Dealer screwed up my speedo

[MechanicMike]

Took my truck in this morning to have finally have the speedo recalibrated for the bigger tires. Before the calibration, the speedo seemed to read slow maybe 5-8 MPH. I printed out a copy of the calibration procedure that I got from this website and brought it with me to avoid any potential problems. At first the tech said that he could not recalibrate the speedo because the truck didn't have its own transmission computer . When I showed him the printout we tried again, this time I was standing next to him when he did it. He kinda glanced at the printout and did his own thing anyway. when it came time to set the pinion factor I gave him the number that I got off tire racks website which was 613 for the Goodyear MTRs. He then asked me about a tone ring # which I'm guessing is the ABS ring on the ring gear. We left that one alone. The calibration took but now the speedo reads fast about 15-20 mph.



My question is, how accurate is the RPM number on tire racks website? All the searches I come up with are for the BFG 315's, and the number they list for them people say is accurate.

I'm thinking that the tech might have entered the wrong number or messed up the procedure because he was rushing through it. I don't wanna blame anyone until I'm sure the number I gave him was correct.

Anyone running Goodyear wrangler MTRs 305/70r17 have the recalibration done. If so what did you use as a pinion fator?

If all else fails guess I gotta get out the tape measure and calclator .



Sorry for the long post.

thanks. Mike

 

[JVolpe]

I use this tire calculator http://www.1010tires.com/TireSizeCalculator.asp . It says 615 for that tire size, certainly not enough variance to make a notable difference. It sometimes varies a small amount from manufacturer numbers, but it seems to be right more than not. I used the 605 rpm for my 315s that it calculated, this was verified by GPS for distance and speed accuracy. Manufacturer showed 601.



As far as I know the only thing that needs to be changed is the "Pinion Factor"(rpm). Maybe you need to have them try again or try another dealer.

 

[MechanicMike]

Thanks for the reply. I kinda figured the number had to be close. I'm gonna call the dealer monday and talk to them about having it redone. This dealer has been good to me sofar so I 'llgive em another chance. I'll also request another tech.

Thanks Mike

 

[TCDiesel]

Also He will have to Program which axle you have 3:73/4:10,when you change rev/per:mile You have to program axle.