2nd Gen Non-Engine/Transmission Speedometer Correction

[mwilson]

Might as well ask two questions in one night. New truck was built with 245 size tires and previous owner replaced with 265's. Needless to say, the speedo is wacked out. Fact sheet has note at bottom stating 98. 5 models read speed from anti-skid sensors in rear end and PCM has to be recalibrated by dealer. The way it reads is people report limited success doing that. Does anyone have experience with this so I can decide to get it done or just live with it? It is off 10 miles on a 120 mile round trip.



Thanks, Mike

 

[WadePatton]

I have seen trucks factory stickered for 245's but OEM equipped with 265's and speedo be dead accurate.



I've read here that the factory PCM can be reprogrammed for a tire larger than 265, but I forget exactly how big. There are devices out there to correct for even bigger tires.



SA- Dealer can recal PCM for 265's and it should be no problem.

 

[Scrappy]

speedo recal.

Your speedometer will be off such a small amount with that tire change that it shouldn't even matter. I don't think that the difference between the two is even 1% = 1 mi. off in 100mi.

 

[WadePatton]

Off enought to get a ticket and mess with your MPG calculations.

 

[IWeiny]

265 do change it

I am going about 70 (GPS) when the speedo reads 66 or so. I don't know the percentage but it is all off now. I might go to the dealer as I have a good reason for the 265's they are 400 pounds better on the rating.

 

[y-knot]

I run 255-85-16's which when measured are about 10% larger (run-out) then the stock ones. So I have to remind myself that when it says 60, i'm really doing 66 mph. Also when figuring your mileage take the amount shown on the odometer, and add in your 10% (300 miles is 330 miles).

 

[RADdodge]

The dealer can change it for the 265s. The DBR tool will only change the setting for tires Dodge sells with the trucks. The Service Manual list the different sizes. They went as high as a 275 Goodyear. The best bet (most accurate) would be to find the RPM (revolutions per mile) for the particular tires you have. Dodge can then put in the RPM for the tire and that should be about as accurate as you can get from the stock system. They do have a limit on the number though. Mine was 594 and it was a no can do. The 265 Goodyear RPM is 660. Hope that helps.

 

[Scrappy]

speedo recal II

the 245's are 30. 35" tall, the 265's are 31. 56" tall. that is a 3 percent increase, so you will be doing 61. 8 mph actual to 60 indicated. I would just leave it alone and remember to add the 3 percent to your miles to figure mileage. I currently am running 315's and have figured that I am 9 percent off and figure it from there.

 

[mwilson]

Thanks for all the responses on this. Am going to call the dealer in the morning and see if the Diesel guy is on duty. It seems to be reading slow. I ran with my son the other night and we figure with my old truck showing 75 the new one reads about 68 or so. Have noticed that when I'm running my normal commute speed of 75 that there is no one running with me and them little white markers are really flying by. Maybe something else is messed up but will start with the recalibration. Will post results next trip.

Mike.

 

[RJ2]

I went from 215's to 235's and the gps says 5 mph more at

70 mph.

 

[MPBerk]

285/75/16's. Had a friend (patrol deputy) hit me with the "LASER". Cruise was set at 70, "the laser" had me @ 75mph.

 

[Loren]

Mike,



Rickson sells the Superlift company's TruSpeed speedometer correction computer for four wheel ABS trucks. It's not cheap (about $190), but it works great.



Superlift has great customer support, too. My TruSpeed failed after about two years in the truck and they sent me a replacement without charge.



If your truck doesn't have four wheel ABS, Rickson also sells a different electronic ratio adaptor for rear wheel ABS trucks.



Both of these devices can be viewed here:

http://www.ricksontruck.com/speedometer.html



My 2000 truck with four wheel ABS did not need any adjustments to anything on the truck after installing the TruSpeed. I never got any fault codes that I was aware of. No lights came on.



Happy hunting.



Loren