[doublexl]

different tire sizes will not effect the speedometer reading because the vehicle speed is picked up via a wheel speed sensor.

 

[doublexl]

Actually different tire sizes will mess up your speedometer.

The amount that the speedo will be off depends on how big of a tire you get.

For example if stock tires are 23 inches tall and you upgrade to a 24 inch tall tire then the speedo will be off by by 9 percent

you are so wrong it hurts.

if the speedo did in fact get its reading from a driveshaft or axel mounted sensor, then YES tiresize would effect the reading. however, i direct you here.....

http://www.lexusf.com/forums/showthread.php?t=460&highlight=is350+gear&page=3 third post from the top. unless dealers are lying to us now....

Pat Ross,
It appears that vehicle speed is picked up from wheel speed sensor. During installation, our head tech looked into speedo gears and found none available through parts. Being that the wheel speed sensor does all the work no change was made. Side by side highway comparisons with altered car vs. stock car showed that the speedometer was accurate. We actually drove these cars down the highway side by side and communicated via the bluetooth phone connection! Thanks,

Doug

kthx