makes you familiar of motorcycle parts.

  3. Dave Harrison Says:

    I have fitted a Kumho 195/65/ 16 run flat to a 06 goldwing running 34 psi and would not go back to a bike tyre by choice. the front is a dunlop elite 3 and as as far as iam concerned it is as close to the perfect combination that i can get. Riding solo and towing a camper i highly reccomend the set up.

    The only problem in Australia is that the insurance companies will not cover me as you just dont put car tyres on bikes.

    What is it like in the States, has any one looked into the insurance side of it.

    • Paul "$hooter" Slonaker Says:

      Dave…I live in Fort Worth, Texas and my insurance company just said…”awwwww…ok…thats nice. Is there suppose to be a problem?” My rates have not changed nor have the rates on my friends scooters changed running the same Kumho tire.

      Safe riding down there bud…

  4. Andrew Jackson Says:

    I put a car tire on my bike only for a time factor. It was Saturday afternoon all the bike shops were closing and the guys wanted to go for a all day ride on sunday (bike shops closed). i went to my nearest tire store and I have not had anything bad to say about the handling of my bike after a played with the tire pressure of course.

  5. JC Says:

    I just went to the darkside on my Yamaha RSTD about 4 days ago and have the same experience! straight line wobble at 75 on interstate, and scary wobble at anything around 70 mph an a sweeping curve. I would say that if you are a rider who does not wind the bike up to pass another car or for any other reason, you may find the handling fine, and in town there is not much change from a bike tire. I am getting mine off ASAP! Until then I am slowing down!

  6. Brian Says:

    I’m going to be giving you engineering facts and not opinions. I have emailed several tire manufacturing companies asked them some serious questions on how a ct runs on a motorcycle and if they would ever consider doing a side by side comparison. The answers I got back would astound many people. To answer the question if they would ever do a side by side comparison was always no, with the exception of Cooper tires but Cooper tires won’t do it because of insurance regulations. One of the reasons why no tire company would ever do a side by side comparison is for safety reasons. The rider of the bike cannot know which tire is on the bike during the tests. If the rider is unaware of the tire it is it could create a catastrophic condition that could harm the rider and others. They are not willing to take that risk.
    As to where I have gotten my engineering facts from:
    TJ Tennent – Lead motorcycle tire engineer for Bridgestone\Firestone
    Virginia Gallant – Tire engineer from Dunlop\Goodyear
    Tire and Rim Association – Joe Pacuit
    Sukoshi Fahey – Lead Motorcycle tire Developer from Cooper\Avon Tires
    I have also received emails back from Metzler but not from anyone in particular.

    I have spent about 2 hours on the phone with TJ Tennent and about an hour on the phone with Joe Pacuit.

    Some of the reading I have been doing is “The Theory of Ground Vehicles” by Jo Yung Wong and “Motorcycling Handling and Chassis Design” by Tony Foale.

    The Tire and Rim Association sets the standard to which all tires and rims are to be designed to in the USA. I have managed to get Joe Pacuit from the Tire and Rim Association to give me a copywrited and patented proprietary trade secrets on that only the tire and rim engineers should have. This was given to me on the understanding that I will not publish nor distribute these pages. I can however, tell you what the design measurements are suppose to be for each of the respective tires and rims. These dimensions are so that the tire interlocks into the rim it was designed for.

    As far as rim widths, they are the same for both the car rim and the motorcycle rim with the following exception. The 5 ½” rim, the car rim is only .5mm smaller than a motorcycle rim and there is no 7” or 7 ½” wide rims for motorcycles.

    The Bead Flange (the area of the rim where the bead of the tire seats against the side of the rim)

    Car Rim 17.5mm (.689″)
    Motorcycle Rim 14mm (.551″)

    The Bead Seat (the area where the tire sits on the rim in between the bead flange and the round hump. The round hump is what helps keeps the bead of the tire against the rim)
    On a Car Rim it is 21mm wide with a 5* negative slope (slopes down from the round hump to the bead flange)
    On a Motorcycle Rim it is 16mm wide with a 5* positive slope (slopes up from the round hump to the bead flange)

    The lower inside corner of the rim where the bead flange and bead seat meet for the bead to interlock the tire in to the rim (the respective tire will have a matching size radius):
    On a Car Rim it has a 6.5mm (.256”) Radius
    On a Motorcycle Rim it is 2.5mm (.098”) Radius

    The outer bead flange radius (the top outer edge of the rim):
    On a Car Rim it has 9.5mm (.374”) radius
    On a Motorcycle Rim it has 3mm (.118”) Radius

    Rim Diameters (Tolerances: For Motorcycles +/- .015″ For Cars +/- .04″)

    CT 14.968″
    MT 15.08″

    CT 15.968″
    MT 15.978

    CT 17.189″
    MT 17.08

    Now let’s get into the design differences between the two types of tires.


    Car tires are steered by being turned. This is what as known as the slip angle. The slip angle will make the tread area distort as it turns. This is better known as tire squirm. Since CT share an axle (beam) the lateral forces generated in steering are shared between the two tire thus they do not need to be designed the lateral forces that a MT gets. MT is steered by leaning (camber angle). By introducing another axis in the steering, camber angle, it creates a different type of equation to determine the lateral forces applied to the tire thus any math done on the CT is invalid for a MT.

    Load Ratings:

    CT on designed for a specific amount of load rate. Since the CT can be put on any wheel on any corner of the vehicle the acceleration loads and braking loads are not as specific as to the tire and to its load rating capacity. Since MT are designed specifically for either the front or rear, the extra load rating of either the acceleration (for rear) or braking (for front) loads are taken into consideration. So the load ratings for motorcycle tire are a little different than a car tire. You should always consult the owner’s manual for the amount of load rating you need. The load rating is not just for the weight of the bike, it also includes the braking and acceleration forces. Now if we do some basic math on load ratings for those that say the CT designed to handle “allot more weight”. An average car with a high GVWR of about 4000 lbs will be used in this example. The Goldwing was a GVWR of 1200 lbs (without the acceleration or braking load rating). Since all CT are not designed for a specific place on the vehicle the must be able to share the load equally thus giving the tire a maximum of 1000 lbs per tire. Since the MT is designed for a specific tire location, they are designed to handle a certain amount weight from the bike. The Goldwing (and most bikes) have a weight distribution of 40/60 (front/rear). So if we take the GVWR and multiply by 60% (.6) we find that the Goldwing MT can handle 720 lbs of dead weight. Again this DOES NOT take into considerations of the acceleration loading on the rear tire. So the CT can handle only 280 extra lbs of dead weight versus the MT.

    Tread designs:

    The correct terminology for the tread area is “Land and Sea Area”. The land is the high points and the sea is the valleys or low areas of the tread. Again, on CT’s the tread is unidirectional and will displace water in any direction of rotation. MT tires are designed completely different. Since MT are directional, the tread only works one way to displace the water. If you run a MT backwards it will have the tendency to push the water under the tire causing the tire to have a hydroplane effect. When running tires on a MC, it is best to use the same brand of tire on both the front and the back. The reason why is because the front tire displaces the majority of water for the rear tire so it can have maximum adhesion to the road surface. When running different brands of tires, the front tire may not remove enough water for the tire rear to acquire maximum adhesion to the road surface thus causing a slight hydroplane effect.


    Both the MT and CT use these two chemicals, carbon black and silica, in their tires. The carbon black gives the tire there black look and the silica gives the tire its grip. By adding more silica in the tire it becomes softer or grippier. When the level of silica goes up the tire wear goes faster. As you add more carbon black, the more tire becomes harder creating a longer wear life. Most CT nowadays are of the radial ply design while most MT are still of the bias ply design. The differences between the two are staggering. First, let’s set some design guide lines. The “crown” of the tire is an imaginary line drawn around the center of the tire at the treads highest point. Second design area will be the tread area (Land and Sea Area), and third would be the sidewall area. We’ll look at bias first.


    Bias tires can have either nylon or steel belt plies that run at a 40* angle to the crown starting at one bead and running under the tread to the other bead. Generally there at least 6 plies but that depends on the tire manufacturer. With plies running from bead to bead and being more plies, it makes for stiff sidewalls.


    Radial car tires have steel belts (plies) that run at a 20* angle to the crown ONLY under the tread area. Depending on the manufacturer, the amount of plies can range from 4-6 with four being the most common. The sidewalls of CT normally only have two plies of cords that run from bead to bead and run perpendicular to the thread and sidewall to give the sidewall room to flex and give a softer ride. Note: that MT that is of the radial design has 4-6 plies run from bead to bead to give a stiffer sidewall that a MT requires.

    Car Tire Designs

    All CT manufactures only allow 40 psi to seat the bead. Any more and it begins to stress the all components of the tire. Excessive air pressure can lead to catastrophic bead failure. It may not happen at the time of the install but could happen later due to stress on the bead. The car tire’s tread area is generally designed to be flat. Some tires do have a slightly rounded edge at the shoulder. Car tire are designed for a maximum of 4* camber (lean) any more than that and the sidewall flex’s and tries to get the tread to lay flat on the road surface. As the sidewall flex’s it tries to make the tire stand straight up. Once the CT gets to 10* of camber it has lost half of its contact patch. At 20* of camber the tire has started to ride on the shoulder and is running on about on third of the contact patch. At 30* of camber the tire is riding on nothing but the shoulder. At 40* of camber the tire is starting to ride on the sidewall. The wider and less profile a CT is the more dependent it is on the correct camber. On Ct the tire compound is the same across the entire width of the tread. All tires regardless if they are CT or MT are designed to operate at a certain temperature to have maximum grip. If a tire runs too cool, it loses its ability to grip the road surface and conversely if a tire runs too hot it will delaminate. The rolling resistance co efficiency will affect the tire temperature. If the tire is operating correctly the air pressure will rise 4-5 degrees when hot. On most CT laminations they use what is called a butt joint when the carcass meets up it will look like this __][__. This again is done because the tire must be able to rotate any direction.

    Motorcycle Tire Designs:

    Motorcycle tires are designed with a round tread area. With the round tread profile, once you counter steer the bike into a corner, it will stay leaned over in the corner till either you lean more or pull it out of the lean. The smaller the radius on the tread the faster the tire will respond in corners. The wider the profile the more stable it is in straight up riding and slower it is to respond in corners. Some tire manufactures have done what is called a variable radius profile. The radius will get smaller the more you get towards the sidewall thus creating a fast handling tire but stable at straight up riding. The compound on MT is very different than that of a CT. Most MT have 5 segments, some have more (racing tires). The first segment will be equal widths on both sides of the crown. This segment has a hard compound for straight up right so to give long wear life. There are two more segments that flank to each side of the center segment. These segments have a softer compound to get more grip in the corner. Then there will be the last two segments flanked on each side of segment two that goes to the sidewall. These segments have very soft compound to get maximum grip in the corners. The lamination on all MT is what is called a feather edge. The edge can over lap any where from an inch to several inches thus the carcass will look like this with varying amount of overlap. __//__ This again is why there is a directional arrow on the sidewall. The tire manufacturer does not want the leading edge of the overlapped carcass going first. It will quite literally try to rip itself apart while cornering. MT need a 100 mile break in period. Most tires will expand in width by about 3-8% because of the heat cycles.

    I hope this helps. I once thought about going darkside on my 1200 sidecar rig. I too once did the “research” by going to the darksider forums and looked at everything like that and thought I was informed until I decided to do the “technical research” and this is allot of what I have found out. So all in all, the only two things a car tire and a motorcycle tire have in common in they both have tread and the both are black.

  7. Luis Sanchez Says:

    Good info! I will just say that I too have tried a CT on my MC and do not see taking it off any time soon. I made the leap after going in for service only to be told that my “look like new” MT tires were in need of replacement. So I gave it a shot.
    There is initial handling difference for sure but like changing your swing ,you have to give a thing some time before you abort or we would all be divorced. The car tire has performed very well slow or fast. I am still aware of the difference when going over bad ruts or grooved pavement. The ride improvement over bumps cannot be had any other way for the money.
    I took note of the contact patch percentages you mention, 10% of a big tire is more than 80% of a smaller round tire.
    Don’t argue the numbers, you get the picture. At the end of the day it is all about saftey(money)and for safteys sake
    the earth is flat. Only through trial and error does change come about, don’t count on the tobacco industry to police itself or should I say, the tire companies to shot thier cash cow. I get the camber, I don’t get what it will take for better longer lasting tires.
    Because the tire was not designed for an application does not mean it will not work with a degree of success. Is it as good as a round tire? In theory no, in application, a case has been made by many. I can get 20,000 to 80,000 mile tires for a car or truck but for my bike I get to spend twice as much every season per tire, what a deal.
    Until a company steps up and builds the next best thing, I am content to ride a sports car tire. Oh look at that, I said sports car. I wonder how those compare to mere passenger tires in all respects, and chiefly profile. You cannot mount a tire for a park avenue on a bike. it has to be within size parameters and these are found mostly for sports cars. I don’t own one but have seen them trying thier best to get on two wheels. Must be the tires.
    My respects to you all, there are pros and cons, when you own the store, the cons tend to stand taller. Until the store owner sees the a need to change his business plan, you get what you get, in this case RAPED, DRY..


  8. Paul "$hooter" Slonaker Says:

    There are some car tires on different bikes that are basically worthless, but I run a Kumho 195/55/16RF on my GoldWing and it is perfect. No wiggle…no wobble,,,no nothing and the bike runs like it is on a rail. I have had it up to over 135 mph on the not correct speedo and it was still as straight as a laser beam with no issues. My traction has improved in both stopping and accelleration but the real treat was riding in the wet stuff. The traction in the wet is unbelieveable…better than a motorcycle tire on a dry road. My last Kumho had over 20,000 miles on it with many more to go, but I was replacing the front Bridgestone 709 and decided to replace the Kumho at the same time…mainly because I was also installing the Cemtramatic Wheel balancers on my Wing and I wanted to start out with new rubber. I gave my old tire to a guy that was thinking about trying it…going DarkSide. My own opinion is that I will NEVER go back to a motorcycle tire on the rear…I am just too impressed with the Kumho. You guys might also want to go here… http://gl1800riders.com/forums/forumdisplay.php?31-Darkside-Riders …and you can pretty much get the best info for what tires to run and what tires to avoid.

    Safe riding all…

    • Brian Says:

      Paul Slonaker the claim you make about getting better traction is an opinion which consequently, is not true. To understand this we must look at the laws of physics concerning friction (traction in our case) and some chemistry make-up of the tire.

      The first law is easy to believe: The friction between two surfaces is proportional to the force pressing one to the other. This force could be the weight of a motorcycle pressing the tire into the pavement, or the clamping force pressing two pieces of wood together. “Proportional” just means that if you double the pressing force you double the friction.

      The second law is where all the trouble starts. To understand it, suppose you set up an experiment. You put a brick on a table and investigate how much force it takes to start the brick sliding. You screw an eyebolt into the brick, run a line from the eyebolt to a pulley on the edge of the table, and then attach weights to the end of the line. You add weight until the brick starts to slide.

      Now here’s the interesting part, and the surprising part. You would notice that the orientation of the brick doesn’t make any difference. That is, the friction is the same whether the brick is on its large face, the smaller side, or the small end.

      The friction is independent of the contact area.

      Don’t believe it? You’re not alone. Bowden and Tabor, in their book Friction , tell about one of the first modern investigators of friction, Guillaume Amontons. In 1699 Amontons published a paper on friction in which he reported on the two laws. As Bowden and Tabor put it, “The second law, that friction is independent of the size of the bodies, was viewed by the [French Royal Academy of Sciences] with astonishment and skepticism. They instructed their senior academician De la Hire (1640-1718) to repeat Amontons’ experiments and check their validity. This he did and confirmed Amontons’ conclusions. Amontons’ laws of friction have remained with us to this day as a very good working approximation.”

      It’d probably be less counterintuitive if we could see the microscopic texture of surfaces. Imagine a flat perfectly smooth metal plate. It’s flat and perfectly smooth, right? If you think so, you’ve never seen a micrograph of a flat perfectly smooth plate. It’s actually scratched and pitted, like a mountain range in the small.

      Now imagine a couple of mountain ranges on plates. Turn one over and put it onto the other. The actual contacts will be parts of the various peaks of the two plates onto whatever part of the other plate happens to match the peak. Those peaks — asperities, the tribologists call them — are where the friction occurs, not, obviously, in the valleys where there is no contact. Press them harder and you’d get more actual contact as the asperities bend under the pressure.

      If you take another pair of mountain ranges/plates of twice the area and pressed them together with the same pressure, the actual contact area of asperities wouldn’t change. You’d have the same number of asperities in contact, but further apart, in the larger plates. Only additional pressure would change the true contact area.

      That, in a nutshell, is the model that people use to make sense of the experimental fact that F=μN: friction F is proportional to the force N pressing two surfaces together, with proportionality constant μ. (Apparent) area of contact does not enter into it.

      Sometimes people object that the above model may be satisfactory for rigid materials like metals, but rubber would flow into the valleys and you’d get better contact. They miss the fact that rubber at the microscopic scale is quite as irregular as metals are. Pressing rubber onto an irregular surface such as pavement will indeed result in greater area of actual contact (as opposed to the apparent macroscopic area) than might be the case with a metal on pavement, but that contact is still between irregular surfaces; there will still be plenty of gaps in contact. Reducing the gaps can be achieved by pressing harder, which will result in more friction — just as the equation F=μN predicts.

      That’s the model, anyway. How well does it match the reality of rubber friction? A careful reading of Robert Horigan Smith’s book Analyzing Friction in the Design of Rubber Products and Their Paired Surfaces (2008, CRC Press) appears to indicate that rubber friction has more components than the single one of adhesion, which is what F=μN models, but that any departures from that model are minor and lost in the noise of real-world tires and pavement. Smith analyzes the published literature of rubber friction and concludes that rubber friction arises from 4 sources. One is due to the wear of the rubber, which is undetectable in non-sliding situations such as tires rolling on pavement. Two others he calls microhysteresis and macrohysteresis, which arise from the not-quite-elastic deformation of the rubber. They are very minor in comparison to the fourth source, adhesive friction, just what is modeled by the above two classical laws of friction.

      Smith argues that engineers concerned with rubber friction — tires, shoes, automotive fan belts — who neglect the hysteresis forces are missing a significant design tool. But by far the dominant contributor to tire friction is adhesion, which is well-described by the two classical laws of friction: It’s proportional to the force pressing the rubber to the road, and independent of apparent contact area.

      With this information and no more, we can understand two important facets of motorcycle operation. The first law, that friction (which we call traction in the context of tires on road) increases as weight increases, explains why the front brake on a motorcycle (and a car for that matter) is so much more effective than the rear brake. As you slow a vehicle, the weight transfers to the front. We all recognize this; it’s why the bag of groceries on the seat slides onto the floor when you get hard on the brakes. So the front tire is now carrying more load than it was; thus it now has more traction than it did. The opposite is happening at the rear: The rear tire is now lighter than it was, and so has less traction. The harder you brake the more the weight and hence the traction transfers forward.

      Everyone knows that you have less traction in a lean than when the motorcycle is straight up and down. This is because, in a lean, there’s less rubber on the road.

      Right? Well, if you’ve been paying attention, you’ll realize that what everyone knows, is wrong. The second law says that friction is independent of contact area. That implies that, if the traction is indeed less, it isn’t because there’s less rubber on the road. The second law says that the amount of rubber on the road is not relevant. (It’s interesting to me that people who know what everyone knows always overlook the fact that there isn’t less rubber on the road in a lean. Motorcycle tires are round. The amount of rubber on the road is the same whether the motorcycle is straight up and down or leaned over.)

      So what everyone knows about why there’s less traction in a lean, is wrong. Maybe everyone is wrong about the reduced traction as well? They are. The first law says that the friction between two surfaces is dependent only on the force pressing them together; in our application, that’s the weight of the motorcycle. Does the motorcycle weigh less in a lean than straight up and down? Of course not; if that were true, we could lose weight simply by leaning over.

      Ok, so we’ve concluded that the amount of traction in a lean is exactly the same as when straight. So what’s the origin of this myth? It’s certainly true that if I’m leaned far over and apply much braking I’ll lose traction and slide. What’s the deal, if there’s just as much traction in a lean as straight? The explanation is that one’s available traction has to be shared between the various users of traction. The Motorcycle Safety Foundation has a good image in their experienced rider course book. The total traction available is represented as an oval or circle, and the things which use traction are partitioned in it.

      So with this in mind, it’s not hard to understand why we can’t brake hard while in a lean. When cornering hard, most of our traction is being used for turning, with some for acceleration, and little or none for braking.

      The size of the circle is the same because we have the same amount of traction as we did while straight, just as the first law requires. Much of our traction is used in cornering. There’s some used in accelerating, if we’re on the gas through the curve. Drag at the wheels is always present so I’ve represented a small amount of traction for that. So what’s left over represents all the traction that we have to work with for any emergency, such as braking for an unexpected obstacle or because we went into the corner too fast. It is the small size of the reserve which gives rise to the myth that traction is lacking in curves. Or, if you prefer, it isn’t a myth, merely worded differently. The traction which one has to work with in curves is much smaller than that available in a straight line.
      So if traction doesn’t depend on amount of rubber, how come high-performance tires are so large? Hunh?

      To understand this, we have to make the first law more precise. The friction between two surfaces is proportional to the force pressing them together. But the friction between these two surfaces can be quite different from the friction between these other two surfaces, even if the force on them is the same. It’s easier to slide a steel plate on pavement than a rubber tire on pavement, even when both are loaded with, say, 5 pounds.

      The two laws can be combined into a single equation: F = μW, where F is the friction between two given surfaces, W is the force pressing them together (the weight, in most of our examples), and μ (the Greek letter mu) is a number called the coefficient of friction. This equation says that the friction is a percentage of the total weight on two surfaces, the percentage being given by the coefficient of friction. (That’s really just the first law, saying that the friction is proportional to the weight, the constant of proportionality being given by μ. The second law is incorporated by the fact that the area of contact does not appear in the equation.)

      The fact that some surfaces are “stickier” than others is reflected in the different coefficients of friction. Steel on pavement has a much lower value of μ than rubber on pavement. And what’s more, different rubber compounds have different values of μ. You want more traction? Just use stickier rubber in your tires. A further complication is that the coefficient of friction varies with various physical parameters. For instance, cold rubber is harder and thus less sticky than warm rubber; the same equation applies but μ is lower for the cold rubber. Static friction, the force necessary to start sliding, is greater than the friction created while sliding. In riding, we’re concerned with rolling friction, which is somewhere between static and sliding friction. Again, same equation, but three different values of μ.

      If you switch to tires with a better coefficient of friction, you’ll immediately notice that stickier rubber is also softer because it has more silica in it and thus it wears out much more quickly. Whereas a tire that has a longer wear life has less silica making a lower coeffienct of friction thus making it a harder tire that does not “flow” into the valleys of the asperities. Thereby actually giving you less traction.

      Motorcyclists accept the need to replace high-performance tires more often than touring-oriented rubber, but the auto types have another option: They can use wider tires to spread the wear over more rubber. And there, finally, is the reason high-performance auto tires are wider. It isn’t to get better traction. Better traction comes from stickier rubber. The tires are wider to get acceptable wear from the stickier, softer rubber. (As well as for other things like heat management, rigidity under the stresses of cornering and braking and acceleration, etc.)

      • Paul "$hooter" Slonaker Says:

        Brian…to put your explanation in a nut shell…YOU ARE WRONG. I am the one with the car tire on…not you. And I know how my bike reacted to the change…again…not you. No offense, but your physics and explanations to me are a joke. I can remember not too long ago…physics whizzes claimed that a double A top fuel dragster could NOT acelerate from a standing start and run a length of 1/4 mile in under 8 seconds or over 200 MPH. I dont know if you have been to a NHRA drag race lately, but that statement has been a joke for years. Top fuel dragsrters run 1000 feet now instead of a quarter mile…mainly because they are too fast. They run 1000 feet from a standing start at well over 300 mph and UNDER 4 seconds. Pro Stock motorcycles run a quarter mile at speeds close to 200 mph and 6 seconds…and by the way…they ALSO run a car tire. You can claim anything you want…no issues with me about that, but for you to tell me that I do not have better traction with a car tire really raises eyebrows with people…and since you have not done it…then I am going to say that you dont have a clue what you are talking about. Not ONLY do I know it, but anyone who is running a car tire knows it…but I will give you a NICE TRY.

      • brian Says:

        Paul, I will give the differences between traction and grip since you can’t understand the differences.

        A good example of traction is if you get stuck in the mud, you bounce a car up and down over the drive axle. As the springs compress they apply more force or weight to the tire so it can get better traction. As the car rebounds the springs remove the force or weight from the tires and tire then begins to spin in the mud.

        A good example of grip is if you have a car with 6″ wide tires on a sheet of ice and try to move you will spin the tires. Even if you put 8″ or 12″ tires you still just spin the tires. So this shows a wider tire DOES NOT give better traction. Again traction is based of weight. In order to move the car we either need to get better traction or better grip. To increase traction we add sacks of concrete over the drive axle, common in the northern climates. To get better grip we need to increase the asperities. So we add 1/4″ dia x 1/4″ long spikes to the tires. This increase the asperities giving us better grip allowing the car to move on a sheet of ice. Thus we DID NOT increase the weight to give us better traction we increased “grip”.

        If hard compound tires give better grip than soft compound tires, why doesn’t NASCAR use them so they can run a race on one set of tires?

      • Paul Slonaker Says:

        You have a nice explanation on traction vs grip, but the only problem with your explanation is that none of us ride on ice. My car tire, a Kumho 195/55/16RF Escta gives me both, traction and grip far more than the motorcycle tire that I pulled off. With the motorcycle tire running straight or in a turn, there is only about 2 to 2-1/2 inches of tire on the ground giving me all the traction and grip that it can. But my Kumho running straight gives me slightly more than 6 inches on the ground running straight and at least 4 inches in turns. Now, I will agree that there are some car tires out there that will not work on a motorcycle, but there are many that will.This is simple physics 101…if there is more surface on the ground, there is more grip and traction…hard tire or soft tire. Now if you want to rely on physics alone, then explain why the F-117 Stealth (Nighthawk)and the B-2 flying wing (Spirit) can actually fly when physics says they cant…and yes, I am a retired pilot.

      • Brian Says:

        Paul, ANYTHING can fly with enough thrust and lift. Rocks can’t fly either but if you throw them, they sure will because they now have thrust. As I tell all darksiders, you are entitled to your own opinion but not your own facts. I have presented to you scientific facts with scientific equations but yet you still believe want you want to believe. You have not yet given ANY refutable proof other than your opinion and you have not disproven any of my statements. You just keep trying to change the subject onto something else. Classical example of when people lose an argument and can’t compete against the facts.

        And yes most do not drive on ice. This was as I said is an EXAMPLE of grip. By adding width to the tire you still are not able to go anywhere because again the mathematical equation for figuring traction is that F=μN: friction F is proportional to the force N pressing two surfaces together, with proportionality constant μ. (Apparent) area of contact does not enter into it. Hard to argue scientific math. Traction is based off weight. Unless you add weight, you CANNOT increase traction. In the example I said we added spikes to the tires to increase the asperities to get better grip. Grip is the how well the two surfaces flow together or as known as asperities. Now lets go back to basic tire construction, carbon black and silica are two main ingredients in a tire. The carbon black gives the tire it’s black look. The amount of silica gives in the tire gives it it’s grip. As silica levels go up, tires become softer and wear faster giving the tire more grip. As the silica levels goes down, the tire becomes harder thus allowing for longer wear life. Thus as they become harder, there are less asperities flowing in the road surface so they are giving up grip. Long wearing tires DO NOT have the same grip level as tires that wear out fast. Until you can disprove ANY of this, anything else you say is your opinion. Please bring fact and not opinion to the table of discussion. Everything I have said is researchable, that is if you want the truth.

      • Paul Slonaker Says:

        Brian…you have made your so-called scientific data report…fine…I am not impressed. I am not trying to chage the subject nor do I care about who wins this argument. Your point is taken and tossed aside just as you have taken my point and tossed it aside. I am the one riding on the tire…you are not, so in order for you to get my attention after this post is for you to go ride about 5000 miles on a bike with a car tire on it. Now I will also say that a car tire on a crotch rocket is probably not a god idea, but to have one on a Goldwing is the cat’s meow. I know how my motorcycle handled and preformed with the motorcycle tires on it and I know how it preforms with the Kumho Escta Run Flat car tire on it and to me…key word here is ME…the bike rides better and it gives me better traction as well as grip than the motorcycle tire did…especially in wet weather. Now I normally do not ride in the rain, but when you are out and you get caught in it, you either find a place to sit and wait it out or you keep going. With the motorcycle tires on my bike, I use to sit and wait it out…now, I just go on. In short, you can show me all the data that you can find against running a car tire on a motorcycle…I will disagree with it and the reason I will disagree with it is because I am riding a bike with a car tire on it and I can feel the difference in the way the bike handles…which to me…again that key word “ME”…is better than the motorcycle tire. It is always the people who have never run a car tire on a bike that put up the biggest fuss over it…or those that have tried a car tire, but they got some ole cheap POS tire that barely operates safely on a car and tried it on a bike. No wonder it didnt work. As I have said in an earlier post, there is a list of exceptional tires that work great and also a list of un-acceptable tires that are worthless on http://gl1800riders.com/forums/forumdisplay.php?31-Darkside-Riders . I am a Darkside and I will not go back to a regular motorcycle tire…sorry.

    • Brian Says:

      Tell ya what Paul, I too live in Fort Worth. If you want to see the actual differences between the two rims, I’d be happy to show you. I have a section of “J” rim (typical car rim that has been in production for decades) and one that came of an 1800 Goldwing. Along with both a car tire and a motorcycle tire sections so you can see how bad they actually fit together. I can also show the design spec’s straight from the Tire and Rim Association 2012 yearbook. Just about every darksiders that once have seen the actuall differences between the two rims and got to handle the car tire fitting into a motorcycle rim have changed their mind. But then again, you don’t want to see the difference and that’s fine too. I have not taken your point and tossed it aside, no quite the contrary, I have just disproved all that you claim. I have said many times, it’s your ride you ride what you want to ride just quit claiming your OPINION is fact because again as I keep saying, disprove any of the FACTS I have presented. The problem is you can’t. And please, if all you say is true about the tire getting better traction, do us all a favor and do write up and prove your opinions to the scientific community because if you do, you will be rich beyond your wildest dreams.

      • Paul Slonaker Says:

        I have no desire to see any facts or scientific data that you might have. My opinion is MY opinion…not yours or anyone elses. I did not toss my opinion out as a fact or make accusations that I did. FYI…I do NOT play well with Liberals…especially Liberals who take anything that I say and twist it…even if it is a small bend. My scooters handles better for me with a Kumho Escat car tire than it did with the motorcycle tire…PERIOD & END OF STORY. And as I said, I will agree that there are many car tires out there that are worthless on a motorcycle, but I did offer the links to anyone who might be interested to go have a look and they can see the tires that many have had excellent results with and they can also see the tires to avoid. I dont know why I am going on about this with you as I feel like I am talking to a stump, so let me sum it up. I dont care what your data says…I dont care what your physics says…I dont care what different tire manufactures say and I certainly dont care how much better someone claims to ride then I do. I ride my way. I dont haul ass thru twisties, I dont give two hoots about it and for my last time to tell you and anyone else…my Goldwing handles better with my car tire on it then it did with the motorcycle tire on it. I have ridden my bike with both tires. Now whether you want to accept that as my opinion or if you want to twist it as fact…again…I do not care. It is my opinion and my fact, my bike is better off with the car tire on it. Now I am thru arguing with your ass over it…you can either accept it or continue to whine about it…either way I am done.

  9. lazyboy249 Says:

    Paul I’ve ridden both, I have over a half million miles on the road and I’ve raced bikes for many many years. You aren’t riding your bike the way I ride bikes and darkside does not work if you ride fast. No motorcycle or tire manufacturer say sit works and I KNOW it doesn’t work. Not the way I ride and I ride much better than you.

    • Paul "$hooter" Slonaker Says:

      Am I suppose to be impressed because you have ridden over half a million miles. Dude…let me be clear with you on this…I dont give a shit how well you ride…you ride your way and I will ride mine. My car tire works for me and thats it. Whether is works for you or not depends on you not taking off the training wheels.

  10. willd Says:

    Working on bikes I had a guy try to get me to mount a car tire on his bike, I did not and would not, that’s just silly.

  11. kadz Says:

    Why don’t they use car tyres in the MGP then is they’re so good?

  12. Paul "$hooter" Slonaker Says:

    There are ONLY 2 tires that the Dark Siders recommend and if you run anything else, then YES…you are asking for trouble. First off dont even consider a bias tire. The two tires recommended are the Kumho Estca RF (Run Flat) and the Michelin Alpine RF. I am on my 3rd Kumho and have never had an issue and I have run my 08 Goldwing up to and over 135 mph on the speedo and no issues. Want to see what it looks like riding with a car tire on a wing…go to my YOU TUBE channel. In the search window on YOU TUBE, type in ” HondaGoldwingGL1800 ” and my channel will come up, then you can actually see for yourself without all these so called “X-Spurts” opinions who have never done it. I consider them as not knowing what they are talking about…sorta like you or me going to a hospitable and telling a surgeon how to do his/her job. BTW, you do know the definition of an X-spurt…X is a has been and a spurt is nothing more than a big drip under pressure. You might also want to vist this web site folks… http://gl1800riders.com/forums/forumdisplay.php?31-Darkside-Riders

  13. Brian Says:

    For those that are truly interested, what I posted here earlier, is a shorter version of the complete write up on Design Difference Between Car/Motorcycle Rim and Tire. This write-up is complete with reference’s as to where I got all my information, complete with pictures of a section of a car tire on a motorcycle rim and CAD drawings to really see the differences. It can viewed here http://www.goldwingfacts.com/forums/2-goldwing-technical-forum/400426-design-differences-between-car-motorcycle-rim-tire.html

  14. k Says:

    if traction is not relative to contact size but weight excerted on a material, why is it so much harder to drag thirty earasers with a total weight of 5 pounds of downforce than it is to drag 1 earaser with 5 pounds of downforce?

  15. Ellery G. Bice Says:

    Here is a link to a very interesting article concerning the mechanics of deathsliding, or more commonly known as darksiding.

  16. shooteraod Says:

    There are always people out and about to prove something wrong…so what else is new in the world today? Those of us running a car tire on our Goldwings are happy with them and more than likely…we are NOT going to change. I am one of the ones that will not change, but I do get somewhat irritated when people try to force feed me stuff that they have no experience with. All I can tell you guys about a car tire is believe whatever you want…I have no issues with it, but before you bad mouth a car tire on a motorcycle…try it first to gain some credibility…dont just toss up some links as gospel. If you are going to try it, again, we as DarkSiders ONLY recommend two tires…either the Kumho Estca RF or the Michelin Alpin PA3 RF. Both tires are RUN FLAT types. I have been running a car tire now for over 3 years…no issues of any kind. All of you are welcome to go to my YOU TUBE channel and there you can see me running on my Kumho car tire as well as Rick (white wing) running on his Kumho tire. This link is of us running across New Mexico one morning and I am running on the Kumho… http://www.youtube.com/watch?v=vrOeyU14rIU&list=PLl51c2Gr7AGW0Y_G8QZtDFXNdB9pgT_7a&index=6 and you can see that we are running at 100+ mph. We just got back on our 2013 trip and you can also see the videos from this. Feel free to vist my channel, http://www.youtube.com/user/HondaGoldwingGL1800 and all the videos from 2010, 2011 and 2013 were done running a car tire.

    • Vern Says:

      Hello, I too had a VN2000 Kawasaki and ran a Michelin on it for approx. 15000 miles. I live in Florida and ran it year around rain or shine wind, loaded, unloaded you name it. Florida roads are different when wet than most roads north of the border especially the ‘pink’ ones Oh Crap ! I’ve had the bike over 150 (Yeah a GPS verified it.) with other bikes all doing the same. No problems at all except for a wobble about 139mph until I found it to be the ‘Ole Lady’ prop on the back of the bike. The wobble went away when the ‘prop’ did twisty roads I never did like and I wouldn’t recommend dragging pegs at 130+ with a car tire on the rear of the VN2000 will it? Yes, it will do I feel good while doing it? No, then again I wouldn’t with the MC tire either. But wet dry or dirty the car tire out performs the MC tire hands down in my experiance. Deals Gap one time, do it again no on any tire. Yeah the bike had a push into the corner at first but I found this was related more to the condition of the front tire than the Michelin on the rear. I rode this thing to and from work an hour each way every day and as a commuter tire and the better traction. FOR ME, and my driving style there is no doubt the CT is the way to go and what will be going on my new GL1800 when it needs a new tire.

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