Wheel/Tire Setup
Thread Starter
Burning Brakes
Joined: Sep 2011
Posts: 960
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Wheel/Tire Setup
Here is a possible C4 wheel/tire setup using tire-rack stock:
Ultraleggeria 19 x 10 40mm wheels, found as front wheels for the C6 Z06
RE-71R tires, in 275/35-19 or 285/35-19
But to get a 305/30-19 tire on the car calls for an 11" wide wheel. A 295/30-19 tire is okay on a 10" wide wheel but for instance I don't usually recommend an AD08 tire for autocross.
Here is a link to an application that compares a proposed wheel/tire setup to a current wheel/tire setup:
http://www.kbhscape.com/wheel.htm
The application produces correct results by working with wheel offset and tire width instead of with wheel width. However, the tire is assumed to be on the spec wheel width for the tire size.
Ultraleggeria 19 x 10 40mm wheels, found as front wheels for the C6 Z06
RE-71R tires, in 275/35-19 or 285/35-19
But to get a 305/30-19 tire on the car calls for an 11" wide wheel. A 295/30-19 tire is okay on a 10" wide wheel but for instance I don't usually recommend an AD08 tire for autocross.
Here is a link to an application that compares a proposed wheel/tire setup to a current wheel/tire setup:
http://www.kbhscape.com/wheel.htm
The application produces correct results by working with wheel offset and tire width instead of with wheel width. However, the tire is assumed to be on the spec wheel width for the tire size.
Last edited by B Stead; Aug 20, 2018 at 10:00 PM.
Le Mans Master
Joined: Aug 2015
Posts: 6,128
Likes: 2,003
From: St. Charles MO
That wheel offset moves the tire 6mm further outside than the 315/30/18 on 11" wheels with 50mm that I run at all four corners. i believe this would work on your C4, because I also have some Hoosier A7s at 315/35/17 mounted on 11.5" wheels, and the extra 0.5" of wheel is all to the outside (i.e. they have the same backspacing as my 18x11 wheels). That would put them within a mm or two of the setup you're proposing. They are right at the outside edge of the fenders, but they never touch. I run a lot of negative camber, so that may help.
FWIW, there is a Continental 200tw tire coming, probably next year. If you don't like the Rival S, it is likely going to be produced in 315/30/18 size and could be a very good alternative.
FWIW, there is a Continental 200tw tire coming, probably next year. If you don't like the Rival S, it is likely going to be produced in 315/30/18 size and could be a very good alternative.
Thread Starter
Burning Brakes
Joined: Sep 2011
Posts: 960
Likes: 40
Just using nominal tire widths, a 285 tire at 40mm wheel offset is 5mm less outside position than a 315 tire at 50mm offset. Or a 295 tire at 40mm wheel offset is the same outside position as a 315 tire at 50mm offset.
Of course the actual tire widths can be looked up in the specifications. And those tire widths are already based on being on the spec wheel widths.
Also, I see some notes that the early model C4's don't have as much inside wheel clearance as later models.
Finally, note that an AD08 tire has an extremely square shoulder and is a difficult fitment.
Of course the actual tire widths can be looked up in the specifications. And those tire widths are already based on being on the spec wheel widths.
Also, I see some notes that the early model C4's don't have as much inside wheel clearance as later models.
Finally, note that an AD08 tire has an extremely square shoulder and is a difficult fitment.
Last edited by B Stead; Aug 21, 2018 at 02:47 PM.
Le Mans Master
Joined: Aug 2015
Posts: 6,128
Likes: 2,003
From: St. Charles MO
Just using nominal tire widths, a 285 tire at 40mm wheel offset is 5mm less outside position than a 315 tire at 50mm offset. Or a 295 tire at 40mm wheel offset is the same outside position as a 315 tire at 50mm offset.
Of course the actual tire widths can be looked up in the specifications. And those tire widths are already based on being on the spec wheel widths.
Of course the actual tire widths can be looked up in the specifications. And those tire widths are already based on being on the spec wheel widths.
Also, I see some notes that the early model C4's don't have as much inside wheel clearance as later models.
Last edited by MatthewMiller; Aug 21, 2018 at 04:47 PM.
Thread Starter
Burning Brakes
Joined: Sep 2011
Posts: 960
Likes: 40
I was expecting the older model C4's with 32mm to 38mm OEM wheel offsets. Now I see newer model C4's with 50mm and 56mm OEM wheel offsets.
So I could find additional wheels for the newer model C4's. (And yeah there is a quick-and-cheap-o setup as "Flow One Race Spec" wheels in 18 x 10.5 54mm and in 19 x 10.5 54mm found as C5 Z06 rear wheels.)
If a 285 tire on a 40mm wheel works on a newer-model 50mm C4 then that is a beneficial handling gain but while possibly increasing steering kickback. Of course these fitments are wider wheels and tires than OEM base and are modern tire compounds. Also this is tire-rack stock instead of custom wheels.
A 285 or 295 tire on a 40mm wheel works better on an older-model 32-38mm C4.
A 295 or 305 tire on a 54mm wheel works on a newer-model 50mm to 56mm C4.
So I could find additional wheels for the newer model C4's. (And yeah there is a quick-and-cheap-o setup as "Flow One Race Spec" wheels in 18 x 10.5 54mm and in 19 x 10.5 54mm found as C5 Z06 rear wheels.)
If a 285 tire on a 40mm wheel works on a newer-model 50mm C4 then that is a beneficial handling gain but while possibly increasing steering kickback. Of course these fitments are wider wheels and tires than OEM base and are modern tire compounds. Also this is tire-rack stock instead of custom wheels.
A 285 or 295 tire on a 40mm wheel works better on an older-model 32-38mm C4.
A 295 or 305 tire on a 54mm wheel works on a newer-model 50mm to 56mm C4.
Last edited by B Stead; Aug 23, 2018 at 04:12 PM.
Le Mans Master
Joined: Aug 2015
Posts: 6,128
Likes: 2,003
From: St. Charles MO
I was expecting the early model C4's with 32mm to 38mm OEM wheel offsets. Now I see later model C4's with 50mm and 56mm OEM wheel offsets.
So I could find additional wheels for the later model cars.
If a 285 tire on a 40mm wheel works on a 50mm C4 then that is a beneficial handling gain but while possibly increasing steering kickback.
So I could find additional wheels for the later model cars.
If a 285 tire on a 40mm wheel works on a 50mm C4 then that is a beneficial handling gain but while possibly increasing steering kickback.
In addition to the downside of more steering kickback, there may be an increase in wheel bearing wear. That's already one of the few weak areas of a C4. Also, for autocross work, there is an argument that a narrower track would be better. It would be interesting to quantify the pros and cons.
But...sticking especially to the autocross realm where the rules require a 200tw minimum tire, it seems that the two likely hot setups for a C4 without doing body work (flares) would be 315/30/18 BFG Rival S on 11" wheel (my current setup) or the 305/0/19 RE71R on an 11" wheel. With 50mm offset, these will fit a later C4 at all four corners, or with about 32mm offset they should fit an early C4. So I'm curious why you're contemplating narrower wheels and tires?
