2tone

iTrader: (3)

hey peeps

we're in a bit of a weird situation that i'd thought i'd ask you guys about. we have a 2007 bmw x3 (which is obviously all wheel drive). we had a flat tire that turned out to be irreparable (screw too close to sidewall). so...buy a new tire right? wrong. discount tire advised us to get at least 2 new tires (for the rears) or all 4 tires...after calling bmw...apparently anything at or over 3/32 difference in tread depth can affect tire size/revolutions enough to be bad for awd cars. never heard of that, but after some research i'm inclined to believe it and accept it.

So...it's the rear pass. tire that's bad. all 4 tires were 235, even though the oe set up is staggered (235 front, 255 rear). the idea is to just get two new rear tires, one to replace the damaged one and at the same time go back to the oe set up of 255's, so 2 new rear tires. still with me? Now, if new tires are 10/32, and the fronts are 7/32, that is RIGHT AT the limit of having it adversely affect tire revolutions/awd, etc. I'm not sure I want to risk that, but I'm not sure I want to fork over another $800 front front tires!

Does any one have experience or knowledge on this? will i be ok having 10/32 in the back and 7/32 in the front on an awd car, or should i bite the bullet and get 4 new tires so i know i'm safe?? i read about tire shaving on tirerack.com...seems like it could be a plausible solution...has anyone tried that? essentially, i'd buy "new" tires that they would wear down to what i request, either 7/32 or 8/32 to match my current tires. i like that idea, if it's legit!!

dannobre

iTrader: (3)

I'ts common practice to shave tires that are used for track.....so you could get them shaved to the same depth as the front if you are worried.

Not sure what tire sizes that they use...but if they are staggerred...it is unlikely that the rolling dia/ circumference is spot on for them even when new...so I doubt that a 3/32 difference will hurt anything

tiltmode43

iTrader: (15)

Tirerack will shave down your new tire(s) to match for an additional $25/tire. You will need to measure your current tires with a tread depth guage and call Tirerack directly for this service.

Personally, I would rather be as close as possible to outder diameter than save an additional $25.

HaydonGS

iTrader: (1)

+1

shaving is really no big deal, and at the least it's $25 for peace of mind

SpencerM1

iTrader: (1)

I wouldn't replace it and just rock the 2mm difference. I would assume that in snow or mud it might make a difference. A very slight difference....

2tone

iTrader: (3)

ah sweet guys, thanks for the responses.

the current size all around is 235/45/19

the oe set up SHOULD BE 235/45/19 up front and 255/40/19 in the back.

235/45/19
sidewall: 4.2
diameter: 27.3
circumference: 85.8
revs/mile: 738.0

255/40/19
sidewall: 4.0
diameter: 27.0
circumference: 84.9
revs/mile: 746.0

so, i guess the point isn't to have them be the SAME front-to-back...just that the way bmw set it up was based on these numbers...so just the fact that the first owner put 235's all around allready has it off a little bit from what it should have been!! add to that if the rears have more tread than the fronts...it'll exacerbate (??) the difference. so it looks like shaving is the answer!

@tilt - thanks...i'm not worried about the $25 fee, that is def worth it. i was trying to prevent having to buy all 4 tires, so this is a good solution i think.

thanks dannobre and haydon!

2tone

iTrader: (3)

oh, separate question:

probably not good practice to swap brands out gradually? i'd prefer to get a different brand for the rears now, b/c the current tire (pirelli's) are quite expensive. i guess they should match and swap out all 4 for a new brand next time?

tiltmode43

iTrader: (15)

Hmm, Ideally I'd imagine you would want to keep all four tires being the same model/manufacturer but on the other hand, I can't see it hurting things going with a different brand/model.

Spin9k

^By all reports, having different tires/brands front to back can be a bad, even dangerous thing. Tire construction and response vary greatly. Ask any tire company/store about this before mixing. Doubtful you'd get any reputable store to even do this.

tiltmode43

iTrader: (15)

Different tires are going to be, well, different - this is why I mentioned it wouldn't be advisable. With that said, though, under standard driving conditions, it may not have a negative effect. This is for AWD, so I am a little hesitant, but I have driven with differing front and rear tires in RWD cars and it really wasn't that big a deal.

9krpmrx8

iTrader: (46)

Just get four brand new tires you cheap bastard

I highly doubt it will have a negative effect. Your over thinking it

Spin9k

http://www.tirerack.com/tires/tirete....jsp?techid=18

Although the OP 'may' luck out w/mismatched tires, he may not...that's the rub...can't know until tires are mounted and driven. "Standard driving conditions" include things like accident avoidance, high speed exits ramps, etc. ... not a good time to discover a problem. I'd ask BMW and if there's any question, be conservative as tires are failrly important being the only thing keeping the car on the straight and narrow. Seems the differentials are where problems can develop, beside the weird handling that is possible.

2tone

iTrader: (3)

thanks gusy - i think i agree w/ the mismatch brands...not worth the risk. i'll just cringe while i'm paying for pirelli's



ha ha, jerk, not all of us are maaaaaaade of money!! besides, money spent on this car is LESS money spent on my 8!!

paimon.soror

iTrader: (15)

My gf got a flat recently and she drives an AWD impreza. I was surprised that all 4 tires had to be swapped out as well. Mainly because they didn't make the model tire that she had anymore, and even something like having one tire that has a different tread pattern than the other 3 can take a toll on the center diff on the car. News to me, but like you said, after doing a bunch of reading it seems to be common knowledge amongst AWD drivers.

9krpmrx8

iTrader: (46)

true that. You honestly might want to check craigslist, I see BMW take offs all the time, you might get lucky. My busy has a tire shop and he just had a brand spanking new 5 series roll in yesterday for 22's and the guy didn't want the stockers so he gave him a break on the new rims and tires and kept them. Too bad they are 18's.

2tone

iTrader: (3)

good to hear i wasn't the only idiot. ha ha. when the guy first told me i was like bullsh-t, don't rip me off. hahaha

ah snap, not a bad idea at all. i'll look into that!! yeah the 19's look sweet, but they're more expensive and harder to find tires for!

tiltmode43

iTrader: (15)

Definitely true, my knowledge for AWD and tire setups is somewhat lacking as I haven't had much personal experience. Mixing tires front and rear doesn't necessarily equate to a dangerous car for RWD/FWD, though, so long as the tires have comparable compounds.

I can't imagine the diff having issues due to a differing tread pattern as AWD cars can run staggered wheels (offset, diameter, and width even) so long as the OD of the tires is close enough. This is certainly a *better safe than sorry* moment though, as 2Tone mentioned.

2tone

iTrader: (3)

update: i ordered the pirelli's from tirerack. i'm a huge discount tire fan, but they don't offer tire shaving! i ordered them shaved down a bit and the price was still about the same as discount tire since there's no tax. anyway, ordered last week, friday i think, and they should arrive today and get thrown on tonight! no more donut!!

2tone

iTrader: (3)

final update: thanks again to everyone. total price installed was just under $750, but that includes shaving them down a bit. the 255's (up from 235) in the back really feel nice, a lot better (like it was meant to be)

REDRX3RX8

If you bought the oem 255/40r19's for the back, according to your specs that the factory wants, the rear will roll 1% faster than the front (738 revs front-746 revs back).

If you shaved the ones on the back that you ordered, you actually made a bigger rev difference from front to back.

New as it comes might work best.

2tone

iTrader: (3)

read my quote above. it's not the fact that the fronts roll differently than the rears...it's that that's how bmw sets up the car from the factory, with this exact staggered set up...so the slippage detection/roll rates/etc. of the wheels is BASED on the very difference we're talking about. so having the SAME SIZE tire front and back...although they'd roll at the same rate, is NOT how bmw has it set up to read it. i went BACK TO the oe set up, b/c when i bought it used it was not staggered, as it should have been.