Staggered tire sizing on identical wheels...

[AZhitman]

I'm preparing to swap wheels, and go from my current 16x7's to a set of 18x8.5's (three pounds lighter per wheel - woo hoo!)

I currently run 255/50/16's with no fitment issues at all.

I'm considering going to 285/35/18's in the rear and 245/40/18's in the front to stay close to my factory overall diameter of 26". Should I try this setup or ditch the whole idea and run 255's on all four corners?

[rsiwicki]

Check out the attached link from tirerack as it displays the width of rim to the size of tire. The size of tire is limited by the width of the rim. The 275's are too wide for a 8.5" rim and the 285's would definetly be of a safety concern. You would be pinching the tire too much around the rim. You can probably go with the 275's but I am not certain.

http://www.tirerack.com/tires/...ition

See the 'Rim Width Range" section also in the link above. Putting a wider tire on a narrower rim actually reduces section width.

For example: a tire in the P205/60R15 size is measured on a 6.0" wide wheel and this size tire has an approved rim width range from 5.5" to 7.5" wide. The tire has a section width of 8.23" (209mm) when mounted on a 6.0" wide wheel. If that tire were mounted on all of the rims within its range, the tire's approximate section width would change as follows:

Diff from Measuring Rim...........Rim Width.....Approximate Tire section width 0.5"narrower...........................5.5"..............8.03" Measuring Rim.........................6.0"..............8.23" 0.5" wider...............................6.5"...............8.43" 1.0" wider...............................7.0"..............8.63" 1.5" wider.............................. 7.5"............ 8.83"

Also keep in mind....load rating. 245/40/18 are only 93 rated while 255/40/18 are 95 rated. See my post about load rating a couple weeks ago for further info what is a risk when going below an OEM load rating.

[Exar-Kun]

AZ: keep with some 245-40-18's all around, those will be plenty wide if you get a sticky tire.-chet

[SmithSR]

235/45-18 98W Continental ContiSport Contact 226.33" OD

Max Load 1664 lbs per tire

280 treadwearTraction AATemp A

We're in the clear as far as load rating is concerned, and width is good, near ideal, within advertised range, so no sweat there...OD is near identical, everything is perfect, IF you want to run the same size 18" this is the tire to use and maintain OE diameter.

Available from TireRack!!

BMW is a player, so the Conti's should do well on your car too.

get the same size f/r so you can rotate tires front to rear, to cut down on front tire shoulder wear eating up the $200 tires prematurely.

Steer clear of the Michelin in this size, as it is close --but not equal to or greater than-- the car's OE load rating requirement.

[Exar-Kun]

getcha some 245-40-18 run flats -chet

[szh]

Putting a wider tire on a narrower rim actually reduces section width.

And tread width, too! Although, this would get compensated slightly - the front-to-back distance would go up to maintain the same contact patch (assuming same tire inflation pressure).

Z

[szh]

getcha some 245-40-18 run flats -chet

Those are a lot more expensive though!

Z

[szh]

I would also suggest 245/45-18 tires. The speedo error is trivial, but the choice of tires (with all the right load index'es) goes up a lot!

Some of the following are available at Tire Rack, some are not, but they have 96 through 100 load index values:

Bridgestone Potenza RE050Bridgestone Potenza S-03 Pole PositionContinental ContiExtremeContactContinental ContiSportContact 2Falken Azenis ST115Falken Beta FK-451Goodyear Eagle F1 GS-D3Michelin Pilot SportMichelin Pilot Sport A/SNitto 555 Extreme PerformancePirelli P-ZeroToyo Proxes T1-S

Z

[AZhitman]

Run flats have a sucky ride and weigh too much.

I'm considering the Conti's or the Falkens... I've been real happy with the Falkens so far...

[WongFeiHung]

I would say get same size all around so you can rotate tires when you get wear....but the narrower tire in the front is nice for steering response...

[SmithSR]

Got ABS? Run same size all four corners!

[Grant@tirerack]

Got ABS? Run same size all four corners!

Aww, come on, isn't braking supposed to be exciting? :shocked Okay, yeah, I'd go with the same size all the way around.

[Dystopia]

no real reason to sagger the size with your maximum width being 8.5

[SmithSR]

Kudos to Grant for most appropriate smiley!!

[szh]

no real reason to sagger the size with your maximum width being 8.5

Your avatar is staggeringly good, though!

Z

[Dystopia]

ya, i remebe vack in the day before vb on nico where we didnt hava avatars....ahh the old days...

this is the irst and only aavatar i have ever had on here

[Grant@tirerack]

this is the irst and only aavatar i have ever had on here

Uh, what? Were we talking about tires, ,, uh, yeah, tires, that's it! (trying hard to focus on tires:D ). LOL

[szh]

That avatar is as pneumatic as a tire!

Z