'85 C10 tire fit/stuff question (not the normal questions you're used to seeing here)

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1x1_Speed_Craig

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Aug 26, 2023
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Location
Chuckey, TN
First Name
Craig
Truck Year
1986/1985
Truck Model
1986 M1008, 1985 M1028/C10 mutt
Engine Size
6.2L diesel
I found a square body-specific low-COG (prerunner) truck that certainly got me salivating. This beaut rolls on 40" tires. :cool:

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ChuckN

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Location
Bellinham, WA
First Name
Chad
Truck Year
1981
Truck Model
C10
Engine Size
350
A quick background before asking my question...

I came from 20 years in the Jeep world, and have always loved low-COG builds with minimal-to-no-lift and big tires. It drives me a little nuts to see vehicles lifted higher than they need to be for a given tire size (I see it daily here in East Tennessee, and online everywhere).


A couple of my previous low-COG builds.

Rare military '86 Jeep CJ-10a converted to 4WD, and running 34 x 9.50 "pizza cutter" Swampers on stock-height front springs and no body lift. Wheels are narrow (5.5"?) Toyota steelies from an '80s-era 4-Runner, IIRC.
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'05 LJ on 1-ton axles, H2 whees with 37" x 12.5" tires and a minimal 3.5" lift. Axle width, wheel/tire sizing, and the AEV highline body kit all helped clear this wheel/tire combination; the flex & tire stuff was amazing. When I was working on this project, people were typically lifting these Jeeps 4.5" to clear much smaller 33" tires, just for some comparative perspective.
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And back to current day, here's my other daily-driver CUCV, an '86 M1008 on sagged OEM front springs, H2 wheels with ~5 5/8" backspacing. They clear the 55/80R-17 (33" x 10") tires beautifully.
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So...now my question.

I'm slowly working on this mutt '85 CUCV/C10 project. Here it is sitting on its "new" '86 GMC C15/C10 chassis and "roller" GMT wheels & tires (these will be replaced).

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Unlike a good portion of the 2WD crowd here, I do not want to lower the truck, unless it's just a little in the back to level things out with the front. What I want to do is stuff the largest tire I can under the stock-height truck, and still clear the sheet metal and frame/suspension at full lock with the steering. Fitting any size in the rear won't be an issue; it's the front that's the big question here. I have not yet decided on the final wheels, so backspacing is completely flexible. I do not want to trim the exterior front fenders; I don't have inner fenders yet, but am willing to cut/weld/modify replacement inner fenders as-needed to clear. I just want to the tires to stuff and clear as they should. FWIW, the donor chassis is equipped with the F60 RPO code indicating the Heavy Duty Front Spring option (the rear is also G51, or Extra Capacity Rear Springs).

I've searched the web far & wide (various forums), and can't seem to find any real-world fitment answers aside from people using the stock 15" Rally wheels, which I won't be doing. I'll likely be using 17" wheels, but am open to slightly larger ones.

Any real-world experience with specific sizing/backspacing details is appreciated.

Thanks,
Craig
Got nothing to add, just wanted to compliment you on that LJ. Had one a while back, loved it. Just couldn’t afford to commute with it with the small gas tank and the gas mileage.
 

1x1_Speed_Craig

Full Access Member
Joined
Aug 26, 2023
Posts
98
Reaction score
207
Location
Chuckey, TN
First Name
Craig
Truck Year
1986/1985
Truck Model
1986 M1008, 1985 M1028/C10 mutt
Engine Size
6.2L diesel
Got nothing to add, just wanted to compliment you on that LJ. Had one a while back, loved it. Just couldn’t afford to commute with it with the small gas tank and the gas mileage.

Thanks. Glad you like the LJ. Here are a few more pics. It flexed nicely. :cool:

Unlike my other Jeeps, I had help with the LJ build by an amazing shop/guy with a strong CNC & wheeling background. He designed the steering, and is 100% to credit for the amazing handling. The shop is no longer in business, but I'm still in awe of the skill the shop had.

Craig

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