hey guys,

im about to pick up a set of custom rims for my 89 iroc and i wanted something thats going to fill up the wheel wells nicely, but at the same time i want to run 275's up front and (if i can) 315's out back. i know a 17x9.5" and 17x11" combo will fit and allow me to run the tire combo that i want (im not afraid to hammer the wells a bit or roll the fender lip), but i was wondering if a 18" wheel will fill up the wheel well perfectly, or is a 17" enough?

also, i have an eibach prokit installed and koni yellows at all 4 corners. i thought since i could make the konis rock hard, an 18" wheel might be feasible, but i was concerned that i wouldnt be able to run as wide a tire with 18's....is any amount of hammering/rolling going to get the 18's with a 315 in the back to fit??? anyone done this???

 

No, you won't safely be able to run 315's but a 295 will fit perfectly, on the 17x9.5 17x11's in a 40 series tire. the 18's are do-able but again according to "WELD-RACING" you'll have to stick with 295's and an aspect ratio of 35's.
They will definitely fill the wheel well and put more rubber on the road.
I'm tossing around the idea of the 18's myself, if I can find a less expensive "light-weight" set.

Visit Weld Racing on the web , makers of "Weld Wheels"....

 

hmm, i read that the largest wheel/tire combo that could be used on a 3rd gen was 17x9.5's and 17x11's with a 315 tire in the back. im positive it requires the fenders to be hammered out and rolled, but i think it can be done. it was the 18's that i wasnt so sure on....

as far as performance goes, getting a huge contact patch is y i wanted to go with 315's, but i heard a smaller diameter wheel is better for straight line performance. it hooks better. i can see why the 18's would lay down more rubber, but will i notice a difference in straight line performance as opposed to a 17" wheel?

 

With anything less than a 50 sidewall tire you don't get flex. Flex=Traction. You wanna put rubber bands on your car go ahead. 18's are too big. 17's are pushing it especially with that big of a tire. Also, you woll lose performance with a contact patch of 315 as opposed to a 275. It takes more power to turn a bigger tire with that much contact area. Don't go crazy, just use your best judgement. Sometimes bigger isn't always better

 

I couldn't decide so I did both.
The 275's in back almost rub on the inside.

 

What I never hear is what is the biggest tire I can run on my 3rd gen equipped with a 4th gen rear. I mean there is a extra 2 inches of backspacing. I was throwing around the idea of 17's in front and 18's out back. But if sidewall comes into play I will just go with 17's all the way around. But that still leaves me wondering what offset and backspacing for rear rims? What size tire can I go with. ie I would like some 65's or some 60's series out back? But I should be able to run some 315/60 R17's right? all that extra backspacing?!?! I want some serious tire to ground contact wouldn't that be easily achieved with a set of 315's?

Some one let me know I will be watching this thread..

Kevin

 

hmm, this may be true but again i think it depends on how your 3rd gen is setup. right now im running a 9" rear (currie) with a 4.11 geared locker. i thought the 4.11's would be able to spin those large wheels/tires with no trouble. even though theyre large, they are pretty light for that size wheel. i imagine a 315/40/r17 would hook just as well as a 275/50/R17....or better. more rubber hitting the pavement.

and i KNOW that a 315 size tire can be run in back, but like i said, some modification needs to be done to have it sit snugly under the fender without sticking out (re: hammering/rolling). oh, and im having my 17x11" rims built with 6.75" backspace for the rear. i think that should keep them tucked away under the fender nicely...

 

Kevin,

Simply speaking, the amount of backspacing you have determines what offset the wheel you choose should have. The ride height of the car and the size of the wheelwells determine how much tire you can run. That being said, the largest tire you can run is NO DIFFERENT than that of a standard 3rd gen. The extra 2 inches of offset you speak of means you have to run a different wheel. The mounting surface of the wheel is 2" further out, but the car's proportions remain the same.

 

how large is the 4th gen rear then? 2 " longer on each side???

 

Its not about your gear ratio, its what kind of power you are making. 4.11's I am sure are great but with a tire as wide as 315 at the racetrack aired down to get grip, you have a lot more rolling resistance to overcome. Might have to do some benefit analysis. Wanna be out guinea pig?

 

heres my 2 cents.
i always thought 18s were too big. till i saw this thread. there is a guy with 315s in there. and too much flex=bad when cornering hard.

 

The width of the tire has little effect on power needed to turn it, burn it maybe?
As for flex,a little can help but too much can hurt. I refer you to the Porche 911 with a 0-60 of 3.2sec and the Dodge Viper at roughly 4.0sec. both with ultra low profile, hard, high speed radials. As said it has more to do with how good your chassis is matched to your tires.
The outer diameter of the tire decreases the effective gear ratio requiring more gear or more power, that's exactly why you see drag cars with 29"diameter tires and 4.88 gears, and us with 26" tires and 3.23/3.42 gears.

I'm still scaning my archives for the "Weld" article. But these guys spent "days" just trying tire and wheel combos on every style hot rod and street machine to find "the Biggest meats you can stuff under your ride..."(mind you they didn't roll the outer fender lips or beat in the inner fender against the springs or anything...)
They just played with cross-section widths, aspect ratio's, rim widths, offsets, backspacing and rim & tire diameters to get the tires to clear everything including: tie-rod ends, hub centers, brake calipers, fenders, wheel-wells etc...

 

hmmm, id love to see that article.


and id love to be a guinea pig. just donate some 18x11 rims and tires and ill do the rest and post the results


seriously though, i think im going to go for the 18's. im planning on getting into road racing soon too, so that has pretty much decided it for me. i still love to drag though, and i still want to be able to hold my own on the street if some punk thinks hes got game so we'll see. ill post pics/times, etc. but that wont be for awhile yet.