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Can I take a 20" off the rear and replace it with a factory 19" for 100 miles or so? Girlfriend curbed a rearwheel...(I know .... I know...) and need to take it off and get it fixed.......want to make sure it won't be any problem for the Limited Slip..
 

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I'd treat the 19" like one of the compact spares on other cars. Drive the car slowly and easily for as short a distance as possible.
 

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I agree with the above comment. If you are going to do many more miles thatn 1000 I would make sure the rolling diameter is same/ simmilar
 

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why don't you just throw the stocks on all four corners?...can't take more than a half an our to do all four, even at a slow pace
 

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your concern is with the circumference of the tire weather it be 18, 19, 20"....the rears should always be the same circumference....to keep the rears wheels working together.
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. So with that I say, no. and keep her away from your car......lol
 

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your concern is with the circumference of the tire weather it be 18, 19, 20"....the rears should always be the same circumference....to keep the rears wheels working together.
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. So with that I say, no. and keep her away from your car......lol
+1 Seriously, just install both rears...:M5thumbs:
 

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I have a related question. I bought my car in Orlando and drove it back to Houston. I have 20" rims with 245/35s in the front and 275/30s in the back. Not sure how common those sizes are so I was thinking that if I got a flat tire along the way I'd probably be SOL. What would be the best thing to do in a situation like that since we don't have run flats or even a spare? Just get whatever is available at the local autoshop (and treat it like a spare) or get the car flat bed to some shop and wait?
 

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I would.

Dont drive too hard on them and you should be fine.
 

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I have a related question. I bought my car in Orlando and drove it back to Houston. I have 20" rims with 245/35s in the front and 275/30s in the back. Not sure how common those sizes are so I was thinking that if I got a flat tire along the way I'd probably be SOL. What would be the best thing to do in a situation like that since we don't have run flats or even a spare? Just get whatever is available at the local autoshop (and treat it like a spare) or get the car flat bed to some shop and wait?
Use the air pump and goo in the trunk and then replace the tire(s), otherwise it is flatbed time.
 

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Use the air pump and goo in the trunk and then replace the tire(s), otherwise it is flatbed time.
Out of curiosity, does the goo actually work well? Can it hold in a hole of say a nail has made ?

I always look at the kit but hope I never have to use it but when you are in the "whoop whoops" in my country and the local tire shop doesn't keep any tires over 18", it goes through my mind how far I could actually drive with the goo in the tire.
 

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It should be fine to seal up a nail hole and drive for quite a while but I would keep it under 80mph and try not to drive it.
 

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or you can just swap out the rear wheels and put both your stock 19s on... burn rubber. :p
 

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I have a related question. I bought my car in Orlando and drove it back to Houston. I have 20" rims with 245/35s in the front and 275/30s in the back. Not sure how common those sizes are so I was thinking that if I got a flat tire along the way I'd probably be SOL. What would be the best thing to do in a situation like that since we don't have run flats or even a spare? Just get whatever is available at the local autoshop (and treat it like a spare) or get the car flat bed to some shop and wait?
I suspect the availability of 20" replacement tires is slim to none outside major metro areas, usually takes me 5-7 days to acquire OEM sizes. BMW's Mobility Kit might give you 100 miles, if the hole is small and in the tread area. Removing the goo from the inside of wheel & tire is a PIA, some shops won't do it.

Unless you relish possibly spending a couple of days in a no-tell-motel, carry a spare when on the road. Its happened to me during holidays . . . . . . . . . .

When I acquired my M5, I purchased an extra front wheel & tire. A freebie jack kit was negotiated. These items are placed in the trunk whenever I leave town. With the front OE 19" diameter of 27.0" and rear diameter of 26.7", I figure the spare can be used on either axle.

As unfoundhorsepower & Glock 32 suggest, its preferable to keep the same diameter on an axle; if you have two 19" mounted tires, install them together if 20" replacements are several days away.

I've also kept a set of used Beast tires in case 2-3 are punctured at the same time, (new home construction in the area.)
 

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Really, it is very hard to answer this question in any sort of practical way.....there are several options: I carry a tire plugging kit, if the tire CAN be plugged I can insert several plugs and fill it with air to limp to a hotel, if at nite, or at day pull in to a dealer or tire shop. If the tire can't be plugged, blown out tow it to a shop or dealer get a tire that day or next, or have the tire shop put a tire on that has the same outer circumfrence....drive home order a set from there.....there are several possibilities. hey i tried...
 

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I recently had a flat and had to put one of my pilot sport cups on the car as a 'spare'. Both OEM 19" wheels, but different tire profiles. Not sure what they are, but the PSCs are lower profile.

I never got an error message, but the car started acting up. The computer realized the circumferences were different and would throw the car in neutral when I took my foot off the gas. Then when I hit the gas, it was almost like doing a neutral drop...the revs would fly up and then it would slam into gear. I had a BMW shop steward ride in the car with me to demonstrate the problem. He put the right size tire back on the wheel with the flat...and all the problems went away.

Short answer, yes, they need to be the same circumference.
 

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^^^ +1

The car will act funny if you have different diameter tires on there. I put a 35 hieght tire on one side of the front, car acted crazy, I thought it was the tranny :eek: Turns out the computer was getting freaked out. Want to know how I found out it was the tire issue and not the tranny?? Did a SEARCH on here!! :M5thumbs:
 

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I recently had a flat and had to put one of my pilot sport cups on the car as a 'spare'. Both OEM 19" wheels, but different tire profiles. Not sure what they are, but the PSCs are lower profile.

I never got an error message, but the car started acting up. The computer realized the circumferences were different and would throw the car in neutral when I took my foot off the gas. Then when I hit the gas, it was almost like doing a neutral drop...the revs would fly up and then it would slam into gear. I had a BMW shop steward ride in the car with me to demonstrate the problem. He put the right size tire back on the wheel with the flat...and all the problems went away.

Short answer, yes, they need to be the same circumference.
What sizes are you running on your M and what was the variance between the two tires? Looking at both TireRack & Michelin's websites, OE sized Sport Cups are not available.

http://www.michelinman.com/tires/ultra-high-performance-sport/pilot-sport-cup/#sizes-and-specifications

http://www.tirerack.com/tires/Spec.jsp?make=Michelin&model=Pilot+Sport+Cup&tirePageLocQty=
 

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What sizes are you running on your M and what was the variance between the two tires? Looking at both TireRack & Michelin's websites, OE sized Sport Cups are not available.

http://www.michelinman.com/tires/ultra-high-performance-sport/pilot-sport-cup/#sizes-and-specifications

http://www.tirerack.com/tires/Spec.jsp?make=Michelin&model=Pilot+Sport+Cup&tirePageLocQty=
You are correct. OE sizes are not available in the Pilot Sport Cups. I use 265/30/19 on all four corners. It works pretty nice with a pretty neutral setup. I don't use these on the street and I don't really look at the speedometer on the track, so it's not a concern for me. Putting one on was just an emergency with a flat.

But, the diameter on the PSCs is 25.3" compared to 27.0" on the stock Contis (255/40/19). Pretty big difference and probably comparable to putting on one 19" wheel and one 20".

There is nothing even close to the OE 27" in PSCs if your question was directed at finding a set for every day use. Hopefully the new M3 will help get some additional sizes produced.
 

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You are correct. OE sizes are not available in the Pilot Sport Cups. I use 265/30/19 on all four corners. It works pretty nice with a pretty neutral setup. I don't use these on the street and I don't really look at the speedometer on the track, so it's not a concern for me. Putting one on was just an emergency with a flat.

But, the diameter on the PSCs is 25.3" compared to 27.0" on the stock Contis (255/40/19). Pretty big difference and probably comparable to putting on one 19" wheel and one 20".

There is nothing even close to the OE 27" in PSCs if your question was directed at finding a set for every day use. Hopefully the new M3 will help get some additional sizes produced.
I make occasional trips so far from civilization that the laws of physics don't apply. :3: Road service takes several hours and Tire Rack is the quickest way to get a replacement tire.

I'm trying to determine how large of a variance per axle might cause ECU faults or transmission problems.

The OE PS2s have a 0.3" variance front to rear, much less than the 1.7" variance when you installed the Sport Cup.

I agree that the new M3, CTS-V and other performance offerings with 19" OE tires may spur tire manufacturers to sell R-compound tires that fit our beasts. :cheers:
 
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