I loadind 91 octane and adjused tire size to 32" my speedometer is still off any suggetions to fix? I checked my speed using a gps

 

Need to figure out the exact tire height on the vehicle or revolutions per mile to be accurate. Probably isn't exactly 32" sitting on the ground.

 

Did you measure your tires diameter from the ground to the top of the tread?

 

no i am running 265x75x16s though. Tried 32 and 31.75 neither are correct

 

Just measured and got 31" will plug that in and see what happens

 

I have stock 32" rubi tires. I thot the superchips was off when it set me to about 30.7. Then I measured. It was right and my speedo matches my gps. The side to side measurement is about 32, but up and down it loses over an inch from the weight, I guess. Makes sense.