You can remedy the size in the tune or just pick the right tires to stay close to the stock setup. Sounds like you'll be spending some money.

San

 

You can run any size rim that clears your brakes; all the ECM is concerned with is the overall diameter of your tires... Smaller rim = taller sidewalls = better straight line traction

 

I'll sacrifice street traction for killer looks all day everyday!

 

Hello guys I have in my C6 20'' wheels with low profile it runs great but when I get to 140mph to 160mph, the tail start shaking a little. What seem to be the problem?

 

Sounds like a warning to slow down!

 

Sorry to the OP.

So, I knew HP Tuners could do this but a number of people told me know to do this a year ago. That said, what's the ideal 18" set up for max street/strip traction w/o rubbing? I have 17x9.5 and 17x11 on my Camaro. Can you do the same with 18's on a C6 Z51 coupe? Does Nitto or MT make a 18" DR? Damn I'm fired up now!!

 

No problem, that's what I meant by open discussion! If you keep the overall diameter close enough, the computer does not care what tire you run. There are plenty of tires in 18, just depends on what you need. I think the ET street is a badass tire. The Nitto hooks pretty good as well.

 

I've wanted to put a 315/40/18 wheel/tire on the back for some time. No wheels (aftermarket) to match the stockers and no tires I can find either.

 

And if I'd be serious I would buy a second set of Hoosers or Khumos anyway

 

HP Tuners can compensate for some difference in overall tire diameter, but if the overall diameters of your tires is stock, or close to stock, you don't have to do anything: the car will never know what size rims it has; 16 - 22, so long as the sidewall grows or shrinks to accomodate the wheel without the overall size of the tire changing.
The best way to plan these things out is to use a Tire Size Calculator to compare the tires your car was designed to run with the tires you want to run.
I've gone through this before, so let me tell you my conclusions:
Stock, our C6s run:

245 40 18
285 35 19

We will begin with the Rears, because if you want new tires, chances are that is where they are failing you :
I wanted to run an 18" diameter rim: it is lighter, the additional sidewall will improve straight line traction, tires will be cheaper, and there are a lot more tires available on that size.
285 40 18 will be 0.45% Smaller
295 35 18 will be 1.62% Smaller
305 35 18 will be 1.68% Bigger
315 35 18 will be .64% Bigger

Those are the only sizes I can recommend. I have seen 325 series tires run before, and a 325 35 18 would be just 0.38% Smaler, but you may have some fitment issues.

Now the fronts:
You can stick with stock sizes (245 40 18), or:
255 40 18 1.25% Smaller
265 35 18 1.6% Larger
275 35 18 0.5% Bigger <= This is the stock C6 Z06 tire size.


Looking at that data, I decided to go with a 305 35 18R, 265 35 18F. Nitto makes a drag radial in that size for the back, the NT555R, and they also make the NT555RII which is the same Drag Radial rubber and tread pattern, but with a stiff sidewall for road acing. That was my choice. For the fronts I will be running Toyo Proxes R888. You can run Toyos back and front too; that was my original plan but I got a good deal on the Nittos so I am trying them out first.

Now that leaves us with just having to figure out WHAT 18" rim to run on the back in order to fit those tires...
I couldn't find one that fit well and didn't cost a fortune or weighted a ton, so I am having my stock ones widened to 18 x 11...

Here are a few threads you may find useful:
Nitto NT555 vs Toyo Proxes R888?
18" Wheels all around: Widened stockers, or ACE wheels?
Thoughts on tire sizes: 265/35R18 and 305/35R18?

 

Excellent! Who is widening your rear wheels for you. This may be the best path for me as well.

 

Weldcraft Wheels in Michigan. It takes 2 weeks and costs $200 per wheel.

I can hardly wait for them to come back!

 

^^ Great post Powerlabs!

FWIW, I run standard C5 wheels (not C5z wheels) with my 275/40/17 and 305/30/18 Nitto 555RII's for years with no problems on the track.

They are a little narrow compared to recommended at 8.5 and 9.5, though they fit perfectly on the car and I've had NO ill effects on the track (they handle like rails...I love R rated tires).

I do have to take off the larger drilled rotors up front, which I do anyway for track purposes, as C5 solid rotors are so cheap.

Matter of fact my 275/40/17 M/T drag radials are on 17x8.5 standard C5 front wheels, and they fit perfectly too, right at the edge of the fender (and obviously provide great traction, and at < 25" per tire (measured last weekend) they provide a nice gearing advantage. C5Z front sizes work well for the rear application also.

Just a data point based on my experience. YRMV.

 

tall sidewall also = poor handleing

 

Really?

Formula 1 tire:




I am told F1 cars handle pretty well... ...
You have to be careful making blanket statements like that... Very tall sidewalls, particularly soft ones on street tires, will definitely hurt handling as sidewall flex makes turn in slower and causes steering to feel vague, but this is not the case here: the world challenge Corvettes run 18 inch rims, not "Dubs", and there is ZERO performance advantage whatsoever to skinny tires on big whels; you need some sidewall for the tires to work, and sidewall stiffness can compensate for sidewall height resulting in a lighter wheel/tire combo that is ultimately faster

The bottom line is very simple:

You want your wheels to be big enough to accomodate the brakes required to stop the car under whatever driving conditions it will be put through, and NO LARGER. Making the wheels any larger than necessary will only slow the car down. Look at any race car and you will see that. From the F1 car pictured above, to rally cars, to lemans cars, etc etc... Unecessarily large rims have no place in a sports car.

 

I didn't know you guys were talking about running Formula 1 tires on the rear of your car...sorry, my bad...lol Sounded like you guys were referring to running drag radials, not Formula 1 tires.

I'm sure those Formula 1 tires won't give you very good straight line traction either, as your blanket statement said. Usually there's a trade-off, if they are good straight line traction tires they probably won't handle that great because they have to have sidewall flex to hook. Just like all-season's...they're equally craptastic in all seasons because they have to try to accomodate all seasons...lol

I like the steering response stiff, smaller sidewalls give, but to a point. I would never go any bigger than the OEM 18/19 combo. Heck, it took me 3 sets of tires to find the tire I liked years ago with my Firehawk. There are only two sets of street tires I will buy now, PS2's and BFG KD's (NOT KDW).

 

Love your wheels, they are beautimuss!!!!!
I'm having the same problems with wheels and tire combos as you are.
My 19/20 look good/handle good, but I can light them up with my A6
tru 3 gear, and I'm in the process of assembling a Katech 427 so my traction is going to get worse.
The idea to just buy some 19 in matching wheels with DR has crossed my mind, but again the weight factor comes up.
keep me up to date on what you end up doing.
I'm leaning towards the 18/18 welded wheel setup (Guy's).
Phil

 

Nothing but the very best for my car

Drag radials don't come in tall sizes so that's a bit of a moot point, but again, if you want to see what a good handling tire is, just look at the winning World Challenge Corvettes:
18 inch wheels and tires all around:

C5R Corvette:
18 inch wheels and tires all around:

C6R Corvette:
18 inch wheels and tires all around:


And you can rest assured they would be even smaller if they could fit big enough brakes to stop a 3000pound car going 200MPH underneath them.
But what do they know, right?

 

Hey AintQik,

What rims are those? Where did you get them?

Steve