Rims And Tyres Too Big?

[No Crust Racing]

I've had a couple of people make this comment about my setup so I'll put it to the masses.

I've got a "just-for-fun" S13 street reg'd but predominately track car.

My track rims are a set of 17" Volks that are 8" wide up front and 9" in the rear. The last set of tyres I had were some 235 semi slicks. Car runs about -2.5 deg camber in the front and about -1.5 in the rear, toe is pretty neutral all round. Coilovers are set about mid range firmness wise and the ride height was only brought down by a small margin as not to put the rest of the suspension out of geometry (think it might be about 330mm from wheel centre to guard lip but dont quote me)

The car seems happy enough and is using tyres well but I'm in the process of getting some new tyres, either some more second hand semis or some new high performance street tyres (like KU36s, RT615s or 595 RS-R's). And when I tell tyre shops I want 235s all round they tell me I'm "over wheel or over tyred" for that car and that I should only be running 225s at the most.

The car doesn't make a huge amount of power, maybe 130kw at the wheels (only a CA18 with T25G and a bit of boost) so am I wasting my money with rubber that big?

Can you guys weigh in on this before I shell out money on tyres, If I need to swap my rims for a set of 8" wide all round and run 225s then that's fine (as I think 225 would be a bit small for a 9" rim).

Cheers

My theory was if the car isn't scrubbing, which it doesn't, and it's using tyres well enough then that implies that the setup is balanced enough.

Edited March 22, 2011 by ActionDan

[Beer Baron]

personally I don't think there is anything wrong with running a set of 235s on both 8 and 9inch rims. if they are road tyres like KU36, RSR, RT615s then you'll find the fronts fit perfectly on the 8s and the rear may be a tiny bit small on the 9s but both still within acceptable sizes. conversely if you're running proper semis (A050's, RE55s etc) then you'll find 235s on the front will be a little big on the wheel, and on the rear they'll be just about right (maybe a tiny bit small) but again both will be acceptable. if you are happy with the handling then go for it. at least it means you can rotate tyres which is important with track rubber.

235 is a fine size for both the 8 and 9 inch wheels. don't worry about it. if you can find a cheap set of 8s then by all means run 8s all round and buy 225s and save a bit of coin the long run. but 235/45/17 is a very common semi slick size so you'll probably find no real saving in going to a 225 anyway.

[No Crust Racing]

Cheers Baron I'll press on as intended, can't wait for new rubber