Totallyrad, I don't believe I got what I requested, (unless by programming 626 RPM's vs. the stock 656 RPM's truly results in a 15mph difference), and I definitely did not get what I wanted that's for sure. I have seen other posts stating they have 315's and used 601 RPM's with no problems so I wasn't sure why my situation was so different which is why I posted and was hoping someone would chime in as to other possible causes. It should have been perfectly fine to change the pinion factor with the stock tires still on it and not result in such a big MPH change I would think. Now that I have the new tires and wheels on, it shows something is still not right as the speedo is still at least 10 mph too fast.

 

Like I stated they may have also changed the tone ring teeth # which is what happened to me the first time then I got a tech who knew what he was doing and redid it seems right now.

 

Come on you guys, going from the stock tire size (654 revs/mile) up to 33's (626 revs/mile) is like a 5% change. Going from 10.5 mile trip to 14 mile trip is a 25% change. The dealer obviously screwed something up!

 

I've got a similar issue but in the opposite. I've had some trans issues and the pinion factor was off cause of my tires ,they changed it and I was perfect on the speedometer but that didn't fix the trans ( I knew it wouldn't) The second visit they decide the valve body in the trans is sticking. Diving home I am doing waht says 56 mph and I am blowing by people doing 65-70 and I feel fast, then I look at my rpm 1800, that is like 300 more then when I am normally at 60. I guess the knuckle head thought it was off or something and did something with the ring gear. Now it will have to be changed when I get the trans fixed. I feel your pain.

 

thats what im sayin if its still off with the new tires they did something wrong.
myfirst trip I was off about 10 mph with new tires remember the 1st tech getting to ring teeth# setting 2nd tech didnt said that was wrong. bottom line is something is wrong have them go back through it all they should get to after tire sizes is manual enter rpm of tire never getting in to ring teeth

 

Booman70, this could very well be the problem. I do remember seeing something like 10.5 or 11.5 which I think is what you are calling tone ring teeth?

 

If you want to get the most accurate revs per mile, measure the radius of the tire to the ground in inches.(center of wheel to ground). That gives you the actual radius under load as the tire flattens.

The equation is as follows

convert inches to feet R/12

Convert Radius to diameter 2 X R

Circumference = Pi (3.1416) x D

revs per mile= 5280/ C

Your tire calculates at 33.354 inches tall and have 604 revs per mile if it was not under load. I'm pretty sure the manufacturers measure Rev's per mile under some specific load, because a 33" tire typically is in the 630 range on manufacturers websites.

 

I think that it is something they did in there like the same problem I had have them redo it should have to go past where they have preselected tire sizes in the menu and manually enter the rpm. you should never get to the tone ring teeth I think it might ask rear 10.5 or 11.5 I remember the first time the the tech got to tone ring the 2nd time the other guy didnt

 

Depending on the year of the truck they will either use the drb scan or the star scan. When the technician is setting up the pinion settings there is an option to change tires, and then it gives an option to change tone ring... they shouldnt touch this, just leave it on the 10.5 11.5 setting. The ecm knows what gears you have if you havent changed them.

Kevin

 

Thanks for all the help guys. I bring it in tonight. Hopefully the mechanic that worked on my truck is available as he explains what he is doing and I can offer the info you guys have given me.

 

Well, took the truck back to the dealer and ended up back at stock tire size setting which corrected the 10-15 mph too fast speed. When the mechanic hooked up the DRB scanner, the revs per mile were set correctly for the new tires, 626 RPM's which is the number from the tire manufacturer. He even checked the axle and ring gear info which didn't appear to have changed from the stock setting. The axle info said 11.5 and the ring teeth said 102 even when he programmed the pinion factor both ways (stock 658 vs new 626). I dunno, but I can live with it set at stock setting as the speedo seems just about right.

Anyway, kudo's to the mechanic as he explained everything he was doing and was willing to try what you guys suggested here. He even offered to do more research and would let me know. Didn't cost me a thing just some time and made a new friend.