Need 15" x 10" Rally Rim & Tire Sizing Help

[1986swb]

Sorry if this is a redundant thread but after searching the forum, I could not find the answers to my questions applicable to my 1986 GMC Fleetside SWB, with stock ride height and using 15" x 10" rear rallies:

What is the most effective (without scraping or rubbing inner and outer fenders) back spacing rim size AND maximum tire size combination for my 86 SWB?

1. Back space = 4.5" ? Max. tire size?
2. Back space = 5.0" ? Max. tire size?

My SWB currently sports the 15" x 8" rallies on 255-70s, with 4.5" back spacing. See pic.

Thanks guys. Your recommendations and expertise are greatly appreciated.

[f.monroe]

I think jdurant has 15x10 rallies and 295/50/15's on his blazer . Searech his posts and it should pop up . I would think you could run a 275/60/15 ,295/50/15 ,or a 285/70/15 depending on what you are after . I think the 275/60/15 would work the bast on the 4.5 inch backspace wheel . It would lookgood with a 15x8 rally on the fronmt with a 255/60/15 tire . If you are going to keep the 255/70 front then I would try to find a 285/70 rear .
Frank

[1986swb]

Thanks Frank for your timely insights. I took at Joe's thread (jdurant) and it was helpful but I'm thinking either 4.5" or 5.0" would work well for my 86 swb. Additionally, I am planning on dropping the truck at some point, nothing too radical, but maybe a 2/4 drop. So tire selection will be crucial. I am hoping to run 15x8 fronts and 15x10 rears.

I think I'm going to go with the 5" bs for the 15x10s unless I hear from someone who had real issues with it.

I'd also like to use my existing 15x8 OEM trim rings on the 15x10s. They should fit the same, right?

Thanks.

[jdurant]

My rears have are 10" with 4.5" BS. Thats what you need to even the track width. You are pretty limited on wide tire sizes for on 15"s these days. Pretty sure you aren't gonna find a 285/70.

If I were you I would just run a 275/60, since you only plan on doing that mild drop. I think that will be the widest, tallest, 15" street tire your gonna find.

[1986swb]

Thanks for the confirmation on the 5" back spacing. I read on one of your threads that you used a GMC/Chevy van trim ring on your 15x10s.

Will my 15x8 OEM trim rings fit nicely on the 10s?

[AceX]

My tires are 255/60/15 up front and 275/60/15 out back.

Suspension has a 2/4 drop.

[1986swb]

Originally Posted by AceX

My tires are 255/60/15 up front and 275/60/15 out back.

Suspension has a 2/4 drop.

Nice truck! Do you have any additional pics of your truck showing the 2/4 drop that you can share? Side views would be great. I'm assuming you used lowering coils in the front with hangers and shackles in the rear. I'm trying to keep the drop mild so that I can still haul and tow stuff without any scraping or bottoming-out issues. Thanks.

[blazer2007]

I found 285/70 15 bf goodrich has them and I run a corvette trim ring which is nice and wide and real hard to take off if someone decides to take them

[1986swb]

Originally Posted by blazer2007

I found 285/70 15 bf goodrich has them and I run a corvette trim ring which is nice and wide and real hard to take off if someone decides to take them

I looked at BFG tires prior to purchasing the Firestone Firehawk tires for my truck (in pics). I liked the tread pattern of the Firestones and they work incredibly well in the wet Seattle weather.

The largest size Firestone carries in the 70 series is a 255 but they have larger sizes in 60 and 50 series:

275/60/15 and 295/50/15

And the prices are also pretty comparable to BFGs.

I was thinking about using my OEM Corvette rally trim rings as well but I'd prefer to keep a consistent look to match the front rings. But I like your thought on fact they are harder to remove than stock truck trim rings.

[blazer2007]

the vette rings fit just as nice on the 15x8,s also

[AceX]

As requested:

[jdurant]

I just looked and couldn't find a 285/70. Either way, that would be a really tall tire. When I was looking for tires before, even places that listed 295s--didn't really have them, they were on backorder or discontinued. You might get lucky and find somebody with some old stock.
And any trim ring that will fit your stock 8"s will also fit the 10"s. The lip is exactly the same.

For those that don't know, this is how you read a tire size.
295/50/15
295-measurement of how wide the tire is in mm.
50-is the height of the sidewall, but an aspect ratio--in this case 50% of 295=147.5mm tall
15-is obviously the diameter of the wheel.

so a 285/70 would be considerably taller than a 275/60--which in my opinion is about as tall as you want to go.

[f.monroe]

The 285/70 would be almost 31 inches tall .

I figure it like this on all tire sizes . 285 x .70 =199.5 , 199.5 x 2(top and bottom) = 399 , 399 divided by 25.4(mm per inch) = 15.7086 , then add the rim diameter which in this case is 15 and the tire is 30.7086 inches tall .
A 295/50/15 is 26.62 inches tall
A 255/70/15 is 29.05 inches tall
a 255/60/15 is 27.04 inches tall

These are based on the size . Some manufacturers tires run a little larger or smaller but this is a close way to calculate it .
Frank

[gearhead427]

Hello I'm new here but i just wanted to toss in my 2 cents. I have in 81 Lwb Gmc that i run 275/60/r15 on all the way around. and there on a 8in rim. is there a reason your looking to move up to 10's? I don't have any rubbing issues at least not yet. its not lowered. I went with the 275s so that i could rotate them and there about the same size as stock so the speedo is just about on. well that was my 2 cents.