Do the rims make a difference?

[eddiewould]

Hi,

Given the same tyres, would different rims affect the things such as how bumpy the ride is and how much bump steer the car has?

Cheers
Eddie

[Emperor]

I guess weight and width will make a difference..

Less weight, quicker to spin, power to the ground quicker..

Wider, more traction

As for the bumpyness, I guess tire pressure would play that part...

[Jebus]

Yes definately, the unsprung weight is a biggie. I went from Heavyish 15 X 6.5" Tuscanas, then after switching to superlightweight 14 X 7 Work wheels, almost all my bumpsteer is gone and is alot less bumpy (a big achievement for a car that sits 10mm from the bumpstops)

Light weights made a big difference for me.

[Akane]

I was told the good rims (3 piece BBS etc) are more circular, and does not flex as much under hard driving.

[$CENSLS1$]

Yes it will make a difference.Unsprung weight is very important to the way a car will handle, deliver its power to the ground and feel through the steering.

[Mr.Phreak]

Also offset plays a big part in how your car handles

[Stealer Of Souls]

Wider, more traction.

This is something of a misnomer. Wider doesn't necessarily translate to more traction.

Very, very basically.
contact patch = ultimate traction
Contact patch = area of tyre in contact with ground
Area of tyre in contact with ground = PSI in tyre divided by mass acting on tyre
PSI = Pounds per square inch. So to make a contact patch of one square inch, with a pressure of 10 psi would take ten pounds of mass acting on the surace.

This is super crude, with multitudes of other factors.
But...
For the same type of tyre (compound, tread pattern, side wall design etc) with the same pressure, and the same mass on the tyre, how can a wider tyre create more contact patch. It creates a different shape of patch. And that shape can affect ride quality.

[RomanV]

Some interesting thoughts on the matter in the FAQ:

viewtopic.php?t=39835

[sergei]

But you are forgetting that wider tyres generally loose heat more readily, as the total surface area of wider tyre is bigger. Thats why it is so easy to smoke the space savers.

[MR2SIK]

. Thats why it is so easy to smoke the space savers.

that and the fact that theyre of a super soft compund, to provide as much grip as possible on such a patheticly small tyre,

softer the tyre, better they smoke up...

My defencive driving instructor told us that one

[Dragger_Dan]

It's not just about the contact patch, it's about how much force is acting on that contact patch. In some cases less of a contact patch is better. Watch a WRC car in the snow, they look like they are running on space savers. This is because they are trying to break through the snow by putting all the weight on the narrower patch. If they were to run wider tyres they would actually have less traction.

Of course I realise you're talking about surfaced roads, but that's something I found intersting. Some people don't realise that the stuff keeping your tyres on the ground (your suspention) can be just as important as the tyres/wheels themselves. But if you have good suspention and crap tyres, you still won't have any traction. It's the workings of both that give you good grip.

[KinLoud]

I'm not sure why you are asking this question? Do you want better handing, more grip or what?
You might need to describe the problem you have a bit more clearly.
Are you having a problem with what might be bump steer?
Or is the car a bit skittery over changing surfaces and road camber?
If you wheel offset is different from the factory setup then the car handling over changing surfaces or camber can be affected. If you go to a wider tyre a similar thing can happen.

Just to clarify your question...
Are you asking for the same tyre will a wider/narrower rim make a difference? e.g. 205/50/15 on a 6" wide rim vs 6.5, 7.0, 7.5 wide rims.
Yes - For the best tyre behaviour go for a wider rim (within reason).
205/50/15 will give more grip and more predictable handling on a 7inch or 7.5 inch rim.
Try to have the sidewall straight not sloping in to the rim (7inch), or maybe sloping a bit out to the rim (7.5inch if you can find it).
(I'm not talking about drifter style setup where skinny tyres are stretched over the widest rim as you might start to give away grip)

However for increase in grip per $ spent I wouldn't spent too much on wider rims.

Hope this helps

Ken
Ham
021 408 863