Jacki&GeneZ16

I'm agonizing over a choice that could be a no brainer for most, especially the for more fun on course.

Shall I stick with the Stock 16x9.5 wheels and buy 4 Kumho V710s 265/45x16? The "advantage" is I would stay in AS, and may beat the turbo charged, all wheel drive Rice Burners, thus boosting my ego.

Or should I use Fikse 17x11 wheels with 315/35x17 Kumho ECSTA V700 on the front and Fikse 17x12 wheels with 335/35x17 Kumho ECSTA V700 on the rear? These are free (wheels are a loaner and tires have one season, with 2 new 315/35x17 Victoracers front back-ups) from a friend who “retired” from autocrossing his ZR-1.

Of course these 17” wheels were not offered in 1987 (and not likely that wide by the factory in the 1980s). Therefore I would not finish the season in AS, leaving the WRXs and Evos to fight it out. But MAYBE these larger wheels and lower and wider tires could help me get closer to the FTD cars? That would likely be the biggest boost to my ego.

My Vette is prepared for autocrossing (Polyurethane bushings, VB&P swaybars, one year old Bilstein shocks) but not a Z51 suspension. It still sits at the stock height. I am not planning on upgrading to bigger brakes, so I'll keep another set of 16x9.5 with 255/50x16 on the car for the street.

So is bigger really better? What is your opinion and experiences?

AUTO_X_AL

we run 17x11 1/2 CCW all around and NOW use 315@all four corners due to the fact the 335's knocked out the rear wheel wells. Just wanted to give you the heads up.

Al

vader86

My 86 Z51 handled much better with the 17x9.5s than it did with stock rims.

Jacki&GeneZ16

Al
Thanks for the warning. To make sure I am not knocking out body parts
I'll need to do a little testing in the neighborhood before the next autocross.
Gene

Jacki&GeneZ16

Thanks vader86,
I assume you used lower profile tires on the 17x9.5s than you had on the 16s. What tire size and brand model do you like?
Gene

astock165

Are you running NCCC or SCCA? I thought poly bushings moved you from stock to street prepared? Admittedly I don't know anything about the NCCC rules.

c4cruiser

The poly bushings will put into SCCA Street Prepared as will the 17" tires/wheels. Most SCCA events won't check for the buishings unless you wind up going to regional or national events. But the tires would be obvious.

Going to B/SP will give you the chance for lots of mods, but competition can be very stiff there, so it comes down to how much you want to convert the car to a dedicated A-X car and not have it a comfortable driver for the street.

Is your car a Z52 car? The 16x9.5 wheels came on the Z52 so that would keep you in AS. Hoosier has a 275/45-16 that will fit the wheels and there is no clearance issues in the wheelwells. Hoosier sells discontinued tires from their website at really cheap prices so that may be a big cost savings compared to the V710. I was able to get a brand new set of A3S05's in 255/50-16's for $107 each delivered

Slalom4me

Combined wheel/tire weight is a consideration that was
at the top of my list when I began looking to upgrade my
wheels to provide more brake clearance.

Shedding static weight is good, shedding dynamic weight is
great. While losing 20lbs of weight that rotates at wheel
speed won't have the acceleration benefit that 20lbs (!) of
engine assembly would have, it is nothing to sneeze at.
In addition to acceleration, this also helps deceleration as
well as vertical motion of the wheels.

Back in the day, lots of Z/06 owners were throwing away
OEM Speedline wheels and and wheel/tire sets. I do not
believe these wheels are so plentiful now but they are
light and if there are issues with them, I haven't noticed
the threads, yet.

.

BrianCunningham

I've got 18x12's in the front and 17x12's in the back with 335's all the way around. Believe me IT'S WORTH IT!

vader86

yes, lower profile, 275/40/ZR17 Kumho Ecsta Supra 712, good for the price

However, these tires are sticky only for a short period, then they become slippery. (about 10K) I leave them on because they are a fairly good rain tire (louisiana).

If i was looking to autocross more, the cheap answer would be Ecsta MX....but I would prefer something like Eagle F1 Supercar or F1 GS-D3.

Jacki&GeneZ16

ASTOCK
I am running SCCA, you are right I guess I should be in Street Prepared. See below.
Gene

Jacki&GeneZ16

c4cruiser
Thanks for your help. This saves me from buying 16 inch race tires. Here in the Greatland we don't only have Regional SCCA autocrosses and local Porsche Club (using SCCA rules) autocrosses.

I had not looked at the Street Prepared rules. Using the 2004 Rules for stock (Topic 13) "Alternate components which are normally expendable and consider replacement parts (e.g., engine..., suspension bushings...etc.) may be used provided they are essentially identical to the standard parts (e.g., have the same type, size, hardness, weight, material etc.)" I assumed the "material" is insignificantly different (polyurehane vs rubber). Also, I could not buy a stock replacement, since the Chevy dealers do not sell bushings (without selling them on suspension part$$). Among the Corvette after market I could only find polyurethane, this contiuned to "justify" my assumption that the change was "essentially identical." With your comments and those of ASTOCK the 2004 Rules for Street Prepared Category (Topic 15.8.C) are obvious that I now have an SP C4.

I'll let the score keepers know and they can review my records for the autocrosses thus far, and then keep me in Street Prepared for the next 2 events.

I really enjoy using this this C4 with the suspension with the polyurethane bushings, Bilstein shocks, and much larger VBP Swaybars. At 150,000+ miles this is a better ride and more comfortable than I have had since buying the Vette 10 years ago with 78,000 miles.

I suppose it is not a Z52, I know it is not a Z51, it did come with 16x8.5 wheels that I use up to the last SCCA Regional autocross. I was not able to buy a single 16x8.5 wheel to replace one bent passenger side wheel, but I found a straight set of 16x9.5 wheels from an 86 C4. Since they were available both on the 86 and 87 I thought that would keep me in the A Stock class, but I'm apparently wrong again. So it is off to SP I go. This makes my choice of changing to 17 inch wheels easier.

Thanks for the suggestion, I am only have clarence issues on the left front (inside forward end) of the tire. I am trying 1/4 inch spacer and will add a shims. Hopefully, without losing too much Positve Caster, I have had it set at +2.2 degrees; and without losing too much Negative Camber, I have had it at -1 degree. I am able to get the 335/35x17 rears on with a 1/4 inch spacer on the passenger side. I wonder if my Vette is straight?

Jacki&GeneZ16

Brian,
I am getting there and I bet it will be worth it, from my post above. with the 315/35x17 tire on 17x11 wheels.

Gene

Jacki&GeneZ16

Thanks Vader86,
When I am in the market to replace tires, I'll keep this in mind.
Gene

Jacki&GeneZ16

Thanks again for your comments Slalom4Me, I'll be going for the less weight.

At this time I'm sticking with the stock brakes, so I can use my stock wheels for the street. When I need more brakes I certainly have to go to the 17 inch wheel for the street also.

Agree!
Jacki scraped one (ZO6 front) wheel and we replaced it with a reconditioned OEM wheel for half the price that looks perfect. Nice and light! Now I need the other 3 for her future race tires.
Gene

Vetracr

I ran same combo on my BSP/ASP autox and then ITE race car. You can't get enough rubber down with a Corvette.

Larry

Jacki&GeneZ16

Al & Larry
I have significantly decreased my autocrossing times this past weekend!!! Yes, SIZE DOES MATTER. Last few Autoxs I was 6 to 7 seconds behind the fast times, now I am only about 2 seconds behind the same drivers/cars! With more seat time for me, they will now be in my range.

With a little preparation sparked by responses/warnings to this thread, I did not have any significant problems. The 335/35ZR17 Kumhos on the 12x17 rear wheels did requires that I replace the studs for the lugnuts on the right rear to studs that were a 10cm longer and used a 10 cm spacer. Otherwise the inside edge of the right rear tire tread would have scrapped on the hardware attaching my rear control arms to the frame.

There is not a clearence problem on the left rear. Maybe the body is not on straight?

On the left front 315/35ZR Kumhos on 11x17 wheels also had scrapping of the left front tire edge on the part of the plastic wheel-well that is against the frame. The scrapping was only when I fully cranked the steering to the right lock, which occurs only when I am parking. So I also replaced the studs for the lugnuts on the left front to studs that were a 10cm longer and used a 10 cm spacer on the left front. This was just noted in the garage.

Under race and parking conditions, after the autocross this past Sunday, I did notice the chalk I put on each inner surface of the right and left fender did get rubbed. I suppose I could put on a little larger spacers on each front. Good news: there is no damage to the tires or the wheel-wells.