petefias

Have you guys seen the 30" wheels on the H2 Hummer done by Unique? Where will it end?

Racer X

You can get that tire height without going to 20" wheels. It makes for a heavier tire wheel combination.

When they out brought the Lotus Elise Series 2(one of the finest handling cars in the world) they brought out with 17/16 instead of the 16/15 wheel combination it had in earlier model. They questioned the engineers why, and they replied it was a "marketing decision".

Actually, that they are larger on the back is strong evidence it is for bling. It adds to the look of rake, that implies speed.

Shorter stiffer sidewalls reduce contact patch.

If it improved traction, both Top Fuel and F1 cars woud have 24" wheels.

Mobile Man

The new tire compounds are amazing, but they can't overcome the laws of physics. The contact patch has to transform 600 ft lbs of torque into violent forward motion for a 3300 lb car!!

Another approach to rapid 0-60 acceleration: take a 1300 lb Ariel Atom, add a 245hp supercharged Ecotec 4 cylinder engine mounted directly over the rear wheels...and get 0-60 in 2.8 seconds! Of course, with the poor aero you hit a virtual brick wall by 80-100mph.

For 0-60 fanboys, go light. Everyone else, welll...you know...

UTVOL06

With a rear wheel drive vehicle its hard to get the power down at these levels of HP. I strugle getting the power down from a stop in my C6 Z06.

If you want sub 3.5sec to 60mph you need AWD and a ton of power.

Thud

Traction.

The same chassis/tires with 1000hp will still do 0-60 in 3.5 seconds.

tuxnharley

Comparing tire characteristics and their associated response dynamics of top fuel and F1 cars is like comparing apples and elephants.

Look at the overall wheel/tire height on a top fuel car - it's huge! They do that with a relatively small wheel and big tire to get a big flexible sidewall. They also run very low tire pressures, so as to allow the sidewall to flex and deform under hard acceleration. The tires are actually screwed to the wheels so as to prevent slippage or bead failure! All of that is designed to facilitate linear grip along the direction of travel by maximizing the contact patch area and duration. They could care less about lateral response.

F1 cars - or auto x as you referenced earlier - put much more emphasis on lateral response (cornering) by having stiffer/shorter sidewalls. Again, for a given maximum overall wheel/tire diameter the best combination of lateral response and maximum contact patch is achieved by having the largest possible wheel and shortest sidewall height. Remember, though, that in F1 the tire sizes, compounds, and tread patten are precisely regulated so as to attempt to equalize everything except the chassis/engine/driver. That's why you don't see bigger sizes in F1, not because it wouldn't be better!

Do you remember the Tyrell F1 car of the 70's which actually had six wheels/four front of smaller diameter in order to both maximize contact patch and reduce aerodynamic drag? It worked - until they regulated it out of existance!

Just because you don't see them using it doesn't mean they haven't thought about it or wouldn't like to!

GetReal

But I heard that 18inch rims are most optimal for racing. So what your saying it true to a certian extent. When rims get bigger past 18inches there's a loss in power through all that transfer... initially. That being said, I think bigger rims would benefit highway driving because you already obtained traction and it for the same force you can travel a greater distance. I'm not claiming this as hard facts... I just heard about it from various ppl.

My feeling about manufactures going bigger with rim sizes probably has to do with bling factor (no performance benefit but it's a benefit non the less) and because bigger rims= better gas mileage. Imagine if the C6 was running 16's, the gas mileage would be poor as hell.

robvuk

You guys are confusing rim size with tire diameter. They are independent.

Thud

Tire diameter vs sidewall width affects traction as mentioned above. With minimal sidewall flex you don't get much more traction as the rear suspension is compressed during launch. Better for cornering though.

But given the same rubber compound and tire diameter, increasing the width of the tire does not increase the contact patch size, it only changes the shape. When going wider, you actually lose forward traction, because the contact patch gets skinnier front-to-back. Again, it's better for cornering.

Serious.

robvuk

TTC5Z

Not sure this makes engineering sense. Contact patch size has not changed .. thus forward traction should remain the same.

Kind of like rubbing your hand on surface in long direction vs sideways. As long as pressure applied is the same ... grip should be same.

I say its tire compound & operating temperatures, tread pattern, sidewall flex, and road surface adhesion variables ... that make for launch traction differences.

Thud

Maybe not... but a mechanical engineer from GA Tech told me this (he owns a BMW performance shop now)

shape matters.


Actually one of the primary reasons race cars use wide tires is for heat dissipation. Thinner tires handling the same load would melt.

robvuk

First, if the weight of the vehicle and the tire pressure remains the same, the tire size will not matter on contact patch area. The wider the tire the shorter the contact patch. The narrower the tire, the longer the patch. Since this is true, it would follow that tire size doesn't matter. But it does, and the only thing different is patch shape. It has been found that a tire grips best when the patch is longer in the direction of the desired traction.

So the concept of a drag tire becomes complex. You can only make a tire patch so long by lowering tire pressure and having flexible sidewalls. At some point, you have to make it wider too.

You want a roadrace tire to have very stiff sidewalls to prevent deformation of the tread to pavement and rollover. The wider the tire, the more LATERAL grip. In this case, lowering the pressure to elongate the patch is not desirable. Although to some degree it will help if it's not so low that it allows the tread to distort from lateral G forces.

Everett Ogilvie

....I'm pretty sure that the tires on this car were not optimized for either 0-60 or 1/4 mile stats. I'm pretty sure they are a low profile sidewall design for cornering prowess, and good top end safety and stability. Sorry, but you 0-60 and 1/4 mile fans will just have to bolt on some temporary wheels/tires to optimize those specs.

DoctorV8

tuxnharley,

That is PRECISELY why the 20" wheel with the attendant 25 series sidewall is all but useless in dragstrip style starts.

DoctorV8

Actually, it's more like 600 ft lbs x 2.29 (1st gear) x 3.42 (axle ratio). So more like 4700 ft lbs!

Of course, that is assuming a 4000+ rpm launch. Even off idle, you're looking at at least 1500 or 2000 ft lbs...

tuxnharley

My original point was that because of that, they went taller as well as wider to get the maximum contact area instead of staying with the
19s.......

DoctorV8

But they didn't go significantly taller on the tire. 25% of 335 mm is not significantly taller than 25% of 325mm (Z06). To have any semblance of improved 0-60 times, they would have used a tire like the Ford GT's 315/40 19.

And clearly a 20" wheel is heavier and harder to accelerate than an equivalent 19"....but the wedge shaped C5 and C6 requires a larger rear diameter wheel. The 20" wheel is a compromise, dictated by form over function.

tuxnharley

Performance Junkie

Just get a bottle of that sticky stuff they use on slot car tracks Works like magic.