Can Modified Cars Achieve 1.5G on the Skidpad?

[T.O.E Dream]

If we were to put two relatively small wheels on the side of a motorcycle would it decrease the performance of the motorcycle?

 

[mgb_phys]

No, and I don't think you are allowed to join the hell's angles if you have stabilzers !

 

[Phrak]

Trikes are OK with Hells Angles. Four wheel's are a no-no except in the junior, under 12, leagues.

 

[mgb_phys]

 

[pallidin]

Well, if the supporting arms of those extra wheels do not flex much, there is a serious problem with higher speed turns. You will flip over!
I know this because I was researching motorized tricycles a while ago and was warned about turning above certain speeds. Those "safe speeds" are much lower than for a 2 wheeled motorcycle.

 

[DaveC426913]

If we were to put two relatively small wheels on the side of a motorcycle would it decrease the performance of the motorcycle?

I don't see how you could do this. Unlike 3- and 4-wheel vehicles, 2-wheel vehicles must roll when they turn. In fact, even going straight, they maintain their balance by adjustments of roll.

Stabilizing wheels would be disastrous.

I would bet money that, if you actually tried this experiment, you would not get above 20mph and 100 feet before you rolled the bike.

 

[Danger]

Actually, the California Superbike School uses specially designed outrigger 'training wheels' to remove the fear of tipping over during cornering.
That's not practical for the street, though. From a scientific standpoint, any addition such as extra wheels will increase aerodynamic drag.

 

[YellowTaxi]

Actually if the stabilizers are far enough apart they could easily improve performace.

For example a car generally has more grip in a curve than a motorbike has simply because its outside wheel is further out from the centre of mass than it is on a leaning bike. (if you took away the inside wheel on the car it would fall inward). In effect a car is always leaning into the curve, even when it's standing still. The same would be true for a 2 wheeled bike with wide enough stabilizers.

 

[DaveC426913]

(if you took away the inside wheel on the car it would fall inward). In effect a car is always leaning into the curve...

This is counterintuitive. Why do you say it is so?

When cars flip out, they do so by flipping outward, not inward.

 

[rcgldr]

For example a car generally has more grip in a curve than a motorbike has simply because its outside wheel is further out from the centre of mass than it is on a leaning bike.

The main reason a car has more grip is that the size of the contact patches are larger on the car. Also if by "generally" you're comparing street cars with a typcial sport motorcycle, the bike has more grip because it uses a softer compound tire, compensating for the smaller contact patch. If you mean racing cars versus racing motorcycle, then the racing cars have better grip.

 

[pallidin]

I agree with Dave.

Maybe it's just me, but I don't understand what's so hard about this!

Get on a regular motorcycle and go, say, just 1mph.
Now, WITHOUT leaning, turn the handle bars slightly.
You will turn.

NOW. Do the same going 10mph(or whatever the minimum is for total weight).
You will flip over!
So, you MUST lean(tilt) the entire motorcylce in order to prevent flipping over.
Right? If you don't believe it I'm not loaning you my motorcycle.

With that in mind, non-flex stabilizer wheels PREVENT LEANING.

Much like a kid's tricycle.
Try going even 5mph on one of them and make a reasonable sharp turn. Forget it, you will flip over!

If the stabilizers have flex(to allow leaning), that's a different story.

 

[MotoH]

Man up and ride a regular motorcycle. The only real reason I could see someone needed training wheels err "stabilizers" is if they are on too big of a bike to safely touch the ground with their toes. Again you shouldn't be on a bike that is too big for you to begin with.

Now to the science thing, If you were to have training wheels, excuse me, stabilizers on your bike you wouldn't be using the bike to its full potential, since they are made to be dropped into turns. Even if the stabilizers were flexible and out far enough, they wouldn't allow the bike to follow its natural progression through the turn.

 

[YellowTaxi]

The main reason a car has more grip is that the size of the contact patches are larger on the car.

sorry jeff, but I don't think that's true. I think the size of the contact patch on a motorbike is huge when taken in proportion to the weight of the vehicles. If tyre size was the only factor, bikes should have tremendous cornering grip when compared with cars. But the fact is that they don't.

Also if by "generally" you're comparing street cars with a typcial sport motorcycle, the bike has more grip because it uses a softer compound tire, compensating for the smaller contact patch.

Well , (you contradict your first statement here btw), but I don't know where you get you're information Jeff but the fastest street legal motorbikes don't corner better than street legal sportscars. There's plenty of videos on the net that illustrate this fact. The bikes leave the porsches/ferraris in a straight line, (and maybe under braking too), but they always loose ground to the cars through the curves.

I think that motorbikes just LOOK faster in a curve because they lean into it. Appearances can be deceptive.

To DaveC426913, if you remove the wheels from the left side of a stationary car it falls to the left. If you did so on a car while it was going through a left hand corner it would still fall to the left.

In other words (the more complicated part), the line drawn from the centre of mass of the car to the outside wheel(s) is always 'leaning closer' to the ground than the same line taken from the centre of mass of a motorbike taking the same curve at the same speed. That's always true. So the car is always 'leaning into the curve' more than the bike is.
In fact it has to, otherwise it would flip over. ;_)

 

[DaveC426913]

You are comparing apples to oranges.

In other words (the more complicated part), the line drawn from the centre of mass of the car to the outside wheel(s) is always 'leaning closer' to the ground than the same line taken from the centre of mass of a motorbike taking the same curve at the same speed. That's always true.So the car is always 'leaning into the curve' more than the bike is.
In fact it has to, otherwise it would flip over. ;_)

No, the car is leaning out of the curve. If it takes the curve too fast, it will start to flip; its centre of mass will rise, lifting its wheels and losing traction and skidding.

The cycle, on the other hand, is leaning into the curve, which is why it will not flip over; what it will do is lose traction, begin to slide outward and its centre of mass will drop.

But I still don't know why you think a car leans into a curve. It most definitely does not.

 

[YellowTaxi]

Sorry for any confusion dave, but maybe you didn't quite understand what I was trying to say. My fault for not being more explicit, or more articulate.

I mean the car is 'leaning into the curve' because almost all of the grip from a car pushed hard through a corner is generated from its 2 outside tyres. The car is now a 'motorcycle', pretty much balancing all its weight on those 2 outside tyres. OK? It's one of the reasons that motor racing is something of an art, the dynamics of the car are constantly changing depending on the situation, and keeping the car on the road takes a lot of skill.

That's one of the reasons I don't agree with Jeff when he says a car has more grip than a bike in a curve because it has 4 tyres etc.. Fact is, in a curve at around 1G, the car is only really using 2 wheels. Apart from that this was probably way off topic

Hope I explained myself properly this time.. (maybe ..).

 

[DannoXYZ]

There are three components to "performance":

1. acceleration
2. cornering
3. braking

When you compare a sport-bike to a sports-car, the bike will only win #1 due to its superior weight-to-power ratio. The car wins in #2 and #3 as documented by numerous motorycle magazine comparisons in the past several decades. Around various racetracks in the country, this duel has been repeated time after time and the top bikes always loses to the top cars.

This doesn't even consider the relatively closer configuration of a sports-bike to its all-out race relative. A top sportscar is much, much further away from a true racecar; yet it can still beat a bike in 2 out of 3 performance areas.

As to T.O.E. Dream's question, what is meant by "performance" and how are these two additional wheels configured?

 

[pallidin]

Sorry for any confusion dave, but maybe you didn't quite understand what I was trying to say. My fault for not being more explicit, or more articulate.

I mean the car is 'leaning into the curve' because almost all of the grip from a car pushed hard through a corner is generated from its 2 outside tyres. The car is now a 'motorcycle', pretty much balancing all its weight on those 2 outside tyres. OK? It's one of the reasons that motor racing is something of an art, the dynamics of the car are constantly changing depending on the situation, and keeping the car on the road takes a lot of skill.

That's one of the reasons I don't agree with Jeff when he says a car has more grip than a bike in a curve because it has 4 tyres etc.. Fact is, in a curve at around 1G, the car is only really using 2 wheels. Apart from that this was probably way off topic

Hope I explained myself properly this time.. (maybe ..).

Um, isn't that why curves in racing(not all racing, of course) are "banked"? To keep all 4 wheels on the ground and in functional use?!

 

[rcgldr]

There are three components to "performance":
1. acceleration
2. cornering
3. braking
When you compare a sport-bike to a sports-car, the bike will only win #1 due to its superior weight-to-power ratio. The car wins in #2 and #3

In some cases, bikes can also out brake cars due to softer compound tires. At Willow Springs 2.5 mile race track, the fast guys can run around 1:28 on stock bikes (like GSXR 1000) with DOT tires. There are few stock sports cars that can match that time. The top race bikes run around 1:20->1:21, back in 2000 when AMA superbike was 1000cc, 1:19.029. Since AMA superbike is now back up to 1000cc again, I assume lap record will drop back down to the low 1:19's again.

Motocycle lap times and records on page 11:
http://my.wsmcracing.com/ul/file/Newsletters/WSMCNews1109.pdf

Race car records:
http://www.willowspringsraceway.com/trackinformation/records.asp

The main reason a car has more grip is that the size of the contact patches are larger on the car.

I don't think that's true. I think the size of the contact patch on a motorbike is huge when taken in proportion to the weight of the vehicles.

Because of the round profile, the contact patch on a motorcycle is small compared to a sports car with 250 to 325mm treadwidth, perhaps the overall contact patch area of the 2 tires on a bike is 1/6th or less than that of the 4 tires on a sports car. The bikes generally run softer compound tires than all but the lightest of cars. The Caterham CSR, at < 1400 lbs, is one of the lightest street legal cars, and is a somewhat popular track car in the UK and Europe.

 

[DannoXYZ]

Total contact area has to do with tyre-pressure. Autos typically use about 40psi hot on the track. Take the case of a 3200lb sportscar, 3200lbs/lbs/sq.in. = 80 sq.in contact patch. Motorcycles typically use 50-55psi hot and end up with more weight per sq.in. on the ground.

Coefficient of friction for rubber changes with vertical loading in a non-linear fashion. I'll try to find a chart of CoF versus vertical loading. I think it was in one of Carroll Smith's "To Win... " series.

And the big track at Willows is a power-track. So the motorcycles will obviously do well. Although a previous-gen. Corvette Z06 will do 1:29 on street tyres. Add DOT-R tyres and you can shave 3-4 seconds off. Here's the results from the http://web.archive.org/web/20030924233239/www.opentrackchallenge.com/trackrecords/willow.htm. Street cars aren't too far off the AMA SuperBikes times. If we really wanted to compare cornering and braking of cars vs. bikes, we'd us the Streets course or Laguna Seca.

 

[YellowTaxi]

Because of the round profile, the contact patch on a motorcycle is small compared to a sports car with 250 to 325mm treadwidth, perhaps the overall contact patch area of the 2 tires on a bike is 1/6th or less than that of the 4 tires on a sports car.

Jeff, you seem to forget that a car can't use all 4 tyres in a curve. That would be against the laws of physics as I'm sure you're aware. In corners at 1G and above the car's only really using the 2 wheels on the outside. So it's just a very heavy motorbike really. A porsche 911 for example weighs around 5 or 6 times that of a sport motorbike, and all of that weight is is on 2 tyres when its pulling 1G or more.

The bikes generally run softer compound tires than all but the lightest of cars. The Caterham CSR, at < 1400 lbs, is one of the lightest street legal cars, and is a somewhat popular track car in the UK and Europe.

If bikes have to resort to using softer, grippier tye compounds to keep pace with the cars through the curves then you're agreeing with my statement that with all else being equal, the car will have more grip in the curve than the bike. In other words the bikes have to 'cheat' to keep up. QED...

Btw, the Caterham is only popular with people who can't drive rear or mid-engined cars. Real sports cars have most their weight on the rear end to keep the vehicle more agile. [You can argue that it's more complicated than that, but agility is what it boils down to] This has nothing to do with bikes v cars though, I just don't think of caterhams as real sports cars...

 

[DannoXYZ]

No, a car doesn't just use 2 wheels in cornering. While it does have more weight & therefore traction on the outside tyres than the inside, but the insides still do contribute to cornering. The lateral weight-transfer is a function of COG-height and track-width. At no point in time is there 100% weight-transfer to the outside wheels (unless you can tilt the car enough to place it's COG over the outside tyres). I suggest you review your Physics of Racing series.

 

[YellowTaxi]

Coefficient of friction for rubber changes with vertical loading in a non-linear fashion. I'll try to find a chart of CoF versus vertical loading. I think it was in one of Carroll Smith's "To Win... " series.

I think you'll find its:
coef of friction is proportional to load ^ -0.2.

So a bike at 1/5 the weight of a porsche 911 has 1.4 times the amount of grip if using identical tyres (identical size, and same compound)

 

[YellowTaxi]

No, a car doesn't just use 2 wheels in cornering. While it does have more weight & therefore traction on the outside tyres than the inside, but the insides still do contribute to cornering. The lateral weight-transfer is a function of COG-height and track-width.

grief that's obvious. But roughly speaking almost all the grip is coming from the 2 outside tyres at and above 1G.

At no point in time is there 100% weight-transfer to the outside wheels..

There is precisely 100% load transfer (not weight transfer btw) just when the car tips onto its side.

Weight transfer is due to body roll which we are not considering in this debate, and in any case contributes next to nothing to the change in the coeficient of friction anyway.

 

[DannoXYZ]

grief that's obvious. But roughly speaking almost all the grip is coming from the 2 outside tyres at and above 1G.

Rather than speaking in all-or-nothing, black & white qualitative terms, why don't you give some equations and calculate the exact lateral weight-transfer of a 911 then? I have yet to see any bike that can pull 1.4x higher cornering-G than a 911. Here's one to get you started: f=mu

Weight transfer is due to body roll which we are not considering in this debate, and in any case contributes next to nothing to the change in the coeficient of friction anyway.

By your logic, if we've got a go-cart with zero suspension travel and zero-lean at 1.5g, does that mean it has zero lateral weight-transfer in cornering? Meaning its outside tyres contribute 50% to total cornering grip?

No, the body-roll is due to weight-transfer and not the other way around. If you've got a car with 5-degree lean at 1g and you stiffen up the suspension so it leans only 2-degrees at 1g, it will STILL have the exact amount of lateral weight-transfer at the same cornering G and speeds. Don't get cause and effect mixed up.I suggest you brush up on your physics first to get the basics down:

Race Car Vehicle Dynamics - Milliken & Milliken
Tyre and Vehicle Dynamics - Hans B. Pacejka

 

[rcgldr]

coef of friction is proportional to load ^ -0.2.

This depends on the tire construction (sidewall stiffness, radial versus bias ply, ...) and the rubber compound used. Wiki has a small article:

http://en.wikipedia.org/wiki/Tire_load_sensitivity

results from the Open Track Challenge.

Those cars are tracked prepped cars, not stock sports cars, and most of those times are similar to the 1:27->1:28 that the fast guys get on high end stock sport bikes at Willow, not the 1:19 to 1:20 that 1000cc racing bikes get there. The racing bikes run about the same lap times as SCCA GT3 class cars.

In corners at 1G and above the car's only really using the 2 wheels on the outside. Caterham is only popular with people who can't drive rear or mid-engined cars. Real sports cars have most their weight on the rear end to keep the vehicle more agile.

A Caterham CSR 260 has a weight bias of 49% front, 51% rear without the driver, and with the driver virtually sitting directly above the rear axle, the actual weight bias is further rearwards. A CSR 260 with stock Avon CR500 tires pulls 1.05 g's in turns. With 13 inch wheels and bias ply racing slicks, the CSR pulls 1.4 to 1.5g's, since it can share the same very soft compound racing slicks used on light (< 1500 lbs) non-downforce race cars like the Formula Ford.

The center of mass on virtually any sports or race car is low enough and track (distance between left and right tires) is wide enough that the car isn't tranferring almost all of its weight to the outside tires due to tire grip, as this could end up with car rolling over on it's side.

 

[DannoXYZ]

Those cars are tracked prepped cars, not stock sports cars, and most of those times are similar to the 1:27->1:28 that the fast guys get on high end stock sport bikes at Willow, not the 1:19 to 1:20 that 1000cc racing bikes get there. The racing bikes run about the same lap times as SCCA GT3 class cars.

I'm trying to compare like-for-like. As mentioned before, stock sportsbikes are much closer to their race cousins than streets cars are to racecars. So a track-prepped street car using soft tyres is more similar to a stock sportsbike.

Look at those OTC results again and all the cars are streets cars prepped for track use with either street tyres or race tyres. The race-tyred cars are more similar to stock sportsbikes (same DOT-R type tyres). Those cars are in the 1:21 range, about 6-7 faster.

If you you want to compare all-out racecars versus racebikes, then again, the racecars are 10-12 seconds faster than the racebikes at a power track like the big course at Willow Springs.

Same results on a real handling-oriented tracks like Laguna Seca (fastest cars are 20-seconds faster than fastest bikes):

SuperBikes: 1:26 Tommy Hayden
GP bikes: 1:23 Dani Pedrosa

250 SuperKart: 1:24 Eddie Lawson (compare with 800cc GP or 1000cc SuperBikes)
F1 car: 1:06 Ricardo Zonta (Toyota)

 

[rcgldr]

I'm trying to compare like-for-like. As mentioned before, stock sportsbikes are much closer to their race cousins than streets cars are to racecars.

That was part of my point.

race cars versus race bikes

I'm aware that all out race cars, especially ones with downforce, are much faster than the all out race bikes, which are closer to the GT3 cars, dependinng on the track. Even without the downforce, the race cars have a lower load factor per unit area of the contact patch on the tires (much wider tires and 4 of them instead of 2), and they can dirft without risk of low or high siding.

Laguna Seca F1 car: 1:06 Ricardo Zonta (Toyota)

Beaten by a Champ Car in 2007:

On August 20, 2006, Toyota F1 test driver Ricardo Zonta set an unofficial lap record of 1'06.039. The previous record time was 1'07.722, set by Helio Castroneves in a Penske Champ Car during qualifying for the 2000 CART Honda Grand Prix of Monterey. The unofficial record was re-taken by a Champ Car on March 10, 2007 by Sébastien Bourdais, who lapped in 1'05.880 during Champ Car Spring Training.

http://en.wikipedia.org/wiki/Mazda_Raceway_Laguna_Seca#Lap_records

 

[xxChrisxx]

Jeff, you seem to forget that a car can't use all 4 tyres in a curve. That would be against the laws of physics as I'm sure you're aware. In corners at 1G and above the car's only really using the 2 wheels on the outside. So it's just a very heavy motorbike really. A porsche 911 for example weighs around 5 or 6 times that of a sport motorbike, and all of that weight is is on 2 tyres when its pulling 1G or more.

You've got to be careful here because 1G of lateral acceleration does NOT mean that all load is transferred to the outer wheels.

Assuming a track of 1650mm and CoG height 550mm, a 1G turn
The load transfer to the outer wheels is: G * height / track.
Meaning in a 1G turn 33% of the load is transferred if the centre of gravity height is 1/3 that of the track.EDIT: DannoXYZ got their first and is perfectly right. Time for you to go and read Milliken and Milliken

Same results on a real handling-oriented tracks like Laguna Seca (fastest cars are 20-seconds faster than fastest bikes):

SuperBikes: 1:26 Tommy Hayden
GP bikes: 1:23 Dani Pedrosa

250 SuperKart: 1:24 Eddie Lawson (compare with 800cc GP or 1000cc SuperBikes)
F1 car: 1:06 Ricardo Zonta (Toyota)

It's a little bit unfair to compare an F1 car to a bike, owing to the fact that the F1 has a couple of tons of downforce.

 

[DannoXYZ]

I need to re-read this thread as I'm not sure where the car vs. bikes comes in answering T.O.E. Dream's question about additional tyres. I agree with Jeff in that a car has more grip due to its larger contact-patch. Here's a chart showing loading on a tyre versus grip:

Tyres are most efficient (highest CoeF) when their per-unit contact has the least load. In the case of ground-effects, you can double the vertical-loading on a tyre, but get only 50% more grip. This is better than adding weight to the car to increase grip because you don't have the extra mass to accelerate, brake or carve around a corner. This is also why lighter cars outperform heavier ones, they don't load the same tyres as much, or can use softer-compound tyres without overheating them.

This loading-effect model also works on tyre-pressure. Higher-pressure tyres add more load per unit area on the tyres and they don't grip as well. Assuming similar tyre-compounds, motorcycles using 50-55psi on their tyres will not have as much grip as auto-tyres using 40psi. Higher-pressure will result in less contact-patch per unit weight than a car, contrary to YellowTaxi's claim.

The simplest comparison then is with the 250 Superkart against the Superbikes and GP bikes. It has similar weights to the bikes, yet vastly inferior power-output. Yet it generates roughly the same lap-times as the bikes due to superior braking and cornering.

Or going back to the results of the Open Track Challenge, street-cars using soft-compound tyres similar to sportbikes are faster. The top 1/2 of the U-class are faster around a power-track than sportbikes on similar soft-compound tyres. The fastest entry, Mumford's Viper is right on top of all-out race bikes. Take 1000-1500lbs off to place it in the same HP:weight ratio as pure race bikes and it'll gobble up them up easily (even without ground effects).

 

[rcgldr]

There are 3 wheelers that lean, such as the Piaggo 3 scooter. There are twin front ends (tires, shocks, brakes, ...) connected to an unsprung, undampered parallelogram set of arms that allow one wheel to move up and the other to move down. There's a "parking" mode that locks the setup into a vertical position. This setup adds a lot of weight though, so I doubt it would be useful for a sport bike.

http://en.wikipedia.org/wiki/Piaggio_MP3

http://thekneeslider.com/archives/2006/05/11/piaggio-3-wheel-mp3-scooter

http://www.motorcycle.com/manufacturer/two-wheels-good-three-wheels-better-17921.html

 

[YellowTaxi]

This depends on the tire construction (sidewall stiffness, radial versus bias ply, ...) and the rubber compound used. Wiki has a small article:

http://en.wikipedia.org/wiki/Tire_load_sensitivity

that wiki article you quote says that coef is proportional to load ^-0.2
therefore it agrees with me entirely. I don't understand your 'argument' here, you are in agreement with my previous statements.

Of course its only an approximation, and factors like tyre geometry and stickiness of the rubber itself by definition also has an effect of the coef - so what. I believe all tyres follow that rule that coef is prop to load ^-0.2. And all what you say here has nothing whatsoever to do with the bike v car argument in any case, so why you're posting it I'm not certain. Maybe to try and confuse the issue.

You keep saying that bikes can pull a lot of G, but only on very sticky tyres. You're proving my point for me. Cheers Jeff ;>

A Caterham CSR 260 has a weight bias of 49% front, 51% rear without the driver, and with the driver virtually sitting directly above the rear axle, the actual weight bias is further rearwards. A CSR 260 with stock Avon CR500 tires pulls 1.05 g's in turns. With 13 inch wheels and bias ply racing slicks, the CSR pulls 1.4 to 1.5g's, since it can share the same very soft compound racing slicks used on light (< 1500 lbs) non-downforce race cars like the Formula Ford.

So what, it's a very light car so it has more grip. Because grip is roughly prop to load^-0.2.

The center of mass on virtually any sports or race car is low enough and track (distance between left and right tires) is wide enough that the car isn't tranferring almost all of its weight to the outside tires due to tire grip, as this could end up with car rolling over on it's side.

That simpliy isn't true Jeff. Tipping is a big problem on European Touring cars which are race cars built from stock, street legal cars like the Audi A4. The driver sits at low as possible in his specially low mounted seat, and the wheels are mounted something like 5 inches outside their normal position just to try and keep the car from tipping over. In other words they're cornering at around 100% load transfer. Occasionaly they do indeed lift both inside wheels or even flip. That's 100% load transfer, no doubt about it.

A stock porsche 911 will start tp tip at around 1.5G. ie it would have 100% load transfer at 1.5G. The tyres they're obliged to use on the road have deliberately limited max grip of 1G, so its not a propblem there. If you fit racing tyres to a porsch it would be a problem, just like it is on those Touring Cars.

 

[xxChrisxx]

that wiki article you quote says that coef is proportional to load ^-0.2

Where?

Also I don't know exactly what the CoG height is for a Porsche 911, but acutally do the calculation for 100% transfer of load.

 

[rcgldr]

that wiki article you quote says that coef is proportional to load ^-0.2

It states a range:

the maximum horizontal force Fy that can be generated is proportional, roughly, to the vertical load Fz raised to the power of somewhere between 0.7 and 0.9, typically.

You keep saying that bikes can pull a lot of G, but only on very sticky tyres.

What I stated was that cars have larger contact area, lower loading per unit area, but that sport bikes generally have stickier tires than sport cars which compensates in stock sport bike versus stock sports car comparasons. Once you're running DOT tires on both, the cars have an advantage.

 

[YellowTaxi]

Where?

It says the lateral force, also known as friction, is prop to load^0.8

well, Friction = Coef x Load
.'. Coef of friction is prop to Friction/Load.
ie [load^0.8]/[load]
ie Coef is prop to load ^ -0.2
OK ?

 

[YellowTaxi]

It states a range:

What I stated was that cars have larger contact area, lower loading per unit area, but that sport bikes generally have stickier tires than sport cars which compensates in stock sport bike versus stock sports car comparasons. Once you're running DOT tires on both, the cars have an advantage.

You said said the bike has around 1/5 or 1/6 the contact patch area of a car tyre.
And I said the car has around 5 or 6 times the weight of the bike all balancing on 2 wheels just like a bike. Therefore the 'loading per unit area' is the same...

Mentioning that adding stickier tyres gives more grip doesn't prove anything - by definition it's obvious anyway.