05 CTD2500

Ok, so I recently installed a set of Toyo 295/70 on the stock wheels. Today went to the dealer armed with the specs from Toyo's website to get the speedo reprogrammed. Get there and all goes well, service writer says they prorammed it to 619 Revolutions Per Mile as per the specs, also says they had to change the setting for the "tone ring" (someone help me out with that) so that I won't get an ABS light, said they got it as close as they could. They get done, I was expecting to have to pay the $49 he quoted me earlier in the week but he says don't worry about it and did it for free.

So I happily take her out on the interstate with my GPS, this is what I found.

GPS/SPEEDO
20/25
40/48
60/72
80/95

...so not only is it off more now but it gets further off the faster I drive. It was closer before the reprogram. Can anyone shed some light on what I need to do at this point?

chipmonk

you can let the dealership know that whatever they did, it isn't right, or you can get a programmer that only does odometer recallibration (around $150), or an actual power programmer (bully dog, smarty, etc.), and take care of it yourself. i'm running 35's, and with my bdtd set to 33.5", my gps tells me that my speedo is dead on.

snoyes

You need to talk to the dealership for sure. You are off by a significant enough amount that they messed something up in the conversion for you. I am also finding with the Smarty it takes some tweaks to get the Speedo calibrated exactly to the GPS. Actually took me a few times of running up and down the street/highway to get it right.

jumper

Make sure when they are in the menu setting the Revolutions per Mile that they also set the "Differential" or similar field to "Factory 10.5/11.5 axle" instead of "Other." That can cause problems like this as well. The tech got that part wrong on mine and the speedo was off by a bunch. As for the varying differences based on MPH, you will be off by a percentage, not a constant MPH. If they do have the Differential setting set to Factory as above, then have them change the 619 by the percentage you are off and you should be good to go. BTW, 619 implies a 32.6 inch diameter tire. Revs/Mile = Tire Diameter (inches) * 18.98.

05 CTD2500

thanks everyone for the input..

jumper, I will make sure they do that when I go back, interesting that the formula shows that as a 32.6" tire, if I found the RPM for a 33.5" tire (what the specs show) I can't imagine how far off it would be.

just afraid if I make another appointment they're just going to tell me that they input everything in the way it should be according to the specs and wont know what to do to make it right.

I'm really looking for some hard data that I can take with me for the next visit so I only have to go once.

Revolutions Per Mile for the stock Rugged Trail T/A's is 658, the Toyo's are 619 (supposedly what it was programmed to now). The speedo was about 2mph to high according to GPS with the stock tires but I'm guessing that is probably due to them being about half worn. Stock tires have 31.4" diameter, Toyo's have 33.5" diameter (according to specs, probably less with weight on them). Someone good at math, please help me out.

Then theres still the question of the other setting they messed with, "tone ring". Can someone explain this to me, does it only affect the ABS like they said, they say they could only get it close and if the light came on to come back, is this what is causing the problems?

Seems like this shouldn't be this difficult, maybe this is my sign to buy a Smarty

jumper

I took a look at Toyo's website and it does indeed state 619 and a 33.5 inch diameter. 33.5 inch calculates out at 602 Revs/Mile. However, they list the tread depth at 19/32. If you subtract twice that from the 33.5 inch tire diameter you get 624 Revs/mile. So a new tire will do 602, a bald one 624 Revs/mile. They've clearly assumed a small bit of tread left on the tire, probably wear bars worth. You're off more that that difference, however, so I'd leave it at 619 and have them check that they got the rear axle to the "Factory 10.5/11.5 axle" setting. I don't know about this tone ring thing.

BTW, the full formula is Revs/mile = (5280 [ft/mile])/((Tire diameter [inches] * 3.14159 [PI]) / 12 [inches/foot]) from your basic geometry class to get the circumference of a circle converted from inches to feet where the circumference equals one revolution. Math is useful. Ignore the constant I gave above and use this formula. The constant doesn't seem to stay constant...

booman70

They did this to my truck to when i had them reprogram for my 315s. the first tech put in the rpms from bfg and then somehow got into the tone ring adjustment and that is where it went wrong. Speedo was way off like yours called dealer and brought it back in for their best tech to look at it. He put it on lift measured circumference of tire and divided mile by it to get different rpm than bfg gave set that and said the tone ring doesnt need to be messed with set that where it was at before. Speedo was real close after that and I paid $50 I've since bought a bully dog triple dog and fine tuned it dead on now

05 CTD2500

thanks again everyone, sounds like all I need to do is tell them to make sure it is still set for the 11.5 AAM and to put the tone ring setting back to stock setting, then maybe some fine tuning on the RPM setting if they're nice enough. Jumper, thanks for taking the time to explain and for the formula, gonna keep that one handy and pass it on.

05 CTD2500

UPDATE:

Finally dealer had time to fix it today. Hooked up the DRB and went through all the settings, tone ring was set to "corporate 10.5/11.5" like it should (even though they said they changed it last time), RPM was set to 619 as the specs show, anyway since everything was right we took it out on the road with the DRB hooked up and got it perfect with the GPS, final setting was 638 RPM. The mechanic and I came to the conclusion that the factory specs probably don't take into account the diameter of the tire with the weight of the truck on them. And they still did it for free

booman70

Glad you got it straight.