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Found this for you to digest till next weekend (My kid has his Eagle Scout project this weekend and next weekend I will be making a video of the rear axle removal and will measure both M135 and the M35 rims).
" Starting with the wheels, the easy part was knowing that the 6 x 8.75" military and civilian bolt patterns were equals. Having now gone deeper, I find record of six wheels on which the military or civilian markets could have used an 11R20" radial or 11-20" bias ply tire. Two Accuride and four Budds.
The first Accuride is their #26357. It is 20" x 7.5", stud piloted, has 6.25" of positive offset, and has a "Military Standard" / "MIL STD" rim/ring design. It is listed as ORD 7389621 for the complete wheel and ring, ORD 7389620 for wheel w/o the ring, and ORD 7389061 for the ring alone.
The other Accuride is their number 27101-C. It is 20" x 7.5", hub piloted, has 6 5/16" positive offset, and has either the Firestone FL-2 or FL-3 two or three piece rim/ring sets.
The first of the Budds is their number R66280-8. It is 20" x 7.5", stud piloted, has 5 1/8" of positive offset, and has the "MIL STD" rim/ring. It alone in all these is listed as sold only to the military. Why is unclear. The "R" means radial tire approved.
The next is R69890-8 described as 20" x 7.5", stud piloted, and having 6.25" of positive offset. Again a MIL STD rim/ring.
Next is R66640-3, stud piloted, 20" x 7.5", 2.5" of positive offset, and having a Goodyear LB rim/ring.
Last is R93470-3, 20" x 7.5", hub piloted, having 3 9/16" of positive offset. It has a Goodyear LW rim/ring design.
Now for the 11" tires. Both radial and bias ply have an 8" "Design Rim Width". They are approved for use on flat base rims that are 7.5", 8.0", 8.5", and 8.50VM". Don't find what differentiates a "VM", but it doesn't matter. Both have a "Section Width" of 11.55", and "Growth Max Width In Service" of 12.47". They have "Minimum Dual Wheel Spacing" of 13.2".
Doubling the offset figure for each wheel must yield a figure equal to or greater than the dual wheel spacing figure for the tires. If your wheels were the 6.25" offset variety you could probably mount duals by adding a small spacer. But given your statements my guess is you found the 5 1/8" variety Budds. Which I fear means duals are not in the cards unless you change tires.
All this is from old print catalogs. Budd is gone, absorbed into the Hayes Lemmerz conglomerate with K-H and Motor Wheel. I'll look online at the Accuride catalogs to see if any newer versions exist. I would guess that the Accuride or Budd numbers will be stamped on your wheels to tell us what you have. If you find other numbers I'll dig deeper, or if I find online something different I'll edit. Stu"
Also found this I wonder if the Budd part numbers show up on our rims:OK, here is my $0.02.
1. A stock M35 will work just fine with dual 11:00x20s bias ply tires in the rear. You WILL lose a little tire to bed clearance, so in extreme off road conditions you may end up with the tires rubbing the underside of the bed.
2. I doubt dual 11:00x20 radials will work, as stated above radials "squish" at the road contact surface which MAY cause the tires to contact each other, which is NOT a desireable condition.
3. Stock M35 rims are 7.5" wide, and can handle up to a 12:00x20 tire. This is stamped on the rims of my M35.
4. M135 rims have about 1" less backspace than a M35 rim (i.e., the mounting surface of the rim is 1" closer to the centerline of the tire than a M35 rim). You CANNOT single out your rears simply by using M135 rims on the rear.
5. To single out the rears, you MUST reverse the rear hubs. The front and rear hubs are the same part number, the front hubs are already flipped. By flipping the rear hubs, you then have the rim mounting surface the same distance from the centerline of the truck, both front and rear. Once you have flipped the rear hubs, it doesn't make much difference whether you use M35 or M135 rims, as long as you use the same front and rear. I would use M35 rims, as the M35 hubs are designed to center the tires between the inner and outer wheel bearings. M135 rims will move the centerline 1" outboard of the bearing centerline. Not much significance, but since you already have the M35 rims on your truck, you might as well use them. All that M135 rims will do at this point is give you about 2" wider track. Might make the singles in the rear a little more esthetically pleasing, but I wouldn't bother! With 11:00 or 12:00 singles in the rear, your tires will now be 5"-6" inboard of the outer edge of the bed, which makes the truck look a little odd. The M34 Eager Beaver was made with single 11:00x20s in the rear, but the bed was several inches narrower, so it looked "normal".
" Starting with the wheels, the easy part was knowing that the 6 x 8.75" military and civilian bolt patterns were equals. Having now gone deeper, I find record of six wheels on which the military or civilian markets could have used an 11R20" radial or 11-20" bias ply tire. Two Accuride and four Budds.
The first Accuride is their #26357. It is 20" x 7.5", stud piloted, has 6.25" of positive offset, and has a "Military Standard" / "MIL STD" rim/ring design. It is listed as ORD 7389621 for the complete wheel and ring, ORD 7389620 for wheel w/o the ring, and ORD 7389061 for the ring alone.
The other Accuride is their number 27101-C. It is 20" x 7.5", hub piloted, has 6 5/16" positive offset, and has either the Firestone FL-2 or FL-3 two or three piece rim/ring sets.
The first of the Budds is their number R66280-8. It is 20" x 7.5", stud piloted, has 5 1/8" of positive offset, and has the "MIL STD" rim/ring. It alone in all these is listed as sold only to the military. Why is unclear. The "R" means radial tire approved.
The next is R69890-8 described as 20" x 7.5", stud piloted, and having 6.25" of positive offset. Again a MIL STD rim/ring.
Next is R66640-3, stud piloted, 20" x 7.5", 2.5" of positive offset, and having a Goodyear LB rim/ring.
Last is R93470-3, 20" x 7.5", hub piloted, having 3 9/16" of positive offset. It has a Goodyear LW rim/ring design.
Now for the 11" tires. Both radial and bias ply have an 8" "Design Rim Width". They are approved for use on flat base rims that are 7.5", 8.0", 8.5", and 8.50VM". Don't find what differentiates a "VM", but it doesn't matter. Both have a "Section Width" of 11.55", and "Growth Max Width In Service" of 12.47". They have "Minimum Dual Wheel Spacing" of 13.2".
Doubling the offset figure for each wheel must yield a figure equal to or greater than the dual wheel spacing figure for the tires. If your wheels were the 6.25" offset variety you could probably mount duals by adding a small spacer. But given your statements my guess is you found the 5 1/8" variety Budds. Which I fear means duals are not in the cards unless you change tires.
All this is from old print catalogs. Budd is gone, absorbed into the Hayes Lemmerz conglomerate with K-H and Motor Wheel. I'll look online at the Accuride catalogs to see if any newer versions exist. I would guess that the Accuride or Budd numbers will be stamped on your wheels to tell us what you have. If you find other numbers I'll dig deeper, or if I find online something different I'll edit. Stu"