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      12-14-2010, 01:49 AM   #1
sig5x
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Drives: e92 ZCP
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Help me choose a space saver spare tire size

I've decided to put together a spare tire kit for my e92 M3. I have the 19" wheel option and I am planning to run wider tires in the future (255/35-19 front and 275/35-19 rear on my ZCP wheels).

I used an online tire calculator program and based on the results, it appears that a 135/80-18 space saver spare tire most closely matches the rear tire size (planned: 275/35-19, current: 265/35-19). I'm thinking that using the rear tire diameter as the target size makes sense as it may reduce to difference in wheel rotations if the spare tire is on the rear, where the differential is. Is this logical and make sense?

The 145/70/-18 size looks close, too, but I haven't been able to source one in the ~ $100 range, so the 135/80-18 at around $100 is looking like a fair candidate. Thoughts?

Here is the calculation:

Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
135/80-18 4.3in 13.3in 26.5in 83.3in 761 0.0%
245/35-19 3.4in 12.9in 25.8in 80.9in 783 -2.8%
265/35-19 3.7in 13.2in 26.3in 82.6in 767 -0.8%
255/35-19 3.5in 13.0in 26.0in 81.8in 775 -1.8%
275/35-19 3.8in 13.3in 26.6in 83.5in 759 0.3%

Last edited by sig5x; 12-14-2010 at 01:51 AM. Reason: format table
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      12-14-2010, 06:42 PM   #2
elh0102
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I found a Bridgestone T145/70-18 at Tire Rack. But, you won't find one for $100; think mine was around $250.
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