[GassedRacing]

So Discount Tire Co. threw me a killer deal on some 16X8 rims with BFG AT/KO's this weekend. They fit, but required some strategic trimming and a couple of turns on the torsion bars. I just got back from the alignment shop where everything still appears to be correct in terms of caster and camber.


The thing looks great, and it rides way better. I don't tow anything really heavy so I felt it OK to go to the "D" load range.


Now, what do I do about the spare tire? I don't think I could run it on the rear with the G80 rearend. Can I run it on the front? what is the largest size spare (largest matching the 32.25" height on my 295/75/16's) that I can run? What is everyone else doing?


Thanks!

 

[Professor]

I'm getting ready to mount a 255/85-16 on my spare wheel. Close enough to the overall diameter of our tires to run on the rear with the G80. Should still fit in the stock location just fine. I think they only make them in a D load but it is still rated at 3000lbs.

 

[bsiler]

I've that you should always run the same size tire all the way around.

 

[bsiler]

Excuse Me

I've heard that you should always run the same size tire all the way around.

 

[Professor]

bsiler


You heard correctly, at least on 4x4 and antilock brake equipped vehicles. However, all that is necessary is that the overall diameter is the same. This would allow you to run a cheaper smaller width tire as a spare taking up less room when stored. And it will also allow you to use the stock wheel as opposed to having to buy a wider wheel. As long as the tire is near the same diameter, the ABS brakes, 4 wheel drive, and the posi unit in the rear will be fine.


A 295/75-16, 285/75-16, 305/75-16 are all within ½” of the 255/85-16. The vehicle systems will allow this easily. Manufacturers will vary about ½ on new tires. Even a worn out LT tire will be almost a full in smaller in diameter than a new one. Where you get into problems is when you put on the stock spare which is as much a 3” inches smaller than the above tires. This can cause damage or additional wear on a limited slip differential. This also can confuse the ABS on the front. I only run a spare long enough to buy a new tire (or a new set) anyway. I still don’t want to be stuck running a tire that is 10% shorter.

 

[tmg115]

well i have run my regular spare with my new tires (285 75 R16's) and i didn't hurt a thing.

 

[Dmax Tim]

Gassed,


(largest matching the 32.25" height on my 295/75/16's)


295 BFG are 33.5" high.

 

[NoWake200]

I would think that just ruuning to the nearest tire shop would not be a problem. Look at the spair tire for autos...not even close the the size tire the they are runnig with. A couple of miles I do no think would hurt.....running for miles on end at 70mph that would be another story. Just my thoughts...I would not get to wrapped up in worrying about it.


FYI- I have my stock 245s with only 50miles on them in my garage they measure 29.75". Edited by: NoWake200

 

[dirty old man]

When I bought my '03 back in Jan., I got friendly with the service manager ay the small dealership. We talked quite a while about various things on the Duramax, maint., mods, warranties, etc.


The one thing he was emphatic about was staying with the factory size on tires, said there wa no way to reprogram the computer to compensate for a different size, and all sorts of problems would surface.


Whether this is BS or not, I can't say, so take FWIW!

 

[NoWake200]

Keeping it stock with 245s!

For starters GM ought to be embarassed for themselves for even mounting such small tire on a HD 4X4 truck!

Actually there is a way to update the computer. Hypertech power programer will ask you for the tire size and I then it updates itself.


But this is the thing....makers of these GM trucks need to realize that some guys are going to add bigger wheels/tires. And all this reading about don't do this and don't do that, voiding warranty is starting to worry me. I bought a TRUCK....I wan to be able to do truck things with it. Next they are going to be telling us not to tow heavy loads with them. Or better yet do not use the 4X4 truck in the dirt for it will void the warranty. All this talk about making sure you keep it stock is, I am sorry chicken poop!

Edited by: NoWake200

 

[Camstyn]

If you're worried about the locking rear dif with two different tire sizes, if you get a rear flat running bigger tires, put the spare on the front and the matching front on where the flat was. A little more work but I think it's worth the extra trouble for piece of mind.

 

[GassedRacing]

Gassed,


(largest matching the 32.25" height on my 295/75/16's)


295 BFG are 33.5" high.

Weird. I walk out to the garage and string a tape measurer from the floor to the top of the tire (in the middle of course) and I see 32+" but not 33. Are you accounting for when the wheel is moving and tire actually swells from the rotation? Do we need to account for that when setting the tire size on the predator or quad?

 

[Mjollnir]

Weird. I walk out to the garage and string a tape measurer from the floor to the top of the tire (in the middle of course) and I see 32+" but not 33. Are you accounting for when the wheel is moving and tire actually swells from the rotation? Do we need to account for that when setting the tire size on the predator or quad?

That's installed height. Weight on the tire compresses the bottom of the tire when it's installed. If you take the tire off the truck and measure with no weight, it will be taller. Measure the diameter from left to right instead of top and bottom and you'll see what I mean.

 

[Dmax Tim]

GASSED, I got my ### from BFG website which should be correct.


I know my 285/70 and 285/75 both measure close to 33" on the truck and yours are bigger yet.

 

[JimWilson]

A mismatched set of rear tires would more then likely make the locker kick in. However, since it automatically disengages above 25 MPH you'd only be locked until that speed. For a short, emergency situation you should be okay with different sized tires, but having a spare the same size is a lot better.

 

[Dmax Tim]

Jim I think u are talking about the E locker on the H2, our trucks have a mechanical locker.


It IS a PIA w/ the locker on the Hummer kicking out in every big mud hole but haven't been stuck yet and the mud really flies.

 

[GMC-2002-Dmax]

If you want to know the true size do what I do, put some white lithium grase on the center of the of the tire on one of the lugs in the tread


I use a BLOB the size of a nickle and drive 2 complete revolutions.


Measure the distance from center to center of the blob and you have the circumference. If it is close, which it should be almost exactly the same then use that number.


If it is off a little bit and you are not sure then add them up and divide by 2 for the average.


Use the math formula in which is the circumference of a circle divided in half is the radius. ( PI )


So if you get 65 inches if travel you have a 32.5 inch tall tire.


The easiest and I think most accurate way to do it.





T

NY

 

[JimWilson]

Jim I think u are talking about the E locker on the H2, our trucks have a mechanical locker.

I'm actually refering to the G80. Is that what the H2 has as well?