Is there any way to recalibrate the RCF speed readings after upgrading to a different size wheel/tire?

 

No, you cannot change speedo calibration and the general rule is to keep the rotational circumference within + or - 3% of the stock circumference.

 

May be via tech stream?

 

You can always use the GPS on your phone. I've always found that to be pretty accurate.

Lou

 

I used the Yellow Box in my IS300 after modding the rear differential with a taller ratio ring & pinion. I sent the car's schematics to the mfr and they came back to me with the instructions on where to splice the box in. The trick is finding the schematics of the RCF.