Wheel weights and track tyres

[Darren M]

Hi,
As you can see from my sig pic, I`m running the standard Coupe wheels on my car. Does anyone know the wheel weights of these and the other wheels BMW make available for the Z4 like the 108`s? I assume the split rims will be lighter?

Also, has anyone run any semi-slicks on the standard BMW rims (108 style or any other?). I may do some track time later this year and am thinking about fitting the same tyres all round (225*35*18) - fitting the same size tyres at the back as are on the front wheels, has anyone tried this? I`m hoping this would help conteract the natural understeer tendancies road cars have. I think 225`s will fit the 8.5 inch wide wheels..... Are we completely sure that standard non-runflat tyres work on the runflat BMW rims okay? I think the semi-slick tyres are very stiff anyway (the sidewalls) so should be similar to runflats in that they sidewalls won`t flex much.

If I go this route I`ll probably buy a new set of wheels for the road (108`s) and use my current wheels on the track with 225`s fitted all round.

I was thinking about buying a cheaper car for some trackdays but given how the prices of our cars are dropping and how suitable they should be on track , I`m very tempted to use the Z4 Coupe

 

[Smokin]

Don't know the weights, but I think someone posted them in the last month or so. There are a couple guys who track their cars, I'm sure they'll jump in.

Nice wheels, by the way.

 

[mmm-five]

I'd stick to the staggered set up on the track as you'll find the stickier rubber will reduce the understeer anyway and then you'll end up with a tail happy car instead.

I did something similar on my M5, where I had 235 fronts and 255 rears (P-Zero Corsas). Half way through the day, the fronts had lots of life left in them, but the rears were almost gone, so I had the birght idea of swapping them front to back. It was the wildest afternoon I've ever had in the car. The front would not understeer anywhere and the back end would just come round on braking

It was fun, but I think I'd not do it again.

I'd keep the staggered set up, but maybe just up the front by one size to 235/40 whilst leaving the rears at 255/35 - I wouldn't go down to 235/35 as you're making a bigger difference in the circumference by going that way which would affect understeer too.

235/40z18 is 1.3% bigger than standard
235/35z18 is 2.4% smaller than standard
245/35z18 is 1.3% bigger than standard (but then I'd probably go to 265/35z18 for the rears to get the balance right)

 

[cj10jeeper]

A 108 (8 1/2J) weights 13kg. Just dropped one on the scales for you. I suspect the front is close to 12.5g by loosing 1/2" of width

I think there are enough people with enough mileage on non RFT's and on 108's to say they are fully safe. IIRC some are on their second set of Falkens.

 

[Darren M]

A 108 (8 1/2J) weights 13kg. Just dropped one on the scales for you.

Thanks for that ! And thanks for the other info guys. I might still go staggered. Increasing fronts to 235`s sounds a good idea. If I do decrease the rears I will be careful to keep the circumference as close to standard.