I've gone from a

275/50/15 M/T ET Street Radial 26.1" Tall

to

275/60/15 M/T ET Street Radial 28" Tall

@ Redline 7100 in 4th Gear still reads 121MPH
actual speed should be about 8-10mph more with taller tire.

Does any know how the Mph reading is controled? Does this sound right?

Thanks
Tim

 

With a taller tire your speedo will read slower than what you're actually going....

 

That sounds right, because your speedometer is setup for the stock tire diameter. I beleive that this can be calibrated though, but it probably requires access into the ECU or the combintation meter. I would check with your local Nissan dealer or a suitable tuner. I'm not sure if you are located anywhere near GTM, but you might check with them.

 

I know there are speed sensors on the diff outputs (halfshaft area). Not sure if that is what is used to calculate speeds. When you change diff gear the speedo is not affected, but when you go to a taller/shorter tire it will be. The computer calculates based of a 26.2in tall tire.