USA1C5

What is the advantage of running 18" rear wheels? Lots of C6 Z06's go to 18" rear wheels for HPDE's when they put on R-Compounds. Why? I've noticed that a lot of C6 Z06's go to 18X11 wheels with 295/30-18 tires for front (some run a 315 front) and 18X13 wheels with 345/35-18 rear. Why not stay with the 19" rear wheel? Why not run a 345/30-19 rear tire? I'm just curious why the 18" rear wheel and not stay with the 19".

GettReal

Gonna guess and go with price and availability of 18's

sothpaw2

cost? Selection? seems as you go bigger the cost skyrockets and selection is diminished. The cost really bothers me because the tire is not any wider, just larger dia. so the circ. is a little larger but not by much. The amount of rubber is probably within 2-5% and the cost is many times 40% more.

USA1C5

You guys have probably nailed it. I just checked Tire Rack and the cost was a bit different and the 18" were in stock.

345/35-18 Hoosier R6's were $376 each plus shipping
345/30-19 Hoosier R6's were $403 each plus shipping

Also the 18" were in stock ready to ship and the 19" were a special order and if you ordered them they would email you if they couldn't be shipped within 7 days. So who knows when they would actually ship.

I think my question has been answered. Thanks

drivinhard

besides cost/availability, a little sidewall is a good thing to. more sidewall = more forward bite. If you can, run the smallest dia wheel that'll clear your brakes

I run 18x10.5" C5Z rears because of availability/weight/price. But would run a 17x11 or 17x10.5" of the ~weight if I had a bunch of them sitting around.

USA1C5

I have never heard that about more sidewall = more forward bite. Good to know, thanks. Just an asumption on my part, but it stands to reason, probably more rearward bite (braking bite) as well if there is such a thing.

Wayne O

Most all serious C6 road racers I know run 18" wheels all-around (even the Corvette Racing C6.R's run 18" wheels). As mentioned, your tire selection is vastly superior than when using 19" wheels. Also, running 18's all-around lends itself to a more level setup of your car.

Exotica

The cost difference is not likely based on amount of material but rather the cost of production versus the number produced and sold. The larger sizes sell in much fewer quantities and the fewer they make the more they must charge to recoup all their costs and still make a profit.

Ever seen the price of heavy equipment tires? Thousands of dollars each.

Check out this site for used tires... How about a set of 12, all with less than 60% tread, for the amazing low price of $210,000 How much can rubber actually cost?

http://www.findconstructionequipment...ment-Tires.htm

LSs1Power

Going 18's will also act like gears. The car accelerate much faster with the 18's. Around my track, i found that i need to stay in 2nd longer in some turns so the 18's did hurt me (bouncing off the rev limiter). I went back to the 19's in the back and it worked better for my lap times.

AU N EGL

weight as well

18" rims weigh less then 19" rims

18" tires are slightly less then 19" tires of the same type

Overall with an 18" rim you might be saving 2 lbs of rotational wt, which is ~ 13 lbs of static weight per rear wheel

26 lbs less of both rear wheels is quite noticeable

Less wt the car will accelerate quicker and stop faster too.

USA1C5

I don't understand the gear change thing if the outside diameter of the 18" wheel tire set up is the same as the 19" wheel tire setup. Yes, you would be geared slightly lower if you use an 18" tire with less diameter and circumference. The 18" wheel tire I'm talking about is the same or very close. 345/30-19 diameter is 26.7" and the 345/35-18 diameter is 26.8" slightly larger but close. If anything the 18" tire would gear you slightly higher not lower. More sidewall on the 18" tire.

USA1C5

I didn't think about the weight.

drivinhard

The barrel of the wheel is a heavy part of the wheel, the closer you can tuck it closer to the axle centerline (moment of inertia) the better.

More sidewall will tolerate higher slip angles, I think the car is more forgiving and offers better feedback at the limit.

A lot of (RWD) autox guys will run a short sidewall front for transient response/turn in, and taller sidewall rears for forward bite. I have done the same (opposite!) on a FWD to get it to help rotate quicker.

LSs1Power

I tried my friends 18's which had 315/30 NT-01's, but i agree if you run 345/30/18 then the overall diameter will be very similar to the 325/30/19.

USA1C5

Are there any other advantages or disadvantages of the 18" rear tire compared to the 19" rear tire?

AU N EGL

Weight is the big disadvantage, costs are a slight disadvantage.

r.hillenbrand

Besides the cost there needs to be one more item discussed here. When running you also need to have the car tuned so it will not check for the Tire pressure sensors or have a spare set in the track wheels and a trackside tool to reset the TPS when changing wheels. If not the C6 (07) and newer will revert to limp mode thinking there is something wrong with the car. Also need to keep in mind the difference between the rake from front to rear. CCW can help on all of this.

USA1C5

I have a new set of CCW C14 wheels 18X11 front and 18X13 rear with Hoosier 295/30-18 front and 345/35-18 rear. According to specs. I could find, front wheel tire diameter is 25.3" and rear diameter is 26.8". This very close to the OEM Goodyear diameter which was 25.6" front and 26.7" rear. Cut all these numbers in half to see ride height difference for front and rear. .15" lower in front and .05" higher in rear. This would effect my rake slightly, but wouldn't this be less rake compared to the OEM wheel/tire setup?

davidfarmer

availability for me personally...........I can get very good scrubs for $75 each, where-as any 19" tire is gonna cost a fortune.

I can adapt my driving better than I can adapt my wallet right now!


btw, TPSM is pretty adaptable to diameter changes, but I turn it all of anyway.

AU N EGL

Take a piece of 3" PVC pipe.

Drill 4 holes in and put the TPMS valves though holes and secure.

Cap the end of the PVC pipe with plumbers glue.

put 32 psi in the pipe.

place and secure in the center of the car

Then program those TPSM to your car.

we have a few guys here in Raleigh that do this.

They talked to Schrader, maker of the TPSM and bought a 100 monitors and are working on prototypes

So no more reprogramming for wheel changes.