Sizing a Spare
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Freshman User
Joined: Jan 2001
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Sizing a Spare
Hi all,
I have a 78 F150 4x4 with 32 x 11.5 tires on 15" aftermarket rims that's missing its spare, so I'm going to make one up from a junkyard rim and new tire. How close does the spare need to come to the existing tires' diameter in order to avoid damaging my differential if I have to drive more than a short distance on the spare? These are the stock diffs, by the way--no limited slip or lockers...
Due to mounting space and wallet constraints, I'd like to keep the spare as narrow and cheap as possible, which is why I'm not just putting together a fifth wheel that's identical to the other 4. Is it even possible to create such a "stockish" wheel/tire combo that will be 32" tall?
--sean
I have a 78 F150 4x4 with 32 x 11.5 tires on 15" aftermarket rims that's missing its spare, so I'm going to make one up from a junkyard rim and new tire. How close does the spare need to come to the existing tires' diameter in order to avoid damaging my differential if I have to drive more than a short distance on the spare? These are the stock diffs, by the way--no limited slip or lockers...
Due to mounting space and wallet constraints, I'd like to keep the spare as narrow and cheap as possible, which is why I'm not just putting together a fifth wheel that's identical to the other 4. Is it even possible to create such a "stockish" wheel/tire combo that will be 32" tall?
--sean
Posting Guru
Joined: Dec 1999
Posts: 1,903
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From: Copley, OH
Sizing a Spare
If you don't have a locker or LS, you can use anything that's round and black. Diameter doesn't much matter in terms or the diff. However, you want to keep the diameter close for steering purposes, probably not less than 30.5"
FWIW you can use an undersized spare with a rear LS as well. You have to put the spare on the front only, which means in the case of a rear flat you have to change 2 tires.
FWIW you can use an undersized spare with a rear LS as well. You have to put the spare on the front only, which means in the case of a rear flat you have to change 2 tires.
Senior User
Joined: Apr 2001
Posts: 172
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Sizing a Spare
Should have absolutely no problem finding a used 265/75R16 tire with at least half tread from anyone who sells used tires. Since it's 16" and thus supposed to be heavier duty a new 265 will cost comparably to a 32x11.5 
Elder User
Joined: Jun 1999
Posts: 861
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From: SE PA
Sizing a Spare
A used 8" wagon wheel with a 30" or 31" tire in the 9.50/10.50 range would be fine (even a bias ply) and should be fairly cheap if gotten well used (hey, it's only the spare). For short distances a LT235/75-15 from a boneyard would even work, that would be about 28-29" tall, on a 6-7" wide rim, depending on tread depth and wouldn't be a problem as a "short term use, not over 40 mph" spare. I think I paid $5 or maybe $7 for a rim at the boneyard for the '83 Ranger with a decent 14" tire included! Got rid of the weenie spare they have with 'em stock.
