First this is for autocrossing.

Can a 275/40-17 inch tire and wheel fit on all four corners of an '88 Fiero?
If so what is the widest rim I can run; 7", 7.5", 8", 8.5", etc?
What offset front and what offset rear?
Sticking out of the wheel well does not matter, nor does light rubbing.

Thank you.

I have 255's on the rear (8 inch wide rim) and 235's (7 inch wide rim) on the front of my 88 GT in 17 inchers.

For 275's, I suspect that you will want a 9 inch rim as I could barely get the 255's on the 8 inch wide rim and they could have used more mounting space. Nothing rubs on the front or rear. I also believe you will need to go to coil-overs to get the larger 275's on the rear to avoid rubbing and hitting the springs.

i thought some of the concerns with running a tire so wide would also be the diameter? 275's would be awesome though, on a 17 inch rim. However, i also noticed something very important (at least for me). But big tires like that also weigh A LOT! Keep that in mind.

at least with my old miata, a heavy set of wheels and tires would absolutely kill the charactor of the car. so i ended up going with a real light set of wheels and tires.

a rubbing problem really sucks! when i had the 245's in the back of my old miata (width 8.5" wheels, and the incorrect offset) i would slap the tire around any aggressive turn (which i was compelled to do with better sticking tires). i was also running 450lb/in springs (ground control) with KYB AGX's and still not stiff enough to avoid rub...

'88 front diameter is about 24.7" and a 275/40-17 is about 25.7". So the difference in diameter is not that much. If I can figure out what will fit I will then buy the lightest wheels I can afford.

even though the diameter doesn't seem like a lot, you need to check out the % of the difference. apparently, anyhting above roughly 2% will make the speedo inaccurate by a considerable amount. Besides, i think you need at least a 9" width to properly run a 275.

Definitely run 275's on a 9" rim. I wouldn't put them on anything smaller.

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1986 Fiero GT - Engine swap in progress
GM Master Tech, ASE Master Tech, ASE Advance Engine Specialist, Hendrick Master Tech

Ok folks I appreciate the input, but this is for competition use, only. The speedo (4% error: http://www.rims-n-tires.com/rt_specs.jsp ) will not be looked at and I have mounted 275/40-17's on 8" wide wheels.

I guess I should have worded the question a little better.

What I'm trying to learn is will they fit?
At what width rim will they fit? Like they will fit with a 9" rim but not with a 11" rim? Or, do I have to pinch them down on a 8" rim?
And if they fit what offset do I need for the front? And, the rear?

Thanks!

quote Originally posted by Primaris: What I'm trying to learn is will they fit? Thanks!

Best tire calculator I've seen:

http://www.1010tires.com/TireSizeCalculator.asp

i saw a guy put 345's on a corvette intended for a 275??? but the tire looke terrible on it, the "shoulders" had serious overhang on the rims... just looked bad and was not intended for a rim smaller than 11"? regardless, what i mean is, you can install a 275 on an 8" rim, but it's not going to perform the way it "should". it's just not the correct application. unless you just want bragging rights (like the vette owner).

The 275 is 10.83" wide, you might with great difficulty be able to mount it on an 8" wide wheel for the sake of proof that almost anything is possible however, it will not seal properly if at all, it will not handle as intended either and the stress associated with the bead being squeezed down to a width much to narrow for its design may cause it to fail prematurely, it's not much unlike jamming a size 9 foot into a size 8 shoe. A 9" wide wheel is the minimum width recommended for a 275/40 series tire and the max is 11". The 40% aspect ratio is to low to provide the sidewall flexibility you need to reduce the structural stress on the tire mounted on an 8" wheel. If it were a 50 series you could probably get away with it but then the tire would be to tall.

This is one area where defying the specifications could cost you, and a reputable shop paying any amount of attention to detail will not mount that tire on an 8" wheel, the difficulty in attempting to do so alone would probably deter them.

quote Originally posted by Primaris: I have mounted 275/40-17's on 8" wide wheels.

And I've put a 225 on a 6 inch wheel, but that doesn't mean that it worked well.
The shorter the sidewall, the less width mismatch is permissible between wheel and tire. A 245/60-15 can run on a 7" wheel, but I wouldn't run a 245/45-17 on anything less than an 8" wheel--GM used 8.5" wheels to run that tire size on C5 Corvettes. GM also uses 9.5" wheels for 275/40-18's on the rear of the C5, so you should take a cue from them...

I'm running 255/50-16's on 16x8-25 wheels on my '87 GT with coilovers. I absolutely would not go wider and I think that 245/50 is a better size for that wheel. GM used that size when the wheels in question were on early '90's Grand Prix.
Artherd (all his posts are in the archives now) ran 18x8.5 rear wheels with (I think) 265/35 tires on his formula. Look up his posts.

If this is for competition use, and you do mount 275's on the rear of your Fiero, you probably don't want to go bigger than 225-235 on the front.

[This message has been edited by Will (edited 12-09-2007).]

I found this very helpful for figuring offset. Hope it helps.
http://www.1010tires.com/WheelOffsetCalculator.asp

Again all. The only thing that matters is the results on the STOPWATCH. I have mounted 245/40-17 Hoosiers on 7" rims and they are faster than 225's & 215's on 7 inch rims. I have mounted 274/40's v710's on 8" rims and they are faster than 245/40 on 8" rims. Are they pinched down some, yes. But with modern radial construction if the tire will seat you do not loose much width no matter how much you pinch it in. Hell, the top dogs in RX8's are running 285/30-18's on 8.5 inch wide wheels.

Lets move on beyond the lecturing of rim width opinion and on to actual knowledge. If you insist a 275 must be mounted on X inch wide rim, fine. What is the correct offset for the front and rear of the car?

Or, do you have some cool technique for figuring out what will fit.

This is the wheel calc I like: http://www.rims-n-tires.com/rt_specs.jsp

It lets you save changes you make via the favorites in IE. If I get a tow vehicle & trailer these will be the Hoosier tires I'll be running: http://tinyurl.com/yofwb2 But, they are out of the question for now at $230 each and only lasting 40 or 50 miles.

I'm running 17x7.5" in the front with 45mm offset and 17x8.5" with 48mm offset with a 10mm spacer (so actual offset is 38mm). Tires are 255/40/17 and 225/45/17. The outer edge of the tire is about as far out as you'd want if you wanted to keep the tires inside the fenders but if you don't mind haveing them portrude then you can reduce the offsets. I think there is room on the front to go deeper to the inside but that would require even more offset than 45. The rears are about as far inboard as possible with 17" so to increase width you would need to decrease offset. These are how mine fit.

quote Originally posted by Primaris: Again all. The only thing that matters is the results on the STOPWATCH. I have mounted 245/40-17 Hoosiers on 7" rims and they are faster than 225's & 215's on 7 inch rims. I have mounted 274/40's v710's on 8" rims and they are faster than 245/40 on 8" rims. Are they pinched down some, yes. But with modern radial construction if the tire will seat you do not loose much width no matter how much you pinch it in. Hell, the top dogs in RX8's are running 285/30-18's on 8.5 inch wide wheels.

Ok, Mr. stopwatch... Would they run faster if they upgraded their wheels to better match their tire sizes? You also forgot to mention that some classes constrain wheel dimensions relative to stock, which might have some bearing on why people try to pack too much rubber on a given wheel. After all, that's what I'd do if I had to keep a certain width to stay in a given class.

But that's a new constraint that wasn't in your original question.

It's also not a constraint under which you're operating because you're talking about non-stock wheel dimensions.

WCF claims to have put a 17x9-45 on the rear, but don't specify early or '88. http://www.westcoastfiero.com/faq/faq.html

And you still don't want 275's at all four corners.

You are completely correct the reason for stuffing such wide tires on to narrow rims is due to rules limitations which don't apply here. The reason for wanting the 275/40-17 is because of tire availability and cost. I am planning on putting quite a bit of money into my car, but the budget is not unlimited so the ideal tire 275/35-15 Hoosier A6 is out for the time being.

My goal is to stuff as much rubber under the car as will fit. If a 315/35ZR17 will fit then that is what I will run. Equal tire sizes will be used on all four corners. If some handling trait develops from running the same sized tires on all four corners then that trait will be addressed via spring rate changes. Rim width by its self is unimportant. Rim width and correct fitting offset is. For example: Someone out there knows an 11" rim is too wide at 0 offset because it hits the front fender when turning, but a 10 inch rim does not. This is what will be helpful. Then I know a 275 mounted on a 10" 0 offset wheel has a very good chance at working. Follow?

I'm just trying to keep this thread, conversation, on topic and away from; that looks bad, they will stick out, that rim is too narrow for X width tire, etc.

Here is the goal in picture form: http://www.sirscca.org/hhs05/photos/photo_22.html

Here are the tire choices: http://www.tirerack.com/tir...mho&model=Ecsta+V710
The v710 lasts 2 to 3 times as long as the Hoosier A6 and is just a tenth or two slower.

At least three references to what fits have been posted, and you haven't acknowledged any. What are you looking for?

16x8-25 is the biggest 16 that can fit on an early car. There is room for a little more backspacing... maybe as much as 1/2" on an 88.

You can run maybe as much as 1" more backspacing on a 17 than on a 16.

The front spacing of a 16x8-25 is as much as you want to run under stock bodywork regardless of wheel diameter.

To get an answer that satisfies you, you are probably going to have to go pull a wheel off your car and measure how much backspacing it can have. Once you know that number, the widest tire you can fit won't be much wider.

Have you ever set up a Fiero or other rear heavy/RWD car before?
By running the same size tires at all four corners, especially big sticky ones, you'll create handling vices that you just can't fix with spring/bar/damper adjustments. You'll end up with a very tempermental car that is extremely difficult to drive at its limits. The end result is that you'll be slower with more rubber because the car requires a level of perfection from the environment (both driver and pavement/course) that is not available.