Dodge Cummins Diesel Forum banner

1 - 8 of 8 Posts

·
Registered
Joined
·
32 Posts
Discussion Starter #1
Hey all. Noticed the other day that my Speedo is way out. With both radar and GPS I’m off by about 10km/h. Truck thinks it’s going faster than it is, so it’s actually counting faster on my odometer as well which is lame. Currently tuned through EFI LIVE, but I’ve heard you can’t adjust for tire size in EFI LIVE. Is there another way to do this without affecting tuning?
2015 Ram 3500
 

·
Registered
Joined
·
4,698 Posts
AlfaOBD can adjust tire size. Will not impact tuning.

Sent from my SM-T500 using Tapatalk
 

·
Registered
'18 G56 CCSB
Joined
·
125 Posts
whoever tuned it should be able to correct that.
my last truck (granted, a 99 GMC) was tuned using EFI Live multiple times: updated tire sizes & differential gear ratios no problem.
 

·
Registered
Joined
·
1,588 Posts
I use interstate mileage markers to dial mine in. You can get very accurate and precise that way vs using radar or instantaneous speed from a GPS. The more miles you measure over, the better. The straighter the highway, the better. Obviously I am comparing it to the odometer (trip meter), not the speedometer, but it's the same thing.
 
  • Like
Reactions: 7492

·
Registered
Joined
·
6,626 Posts
Hey all. Noticed the other day that my Speedo is way out. With both radar and GPS I’m off by about 10km/h. Truck thinks it’s going faster than it is, so it’s actually counting faster on my odometer as well which is lame. Currently tuned through EFI LIVE, but I’ve heard you can’t adjust for tire size in EFI LIVE. Is there another way to do this without affecting tuning?
2015 Ram 3500
If all was good before the tune, I'll blame the tune.
 

·
Registered
Joined
·
3,705 Posts
If all was good before the tune, I'll blame the tune.
Has nothing to do with the "tune."

However, OP has bigger tires if the pic in his profile is correct. And if the truck is going slower than the speedo reads WITH big tires, then someone along the line adjusted the tire size/speedo reading.

Our 2016 was unlocked with a Bullydog, then EFI tuned by the original owner. We just got the truck recently. Orig owner adjusted the tire size to 37" with the Bullydog (truck is on 37s), but I noticed the same thing as the OP right after buying it. Truck was running slower than the speedo. I adjusted the size down to 35" and it corrected the speedo reading. Orig owner just blindly set it to 37". That is not necessarily the case say a 37 is 36.5" dia fully aired up, brand new. Then you have a little squish in the drive tire so it's effectively running at a smaller diameter, then add in tire wear, how the tire fits on a particular rim wide or narrow and the theoretical "diameter" is not the same as the actual diameter.
However I figure the truck has racked up close to 5000 "extra" miles to date.
 
1 - 8 of 8 Posts
Top