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.)