What to do about spare tire

GGM · Feb 4, 2004

For you guys who upgraded to larger rims what do you do to the spare? I'm thinking about going up to 18" from 17" and wondering if i get a flat would i still be able to use my old spare for a bit or would that cause problems?

Tom · Feb 4, 2004

You sure can, I have 19"s on my M3 and keep my stock 18" as a spare on long distance trips. Just make sure you don't drive very long with the spare on since it will affect the wearing on your larger tires.

Big Daddy · Feb 4, 2004

I have upgarded the factory 14's on my daughter's 318is to 15 inch wheels for her summer wheels (put snows on the 14's), but she keeps a 14 for a spare. Just as Tom says, it is for emergencies only, short distances and slower speeds.

My M roadster does not have a spare! I have the factory pump and a can of sealer.

jrt67ss350 · Feb 4, 2004

Tom said:

Not just that, but if you get a flat on one of the rear tires, and you put your smaller spare on and drive for a long time on it, it'll destroy your differential. Having two different tire diameters on the rear makes the two different wheels turn at different RPMs, and so the spider gears in the differential will constantly be turning when going straight (normally, when driving straight, the spider gears are stationary). This can overheat the differential (particularly the spider gears) due to the added constant friction and lead to excessive spider gear wear or worse. I imagine that in a car with a limited slip differential, this would cause tremendous problems - the differential "thinks" the smaller diameter wheel is slipping since it is rotating faster. As such, the clutches will try to equalize the speeds between the two wheels. However, they won't be able to equalize the speeds since the wheel is not actually slipping, and it'll burn out your limited slip clutches.

Shouldn't be a problem in a car with an open differential if it's just a short term thing. Don't drive across the country with mismatched tire diameters or continue driving on them for weeks after getting a flat. On the other hand, if you have a limited slip differential, I'd be very careful of it.

MrElussive · Feb 4, 2004

If you have Verizon or T-Mobile cell phone services, you can get Roadside Assistance for like $2 or $3 a month. I know it sounds stupid, but I'm completely serious...you may wanna consider that !! They will send a tow truck out to you mad quick if you ever get a flat tire and need to be flat-bedded.

epj3 · Feb 4, 2004

jrt67ss350 said:

Not just that, but if you get a flat on one of the rear tires, and you put your smaller spare on and drive for a long time on it, it'll destroy your differential. Having two different tire diameters on the rear makes the two different wheels turn at different RPMs, and so the spider gears in the differential will constantly be turning when going straight (normally, when driving straight, the spider gears are stationary). This can overheat the differential (particularly the spider gears) due to the added constant friction and lead to excessive spider gear wear or worse. I imagine that in a car with a limited slip differential, this would cause tremendous problems - the differential "thinks" the smaller diameter wheel is slipping since it is rotating faster. As such, the clutches will try to equalize the speeds between the two wheels. However, they won't be able to equalize the speeds since the wheel is not actually slipping, and it'll burn out your limited slip clutches.

Shouldn't be a problem in a car with an open differential if it's just a short term thing. Don't drive across the country with mismatched tire diameters or continue driving on them for weeks after getting a flat. On the other hand, if you have a limited slip differential, I'd be very careful of it.

Or just put the smaller spare on the front, and move the larger tire back from the front.

jrt67ss350 · Feb 4, 2004

epj3 said:

Yeah, that'll work if you don't have an M3 or a 330 with staggered tire sizes.

andreyiv · Feb 4, 2004

MrElussive, what about the tow truck? Do you still have to pay for it? If so, can't you just use 411 and ask them for a number of the closest tow company?

Average Jae · Feb 4, 2004

i'd say no problem. my 18s came w/ crappy, thin as a bike tire doughnuts, so i'm sure your old spares would be just fine. and remember, spares are only there as a spare, they should be changed back asap anyway.

you gonna slap some snows on the 17s?

another, and more expensive option is to go w/ run flats, but that's whole another story right?

Ghost · Feb 5, 2004

jrt67ss350 said:

I agree with jrt, and I would suggest that you buy a tire for the spare (if it's full size)that will be equal in diameter to the other tires on the vehicle. If you have unidirectional tires on your vehicle remember to make sure that your spare is not, so that it can be put on both sides of the vehicle. I’m all for roadside assistance, but if you get a flat tire late at night and IF they have a spare it will probably be a stock size. The stores are closed and you’re back to square one.

Abdoman · Feb 5, 2004

Hold on here, just because you have a larger rim does not mean that the OD of the tire is different. I have a 528i with 17" wheels and use to have a 15" spare. The OD was the same - I upgraded wheel size, but not OD of the tire.

Ghost · Feb 5, 2004

Abdoman said:

I agree but some people have chosen to upgrade both and that is what I was referring to.

MrElussive · Feb 5, 2004

andreyiv said:

I believe you call 411 and they send you the tow truck. They contact the nearest tow truck company and they send the truck out to you. The tow only covers a certain distance, thereafter you have to pay for it based on mileage, but I don't think it's much at all. Personally, my car comes with a 4-year Infiniti roadside assistance program so I'm chill with that, but I think an extra $2 or $3 a month can go a long way if you prefer to be towed whenever you get a flat tire.

epj3 · Feb 5, 2004

jrt67ss350 said:

Oooh good point!! I thought I was clever [?|]

MrElussive · Feb 5, 2004

epj3 said:

Lol, that also would have been more work than I would ever consider doing. Hey is anybody actually AFRAID of using their spare tire? My car has the massive 18" wheels stock and packed under my trunk is a donut spare tire comparable to my bicycle tire. I wouldn't even consider using the spare if I had a flat tire.

andreyiv · Feb 5, 2004

I have sport package so the spare is smaller, I think I'll just get an extra wheel (the ones I have go for about 60 bucks on ebay) and an extra tire and when I get a flat, swap it out and worry about the flat when I have the time. I think thats a great way to go unless you have a $700+ wheel, that's about how much yours cost, right MrElussive?

Bmw 325i 7803 · Feb 5, 2004

Doesn't the e46 325i come with a regular wheel spare?

GGM · Feb 6, 2004

thanks for the info guys. right now my tires are 205/50/17 and i'm looking at 225/40/18 so i think the 17" full size spare would be alright if used for a bit. Hopefully i won't have to use it [;)]

MrElussive · Feb 6, 2004

GGM, you may wanna consider 45-series tires (225/45-18 size). With 40-series tires, you may be risking a flat tire over potholes and road irregularities, which is exactly what you're trying to avoid! I have 225/45-18's in the front and they are perfect...even in NYC I haven't gotten a flat tire yet. Anybody running 225/40-18's safely??

GGM · Feb 6, 2004

MrElussive, the guy at the shop said that the size, comparing to the tire i have now, should be that if i was upgrading to 18" and thats the recommended size on tire rack also for the rim i want to get. What is the difference between the 40 & 45 series? now i'm getting all confused... [confused]

What to do about spare tire

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