I did some searching, but didn't see any direct info for this. I know some of you have run across this in the past. I have a '07 luxury and I upgraded the 4 tires to 285 from 265 with 285/75R16 Duratracs. The spare is still 265/75/R16. I can't decide if I want to pay a couple hundred bucks to have a spare 285 on the back just for show or if I could get by with just buying a tire cover for the 265. I know with AWD it wouldn't be good to drive for long with the smaller spare on the truck, but I assume it wouldn't be a big deal to use it to limp until I can get the tire fixed... anyone else going this route or have in the past?

 

I have heard a few going that route. I just would not feel comfortable having a smaller spare. It might work as a quick fix in a jam, but you never know how far you will have to drive to get out of a mess. I think having a full size spare is the way to go for the extra couple hundred bucks rather than the money you could spend on a tow or any problems to your drivetrain

 

Your assumption about OK to drive with a smaller spare for a short distance is wrong. Unless of course you mean perhaps 20 feet? Or a short distance on an ice covered lake?

There are some threads on this, a couple are pretty figgin hilarious where one dude even tried to argue that you just let some air out of the 3 larger tires to make up for the inch in diameter? I had to remind him that this little measurement called "circumference" that remains constant.... doh! A 33 is over 3 inches longer in circumference than the 32.

You will cook your T case every time. If you do the math, the difference in revolutions per mile for a 32 is significantly more than a 33, and it won't take long to do permanent damage. Basically, the 32 has to rotate 23 times more than the 33 in one mile! So right now, you are carting around a tire that is not a spare IMHO.

 

Don't do it! Doc is correct. Got a buddy right here in town that put 305's on his and still had a 285 spare. Got ready to leave work and had a flat. He put the 285 spare on it just to get to town and have the flat fixed. Only 7 miles. He didn't make it! I felt bad for him so I didn't do the "I told ya so" Cost him over 3000 to get if fixed. A 305 spare would have cost him 250? You do the math.... then go get you a spare!!!! I bought 5, 315 Coopers. You can rotate the spare in the rotations and extend out your next tire replacement by 1/4. I rotate my tires every 5k to keep them wearing equally.

 

Thank you for the replies on that, I will definitely be ordering a 285 duratrac for the back... glad I asked before I bought the tire cover lol

 

a while back we had a similar discussion.
someone pointed out that some awd caddys have a donut spare, tiny.

i wondered why you can drive in circles where all 4 tires turn at different speeds,IN OPEN MODE.

i can see the problem in locked mode,so why dont the diffs handle the speed difference in open mode.
then front/rear and the tr case are all in open mode?
so is the tire size different from tire speed when running around in circles?


driving with the inside tire on a 50 foot diameter,the outside tire is appx 60 feet.
thats roughly(3x) 150 feet and 180 feet circumference's, almost 1000 feet in a mile?


later, searching other forums for help, i find,,re;spare
"After mounting it I discovered it was a P255/70/18 LTX A/S. My tires are 275/65/18."

so some trucks are getting real tires for spares,but,!!different sizes??

nowhere do i find mention of problems driving with diff sizes,,,oh what to do?!!

think the abs sensors would get confused?

 

i find these comments,,,fwiw
9 months ago I got four new tires on my car. Since then I have driven more than 10 000 miles. My car was recently serviced and they discovered that the right-hand tires are a slightly different size to the left-hand tires. This was an error made by the garage that fitted them and means that the car has not been legal for the last nine months.



Other than causing the car to lean to one side (apparently it wasn't that bad or you would have noticed it), it hasn't really hurt anything. Technically, it would have caused slightly more wear on the differential gears since they would have been differentiating slightly on straight roads, but the actual effect is similar to driving a very slightly curved road for a long time instead of a straight one.


for one, the differential has been working over time. it is not a good idea.
Source(s):
ase certified master tech.


IDEALY.. on the drive axle end of the vehicle (front in your case), you should use the same size tires so as not to unecissarily work the differential spider gears, however the rear of your car wont matter.

cant find anyone who says its a super problem.
my h3 svc manual says nothing,,hmm?

 

Like I always say, Do what your doc says (Doc Olds)

 

Interesting, Don't know what caused jimmys to tear up with the smaller spare on there but that would have been a huge coincidence that it decided to let go at that time. All I know for sure Is he used my jack to put it on there, I raised my concerns about it when I saw his spare was a diff. size, He didn't make it to town and was with out his prized ride for about a month..... Could it have anything to do with full time 4wd? I don't think he was having any trouble out of anything before the incicdent or at least he didn't mention anything to me about it. We talk regularly about upgrades, mpg, what were doing, mud holes we made it through etc...

 

a lot of people here get into lock mode and dont know,sometime when its late??who knows

full time 4wd, 4 hi, is open t case and both diffs. its the only way it can be f t 4wd