[doublexl]

My 2 cents if I may:
overall diameter of these various tire sizes.

OE: 255/35/19 overall diameter = 26.00 inches

275/30/19 overall diameter = 25.50 inches

275/35/19 overall diameter = 26.50 inches

About a 1/2 inch difference in O.D. either size from factory. Divide that 1/2 by 2 since it's a round tire and you end up with about a 1/4" difference top and bottom from factory spec. Not really enough to make significant difference in the speedo IMO. Probably would be off be 2-4 mph.

once again, i say. isnt the speed picked up via wheel speed sensor. aka not in the driveline. so tire size should not matter.

 

[doublexl]

I wish someone could verify what Doublexl is saying. I will check with mile markers as soon as possible.

search the forums for a thread where they put a 4.08 rear differential in the IS F. factory is a 2.93 rear gear. it was a dealership that did it, im not sure who, i cant remember. they said they drove 2 IS F's side by side, one with the new diff, one without, and the speedo's were exactly the same. so if the diff gear change doesnt make a difference, why would tire size.

 

[doublexl]

http://www.lexusf.com/forums/showthread.php?t=460&highlight=rear+gear

there is the thread. specifically posts 22 and 23 on page 3. 2nd and 3rd posts on the page.

it was FchampOH that said this....