Had 265/35/18 installed on my 330i zsp stock 18" rear, ok or not?

I took out my car this afternoon only to find 2 huge nails on my rear right tire. My rear tires are pretty much worn out and I was planning to have them replaced soon. Since it was a Saturday afternoon when most shops were about to shut down till Monday, I decided that I'd better have it done asap. I called around a few tire stores nearby but none of them has the oem size 255/35/18 in stock. So I walked into a discount tire store and this guy told me that 265/35/18 would fit perfectly, or even better on my stock rims, and he happened to have a few in stock at some ridiculously low prices.

So I trusted him and bought 2 Cooper Zeon 2xs 265/35/18 for $155 each. With installation and warranty plus tax the total was under $400. Yeah I know it was a cheap brand, but that was like the only choice of tires I had at that time and the price seemed unbeatable. So far the ride felt okay. Noise, comfort, grip etc while not amazingly good, are at least above average and well acceptable. The "look" was defintely bigger and better though.

I'm just a little concerned about this setup. I want to know if this will hurt anything in the long run. Any of you guys use this size on your stock 18"? The discount tire dude swore that the fit was perfect.

Well, you can do the math.

255 * .35 = 78.75. Each sidewall of your stock tire is 78.75mm tall.
265 * .35 = 92.75. Each sidewall of your new tire is 92.75mm tall.

What's this mean? It means that it has slightly changed your gearing. Your odometer and speedometer will be roughly 4.5% fast.

In the end, it's not that big of a deal. I'd be more concerned about mismatched tire types msyelf.... but I tend to drive rather hard.

Originally Posted by KrisL

255 * .35 = 78.75. Each sidewall of your stock tire is 78.75mm tall.

255 * .35 = 89.25

Originally Posted by KrisL

Well, you can do the math.

255 * .35 = 78.75. Each sidewall of your stock tire is 78.75mm tall.
265 * .35 = 92.75. Each sidewall of your new tire is 92.75mm tall.

What's this mean? It means that it has slightly changed your gearing. Your odometer and speedometer will be roughly 4.5% fast.

In the end, it's not that big of a deal. I'd be more concerned about mismatched tire types msyelf.... but I tend to drive rather hard.

Ummm, so if the speedometer says I'm at 45mph, its actually going 43?

Originally Posted by mkh

255 * .35 = 89.25

haha... I knew something looked wrong... must've hit the wrong key, damn laptop keyboard..

Originally Posted by startover

Ummm, so if the speedometer says I'm at 45mph, its actually going 43?

The speedo is actually much less incorrect than I specified.. almost negligible.

http://www.powerdog.com/tiresize.cgi

The difference from 255/35-18 to 265/35-18 is 1.1% (i.e. almost negligible). Since the new diameter is larger, the speedometer and odometer will read lower than actual by 1.1%.

The real question is whether or not the tires the guy sold you are complete pieces of garbage. 265 fits fine, although it would nominally increase the car's tendency to understeer.

Originally Posted by Nick325xiT 5spd

The real question is whether or not the tires the guy sold you are complete pieces of garbage. 265 fits fine, although it would nominally increase the car's tendency to understeer.

I think we're too late on that one. Now he has to get matching Cooper tires for the front too.

Originally Posted by Nick325xiT 5spd

The real question is whether or not the tires the guy sold you are complete pieces of garbage. 265 fits fine, although it would nominally increase the car's tendency to understeer.

The fact that they are (assumably) less sticky tires would cancel that out .

Originally Posted by PhilH

I think we're too late on that one. Now he has to get matching Cooper tires for the front too.

I think those tires are not that bad.

Do I *have* to get matching tires for the front? My front tires still have about 80% thread left.

Originally Posted by startover

I think those tires are not that bad.

Do I *have* to get matching tires for the front? My front tires still have about 80% thread left.

The quick answer is no, of course not.

That being said, if you drive spiritedly, you should definitely watch out for a bit of unpredictability when it comes to front vs rear traction.

In other words, keep DSC on.

Originally Posted by startover

Do I *have* to get matching tires for the front? My front tires still have about 80% thread left.

I'm surprised that your fronts still have 80% left. When my rears worn out, my fronts had only about 30% left. That means your rears wear about 5 times as fast as your fronts. And if your rears last 20k miles, then the fronts can go up to 100k? Hmm... hard to believe!

Regarding matching front and rear tires, take a look at this thread:

http://www.bimmerfest.com/forums/showthread.php?t=96619

Originally Posted by mkh

I'm surprised that your fronts still have 80% left. When my rears worn out, my fronts had only about 30% left. That means your rears wear about 5 times as fast as your fronts. And if your rears last 20k miles, then the fronts can go up to 100k? Hmm... hard to believe!

Regarding matching front and rear tires, take a look at this thread:

http://www.bimmerfest.com/forums/showthread.php?t=96619

I bought the car used, so I wouldn't know why. My guess is that the previous owner changed the tires at different intervals.