How Bad is it if Spares Not Exactly Same Size?
11-08-2018, 03:59 PM
#1
Melting Slicks
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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
Last edited by Lotsacubes; 11-08-2018 at 04:05 PM.
11-08-2018, 04:12 PM
#2
Le Mans Master
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
11-08-2018, 04:32 PM
#3
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St. Jude Donor '15
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
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ZERRY 316 (11-10-2018)
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Lotsacubes (11-08-2018)
11-08-2018, 06:22 PM
#6
Burning Brakes
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.
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Lotsacubes (11-08-2018)
11-08-2018, 06:27 PM
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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
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Lotsacubes (11-08-2018)
11-08-2018, 06:37 PM
#8
Burning Brakes
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I purchased a used correct size BiasPly as a spare for my ‘54. It’ll work as a spare and fits perfectly in the spare tire tub.
Last edited by DAN70; 11-08-2018 at 06:39 PM.
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Lotsacubes (11-08-2018)
11-08-2018, 06:40 PM
#9
Melting Slicks
Who is getting all these flat tires?
11-08-2018, 06:52 PM
#10
Team Owner
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.
11-08-2018, 07:02 PM
#11
Drifting
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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
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Lotsacubes (11-08-2018)
11-08-2018, 07:13 PM
#12
Team Owner
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.
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Lotsacubes (11-08-2018)
11-08-2018, 08:21 PM
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Lotsacubes (11-08-2018)
11-08-2018, 08:38 PM
#16
Melting Slicks
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Maybe the bigger problem is where to put the big, flat tire. Sure won’t fit in the carrier. I like the big slow turn example FTF. Thanks all. I think I’ve found a skinny trailer tire.
11-08-2018, 08:54 PM
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I think the answer to the OP's concern is: you'll be fine. These old non-electronic non- nannified systems are far, far more resilient to differences like 1/2" differences in tire measurements. Seriously. That's not to say that one should drive hundreds of miles with such a difference, but for spare tire use, you'll be just fine. Enjoy!
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Lotsacubes (11-08-2018)
11-08-2018, 09:36 PM
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11-08-2018, 10:09 PM
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