rx7m5guy

My tire installer says he can not get the Kumho V710 305/30-18 to fit on the 9.5" wide front wheel of my C6 Z06, i.e., the tire is too wide.

Is this the universal experience, or is it just this installer and I should encourage him to continue or find another installer? (I have a set of C5 10.5" X 18" rear wheels I could use, but that puts me in ASP)

Thanks for your advice.

Cheers, Philip

Z06Fix

295/30/18 Hoosier A6. Pretty much the standard for the C6Z.

I don't think going any wider than that will gain you anything.

froggy47

I don't see why an installer can't get it on the rim if he knows what he's doing, but it might be too much tire (rubbing).

My guy has zero problems getting 295x17 on my front stock c5z rim

rx7m5guy

I am taking off the Hoosier. For the surfaces I run on, it heat cycled out and the grip went away much quicker than my experience with Kumhos on my C5. The 305 Kumho is the only comparable size to the 295 Hoosier, so I am not trying for more width, just trying to get Kumho characteristics, which I prefer. The 285 is too short in my opinion.

So thanks for the advice, but the question remains, has anybody made the 305 Kumho fit the 9.5" wheel?

Cheers, Philip

rx7m5guy

Reply to Froggy:

Thanks for the comment with regards to the 295 on the C5 wheel. I have done the same on my previous C5. As far as rubbing, I have had the C5 rear wheels on the front of the C6 with 315 Kumhos at a Test & Tune. The sidewall only rubbed on the brake cooling duct at full lock. The 315 is taller than the 305, and the 305 has a narrower section width, obviously. Also the 315 is the older round shoulder style and the 305 is the new square shoulder style. I will be trying the 305 regardless since I own them, just trying to stay in SS class.

Cheers, Philip

steponc

Go to the spec page for the tire. I usually use Tire Rack for this. Find your tire size and see what the recommended rim widths are. If the width starts at 10" then the tire will be too wide for the rim. It will physically go on the rim but you will not get the performance from the tire as designed, and may actually get less performance than going with a smaller size tire that is designed for the 9.5" rim. When the tire is out of spec for the rim it causes the casing to bulge out of shape and not stay flat at the contact patch due to the mis-shape. You will be riding on a portion of the contact patch with the shoulders curled up.
Most tire companies give a measurement for the width at a certain rim size. This rim size is the designed width best suited for the tire but the variation in either direction listed does not hamper performance.
I learned most of this by trial and big error.
After all of this being said, if your tire and rim size fall within spec then I would take the pertinent info to your current installer and let him review it. I'm sure he is only concerned with his liability of causing your car or you damage. This is a good thing.

rx7m5guy

Reply to steponc,

You got me there on looking at the specs, because I did that carefully and knew I was taking a chance. (The minimum listed size is 10.5") I was just doing what a lot of stock class autocrossers have to do to get the tires they want onto their restricted rim sizes even though they may be outside the recommended specs.

Cheers, Philip

Jason

I'd try somewhere else. I've seen some extreme combos over the years. I'd think that would work.

VetteDrmr

I'm running Toyo RA-1 305s on 18x9.5 rear wagon wheels with absolutely no problems. Tire wear has been exactly as expected, requiring one flip of the tires about halfway through their treadlife.

steponc's comment is one that I hear quite frequently from people that say my setup can't POSSIBLY work, and that I'm leaving a lot of performance on the table.

So, if you're tire mounting guy says he can't mount the tire, unless you've got a really good working relationship with him, I'd look for someone else.

BTW, I'm also running 275s on 17x8.5" front wheels as well.

HTH, and have a good one,
Mike

drivinhard

305/30R18 V710

Rim Width Range - 10.5-11.5"
Measured Rim Width - 11"
Section Width - 12.3"

That's a whole lotta tire to stretch on a 9.5" rim, especially in 18" size with a short sidewall.

Some (older) machines don't have the hydraulic muscle to mount really low profile (and very stiff) race tires. I know because I've used them

Do you know what machine he uses?

R Mackow

I've used A3SO4s(in 305 width) on stock C5 wagon wheels: 9.5x18.

Wayne O

I run Kumho 305/30/ZR18's on the front on 11" rims (using a hub extender/spacer).

froggy47

How much spacer do you need?

waktasz

Kumhos are way harder to mount than a comparable Hoosier.