FireInMe17

Hey guys, trying to get my car back on the road for the spring. I'm waiting for my 18x8 IROCs to get here and I'm trying to figure out some tire sizes I could run on it.

Seems many of you on here no longer use the stock 15 or 16 inch wheels, and I'm not too sure what to get.

I was thinking 245 40 18 front and 275 35 18 on the rear, anyone ever run a combo like this? Looking for some input. Hopefully have them mounted and balanced and on the car by next week, can't wait!

FireInMe17

I need something wider in the rear with the new 355 under the hood, but I still need it to fit and look good with the front tires. Not sure which way to go with it...

paul_huryk

245-40-18 is the right size for the 8" wide wheels you are getting.

275 tire needs at minimum a 9" wheel - 9.5" or 10" is optimal.

Thirdgen89GTA

iTrader: (5)

245/40/18 Michelin Pilot SuperSports. http://www.tirerack.com/tires/tires....omCompare1=yes

Its the best summer tire for the street right now. I run it on my Focus ST in that size and the grip is excellent. Like passenger's face on window excellent.

Or you can move to a more R compound like tire like a direzza Z II star spec. But then you are looking at 200UTGR rating tires which won't last much more than 10-15k with "fun" usage.

FireInMe17

Anyone run anything wider on the rear for an 18x8?

I bought the 18's with the hope of going wider on the rear. Either way its going to look better but if I tried a 275 would that make it looked ballooned out or what? Haha I don't have any experience with mix-matching tire sizes like this. All your help is greatly appreciated!

//<86TA>\\

iTrader: (14)

A good tire shop won't put the 275 on a 8" wheel.
Your pretty much stuck with 245's, maybe a 255 if you can find one

cosmick

Getting a 275/60R15 onto a 15x7 is possible because of all the sidewall height. A 275/35 has none, so it really does need at least a 9, ideally a 10, it can go on a 10.5, the ricers stretch them onto 11s.

Thirdgen89GTA

iTrader: (5)

Worry less about section width, and more about compound quality.

If you put a PSS, or Direzza, or other top notch tire even in a 245 width you will have more traction and better handling than if you tried to stuff a 275 on the rim.

If you go too wide for the rim, what happens is the sidewalls lose their stiffness and your turn in suffers. This is because the tire contact patch will move independently rim with side loads. It will make it feel like you are driving on marshmallows.

A good 245 tire is all you need. With the right tire and suspension setup you can still pull 1G lateral grip. High Performance Pontiac did it back in the early 90's or late 80's, I have the article around somewhere.

If you want to run a 275 tire you should step up to a 9-9.5" rim.

Besides, with your engine you'll have maybe 300whp or so. You'll have a ton of torque, but you don't need a super fat tire.

FireInMe17

Thanks guys, everything I was looking for. Decided to get 255 rear 245 front. Gonna give that a shot.

Thirdgen89GTA

iTrader: (5)

Don't even bother. Run a square setup. Those 10mm won't do jack squat for you. With a square setup you can rotate the tires.

You want more traction at the back run a drag radial.

paul_huryk

https://thirdgenfbody.wordpress.com/2011/03/31/124/

https://thirdgenfbody.wordpress.com/...aft-july-1990/

Indeed you can get close to 1g with 245 tires and the right suspension.

But you need a 275 all around to get to the next level of handling & braking...

Thirdgen89GTA

iTrader: (5)

Hadn't read the first one, or seen it before.

But I have a copy of the Slight of Handling article.

FireInMe17

Already ordered the tires guys. Maybe once I burn off the rear tires I'll get 18x9 or 1810 and step up in the rear. I have big plans, just want to get it back on the road for the spring. Been almost 5 years since I drove the car..

cosmick

Lots of guys pinch a 275/40 onto a 9.0, GM did it, and it drives safely enough, even with spirited cornering, but it isn't right. GM does it to save cost, and because owners cheap out on replacements and go 245/45.
The original Viper put 275/40s on 10s, as it should be. They learned from GM's mistake of 9.5s on the 'vettes.
Every tire has a best wheel width, and if you're going to use something else, better to use a slightly wider wheel. It makes the sidewalls vulnerable, and maybe the wheel itself if you curb it, but it improves grip and response, it makes handling more predictable, especially mid-corner bumps, so you're less likely to end up off the pavement.
OP; why did you order 8s if you're serious about performance? Sell the whole mess, order some 18x10.5s, they're cheap and they're all you can tuck, and there are plenty of good 285-width tires available.

paul_huryk

I agree 100%.

BMW uses the following formula for sizing tires and the wheels they place on them for their performance cars: tire section width - 0.5" to 1.0" = optimal wheel width. So they put a 255 tire (10.02") on a 9" wheel and a 225 tire (8.86") on an 8" wheel. Having a solid wheel width is one key thing to sidewall stability, turn-in, and balance. GM put a 245 tire on 8" wheels - should have been 8.5" according to the formula.

As for the 4th gens, putting a 275 tire on a 9" wheel is just a way to save a few nickels per wheel - considering how little $ additional a 9.5" wheel would have been. Add that shortcoming to the list of cost saving items GM did put on 3rd gens (sheetmetal suspension parts, 7.5" rear, and cheap engine parts like clutch fans and plastic radiators and you can understand why many think the cars were junk (from the factory).

FireInMe17

It didn't even cross my mind when I ordered. I wanted the 18" IROC replcias so I got them. Didn't cross my mind and I wasn't thinking about it because I have a 315 shoved onto a 16x8 on my truck and thats how I've been driving it like that for two years but its a 315/75R16 so I have sidewall width to make it fit. Wheels and tires look good on the car though. I'll post a picture.

FireInMe17