Bike vs Car

[Erunanethiel]

Against a no-downforce car, what would the bike do, in terms of cornering g. Assuming no driver/rider error, and exactly the same tire compound?

[ChrisF1]

Where's the "Oh no, not this sh*t again" picture, I swear we just did this in another thread...

[Andres125sx]

Against a no-downforce car, what would the bike do, in terms of cornering g. Assuming no driver/rider error, and exactly the same tire compound?

Few weeks ago there was a thread discussing exactly that

Summary, cars are faster cornering and braking, bikes are much faster on the straights. Please stop it here

[Erunanethiel]

Against a no-downforce car, what would the bike do, in terms of cornering g. Assuming no driver/rider error, and exactly the same tire compound?

Few weeks ago there was a thread discussing exactly that

Summary, cars are faster cornering and braking, bikes are much faster on the straights. Please stop it here

Well, in braking, the limiting factor is the high CoG of the bike, which makes the rear tire lift up from the ground. But cornering is another story, because of the lean, CoG isnt the limiting factor, the tires μ is. And since we are using the same copmound tires on both the car and the bike, the cornering g's must be the same.

Can you also post the link of that thread please? I did a search but the threads i found were all with downforce cars, which just changes everything.

[Phil]

Well, in braking, the limiting factor is the high CoG of the bike, which makes the rear tire lift up from the ground. But cornering is another story, because of the lean, CoG isnt the limiting factor, the tires μ is. And since we are using the same copmound tires on both the car and the bike, the cornering g's must be the same.

Same tyre compound = same grip per mm^2 or contact patch, but a car has more contact patch! This is stacked against the force or weight of the vehicle pulling you out. In other words, heavier cars need more tyre contact patch (wider tyres) for equal cornering speed (than lighter cars). Which is whiy in high speed corners, a bike can hold its own against even very grippy cars. A nice example of this is a TopGear video where they pit a racing truck against a Ferrari 360CS on the track.

Also relevant; How fast can a rider get his CoG down, especially in sharp left-right-left corners in close succession?

[Tim.Wright]

I wouldn't bother about the other thread - it was a complete abortion and was rightly locked.

Even with the same compound, a car and a bike one other major difference regarding the tyres and that is the construction. This affects the contact patch size and therefore the cornering stiffness as well as the sensitivity to camber angle.

A car tyre has a larger contact patch and this (generally) allows a lot more cornering force. Tyres don't use pure coulomb friction but rather a mix of coulomb and chemical/adhesive forces so they don't have a constant coefficient of friction. Due to this, a larger contact patch will give you more grip due to the chemical/adhesive which works on contact patch area.

Regarding the construction, the motorcycle tyres are obviously rounded to deal with the large tilt angles - and from a quick glance at some examples of the tyre curves in Pacejka's book it seems that the tyres aren't so sensitive to camber angle at their limit (but they are very sensitive in the linear range). Car tyres on the other hand can usually increase their peak lateral force a reasonable amount by changing the inclination angle (camber).

One thing the bike tyres have as an advantage is a lower weight force which usually helps obtain a higher peak friction coefficient.

I haven't done a comparison of bike and car tyre directly but given the above I'd suggest that in steady state cornering a car would be quicker - mainly due to the larger contact patch area.

[Tim.Wright]

Same tyre compound = same grip per mm^2 of contact patch

Although I do believe contact patch area has a lot to do with it, its not quite correct to equate the compound to the grip (force) per mm^2 of contact patch area.

The total grip force, as I mentioned, is the sum of adhesive and coulomb effects. The adhesives effects are proportional to contact patch area and the coulomb effects are independent of it.

That and the fact that the 2 tyres have a completely different construction I doubt that the "normalised contact pach force" (force/area) would be anywhere near similar between a bike tyre and a car tyre.

[Phil]

Tim, you are of course correct. Very nice post.

[George-Jung]

[Erunanethiel]

I wouldn't bother about the other thread - it was a complete abortion and was rightly locked.

Even with the same compound, a car and a bike one other major difference regarding the tyres and that is the construction. This affects the contact patch size and therefore the cornering stiffness as well as the sensitivity to camber angle.

A car tyre has a larger contact patch and this (generally) allows a lot more cornering force. Tyres don't use pure coulomb friction but rather a mix of coulomb and chemical/adhesive forces so they don't have a constant coefficient of friction. Due to this, a larger contact patch will give you more grip due to the chemical/adhesive which works on contact patch area.

Regarding the construction, the motorcycle tyres are obviously rounded to deal with the large tilt angles - and from a quick glance at some examples of the tyre curves in Pacejka's book it seems that the tyres aren't so sensitive to camber angle at their limit (but they are very sensitive in the linear range). Car tyres on the other hand can usually increase their peak lateral force a reasonable amount by changing the inclination angle (camber).

One thing the bike tyres have as an advantage is a lower weight force which usually helps obtain a higher peak friction coefficient.

I haven't done a comparison of bike and car tyre directly but given the above I'd suggest that in steady state cornering a car would be quicker - mainly due to the larger contact patch area.

How much of a difference do you reckon will there be in terms of cornering force, assuming both are set up perfectly, driven perfectly, and with the same compound.

[Phil]

That depends on tyre contact patch and weight of the car, as well as the corner in question.

I think the general point is, the cars advantage is that you have 4 tyres which you can add wider tyres to. Can't do the same on a bike, since there is a limit to the width and therefore the achievable contact patch. In other words, assuming the perfect driven bike, in the end, you can't overcome the inherent limit of how to extend the contact patch.

Depending on the corner in question, this may be more or less of an advantage. A highspeed corner equals higher forces, so a heavier car will need more grip to overcome it.

To evolve this discussion, you would need specific examples; I.e. a car with tyre X, weight Y vs. general bike at weight Q and a specific corner with radius R. Then you calculate the theoretical maximum velocity at that corner for both.

[Tim.Wright]

How much of a difference do you reckon will there be in terms of cornering force, assuming both are set up perfectly, driven perfectly, and with the same compound.

What's of interest is not cornering force but cornering force per kg of weight force. Basically the coefficient of friction. The force will always be higher on a road car tyre because it has a higher weight force acting on it.

Unfortunately I don't have data on any bike tyres but I'd assume their peak friction is lower than those from a car for the reasons I listed above.

I think its better to avoid paying to much attention to youtube videos (especially ones supported by manufacturers who have an agenda to maintain). Otherwise the discussion will quickly go the way of the previous one...

[Andres125sx]

I wouldn't bother about the other thread - it was a complete abortion and was rightly locked.

Even with the same compound, a car and a bike one other major difference regarding the tyres and that is the construction. This affects the contact patch size and therefore the cornering stiffness as well as the sensitivity to camber angle.

A car tyre has a larger contact patch and this (generally) allows a lot more cornering force. Tyres don't use pure coulomb friction but rather a mix of coulomb and chemical/adhesive forces so they don't have a constant coefficient of friction. Due to this, a larger contact patch will give you more grip due to the chemical/adhesive which works on contact patch area.

Regarding the construction, the motorcycle tyres are obviously rounded to deal with the large tilt angles - and from a quick glance at some examples of the tyre curves in Pacejka's book it seems that the tyres aren't so sensitive to camber angle at their limit (but they are very sensitive in the linear range). Car tyres on the other hand can usually increase their peak lateral force a reasonable amount by changing the inclination angle (camber).

One thing the bike tyres have as an advantage is a lower weight force which usually helps obtain a higher peak friction coefficient.

I haven't done a comparison of bike and car tyre directly but given the above I'd suggest that in steady state cornering a car would be quicker - mainly due to the larger contact patch area.

How much of a difference do you reckon will there be in terms of cornering force, assuming both are set up perfectly, driven perfectly, and with the same compound.

Comparing what car with what bike?

Moto3 bikes are faster cornering wise than MotoGP bikes. Same with cars, a Veyron is a beast, but it´s so heavy any Lotus will be faster at any corner. So you can get different ratios depending on the car or bike you choose to compare.

Comparing around a track is even more misleading, as you have to add another basic parameter wich will change it all, the percentage of full throtle used around the track (and percentage of low/high speed corners). Basically you can get the results you want depending on the track used, but usually tracks have too many straights to compensate the better acceleration of bikes

[Andres125sx]

This made me wonder.....


What if you choose a bike and a car with similar perfomance both in straights and corners? For that you´d need a light bike with a fast cornering speed (compared to other bikes) wich obviously wouldn´t provide rocket style accelerations, so perfomance with the car both on corners and straights will be similar and more comparable

Phil, have you raced against any light bike?

I guess even so a car will be faster than the bike around a corner, but the bike will lose its advantage at the straights, but that´s a test I´d love to do/see

[Tim.Wright]

Ease up there turbo, the original question was regarding cornering only. Let not get sidetracked again...