tkrussell

Does anyone have a source with experience or knowledge in reprogramming the RX speedometer calibration for different tire sizes?

I run 245/45-18 on the stock 18 x 7 wheels. The handling is fantastic and the ride not much different from stock. Only problem is the tires are about 1/2" shorter than stock. They look good, but the speedometer reads several mph high at 60 mph.

The dealer says " they think it can be done" but will not, citing some nebulous Lexus dealer policy.

On the Lexus/Toyota Technical site, there is a "Calibration CD" which requires a special interface to connect with the vehicle ECM. Does anyone have any experience with this CD?
Does it allow tire size changes as one of the programming options?

By analogy, some other car makes allow the tire size to be set, eg, 27.5", in increments to allow precise reading of the speedometer and odometer.

Thanks for everyone's help on this.

rxdriver

I was told by a Toyota dealer that they don't have a way to calibrate the speedo. It's not that accurate anyway - the factory doesn't calibrate a specific car based on a specific wheel option. The default speedo program ends up being a compromise across all of the various wheel options available for that model.

My experience has been that Toyota makes the speedo read high anyway, so it's probably not just your tires. My RX 330 is somewhere around 5% high, and I've got the 18" wheel option. When it says I'm going 70 mph, I'm really going around 66-67 mph.