Is this statement true:

"You can never have too much tire on a car. More rubber = more traction to go around corners = faster lap times"

I've run out of ways to argue my side of this with a friend of mine.

Please explain your answer in the most technical way possible. Charts and graphs would be cool to.

 

Too much tire = not enough heat = no grip = going slow. Then there's unsprung weight, rotational weight issues. No graphs though.

 

Just an opinion but I think you can have too much rubber on some cars. There is a limit to traction versus weight as well as traction versus HP. Real large wide tires on, lets say my 90 HP 912, would result in lower lap times as the top speeds, acceleration and deceleration would be hampered by un sprung weight, centripetal force, wind resistance and other factors in the straights and after a point more than any added corner speeds would give back. The cornering speeds might go up to a point but you will reach suspension and weight limits. After that more tire is only degrading the overall times as the weight/ down force per SQ/in drops and thwe tire is under used and does not come up to optium heat. Even leaving heat range out there is still a point that the tire is just not being pressed down hard enough to work well.

 

Not to mention rolling resistance.

 

True but rolling reistance tends to go down and weight pwr sq/in goes down too all other things such as carcas build and composition being the same.

 

Aerodynamic resistance counts too - fat tires = drag. Fat fenders to cover fat tires = more drag and lower top speeds.

Cars with a lot of downforce can use fatter tires (in fact probably need them) and get them up to proper operating temps.

 

I agree with the above.

With low hp low weight cars too much tire can be an issue.

It all comes down to rotational mass, unsprung weight, rolling resistance,air drag and of course tire temps.

Tire size is really a function of hp, weight and downforce.

The ideally you want small tires as it minimizes mass and resistance. The problem comes if you overheat the tires in corners will too much download (weight & downforce) and side load (weight and hp). Thus you need more tire to keep the temps in the proper range.

Now most street driven cars are under tired from factory for racing. Reason is thay are optimized more for economy than performance. That is why more tire = better for most street cars. However without the power to drag the tires around and the weight to get heat in them they can be a hinderance.

For example.

Spec miatas run on 205 width tires. I am sure they could be quicker on 225's. But 245's. Probably not as that is alot more rubber to drag around. Of course and 50 hp and 500lbs and then the 245's might work out.

 

Makes you wonder why the 2000 pound GT4S cars are using the biggest rubber and flares they can. Seems the guys with the 315s are going a lot faster than the guys with 245s. I don't think they make street tires TOO BIG for a 300hp 2000 pound car yet. Maybe for a 150HP 2000 pound car the 315s would be too big?

I am considering going to 245/275 tires on my 2300 pound 200HP RS... they are CERTAINLY faster than 225/245s on a 2700 pound 200HP 911 (3.2 carerra). I am sure they will be also faster on my car.

 

I like M758's answer. I'll add that if you just use a super-fat tire on your same rim, you'll end up losing the proper sidewall geometry and cause problems due to sidewall flex. Still, I can't help but think that as a practical matter, more tire is better... [flame suit on]

 

bigger is better in most all cases. ive gone from 225 to 235, to 245, to 255 to 275 to 305 and then to 335. the 305 and the 335 were pretty close in feel, but all the smaller tires were much worse as far as handling for the same weight range (ie 2700lbs to 3200lbs). i think if you go too big, the tire doesnt work quite the same as it should. I finally noticed very slight narrower wear patterns when i used the 335s, but the grip was still the same overall.

Just look at formula type cars. they are big meats on 1200lbs cars (formula mazdas, etc)

I wouldnt worry too much about the rolling resistance that is fairly constant, and the aerodynamic drag, unless you are visiting Daytona often! the GT3RS vs the GT3 with mod'ed engine run pretty close, even though the GT3RS has more power. Its larger body, not tires are the reason it can be slower on the straights. (aero drag)
unsprung weight???? nahh, thats not a big deal for most smooth tracks. loss of hp due to heavier weight tires....also, not measureable, due to the times accelerating in gears used on a road course. (ie 4-10 seconds of time spent accelerating in 3rd or greater gears) the 10lbs of savings (dramatic) would only be in the sub 2 hp range, while the possible 1-2 second a lap better grip would be a more than equitable trade off. BUT, there really wouldnt be much of a trade off due to the reasons stated.
mk

 

2000# GT4S or R guys are likely also adding some form of downforce. Most anything has an absurdun ad infunitum point.

 

The further apart the wheels on each axle, the better the cornering performance. The practical limit to this has not been encountered on Le Mans type cars. So the GT1s and 2s go as far out to 2 metres (max allowed) as they can and will use spacers if required.
The Bentley LMP1GT cars were faster on Mulsanne than the R8s because they were restricted to narrower tyres and the aerodynamics affected top top speed.
R+C

 

One other factor....the driver. More than once i have seen an unskilled driver buy a fat tired (315-335) lightweight full race car and not be able to get the tires hot enough to get any grip.

I believe the answer is yes, you can have too much tire for a given car...BUT, most production based cars can't get that much tire under them, so the limit isn't often reached.

 

Bigger is better, as long as you can get tires designed properly for your application.

If you are forced to use tires that are the wrong compound or construction or too big for the wheel, then they won't help.

They don't have maximum tire size rules in pro racing for nothing. Without those rules, the tires would as wide as the tire company could physically make them.

Cornering speed is WAY more important than drag or acceleration. This is obvious if you compare the lap times of cars that accelerate hard and corner poorly (i.e. fast street cars) vs. cars that accelerate slowly but corner well.

Chris Cervelli
Premier Motorsports

 

Looks like I'm buying beer after the next event.


Thanks guys!