Migo
03-12-2007, 02:15 PM
All-wheel drive cars have a slightly more complicated form of replacing a spare tire... because all four tires must be the same diameter or the differentials will get damaged over time.
What happens when for example, I'm running an overall diameter that a bit larger or smaller than OEM? That means that the spare tire cannot be used. At the most, I don't know if I'd want to run it more than 50kms. What happens if I'm stuck out in the middle of the highway, and the nearest repair shop is 150kms away?
There are only a few options I can think of.
1. Carry a full-size spare that has an identical diameter (even if my tires are worn-out and this one's brand new, it'll be a 0.8% difference in diameter at most).
2. Ditch the spare tire altogether and get that run-flat liquid that you spray inside the tire.
3. Run OEM size all the time (which sometimes isn't ideal for autocrossers/track/winter)
4. Carry a tire repair kit and hope that I don't get a flat in winter at -40 C in the middle of nowhere.
5. Use run-flat tires all the time.
Or... will it really make that much of a difference running the spare tire? It's recommended to replace all 4 tires if you're down below 80% tread and you need to replace a damaged tire. Logic would then dictate that running the spare tire that is several times smaller/larger than a 20% tread difference between the old tires and new replacement one would mean that it too will not be recommended.
I'm quite sure that the generic answer will be "If you run it for a short amount of time it won't be too bad" but just how bad is "won't be too bad"?
My stock/OEM tire size is 195/60R15 while last summer I was running 225/40R18.... 3.6% taller (615mm/24.2" versus 637mm/25.1"). If I had gotten a flat tire, I would have had to run three tires at 637mm and one tire at what I'd assume would be the stock 615mm if not slightly smaller.
What happens when for example, I'm running an overall diameter that a bit larger or smaller than OEM? That means that the spare tire cannot be used. At the most, I don't know if I'd want to run it more than 50kms. What happens if I'm stuck out in the middle of the highway, and the nearest repair shop is 150kms away?
There are only a few options I can think of.
1. Carry a full-size spare that has an identical diameter (even if my tires are worn-out and this one's brand new, it'll be a 0.8% difference in diameter at most).
2. Ditch the spare tire altogether and get that run-flat liquid that you spray inside the tire.
3. Run OEM size all the time (which sometimes isn't ideal for autocrossers/track/winter)
4. Carry a tire repair kit and hope that I don't get a flat in winter at -40 C in the middle of nowhere.
5. Use run-flat tires all the time.
Or... will it really make that much of a difference running the spare tire? It's recommended to replace all 4 tires if you're down below 80% tread and you need to replace a damaged tire. Logic would then dictate that running the spare tire that is several times smaller/larger than a 20% tread difference between the old tires and new replacement one would mean that it too will not be recommended.
I'm quite sure that the generic answer will be "If you run it for a short amount of time it won't be too bad" but just how bad is "won't be too bad"?
My stock/OEM tire size is 195/60R15 while last summer I was running 225/40R18.... 3.6% taller (615mm/24.2" versus 637mm/25.1"). If I had gotten a flat tire, I would have had to run three tires at 637mm and one tire at what I'd assume would be the stock 615mm if not slightly smaller.