Just out of interest I weighed the 17" forged m3 wheels i've got, with the tyre on they're 17kg. these are the staggered wheel set.

How does that compare to 15/16" wheels, I can't go smaller as my brakes are 286mm.

I was/am going to use the bmw wheels to save cost and I like the look of them

With all this talk of not being able to put the power down and power to weight ratio's got me thinking... being honest I think with the 6pot m3 lump/roll cage i'll be looking at a <700kg's and 305bhp crank est/275bhp measured at the wheels.

Am I right in thinking the bigger contact patch will help me get the power to the road? Smaller wheels will just help with the last few tenths on track?

nah mate, those wheels will slow the car down to a crawl

m3's are notoriously slow
they'll be fine

That quite good for a 17" wheel and tyre I think.

It all depends on the make and construction but a lot of 15" tyres are the best part of 10Kg and at 15" a light wheel is approx 5Kg so put that together and its not far off what you've quoted.

That said more of the weight is further from the centre on a larger wheel - so even at the same overall weight there is still a slight disadvantage.

You might get 286mm brakes under 15's as 15" = 381 OD - surely the ID is larger than 286mm?

13 inch 205/60 section R888s are 8.7kg.

17s on the other hand are 10.2kg (215/45)

The lightest 13 inch wheels going are between 4 and 5 kg so youre a few kg up on the basic minimum of about 13kg but not toooo bad.

the rears I've got for the dax are 19.9kg each

thats for 245/45 R16 on a 9" wide rim (toyo T1R + borbet rim)

888's are a fair bit lighter I think (but I thet are track tyres not road ones)

[Edited on 2/3/10 by mcerd1]

What do most CEC with a cage tend to weigh in at then?

The ONLY problem with using the bmw gear is that its slightly heavier due to it being "over-engineered". However I could do with loosing a few stone anyway!

Edit....

Just had a re-weigh 235/40/17 fronts 18.2kg 245/40/17 rears 20kg.

center of the hub to top of the caliper is 173mm so 346mm of space needed.

[Edited on 2/3/10 by franky]

Normal road tyre on standardish 15" wheels are 16-17kg whenever I've measured them. 13" team dynamics with slicks are 10kg

My boggo 15" with 195/50s were about 16kg from memory. A little more than half of that was the rim. OZ superleggera rims are about 3kg lighter each and so are "normal" 13" alloys. Light weight 13s are lighter still. I'd say your 17kg for 17s isn't bad but lighter is better. The best place to save weight on a car is the wheels. If I were building again, this is where I'd spend my money.

15" cxr's and R888's weigh about 18Kg.

This tyre is slightly heavier than most due to a thicker sidewall.

Steve

so basically i've got nothing to worry about

my new 13" trackday wheels with 185/60 tyres are only 12kg

i couldn't go to 13" as my brakes are just about that big. it'd have to be 15 or 16 inch but its not worth the cost to me.