cxc511

I have a question regarding the tire sizes for the 18" staggered sport wheels on my girlfriend's IS 250 - 225/40/18 front and 255/40/18 rear. Given the same apsect ratio and a wider tire in the rear, it is about 1" taller than the front.

-Since the front tires have to rotate a bit more quickly that the rears at any speed, which axle does the car monitor to determine vehicle speed?

FYI I drive a BMW 328 coupe, also with sport package. Tire sizing is the same up front as the IS, but rears are 255/35/18 (which are the same height as 225/40/18.) I prefer the BMW sizing - it make life a lot easier when it comes to to put on snow tires/wheels since a 225/45/17 will fit properly on all four corners. Also you can buy/sell a set a wheels and tires from an AWD 3 series and put them on a RWD without any issues.

-Would you prefer the 255/40/18 or a 255/35/18 rear tire on the RWD IS?

NYKnick101

1 inch is actually a lot for one pair of tires to be taller than the other pair. I am not sure what the speed sensor is driven someone else could chime in on but my question to you is have you measured it? Are you sure you have staggered sport wheels and not AWD wheels where is 18x8 all around and not 18x8 F and 18x8.5 R.

I saw another members car was like that and and put staggered tires on his car to later found out the wheels werent actually staggered so the 255 made it look a lot taller than the front

cxc511

These are the stock wheels for a 2007 IS 250 RWD sport package. I am nearly certain they are 8" front and 8.5" rear.

I used the wheel tire calculator from e90post shown in the link below, and it shows rears to be almost an inch taller( .95.") The side wall on the rear tires is also visibly taller than the front.

http://www.e90post.com/forums/forumdisplay.php?f=12

flowrider

iTrader: (9)

^ ^ ^ ^ You are correct. Scroll down to "F SPORT Vehicle".

http://www.lexus.com/cpo/model_libra...2_options.html

Lou

cxc511

Just took a quick look at tire rack, and the sizing on IS staggered tires seems more common than a rear tire of the same height for performance oriented RWD vehicles. Even the BMW M3 has a slightly taller rear tire that the front. I personally prefer the rear tire on my 328 with the same height and amount of sidewall as the front, and the ability to run a square set of winter tires and wheels. Just a matter of opinion.

I would have to believe the IS 250 looks at the speed of the rear tire with RWD since traction control and the like are all taking place on the drive axle. Assuming this is the case, would there be any issues besides speedometer error putting a 225/45/17 (nearly same height as 225/40/18 and hence an inch shorter than the current rear tire) on all four corners of a RWD IS 250 during winter?