Looking to put 31x18.5x15 tires on my 86 swb

[70CHEVYBB]

Any pics of how you guys put 31x18.5x15 tires under a 73/87 short bed? Looking for frame mod pics or any inut on this modification?

Thanks, Wes

[cadillac_al]

Dang, why so short and wide? I would like to see that size on a truck for the heck of it but I can't see it being a good mud/sand tire. I'm curious.

[slotard]

I wonder if those are the widest DOTs available... what engine/tranny/axle? What's the measurement from frame to edge of bed? Will you be tubbing it?

[70CHEVYBB]

2wd. 24" from frame to bedside. I have room for a 4 link outside the frame but have thought about inside the frame. I will use coil overs off the rear of the axle. 4.11 gears with 31's will be like a 3.73 down the highway. not looking for a superfast truck so Im leaving the stock rearend but new posi and axles.

[68c10owner]

Originally Posted by cadillac_al

Dang, why so short and wide? I would like to see that size on a truck for the heck of it but I can't see it being a good mud/sand tire. I'm curious.

It's a pro street or hot rod tire size. Not off road.

[68c10owner]

Originally Posted by 70CHEVYBB

2wd. 24" from frame to bedside. I have room for a 4 link outside the frame but have thought about inside the frame. I will use coil overs off the rear of the axle. 4.11 gears with 31's will be like a 3.73 down the highway. not looking for a superfast truck so Im leaving the stock rearend but new posi and axles.

We have a member with a 29x 18.5 tire under his truck and all he did was move the leaf springs inboard. Search for JKnight. I'm sure the 31x18.5's would fit as well. Years ago there was a company that sold a kit to fit a 33x21.5 tire with the stock frame rails but they are long out of business. There is a lot of room under these trucks. I have considered the 29x18.5's myself.

[aggie91]

Originally Posted by slotard

I wonder if those are the widest DOTs available... what engine/tranny/axle? What's the measurement from frame to edge of bed? Will you be tubbing it?

MT Sportsman Pro: 33X21.50-15LT has a section with of 19.6" and a tread with of 16.6"

Hoosier Pro Street Radial: 33x21.5R-15LT has a section with of 21.3" and a tread with of 16.8"


Those are the widest DOT tires available to my knowledge...

[70CHEVYBB]

I do not want to narrow the axle. I measured the back spacing and a 15x15 rim with 10.5 of backspace will make it work. I also want to use truck rally wheel centers and have them welded in the 15 inch wide wheels to keep the center caps and rings.

[slotard]

Originally Posted by 70CHEVYBB

2wd. 24" from frame to bedside. I have room for a 4 link outside the frame but have thought about inside the frame. I will use coil overs off the rear of the axle. 4.11 gears with 31's will be like a 3.73 down the highway. not looking for a superfast truck so Im leaving the stock rearend but new posi and axles.

I have 4.10s and the math on my tires work out to 30.5" tall (haven't put a tape measure on them), 350/350 and that isn't so pleasant on the highway but mine's a truck engine rather than something that wants to spin fast.

[70CHEVYBB]

I read it as 4.10 /31 tires and 55mph = 2510 rpm. Im only 17 miles from work.

[68Timber]

Originally Posted by 70CHEVYBB

I do not want to narrow the axle. I measured the back spacing and a 15x15 rim with 10.5 of backspace will make it work. I also want to use truck rally wheel centers and have them welded in the 15 inch wide wheels to keep the center caps and rings.

That sounds awesome, I want to see this.

[slotard]

Originally Posted by 70CHEVYBB

I read it as 4.10 /31 tires and 55mph = 2510 rpm. Im only 17 miles from work.

Plus whatever torque converter slip happens if you don't have lockup. It isn't outrageous, but I wouldn't want to drive it a few hundred miles in a day.

[70CHEVYBB]

Just going to cruze around and look cool. Big burnout once in awhile.

[J Knight]

Originally Posted by 70CHEVYBB

Any pics of how you guys put 31x18.5x15 tires under a 73/87 short bed? Looking for frame mod pics or any inut on this modification?

Thanks, Wes

I did it with stock suspesion.

[70CHEVYBB]

Originally Posted by J Knight

I did it with stock suspesion.

Any pictures of the leaf spring mounting points and what size tires, rims and do you remember what the back spacing is?

[mud.man.rj]

Nice job J. Knight, springs inboard are a nice fab.

[slotard]

I can't tell in the pics, did you box the frame where you inboarded everything?

Do you have a swaybar? I'd expect the closer spaced leaf springs would allow more body roll. Not sure how much it matters.

[J Knight]

Originally Posted by 70CHEVYBB

Any pictures of the leaf spring mounting points and what size tires, rims and do you remember what the back spacing is?

Yes I do. 29/18.5/15 on 15x14/4.5in bs.

Originally Posted by mud.man.rj

Nice job J. Knight, springs inboard are a nice fab.

Thanks, it was easier AND harder that I thought it would be.

Originally Posted by slotard

I can't tell in the pics, did you box the frame where you inboarded everything?

Do you have a swaybar? I'd expect the closer spaced leaf springs would allow more body roll. Not sure how much it matters.

No I didn't box anything, I didn't feel it was needed. I do have a sway bar yet but the slight sway is barely noticeable imo.

[J Knight]

...

[68Timber]

Sweet. I see a 9" peeking back. Did you narrow it or buy it built?

[J Knight]

Originally Posted by BRUISER

Sweet. I see a 9" peeking back. Did you narrow it or buy it built?

I found an old 9in and took it to a local rear end shop by my house and had it narrowed and completely rebuilt.

[LiveAnimals]

I've always liked your rig J

[J Knight]

Originally Posted by LiveAnimals

I've always liked your rig J

I appreciate it Kam!

[68Timber]

Did they put custom axles in, or shorten the stock ones and redrill the flanges for the GM 5 on 5 pattern?

[J Knight]

Originally Posted by BRUISER

Did they put custom axles in, or shorten the stock ones and redrill the flanges for the GM 5 on 5 pattern?

They ordered new axles to fit in 5x5.