mdgrwl

iTrader: (7)

I was tire shopping and speaking with a rep at Tirerack.com who stated "Lexus specs to keep the rear tire diameter at least 0.5"" larger then front tire". I was looking to go with something like a 275/30/19rear & 235/45/19 fronts - but with these specs, the front tires are actually slightly larger in diameter overall (0.1"?)... the rep said Lexus states not to do this.... to keep the rears larger by going with something like 255/35/19rear & 225/35/19front - which is a 0.7" difference.

He didn't know exactly why and guessed it had something to do w/ the speedometer (which I don't really care about), but also said it could be throwing off the cars braking system...

Whats the deal on this? Any Lexus tech's know if were damaing our 250/350RWD's if the rear tire isn't at least 0.5" larger then the fronts?

EDIT: I should mention, going plus sizes isn't the issue. Its just keeping the rears at least 0.5" or greater that concerned me...

PMok

don't know for sure, someone here with more technical knowledge can chime in, but I think the wheel diameter affects things like ABS, traction control, VDIM etc. They measure your speed and traction based on wheel rotations and going too far off the standard diameters may throw them off and give you weird behavior. Why would you go with 235/45 in front? In general keep the profile number the same on both tires (for 19", stick with 30 or 35) and you should be ok.

PMok

I just noticed that you have a AWD but are asking about RWD cars???
Are you trying to run staggered wheels but keep the same wheel diameter all around for the AWD?

mdgrwl

iTrader: (7)

woops, meant 245/35... sorry, typo.
Also, yes my sig has an AWD, but I also own a RWD as well...

FMJ IS

wow, you must be the first to own 2 2IS? you really love this car that much??

does the tire size has anything to do with the Diff?

mdgrwl

iTrader: (7)

well the IS250 that you see in my sig JUST went to my wife, she now drives it.
I just haven't updated my profile yet, I'm lazy...
I'm also waiting for all the mods to get done on the IS350 before I start showing it.... its almost there.

obthirteen

I was also in contact with a rep from Tire Rack asking the same questions. He told me that running 235/35/19 (front) and 265/35/19 (rear) is the way to go. I even asked about the 275/30/19s and he said that it would be too large and to stick with the 265/35. I wonder why we are getting different answers from them. I would like to hear from a tire guru from the forum.

IS-SV

btw - It's apparent that the guys on the phone at Tire Rack are not necessarily top notch tire authorities. I've had similar experiences in the past.

mdgrwl

iTrader: (7)

Yeah, thats consistant w/ what I was told, except for 1 size down - 225/35/19 & 255/35/19. For some reason, going with something like a 265/30 or 275/30 is a no no.

I'm not sure where he was coming from regarding the 275/30 because I was told in specific to keep the tires at a minimum of 0.5" different. The 275/30 is only 0.1" I believe... Weird... LEXUS TECH'S WHERE YOU AT!!!!

sinister2c

I run 275/30/20 with no problems...saving 10% on my miles. I know plenty of people running this size.

google tire calculator and a bunch will pop up. You can try all the sizes you are looking at. I know that 255/30/20 is the exact overall diameter as a stock 255/40/18, less than 1%.

projectdna

iTrader: (56)

rule of thumb is to keep rolling diameters withing 3% of stock rolling diameter. you'll throw off the speedometer and odometer if you don't.

as3.0cl

iTrader: (2)

i'm an awd, running a 235/35.19 and a 275/30/19. i have a .1% difference rolling diameter. on an awd you must have the same front and rear rolling diameters. front rim is 19X8.5 and rear is 19X9.5, i have no issues what so ever and both tires have the same sidewall height.

plus now my navi and speedo agree on mph.

you shouldn't have an issue at all. if you wanted to run a thinker sidewall you could.

i suggest you talk to some of the sponsors on here, like D2autosports, MrMark, B2autodesigns ect to stear you in the right direction.

VikH

iTrader: (5)

Ideal is 225/35-19 255/35-19. The next best thing is 235/35-19 and 265/35-19.

IS-SV

That's the same tire setup I'm running on IS350 for same reasons (equal rolling diameter and sidewall heights essentially).