truspeed info update

[WBarber2]

Looked through all the posts today on correcting speedo/odo after getting larger tires - found nothing available currently. I called Superlift who supplies the Truspeed. I talked to someone named Jeff who said they expect to have a the new version for the '03 2500/3500s available shortly - maybe this month.



Knowing how new products go the availability may be that part of this month which falls in early December, but at least they are actively working on it.

 

[DPKetchum]

I thought that dealer could set speedo by tire revolutions per mile with DRB(scan Tool)at least that is what Ricksons the wheel folks said.

 

[DLeno]

I understand (but not independantly validated) that the factory ECM is capable of going down to 599 revs per mile. a BFG 315/70-17 tire is 601 revs per mile.

 

[WBarber2]

If the ECM could do 599 that would be great. But all the info I found so far says 636 in the minimum - great for 285s. Also, I asked my dealer and they were pretty sure they couldn't get anywhere near 601.



What would be nice is if the ECM could be used to set the final drive ratio to 4. 10. 4. 10s with the 315s yields an effective 3. 78. Close enough for me. I do intend to talk to the dealer about this some more.

 

[rbattelle]

Isspro makes a programmable compensator unit. You just wire it up to your speedo and program it for the % increase/decrease in wheel rotational speed.

 

[WBarber2]

That sounds interesting. Is this the R4610 or some other isspro unit. Also, do you know if it just corrects the speedo or can it be connected to correct the tac and ABS feed values ??

 

[nickleinonen]

Originally posted by WBarber2

If the ECM could do 599 that would be great. But all the info I found so far says 636 in the minimum - great for 285s. Also, I asked my dealer and they were pretty sure they couldn't get anywhere near 601.



What would be nice is if the ECM could be used to set the final drive ratio to 4. 10. 4. 10s with the 315s yields an effective 3. 78. Close enough for me. I do intend to talk to the dealer about this some more.

i don't think that would work... i believe that the speed signal is taken off a tone wheel attach to the ring gear in the diff. i may be wrong if it is not taken there, but if it is, it'll always show the speed the gear is turning. r&p ratio will not change it, tire size will...

 

[rbattelle]

Yeah, I meant the R4610. Not sure whether you could also compensate the ABS, but I doubt the change in vehicle speed indicated to the ABS computer would make much difference in it's operation. Not sure what you mean by "tac"... did you mean "tach" as in tachometer? If so, tire size has no effect on the tach indication.

 

[CIverson]

The thing about the tone ring is true. The gear ratio will not affect the reading.



Isn't the Truespeed unit just like a potentiometer? If you just installed one inline w/ the wires from the tone ring you might be able to get the reading right using a GPS to coordinate the speedo.



Also, I believe the rear abs uses the same signal from the VSS so that would be right, and the front uses a pickup on the hub so I would think those values would be correct also.

 

[WBarber2]

Oops. My screwup writing 'tac adjust'. I know better. Meant odometer. Thanks for pointing out the error.



Too bad about about the tone ring, but it makes sense.

 

[rbattelle]

I believe the odometer and speedo use the same signal, so the box would correct keep the mileage accurate too.

 

[GSaltzman]

Speedo Calibration

Just had my speedo recalibrated at the dealer last week. I have Goodyear LT 305 MT/R's. I can't recall the RPM for this size tire but they were able to correct for this tire size. It took about 20 minutes and they charged me $36. 00. Once I get back home next week I will check it against a GPS just to see but it seems to be very close if not spot on when I checked the mileage on my drive to work.

 

[nickleinonen]

that 305/70/17 tire is just over 33" in diameter. if the computer that controls the cab functinons is similar or same as the ones in the 1500's, they can calibrate the cpu to think the tires are 275/60/20's that come on the 4x4 1500's with the 20" wheel package... it'll be a little low, but pretty close [305's are 33. 8", 275's are 32. 99"]