Tire Upgrade

[nocok5]

I just purchased this 1990 GMC Jimmy. I'm pretty stoked about it since there appears to be zero rust and I got it for a pretty decent price. It's a stripped truck with manual windows and 15x6 steel wheels. I would like to upgrade to a larger tire, but not sure what I can safely fit on the stock rims. Not looking to lift it or change rims right now just want to put some new tires on that are bigger than the 235/75/15's that are on it now. Any suggestions on how big I can go?

 

[The Griff]

Well I had 33x9.50X15's on my factory steel wheels, and there were no clearance issues, but now I have a set of 31x10.50R15 Super Swampers on it now.

 

[Metrodps]

FYI the running boards on backwards. I had posted this in tires for Big Red the Dante's Peak Suburban.

FWIW

OK so the p235/75 R15 are smaller than the 31x10.5 R15LT

So I know it has been posted but how much larger can I go with out rub or cutting?

32x11.50, 33x10.50 should fit.

I've seen the odd truck that will roll 33x12.5's with no cutting.

My blazer had 33/12.50's without anything done it...

Stock for 3/4 tons was a 32"/ metric.

 

[nocok5]

FYI the running boards on backwards. I had posted this in tires for Big Red the Dante's Peak Suburban.

FWIW

Lol the first thing I was planning on doing was taking those off. Supposedly an older couple owned it.

 

[Metrodps]

Lol the first thing I was planning on doing was taking those off. Supposedly an older couple owned it.

Yea us old farts and gravitationally challenged need them.

 

[Deuling]

Great looking rig, hope you keep it that way . You should be able to fit 33s in there.

 

[82355]

I would just go with a 31x10.5x15". What gears are in it? They are usually higher geared when they have the little tire on them.

Martin

 

[nocok5]

I would just go with a 31x10.5x15". What gears are in it? They are usually higher geared when they have the little tire on them.

Martin

The code on the glove box is GU6, which from what I've researched means 3.42. I have no reason to believe they were changed but I guess it's possible.

Got the running boards off and it looks much better

 

[82355]

Automatic or four speed? 3.42's is a higher gear, usually they have 3.73's with 31x10.5x15's. That being said, 3.42 I'd deep enough for 31's. especially if it has an SM465.

Martin

 

[nocok5]

Automatic or four speed? 3.42's is a higher gear, usually they have 3.73's with 31x10.5x15's. That being said, 3.42 I'd deep enough for 31's. especially if it has an SM465.

Martin

Thanks for the feedback. It's an automatic. I ordered a set of 30x9.5x15's from Discount Tire Direct. I'm just going to run those for now. Might upgrade to 33's eventually, but this is pretty much going to be a daily driver so I'll see how I like the smaller tires.

 

[82355]

I'm actually looking at one right now that has 3.73's (GT4), and had 235/75R15 tires factory (has 33's on it now).

Martin

 

[dyeager535]

The 33x9.5R15 would probably be ok, you've got pretty thin wheels already. However, the 33x10.5R15 fits most of these trucks with no clearance issues.

I'm running 3.42's in my truck with the manual and 33x10.5R15, and still use "2nd" (not low) to start out under pretty much all conditions. I don't think it would be an issue with a 700, seeing as the early trucks were 3.08's with 31" tires, and if held in gear, still got moving ok.

 

[snowdriver]

my 1990 had 31-10.5 15 on it from the factory,at one point i went to 32 on it,never had any clearance issues,but with a basically stock rig that is a DD,drivability was better with the 31's

 

[dyeager535]

That is a good point...some of your tires will have some pretty stiff sidewalls. The ride will definitely be worse if they are. I say it all the time, but my BFG's ride like bricks until I drop them down to around 20PSI, which you wouldn't want to do on the street. But in 33x9.5 or 10.5, if you want the best chance of no rubbing, at stock height they are the only game in town, except apparently swamper.

 

[blazinzuk]

So If I were going to leave one mostly stock I would get new shackles from ORD and lift shackle for the back ( read shorter than stock). And zero rates front and rear.

That will give plenty of room for 33x12.50s because of the fact it moves the axle ( you would need to get the axle forward an inch to fit 33s really well) and look cool because its not much lift at all only about 1.5"

 

[nocok5]

Appreciate all the feedback. I went with 30x9.5x15 Falken Rocky Mountain ATS tires. Still look a little small but were pretty inexpensive and will work for now. I may eventually put on a small lift and get taller tires, but just want to drive the truck in stock form for now. Need to get a few minor mechanical things sorted out with it and hopefully it will be a reliable DD.

 

[chulisohombre]

You will get better mileage with smaller tires. With 3.42 gears I wouldn't run much bigger than a 32x10.5 to not have any rubbing issues for the most part unless you are going crzy offroad. At least when you decide bigger tires when you need new ones. A small two inch lift and you could do 33s and it would look real good. Much better without the side steps.