Wheel width configuration question. (Page 1/1)
4thfiero AUG 19, 06:27 PM
Hey guys,

Can someone possible help me out with wheel/tire sizing? Im having a hard time looking at diagrams and doing the maths to try and see what I need to do to make certain wheels fit.

Tire Size I would like...

Front: 225-245/40/18 Rear: 295-305/35/18

This will require me to have front wheel width of 8.5 inches and rear of 10.5.

Question: Besides some fender flares and possible stock fender cutting, will these size wheels fit on a Fiero, without hitting suspension or anything? Do i need custom suspension of any kind in the rear or front to accomidate this setup?

(im looking to run offsets from -15 - 0 to get approx 3'' poke in the front and approx 3.5 in the rear.
1985 Fiero GT AUG 19, 06:50 PM

quote
Originally posted by 4thfiero:

Hey guys,

Can someone possible help me out with wheel/tire sizing? Im having a hard time looking at diagrams and doing the maths to try and see what I need to do to make certain wheels fit.

Tire Size I would like...

Front: 225-245/40/18 Rear: 295-305/35/18

This will require me to have front wheel width of 8.5 inches and rear of 10.5.

Question: Besides some fender flares and possible stock fender cutting, will these size wheels fit on a Fiero, without hitting suspension or anything? Do i need custom suspension of any kind in the rear or front to accomidate this setup?

(im looking to run offsets from -15 - 0 to get approx 3'' poke in the front and approx 3.5 in the rear.



Front will severely wrench the wheel out of your hands over bumps setup like that (assuming 84-87 suspension, less so with the 88), also wheel bearings will not like any lower offsets then close to stock, higher offsets in the front for 84-87 give a substantially better experience, at least for me. I have 205/55r16 front on a 16x7" +42mm offset, no rubbing, lighter steering, and a much less jerky steering wheel.

Rear for me is 235/50r17, 17x7.5" +42mm offset, and it was rubbing on the spring perch (only slightly, it was so little I was able to move my car around once, but wouldn't have really driven like that). Coilovers fixed that.

The bearings are designed to run basically central to the wheel/tread, which means it needs an "offset" on the wheel mounting surface to allow the whole bearing/hub assembly to be more centered to the wheel. Having offsets between -15 and 0 would make the wheel essentially a longer lever arm, so that instead of sitting "on" the bearings, all the weight is trying to twist the bearing upwards, likely to damage them very fast. The reason it's "hard" to fit super wide tires is because to maintain good enough bearing life, they need to extend into the wheel well as much as it extends out of the wheel well, if stock is 7"wide, +35mm offset, if you fit 9" wheels, that would optimally extend 1 inch farther in, 1 inch farther out, to remain centered on the bearings. Because the strut and spring are there in the back, as basically a hard limit to how far in the wheel/tire can go, that also limits how far out it can go, without damaging the bearings. On the front it is more open, but front size is limited by the difference you want front to rear and how big you can get the rear.

In some cases higher offsets (my 42mm offset) is ok because the designers chose to run slightly lower offsets then optimal to get the looks they wanted (the chevette front suspension would have been for a narrower bodied vehicle, put on the wide Fiero and they used either 30 or 35mm offset wheels to even it out, the 88 front suspension was wider to start with, so they used higher offset wheels and had less steering kickback. For me using 1" wider front wheels than stock, they don't poke out any further, because of the higher offset, the full 1"goes into the wheel well, reducing kickback, and maybe improving bearing life, but not decreasing it at least.

[This message has been edited by 1985 Fiero GT (edited 08-19-2025).]

cvxjet AUG 19, 07:22 PM
I would like to mention some facts about our Fieros- they do not have the modern, perfectly designed suspension setups, so the ability of our cars to deal with giant wheels and tires- especially the weight these bring with them- is severely limited.

I switched to 16 x 7 wheels and 205/225 tires from some off-brand 15 x 7 wheels and 215/225 tires....I took 3 lbs off each rear and 6 lbs off each front- the difference was amazing- it went from driving like a truck to driving very much like a modern car. To give you an idea what light-weight tire/wheel setups can do for performance, the Ford GT350 "R" version's main performance change is carbon fiber wheels which takes 10 lbs off each corner. (Gosh, I wish I could find/afford some CF wheels for my Fiero!!!)

I went with 205/55-16s up front and 225/55-16s in back- these were common sizes on many popular cars back in the 90s, so there are many options- both companies and performance categories...I like the General Gmax tires- they rate very highly in testing at the Tire-Rack and are a few lbs lighter than competitors tires..

Consider that the C8 Vette weighs at least 3600 lbs vs the 2700 lbs a Fiero GT weighs- that is a ratio of 1.3333 to 1.....So my front 205s would be equal to 275s on the C8...the 225s on the rear would be equal to 300 mm wide on the C8s rear.....that is wider than the stock tires up front and (basically) the same as the rear on the basic Vette! (C8 Front 245, rear is 305)

[This message has been edited by cvxjet (edited 08-19-2025).]

olejoedad AUG 19, 09:14 PM
Large diameter, wide wheels and 40/35 series tires may look cool - but that's all.

Your handling will be compromised compared to stock.

And your car will ride like a log wagon.

On my V-8 Formula, I run 215/50/17 front and 235/50/17 rear with very lightweight wheels, 7" wide, 40 offset.
Handling and ride are as good or better than stock and the car is very driveable in the dry and the wet.

The front sits a tad lower since this picture was taken, as I cut one coil off of the front springs.
fieroguru AUG 19, 09:16 PM
For the money you are looking at spending for the wheel and tire package, you are much better off buying a tool so you can mock them up vs. taking some random recommendation on the internet.

chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://static.summitracing.com/global/images/instructions/php-01201.pdf
IMSA GT AUG 19, 10:23 PM
I agree with Guru above. The tool is not too expensive and will save you headaches by making sure the wheels you're ordering will fit. Here's one for $55 on Ebay.
https://tinyurl.com/Wheelrite

[This message has been edited by IMSA GT (edited 08-19-2025).]