straightaxle

If these trucks are anything like the older ones, especially the super duties, changing the gear ratio in the computer will only mess up the trans, won't effect the speedo. Ford has used the abs ring to determine speed in the past, not output shaft speed. I would check it out before having someone change the gear ratio in the computer.

TCR

Yes it did, or it was jacked up to begin with. They come programmed for 31.9-32" tires. I have 275/60/20s exactly 33" and I'm off 3mph. Do you have an external GPS to compare to?

Wyo11Scab

iTrader: (1)

X2

kk_kalina

I used a couple different speedo apps from my phone tried them before the new tires and after and was accurate both times also had my dad clock me in his police truck was accurate

BassAckwards

Congrats you just defied the laws of physics if your speedo wasn't incorrect to begin with lol

It's not a matter of opinion as to wether or not your speedo is off with the change in tire size, it IS off. So most likely the speedo apps and radar have a margin of error of about +/- 3mph

dcfluid

Just so everyone is aware the 2011 speedometers are 3 to 4% optimistic but the odometer is within 1/2%. So a bigger tire could make the speedometers read more accurate but the odometer will be off by the % of change.