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[Jonnyz2]

I've recently acquired an E93 M3 and want to have a spare for long distance southwest and mountain driving where I expect getting a tow could take a very long time.

One of the posts on the topic of what setup to use for a spare mentions that too much of a size difference between the spare and permanent wheel/tire could damage the differential.

I understand the concern but don't know what size difference could put the differential at risk of damage. I suspect too that driving distance and speed could also affect the risk.

Searches on the topic haven't turned up anything useful; so, I need advice!

My current wheels/tires are as follows:

Front: 245/35 R19: 25.8" diameter
Rear: 265/35R19 26.3" diameter

Spare options:

1. BMW steel Rim with 135/70R18 at 25.4" (seems to be most common solution posted on this forum, requires centering ring)
2. BMW steel Rim with 145/70R18 at 26" (much more expensive tire and requires centering ring)
3. BMW alloy rim with 125/80R17 at 24.9 (BMW Part 36110445045, reported to work by several forum members, no centering ring or hub spacer required)
4. BMW alloy rim with 135/90R17 at 26.57" (no centering ring or hub spacer required)
5. ModernSpare alloy rim with metal hub spacer with 135/70R18 at 25.4"

Worst case, I might need to drive 100-150 miles to get a new tire and would like to find a solution which would be safe for the differential at highway or near highway speeds and for longer distances if necessary.

If not a risk to the differential, my first choice is #3 because it would be light weight and not have additional parts (hub spacer or centering ring). Because of that, it should be easier for someone else to change if I'm not nearby to help or reachable to give instructions by phone.

Please share your thoughts/comments!

[Throatpunch]

Option 2 and a tire repair kit and pump if u ever used one before.