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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Wheels and Tires Forum Sponsored by The Tire Rack > Questions about tire bulge



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      11-16-2018, 11:09 AM   #1
GoDores
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Questions about tire bulge

I have a bulge in the sidewall of one of my tires and I assume replacement is recommended. Couple questions:

Is replacement necessary?

Can I replace just this tire or will that cause problems with xDrive? Tread depth is between 8 and 9/32 on all tires. I rotate them every 5k if that matters.

What is the tire? It’s a Bridgestone run-flat, 225/45 17”, but I don’t see any model name that matches anything on Tire Rack. (I’d love to be rid of the run flats but don’t want to throw away 4 fairly new tires if I don’t have to.)

Pics of tire and bulge attached. Thanks!


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      11-16-2018, 11:15 AM   #2
nsjames
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that tire is wasted. sidewall bulges are almost always broken casing belts.

BMW says no more than 1% rotations per mile difference. So whether or not you need to replace more than 1 depends on new tire tread depth.
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      11-16-2018, 11:16 AM   #3
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I'd part that thing out man.
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      11-16-2018, 11:56 AM   #4
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You can just buy 2 new tires that are not runflats.
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      11-16-2018, 12:52 PM   #5
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How's this math look?

New tire:
225mm * 0.45 = 101.25 sidewall height
(101.25) * 2 + (17" * 25.4mm/in) = 634.3mm tire diameter
634.3mm * π = 1992.7mm new tire circumference

New tread height 11/32" = 8.73mm
Current minimum tread height 8/32" = 6.35mm
8.73mm - 6.35mm * 2 = 4.76mm difference in diameter

634.3mm - 4.76mm = 629.54mm current tire diameter
629.54mm * π = 1977.8 current tire circumference
1992.7mm - 1977.8mm / 1992.7mm = 0.0075 = 0.75% difference in circumference

So if 1% is the limit, it seems like it would be okay to just replace the one, if I could figure out what it is.

Is the 1% limit just across each "axle" or does it apply front to back too?
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      11-16-2018, 01:13 PM   #6
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Figured it out. It's a Bridgestone Driveguard: https://www.tirerack.com/tires/tires...um=245WR7DGRFT

My local tire shop can install one Monday for a little cheaper than Tire Rack, and they're a race shop so they can shave the tire to match the other tread depths. So problem solved for now. Still curious to know if the 1% rotational limit applies front-to-back or just across.
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      11-16-2018, 05:15 PM   #7
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Quote:
Originally Posted by GoDores View Post
Still curious to know if the 1% rotational limit applies front-to-back or just across.
Likely both.
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      11-16-2018, 08:00 PM   #8
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well across still changes the pinion speed via the spiders, so it doesn't matter.

the end goal is for driveshafts to not rotate more than 1% speed difference, as the clutches in the transferbox are always preloaded and engaged.

if you have driveshaft speed differences you will wear out the transferbox's clutch packs.
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      11-16-2018, 08:12 PM   #9
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Quote:
Originally Posted by FCobra94 View Post
Quote:
Originally Posted by GoDores View Post
Still curious to know if the 1% rotational limit applies front-to-back or just across.
Likely both.
If it was 2wd I'd say it only mattered side to side. AWD might be different; I dont know about that voodoo.
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      11-16-2018, 09:26 PM   #10
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wow over thinking the 1%
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      11-16-2018, 09:41 PM   #11
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get 4 new tires and call it a day.....you'll love non-runflats and knowing you have fresh equal rubber round without worring about the 1%ers ...sets are cheaper to buy than individual tires.
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