Hello to all, first time poster here but i've been lurking these forums for a while

Now it seems my speedo is reading inaccurately. and not just by a small amount, but by 20 km/h.

Vehicle specs/mods
2002 dodge ram 1500 4.7L
285/70/17 tires measuring true height at 32.7 inches
superchips 3865 updated to latest version

now the stock tires were 31.5- so i bought the superchips to change the speedo so it woud be correct. Stock it was out a little but now its out by alot! so after much testing and driving behind my girlfriends new chevy cavalier i have had to set the tire size to 39 inches to get a speedo reading that is as close as i can

also when i run the data logging to see what my speed is. the superchip programmer is correct in what speed i am actually doing, but the needle isn't at all

so i guess what i need to know is has anyone had a speedo this far out before? and is there anything i can try before going to the stealership.

also i have searched the forums and read some topics that are similar to this but not with the same symptons

any help is much appreciated,

Daniel

 

So the speedometer is reading too high? The stock tire is 245/70x17. My 285/70x17s made my speedometer 4.3% slow. I just live with it. Indicated 76=80. Have you used a GPS to determine your true speed?

 

There should never be a difference between the speedo and the speed reported by the datalogger. It sounds to me like someone has had your speedo needle off in the past, or in the worst case, your cluster is going bad.

 

I went from stock 265's to 285's on mine, the speedo was way off, then I bought a new gps, decided to make it right--I have a diablo---to get it right, I ended up changing it from the 285 setting using my tuner back to a 265/70r17---right on the money well 2/10th's of a mph.

I really don't understand the why of it, but even the "you're going this fast" radar signs confirm it.

Get a cheap GPS that gives mph readings and start there

 

Good point. Since the source for both the data logger and the speedometer is the same, they should match with equal inaccuracy.

 

John M thats what i was thinking as well. That if the dataogger showed correct speed that the needle should as well.

So i played with it once more today just to test it out and set it back at 33 inches and it appears to be correct. i will check it tomorrow with my girlfriends car and update then