How Bad is it if Spares Not Exactly Same Size?
 

My rears are 26.3" and it appears a matching 15" diameter is a 205/70R15. But that's too wide for the spare carrier. I may be going with a trailer tire to match diameter for a spare, unless 185/65R15 at 25.7" diameter would be ok for short distances. I don't know how much diameter mismatch could damage the posi rear end for short distances. If the spare was 1/2" smaller and limited to.... say 20-30 miles would that hurt the posi? Thanks

I know what you mean. I bought a 16" S-10 spare tire and rim at a junk yard. It fits in the carrier with no problem. If I get a flat in the rear, I can put the S-10 tire on the front and the front tire on the back. It sounds like a pain, but easier to change than a posi unit. No flats as of yet. Jerry

thats what insurance is for.....flat bed tow service....

the spare tire carrier was actually made for a conventional tire, the radial needs to be really jammed in there

this is a very good question, I hope someone provides a definitive answer
:cheers:
Bill

Just do the math. The tire with the 26.3" OD travels 766.8 revolutions per mile. The tire with the 25.7" OD travels 784.7 revolutions per mile. Or 21.9 more revolutions per mile. If you go 20 miles the shorter tire will have to turn 438 more times than the taller tire. This will create lots of heat in the posi unit.

Don't worry about it if you use it like a spare should be used. Get home or to a tire shop to fix the other tire or replace it.

Who is getting all these flat tires?

if you have to drive it more than a few miles on the spare, move a front tire to the rear and put the spare on the front. I personally don't think it'll hurt the posi but that's up to you.

I hate to make a jinx on myself, but I will go out on a limb and say, I'm 63 and only ever had to put the spare on one time out on the road. Keep good tires on your car, avoid large pot holes, am I just lucky or is it not the 1920 or 40's when road side tire changes were common, a part of life. If you get a lot of flats be prepared, have two spares, and the perfect second car(towtruck). Chip

Yes, the differential thinks its in a LONG turn and acts accordingly...

these are all good workarounds, but no one has answered the question
Bill

Minimum, need spare to limp to where ever, or a same same spare to continue on your journey. Chip

I did in post #7

nope, a 'normal' spare is the same size as all 4 tires and can be used for as short or long a distance as needed

Bill

That's why I only drive mine on straight roads.