76 gmc maximum tire size

[meatbag]

I imagine yall have answered this before, but I have a halfton 76 gmc truck, 15 ralleye wheels, putting a spring assist in the rear for hauling firewood. It's my all around truck I also plow snow with it, wondering what's the maximum tire size, I'm guessing the 33,12.5,15. But would like that confirmed and what the metric conversion for that tire size or closest one. Thanks yall

 

[bucket]

Four buh four, I assume? Yeah, 33x12.5 is about the limit and will require at least a very small amount of trimming for clearance. More trimming will be required if you have wide rims.

Most anything that is the metric equivalent will put you in a 16+ rim size I believe. 305/70/r16 for example would be the 16" equivalent.

 

[meatbag]

Thanks alot. Yeah she's 4x4.

 

[45tt]

With no lift, the biggest I ever went was 32x11.50x15. I noticed anything bigger would rub on certain angles of approach/descent, unless you trim fenders, like bucket mentioned

 

[Grit dog]

See what it looks like for clearance with the plow hanging. I can’t imagine 33s or even 32x 11.50s will fit without rubbing with the plow. Especially if the original 45 year old springs are holding it up.
It’s pretty easy to check with your current tires if you’re not changing rim offset
Measure clearance at the closest spots while turning the steering wheel and then compare addl height and width from the larger size tire.

 

[meatbag]

Okay thanks alot yall

 

[meatbag]

Would 33s in the rear and 31s in the front be ridiculous? I plan on putting spring assists in the rear for carrying firewood. So that might lift the rear a couple inches from what I heard. I'm also swapping out my 400sb for a 454 lb, so I'm guessing 454 is a little more heavy along with the plow. I just haven't messed with tires and wheels as much, being a young man.

 

[Dutch Rutter]

Would 33s in the rear and 31s in the front be ridiculous? I plan on putting spring assists in the rear for carrying firewood. So that might lift the rear a couple inches from what I heard. I'm also swapping out my 400sb for a 454 lb, so I'm guessing 454 is a little more heavy along with the plow. I just haven't messed with tires and wheels as much, being a young man.

It being a 4wd you do not want to mix and match tire sizes. Unless you plan on never using 4wd without blowing out your transfer case.

A simple 2" lift (blocks in the rear and taller leafs in the front) should be able to clear 33s. If you went with HD front leaf springs in the front that would also help support the added weight from a plow and even a heavier powerplant.

 

[meatbag]

Thanks alot. I agree, needs new springs anyway, might as well lift it a little bit. Probably only a 2 or 3 inch lift, since I'm throwing firewood in the bed.

 

[meatbag]

Reminds me, I have a 83 squarebody 3/4 on my property, most lift kits only include front springs. Could I use 3/4 ton springs on a halfton pickup? In the rear? Sorry for all the questions, I'm good at some areas and clueless in others

 

[CheemsK1500]

What gear ratio does that truck have? If you have high gears, you may want to change those before going dramatically larger in tire size. This isn't a requirement by any means, but it can definitely affect performance depending on what gears you currently have.

 

[meatbag]

Gear ratio? No clue. It's a 76 with the original 400 sb and 350 transmission, it should be all original outta the factory

 

[CheemsK1500]

Gear ratio? No clue. It's a 76 with the original 400 sb and 350 transmission, it should be all original outta the factory

If the SPID sheet is still on the driver side inner wheel well, it should tell you. However, it's possible the truck could've been regeared at some point in its life to something other than what the SPID sheet says it is. The most reliable way to confirm gear ratio, is the old fashioned way:

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For your application, and desired tire size, I'd recommend a 3:73.