my brother just got a 98 F-150 and it came with aftermarket 265-70-16's on it,,,,,,he got a ticket a few days ago and said his speedo was right,,,i checked his door sticker and as a stock truck it should have had 235-70-16's.....what is the speed difference between the 265-70-16 and the 235-70-16......also if you can answer,,,he has to take it in for recalibration,,,,,,how is that done?

Use this calculator
http://www.therangerstation.com/Speedometer_Change_From_Tires.html

and use this for orginal tire size: 29
new tire size: 30.6

All you have to do is a plug in the speed your speedo said you were goign and it will tell you your actual speed, I plugged in 35 and it said acutal speed 36.9

that can't be right,,,,,,he said he saw the cop and slowed to 45...cop said 59...also says if he rides normal that he passes cars like they're sitting still

than something else has been done because i have one size bigger and when my spedo says 60 i am going 62.6 i would tell him to fight it bring it into a 4x4 shop and have them check it out

I went from stock 14" (235/70/14) to 15" (31/10.5/15) and the speedo difference with my GPS was 6 MPH. Went down to 215/70/15 tire and the measured GPS difference is 3 MPH.

RD