Engine/Transmission (1998.5 - 2002) Tire Size Affecting Speedo

[klaybus]

I drive a 99 QB LB & am running 285's... My speedo appears to be about 5-7 mph fast. Has anyone else had this problem & is there anyway to adjust the speedo... . I was told that it runs off the ABS sys...



TIA,

Clay

 

[Gary - K7GLD]

My '02 came spec'd with 245's, was upgraded to 265's, and apparently the speedo was NOT recalibrated for the larger tires - mine is SLOW in odometer readings by about 8% - but when I approached my local service department about correcting it, they seemed so puzzled and confused as to means to fix it, I figured I was better off living with it than having them screwing around with it...

 

[curatchko]

That tire size should slow your speedo down. I put 285's on also, and I am about 7-8 percent slower on the speedo.



Which means at 25 mph the speedo is less off, than when I'm at 75 mph.



Chris

 

[klaybus]

Hmmm...

I guess I need to check the odometer next trip down the freeway. I thought that with the bigger tires they would rotate less thus lowering my speedo reading but it appears that the speedo is reading faster. Different problem? I guess I'll know more after checking odometer.



Thanks. .

 

[WTBurke]

Superlift True-speed or the Abbot (sic) boxes correct this problem.

I checked with two different Dodge dealers and they reported that they can reflash your truck but only tire sizes that DC placed into the system to begin with. Radical departures in size require the previous after market boxes to correct the VSS pulse timing.

I have the True-speed box and it is very good at correction.



William

 

[athompson]

I have a brand new TruSpeed that I decided not to use. If you're interested, PM me.

 

[Weidner]

Is there a truspeed module to correct the 285-75-16's? If so where can I buy one and how do they install?

 

[athompson]

The TruSpeed has a switch that allows correction for any two tire sizes.

 

[WTBurke]

Yes the Truspeed box is very trick with the mini-toggel to select between two different size tires. The install is very simple and the packaged instructions are excelent. The unit,once calibrated is very stable. I used a GPS device to fine tune it however, if you follow the instructions table it's very close to being dead on.



William

 

[FDNYMOPARGUY]

THE BIGGEST TIRE THE DEALER CAN REPROGRAM TO COMPUTER FOR IS A 265/75R16. I HAD MINE DONE WHEN I WENT FROM 245 TO 265'S. NOW WITH 285'S MY SPEEDO IS ONLY OFF BY 4% AS VERIFED BY GPS. AT ACTUAL 74 MPH, MY SPEEDO SHOWS 71 MPH. BTW, DEALER PERFORMED REPROGRAM FOR FREE.

 

[klaybus]

Speedo Test

OK, On the way to work this morning I ran an odometer check & over a 10 mile test I was exactly 1th of a mile FAST! As I traveled, for every mile I went my speedo read 1. 1 mile.

I'm running 285's which should make my speedo read slow but it's reading fast. Any ideas? I just don't get it... .



Thanks, Clay

 

[mschoenheider]

Did you, or a previous owner change gear ratios?

mark

 

[klaybus]

Gear Ratios

Good question? I didn't but unsure of previos owner. The tag on underside of hood says it has 3. 5 gears but I guess I should jack up the truck & spin a wheel & count the turns & see if they are actually 3. 5 gears.



Thanks

 

[Huff N Puff]

All you need is a scan tool e.g. Snap On Scanner

You can go into the pinion factor to re calibrate your speedo with a SnapOnScanner go into pinion factor file it will then ask you for tire size. Most repair shops witha scanner and upto date soft ware can recalibrate a speedo.

 

[athompson]

Since the speedometer is driven from the ABS signals, R&P changes have no effect. Perhaps you already have an adjuster box installed and set for 36" tires.

 

[klaybus]

Adjuster Box

I'll crawl under the truck today & see if I can find anything. I just did a search & now know what to look for. Perhaps it's tucked away under the hood somewhere. Thanks ALL!



Clay