The Stovebolt Site Forums The Shop Area Engine Shop Tire size and wheel question

I have a set of wheels I'd like to use on my next project. I've had these wheels forever (since 1983) and am having some trouble figuring out what tires to put on them.

The truck is a '54 GMC and I picture it having the same aggressive stance you might see with some of the late 80s early 90s 4x4 Toyotas I see running around. Though I expect to routinely eat their lunch if provoked. It will be powered by a TBI 454 and setting on S-10 4x4 underpinnings.

The wheels are 8.5 x 15 slotted mags. It seems 15 inch tires are getting a little harder to find and while I can translate 8.5 into millimeters I'm not real sure what range of tire widths are appropriate on these wheels.

I had a set of 235/70-15 tires on 8-inch wheels a few years ago and based on that my guess is I need 255 or 265 for these wheels. But this isn't something I really know much about...

The width component is the part I feel I need help with. I want to run a light truck tire (LT) and relatively tall like a 75 with an agressive all-weather or M/S tread.

The truck is going to be a 1/2-ton with four-wheel-drive that will be used on those two or three days every third year when it snows around here.

It will be the shortest truck I have and it will probably be used to move my trailer around my place when a longer truck won't bend sharp enough, though this truck is not likely ever to pull the trailer off my place unless the trailer is empty and going to stay that way. The shortness, combined with four-wheel-drive and plenty of power should make this a very serviceable yard truck when I'm not using it for fun.

I want to be able to search craigslist for some cheap used tires to serve as rollers while I build the project. So if I ask a tire shop I feel like I'd be abusing them.

Anyone here know what size tire I really need? xxx/yy-15?

Thanks for your help!

30x9.50x15 is the largest that will fit on an S10 4x4 chassis in stock form, 31x10.50sx15 will work if it's a ZR-2 off rad package chassis. If you want LT Metric, LT235/75/15 is the only 15" size available, it will be a 6 ply C load range. Anything esle will be a Passenger rated, and even then, 255/70/15 is about the largest you'll find.
Given the engine that you plan to run, I would strongly advise swapping in at least the rear axle from the late ZR-2 S 10, as they used a narroewd version of the full size truck 10 bolt, which is not only much stronger, but on trucks after '97, have rear disk brakes.

If I were in your shoes I'd investigate the tires I really wanted to run.
Then find the tire manufacturers spec sheet for that style and size tire.
On the spec sheet are a few recommended rim widths.
If your rim width matches you now have your answer.
If they call for a different width then adjust your preferred tire size/style or the rim width to suit.

I'm sure there is a general rule as to what rim widths are acceptable for a standard size tire, but I'd defer to the actual tire in question, you can't get a more correct answer than that.

http://www.accuridewheels.com/completeversion.pdf
About page 39 is the kind of general info you're looking for, although that doesn't cover 15" wheels. somewhere there is a version that does..

Grigg

Rule of thumb is that the rim be approximatly 2" narrower than the section width of the tire, with about 1" tolerance. So an 8.5" wide rim would call for a 10-11 inch wide tire. a 9" tire would be ok, though the wider tire would be better. The problem that will come up here is the chassis that is going to be used. The S truck chassis will have tire rub issues with 10" or wider tires on the front, they will rub on the front sway bar in the turns. The ZR-2 chassis used different control arms and sway bars, and can tolerate wider tires, but even then there's a limit, due to the lack of strength in the axles and brake size. If the wheels in question are a RWD style offset, you could probably get away with a bit wider tire than what would go on a stock S10 4x4 wheel. You will be looking at floatation sizes to get the width and load range you're looking for.

Bill when you say the largest that will fit the S-10 chassis what is interfering? The 235s want narrower wheels than the ones I'm trying to fit, and so do the 30x9.5 though they are close.

I think I've found an 8.5 10-bolt and I'm sure I could break it if I try. Hopefully I'll remember some restraint...

The 31x10.50rx15 will fit my wheels, or at least the Michelin tires I looked up would fit, I didn't check any other brands.

Grigg Accuride refers to a Tire and Rim Association document that doesn't seem to be available without purchasing it for $85. It was looking for that kind of information after discovering that something like an LT265/75-15 wasn't available that prompted me to look for help.

The tire I'd really may not exist. 30 years ago I had Armstrong Tru-Trac on my mildly hot-rodded Blazer. I think I'd like those same tires, but with a Michelin reputation for quality. Of course those tires probably aren't made any more and I'm not going to run 30 year old tires on a driver.

Apparently Armstrong was bought and the brand disappeared.

My next step is probably to pose a related question over at Pirate4x4 and see if those guys can point me to a tire similar to the Tru-Trac but intended for mostly street use. Then I'll see what sizes those are available in.

Starting with the tires would be logical, but in this case I want to start with these wheels I already have. There is some nostalgia at work here. If that means running the 31x10.5 tires that is probably where I'm headed.

Bill these wheels are serious RWD offset. One of my concerns is that they may be too wide for the front, but I really need some tires on them to put them on the chassis and measure and test fit things.

This project is in the very early stages since I really need to finish my 1-ton first.

The interference is primarily at the sway bar, though I have seen them rub the frame at the rear. This is with stock offset S truck 4x4 wheels. You might be ok with a rwd offset, though you might need to check for fender opening clearance, as the wider wheels and rwd offset will alter the scrub radius. I think you're definetly on the right track test fitting. 31x10.50s should be easy to find used, they were stock size on the ZR-2 S10s, though some years did use a P rated 265/75/15. Unfortunatly, that size has gone obsoltete, and, as you mention, is very hard to get. We run into problems with that size often, especially when we get an S10, early '90s Ford, or Colorado with the off road package. Those all use that size tire, and there's just not much available. but 31x10.50x15 is very close, maybe about a half and inch taller and maby .20" narrower.

I think those 31x10.50s may be my best bet. The wheels I want to use are very deep dish so the swap bar issue may go away.

Since I'm putting a '54 GMC cab on the S-10 I want to be able to test fit this thing with the tires on it so I can mount the cab to avoid any issues.

I've posed some questions on Pirate 4x4 and will wait until I see what the response there is, but I think you've probably answered my question with that tire size.

Thanks!

Try contacting coker tire they will most likely have what you need.
http://www.cokertire.com/

Bob

Coker like most tire sites starts by asking what your vehicle is. That's where my problems start, my vehicle isn't going to be found in a drop down list.

"Coker like most tire sites starts by asking what your vehicle is. That's where my problems start, my vehicle isn't going to be found in a drop down list."

Gee...just like those kids at the auto parts stores, huh?
_________________________

Yeah. Color me not impressed.

I got some leads there, but don't feel real satisfied with where they went.

I can find 265/75-15s in a passenger radial with a more aggressive tread pattern that might make sense for my use. The BF Goodrich Long Trail T/A is available in my size, looks like a reasonable choice and is cheap enough I can see me buying them. The specs say they will fit my wheels reasonably well.

What is the practical difference between a P and an LT tire? The P265/75-15 is rated at over 2400 pounds per tire which should be adequate on a half ton that will rarely be asked to haul a load. That totals 9600 pounds and I doubt the truck will ever see 5000 total unless I'm pulling a trailer, and most that weight will not be on the truck's tires.

Except for occasional tractor duty at home this truck will be expected to do the same work my Corvette does. Just get me to and from work. The difference is it will be asked to do it on days when the weather isn't nice enough for the Corvette.

P rated is essentially the same as a 4 ply, unless it's XL rated, which is a 5 ply rating. LT tires are rated for heavier use, thye generally start at 6 ply, and are built for extended heavy load usage. For what you're loking at, a P rated will probably do fine.
I agree with the Coker issue. Nothing against Coker tire at all, but they really are more geared towards the restoration/hot rod crowd. What we're dealing with here is a completely different deal.

Well then the P265/75-15 if I can find a cheap set of used ones, will do just fine for my mock-up phase of this project and for rolling it around. If I buy new tires now they might rot before I finish it, so I'll start searching craigslist for some used tires.

Thanks!

best bet is stay with the king's measurements
31/10.50/15
33/12.50/15
35/12.50/15
first number is overall height of tire, second is width of tread section, third # is size of hole in the middle
All 3 sizes will fit your rims safely, you just need to consider wheel well clearance

I'm inclined to go with the P265 if I can find it. The 33 and 35 inch tall tires worry me a little because I'm putting a 454 in a truck with a 7.2 front diff.

I don't want to break that differential, and the taller bigger tire I run the more like that is to happen.