Hi all,

1999 C5. Previous owner went 1" up on the wheel sizes and kept the same aspect ratio, so currently running 245/45/18 fronts and 275/40/19 rears. Suspension is stock and slightly lowered, tires are old. The car understeers badly on the limit. My use case is spirited road driving in the mountains, some touring, and maybe a trackday or two. My objective is to make the limit handling much more neutral and improve handling in general. I'm not concerned with maximizing ultimate cornering grip, not chasing lap times.

I'm considering a square setup of 275/35/18 tires, Michelin Pilot Sport 4S, with 18x9.5 wheels. The Enkei NT03+M is available in this size with a 58mm offset, which should weigh 19.x lbs. (Links: Enkei and distributor.)

Would the offset be a problem? By my understanding, this would place the wheels 7mm further outwards compared to the stock offset of 65mm. Is that correct? This guy here apparently ran 55mm offset, for whatever that's worth. The more common square setup seems to be 295/35/18 where the NT03+M comes in a 64mm offset, but 295 is the width of the rears on the new GMA T50 which uses the exact same tires and has 650hp, so I don't think 295 is necessary.

Has anyone had a problem with 35/18 rears? Obviously the speedometer will be slightly off. I'm considering the older Pilot Super Sport which comes in 275/40/18 as an alternative.


Angus

 

18x9.5's with a 58 offset will fit and work fine. A 275/35/18 @ 25.6" tall will look fine on the front but too short on the rear, IMO. If it were my car, I would look at a taller rear tire, something like a 275/40/18 @ 26.7" tall or a 285/40/18 @ 27" tall. Even a 295/35/18 @ 26.1" tall would work, though that width tire is pushing it on a 9.5" width wheel.
Other options:
255/35/18 @ 25" tall or 255/40/18 @ 26" tall on the front and a 275/40/18, 285/40/18, or 295/35/18 rear.

 

Square will be fine. I run a 275/40-18 all the way around and don't have rubbing unless I'm at full lock, and it touches my DRM brake ducts. Without them, I am 100% confident you'd have no issue.

I wish I went with a 275/35 for a slightly less chunky look, but these were on sale and saved me about $150 so I said to hell with it. Never felt any understeer at the limit - really happy with how the car is now actually.

 

Thanks both. Yes, 275/35/18 will be looking small at the rear. I'm not too concerned with the looks though, more trying to take out as much unsprung weight as I can to liven up the handling. The car certainly doesn't lack power and noise!

Stingaroo:
- "never felt any understeer" - how much oversteer?
- How's the comfort and road noise with 40s? Would you be happy to drive all day on pothole-strewn public roads with 35s? What tires are you using?

Comparison of current rear tire to new proposed rear tire.

 

Weird. I can see that OP replied but the post isn't displaying on the thread

 

Oh wow there we go - now it's here. Strange forum glitch, I guess.


Oversteer - honestly, the car feels pretty neutral to me. I like it - the front goes where I point it and it seems to stay there. Unfortunately the only track event I've done with the setup since install was a wet day, so hard to judge, but on the street it's been great. I do daily the car so no issues there. I wouldn't be concerned daily driving on 275/35s either. Old setup had 285/35-19s on C6 wheels and it was fine.

 

I have run 275/35R18 square on 18x10.5 wheels on several C5s. It is a little short in the rear but doesnt look bad. I also use 285/30 on 18x11 wheels square on my current car which are even shorter. For a street car 275/35R18 would be fine.

275/35R18


285/30R18

 

Man I really wish I went 275/35 instead of 275/40 now. That looks better to me. lol

 

Thanks, looks good. Which wheels did you use? I'm looking for the lightest possible wheels to improve the handling, but....

I've checked with suppliers and both the Corvette-suitable wheels from Enkei are supposedly no longer in production. NT03+M 18x9.5 58mm Offset 5x120.7 72.6mm Bore and the equivalent 18x10.5 64mm offset.

The 9.5" quoted weight was 19lbs. The only other wheel I've found close to than weight is the original magnesium rears.

 

I have a set of 4 OE Z06 rears which are 18x10.5 and less than 22lb. Now that I have the 18x11 Apex wheels I just use the Z06 wheels for my street tires.

 

Flow One F4s are 18x10.5 and +54 and weight 21.2 pounds each.

$982.16 for a set on TireRack right now. Possibly less from other vendors. I know Sam Strano of stranoparts.com sells them - I would personally rather shop with Sam than TR if the deal were similar.

 

I have seen those, and they would be fine for street use, but I wouldnt use them on track. There is a reason they are light and cheap. A friend of mine is on his 4th set because the first 3 bent the inner barrels going over curbs on track. Retail is about $1500 for my Apex wheels (I got in on the group buy), and I can jump curbs all day without hurting one.

 

I was considering 18x10.5 square for a track setup - sticking with 19 + 18 for street. Still looking for a cheap set of wheels….

 

Which model Apex wheel do you use, and how much do they weigh? Looks like the EC-7R comes in the right size, and is very light weight. Link



Edit: The ARC-8 weighs only 18.2lbs and costs only $334!! Link



I confirmed with Enkei that the Corvette-suitable wheels are both discontinued. Also confirmed with Bob from House of Wheels that they do not sell the magnesium wheels.

 

I use the EC-7 in 18x11 for the Corvette specific fitment. The EC-7R and Arc-8 are not made in Corvette fitments. They are $384ea. and are about 24lbs. The inner bead in reinforced so they do not bend going over curbs. At my budget I will sacrifice a few pounds to have durable long lasting wheels. Also, if I do bend or damage an Apex wheel they offer a 50% replacement.

https://www.apexraceparts.com/shop-b...tte-wheel.html

 

Ah ok, thank you. Do you know what about the EC-7 specifically makes them a Corvette fitment? The basic specs on the ARC-8 (below) seem to be suitable but I don't want to run into problems. I'm running stock brakes.

Edit: Looks like the center bore on these might be too large(?). The EC-7 is 70.3mm.

 

If the centerbore is the only difference, you could just run a hub ring to close up the gap and run either one.

 

The bolt pattern is also 5x120mm vs the Corvette 5x120.65. Its a small difference yes, but I wouldnt put the studs under more stress on track than they already are. Also, the spoke clearance to the caliper is designed into the Corvette wheels. If you upgrade your brakes later you may not have enough room to clear the caliper.

 

Brake clearance is definitely a good point. They designed those to fit most of the popular BBKs for these car.

 

The wheels that you've shown here unfortunately are not for your car. The bolt pattern is different and we do not recommend using them. The good news is we do have Corvette specific wheels as Mike pointed out above on his beautiful Z06. They are offered in 18x10" ET58 and 18x11" ET57 with reinforced inner lips and big load ratings that exceed JWL/VIA standards by 20%

I'd suggest going with the 18x10 as it better supports the 275 tire you want to run, which in turn will put more of that tire on the ground. Here's a link to the product page: https://www.apexraceparts.com/shop-b...tte-wheel.html