Speedometer Correction

bmarlatt

bmarlatt

Mirrors Down
Joined
Sep 19, 2008
Messages
390
What is the best option for correcting the speedometer on my 98. I'm running 285's and know it's something like 10% off or so. Only reason I'm finally bothering to correct it is that I'm using it for work alot know and get reimbursed mileage. That would pay much better if the odometer read 1 mile for every mile instead of .9. I searched on here and it pulled up a thread from 06 and didn't know if anything new had came out.

Thanks
 
285's should be 7% off.

As far as correcting it on a 98' 12 valve, I don't know other than taking it to a dealer and having them reflash the different tire size.
 
Dealer, may cost ya $40.

I've had my last 2 trucks done.



Sent from my Comp D mobile thingy
 
I need to look into getting this done also. Saw that truspeed thing but didnt want to spend 200 bucks on one though. Might check into the dealership.
 
How do you tell the size of his tire if he only listed the width? Do you assume the aspect ratio and rim size are stock?
 
Gasoline Sucks said:
How do you tell the size of his tire if he only listed the width? Do you assume the aspect ratio and rim size are stock?
Click to expand...

I'm guessing BigBlue just went with 285/75R16's and did the math, I just guessed 10% based off my last speeding ticket lol
 
Will a second gen smarty do it?

The dealer will set the "pinion factor". They have to figure out the revs per mile.

When I worked at a dealer, some of the guys would take the tire size and do some math to figure it out. I don't like that method, because actual sizes vary from brand to brand.

I marked the ground where the tire was and rolled the rig ahead three tire revs and measured how far it went. Then did the math.

Might be overkill, but I know exactly how fast I'm going.
 
ive always wondered if a smarty for a 2nd gen would work. anyone know? i just have the truspeed but the dealer couldnt re-calculate for 37's. said the biggest they could go is 35
 
or you could change the speedometer gear in the transfercase? But I never heard of the dealership correcting it, so they just reflash the truck?
 
what about a 96 i would like to run 235/85/16 i use the truck of hauling and need to know the right mileage to get paid
 
Think I paid around $45.00 to speed check on small dyno. Mine came out to be .08 off. I multiply mi x1.08.

The reason I'm responding is The odometer was correct but the MPH was off by .o8 stock, After I changed to 285/17R16 the odometer was off by .08 and the speedo was correct to .01. Go figure
 
Some of the aftermarket ABS Scanners have the ability to change Pinion Factor, I'm able to adjust it on the 98 and newer Dodges with my Snap-On Modis.

As for the 94-97's you should be able to order different speedo gears from the dealer or Rickson Wheel.
 
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