Project Z06: A Set of New Shoes

A new season means new rubber, and this year we didn’t want to make any excuses in the tire department. Our C5 Z06 is being prepped for the SCCA’s Classic American Muscle autocross class, where the only wheel and tire rules say that tires must be 200tw or above. For us, that means a BFGoodrich Rival S, and the widest Rival S we can get is a 335/30 R18.

Unfortunately, that 335 won’t work in the front of a C5 Corvette without some serious fender liner surgery. It’s not a width issue, but rather one of diameter. In the front, those 335mm wide tires rub the leading and trailing surfaces of the wheel wells a few inches in from the fender lip. There’s also some potential fender clearance issues under full compression. We didn’t want to risk damage with wider tires and potentially throw off our scrub radius even more than we already have in the front, so we went with a set of 315/30 R18 front BFGs mounted on some brand new MOMO RF-20 rotary forged wheels. Momo has been around for a while with premium wheels for premium cars, but it’s exciting to see them enter the arena of high-quality flow-forged and rotary-forged wheels, which bring structural integrity and high customizability to a very affordable price point. These Momo RF-20s are just hitting the market now. If you want a set of your own, Sam Strano at Stranoparts can hook you up. Street price on a setup similar to ours is just a little over $2000.

Those front 315mm-wide Rivals are held up on a set of 18 x 11 +53 RF-20s weighing in at 24lbs each. There’s an immense amount of brake clearance—even with our big Wilwood 6-piston calipers— and fit and finish are impeccable.

In the rear we wanted to experiment with more precise spacing, so we had Momo supply the wheels with a bit more offset than we knew we’d need so we could tune the precise fit with spacers. The 18 x 12 rear RF-20s weigh in at 26lbs each, and hold those aforementioned 335/30 R18 BFG Rivals quite nicely. We spaced them so we’d have just a couple millimeters of clearance to the inside upper wheel liners at full compression, which should allow for a bit of tire flex with negligible rubbing. This left us at the equivalencies of a +52 offset, and about 1.5” of tire poking from the rear fender.

Plenty of autocross Corvettes running similar setups just live with the poke—with proper ride height and the aggressive springs seen on competition Corvettes, there’s little risk of getting into fender rub issues—but we wanted a bit more finished appearance. So, we bolted on a $22 set of eBay universal fender flares. Sure you can get custom flared fenders for the rear of your C5, but for $22 we’ll take the old-school, exposed-screw-head look.

Comments

deaconblue New Reader
2/15/19 10:50 a.m.

Okay so I know you are going to take some heat for this, but you spend $2K for a set of really cool forged rims and then you cheaped out of a set of $22 eBay fender flares that would honestly look better on a pickup truck? A set of real C5 wide body rear fenders are about $700.

Not going to comment on the style of those rims or if they are going to be easy or not to keep clean with track pads, but they are a bit on the heavy side for forged rims. I would have thought say a set of Forgestar F14 would be lighter and less expensive, plus with the money saved you could have bought a set of proper wide body rear fenders. Heck if you don't mind the miss matched look and wanted to save even more cash, you could have run the 21 lbs C5 Z06 factory 18 x 10.5 +58mm rear rims (that came with the car) on the front with those 315 tires.

Either way that wide 315/335 Rival S combo should rock on the autocross course!

alfabeach New Reader
2/15/19 11:48 a.m.

In reply to deaconblue :

How much faster are the $700 vs $35 flares?

gardnpc
2/15/19 6:36 p.m.

Wow, different world. My Miata 15" RPF-1's weigh less than 10 lbs. Those Momo wheels cost more than many NA's for sale out there.

JG Pasterjak Production/Art Director
2/15/19 8:23 p.m.

deaconblue said:
Not going to comment on the style of those rims or if they are going to be easy or not to keep clean with track pads

I can't believe you think these beautiful light grey rims would be hard to clean. They're a top quality set of fine dark grey rims. I love my black rims.

JG Pasterjak Production/Art Director
2/15/19 8:25 p.m.

alfabeach said:
In reply to deaconblue :

How much faster are the $700 vs $35 flares?

This [we really need a "pointing up" emoji].

Sure the fenders are $700. How much is paint? How much work are they going to take to fit?

Are these perfect? Maybe not.

Are they 80% as nice for 2.5% the cost? Oh yeah.

JG Pasterjak Production/Art Director
2/15/19 8:30 p.m.

deaconblue said:
I would have thought say a set of Forgestar F14 would be lighter and less expensive, plus with the money saved you could have bought a set of proper wide body rear fenders. Heck if you don't mind the miss matched look and wanted to save even more cash, you could have run the 21 lbs C5 Z06 factory 18 x 10.5 +58mm rear rims (that came with the car) on the front with those 315 tires.

From what I've been hearing, the Forgestars are about 1lb lighter per corner for pretty close to the same street price.

We actually had been running 315s on Z06 rears all around, but they were heavier repros. Real Z06 Speedlines are getting rarer and more expensive by the day it seems. We also found that the 315s on the 11s put more than 3/8" of tread width on the ground vs the 10.5s.

te72 Reader
2/16/19 7:31 p.m.

gardnpc said:
Wow, different world. My Miata 15" RPF-1's weigh less than 10 lbs. Those Momo wheels cost more than many NA's for sale out there.

I have a set of the 14" RPF-1's myself, still feels eerie to lift those after lugging around the 16+ lbs RPF-1's I have for my Supra haha. Definitely a different world though, Miatas are around what, 30 lbs per corner with wheel and tire? My Supra runs something like 43 lbs per corner.

All that said, big cars with power are a different type of car to drive from a lightweight momentum car. That's why I like having one of each, to appreciate a totally different experience. =)

te72 Reader
2/16/19 7:33 p.m.

JG Pasterjak said:
deaconblue said:
Not going to comment on the style of those rims or if they are going to be easy or not to keep clean with track pads

I can't believe you think these beautiful light grey rims would be hard to clean. They're a top quality set of fine dark grey rims. I love my black rims.

Haha, that's great man. True story though! Two of my sets of wheels are dark colored, you barely notice (IF you notice at all) the dust, but my brilliant silver RPF-1 setup for the Supra? I literally wipe them down after each autocross event of they look awful.

stewdesignjts New Reader
2/17/19 7:10 a.m.

Did you guys end up trimming the wheel opening of the rear fenders?

JG Pasterjak Production/Art Director
2/17/19 8:36 a.m.

stewdesignjts said:
Did you guys end up trimming the wheel opening of the rear fenders?

Not yet. Ran an event the weekend after doing this at a fairly bumpy site, and I taped up the fender lips pretty good to see any signs of rubbing and got nothing. Looks like they'll live a little while longer.