ok, 315's are gonna go on tomorrow , i was wonderin how far off my speedo will be, it came out with 265's
this will get me close until the smarty comes in
thanks

 

i think the BFG website has a little tool for calculating what speeds will be with diff tires.. If its a 315/75/R16 that is comparable to a 35" tire... Your speed should be off like.. 6-7 MPH take it to the dealer with the Revs Per Mile of your tires and they can reprogram it..

From the BFG Site... a 265/75 is a 31.7 inch tire. a 315/75 is a 34.6 inch tire... at 75 MPH on your speedo you are actually doing 81 MPH.. at 55 MPH on your speedo you are doing 60 MPH.. so there you go..

 

none as soon as you get your SMARTY

 

Quick close reference - add 10% to your speedo reading. 70 = 77, 60 = 66, 50 = 55, etc.

 

My 315's are exactly 11% off. My truck came with 245's stock not 265's. Best way to tell is to drive down the highway and start tripometer right as you pass a mile post and then after ten mile posts, see what your tripo says. If it reads, 9 miles, you are 10% slow etc. Every tenth= 1%. For me, 60 MPH on speedo = 66.6 MPH on the road.