GEEEEZ DRTOM.....you really had to dig in the archives for that one! Definitely gave an interesting, simple explanation of how a diff works.

 

So the consensus is a 265 will replace a flat 285 for a short run to the tire shop?

 

If a smaller tire would cause a problem driving from a location where a flat occurred to a repair shop, I don't think all the OEM's would be using these new, small, weight/space saving spares.

 

now thats a good point,,,keepin it simple

 

No AWD or full time 4WD vehicle has a doughnut spare that I know of? If they do it is the same diameter as the OE tire, just not as wide.

OP: I would not personally take that kind of chance, if you are 200 miles from the closest repair facility @ 2am (or on the trail) you would be SOL! Plus you will have to buy the new tire (or have the old one fixed) and you may not have the $ at that time. Buy a 285 and replace the 265 ASAP (or just get 5 315s and be done with it!) . My $0.02.

 

Can't say for sure about the diameter, but I know, the AWD Cadillacs use the donuts.

 

I'm the OP and I think you may confused my posts with someone elses. I'm with you, if I get a flat before I get a new tire I'm calling a flatbed. Maybe if I'm under a mile I'd consider driving with a 265, but certainly not a long distance.

My thoughts on it are if you turn off the traction control it is probably ok - the diffs are open not limited slip. Unfortunately I don't know much about the transfer case in these H3s. If they are simple gear driven differential types when in 4-hi it's probably ok for short distances.

I spoke with the sales guy I bought it from (service department was closed) and he started to give me the "sorry, that's a normal thing with used cars, it passed certification so there is nothing I can do" line then I cut him off and told him "while it's a new H3 spare, it's not from an Adventure package and because of the AWD it's useless, I will not drive on it. If you don't make it right, I will have to buy a new spare." At that point he promised to speak with his tire guys. I suspect they are going to offer me some old used 285 they pulled off some other vehicle. That's fine with me, I'll probably buy 5 duratracs in the spring so any usable spare works for now.

On a positive note, they are going to fix the plastic trim around the outside of the windshield. I'm not really sure how the clip broke, one of the people I was wheeling with noticed it. Might have happened while wheeling, might have been like that for a while. It's funny, I back into my driveway and often back into parking spaces - I drive somewhere every day but I can easily go a week without seeing the front of my H3.

 

If they are simple gear driven differential types when in 4-hi it's probably ok for short distances.,,,(he said)

the tc is open or locked. in hi its open. hi lock is,,,locked,which locks the fr/rear driveshafts,diffs are open unless they are lockers.

i dont know what trac control would do

 

Ya, I know in 4 hi it's "open" and 4 lock it's locked. I just don't know if it's some kind of viscous coupling or gears or georotor, etc. I'm guessing it's just plain old differential type gears but I don't know. New to Hummers and all that.

edit: The axles are open, but as I understand it turning off the Stability system (stabilitrac) does not turn off traction control. No clue how much slipping is allowed before it kicks in. Driving with a smaller tire that is turning faster will be detected as slip but no idea if it's enough to cause traction control to start pumping the brakes.

 

I would think a 265 vs a 285 with about a 1 inch difference in diameter should not make that much difference for the sensor. A heavily worn tire on one wheel end with new on the others would throw off the sensor if this was true.