Wheel size vs Brake size

[dtype38]

Originally Posted by Notso Swift

If you are making big changes to the wheels, like 15 to 18, much more of an effect, but the case we are presented with is a plus 1" scenario, in this case I am saying that other factors will have more of an effect than just the wheel size.

Been through that loop and can give some actual experience of the differences. I've got two sets of wheels/tyres due to the regs difference in two of the race series I'm in:
Set 1 15"x7" rims, 225/60/15 tyres (yoko A032), total weight ~20kg each
Set 2 18"x8" rims, 235/40/18 tyres (toyo R888), total weight ~21kg each
I use the same spring/damper settings on both (just lazy) and I have 300mm front rotors with 4pot calipers and 270mm rear rotors with 2pot calipers.

On a hot sunny day Set 2 are much better. The brakes run quite a bit cooler and the tyres don't go off after half a doz laps. Unsurprisingly, braking is harder work on the pedal, but the extra bit of rubber on the road and more stable tyres more than make up for it. Overall lap times are up to a second better with Set 2.

On a cold dry though, I'd say Set 1 are slightly better, mainly because it all comes up to temperature more quicker so I can push hard on lap 1. Lap times are similar.

On a wet day there's little to choose between them, but I'd say Set 2 have the edge, possibly because the Toyo's just have a surprising amount of grip and water clearing ability.

Not very scientific I'm afraid, but if it wasn't for the limitations of the regs, I think I'd just stick to my 18" rims.

[EdLeake]

Interesting advice and informative, thanks so far guys, plenty for me to think about.

[Al Weyman]

You can't put 18" rims on the CRX Ed that would be silly! ;-)

[AU N EGL]

I happen to have the pleaser of driving a special car that had 19" and 20" wheels on with 15.8" CCB rotors and BIG 6-pot fronts and 4-pot rear brakes a week ago.

Took it for several or many laps on my home track.

The brakes were almost unbelievable in stopping power, but the big wheels , one could feel the wt in accceleration out of corners. Still with 620 some BHP it was a rocket ship non the less.

Would love to have the opportunity to drive with 18" wheels and some sticky Hoosier A compounds.

[EdLeake]

Originally Posted by Al Weyman

You can't put 18" rims on the CRX Ed that would be silly! ;-)

The CRX is just a play thing and 15's suffice, the big guns come out at the end of the year.