Why would my odometer be correct but my speedo can be 6 mph off. With 285/75/16 tires the speedo was 10 mph off. That seems a little off. Shouldnt it only be 5 off? When i used a hypertech to reprogram the odometer was right but the speedo was still 5 mph off.

 

How do you know for sure your odometer is right?

 

and how do you know how far off your speed is? do you have someone tailing to and telling you on the phone?? also measure your tires.. 285's arent always 33's

 

Your speedo isn't going to be a #MPH different, but rather a % differnce...If your truck came with 245's on it, then it will be roughly 8% off...This is calculated based on tire diameter.

 

yea because at different speeds it would be progressivly more off than at other speeds like proportionally. i would think

 

high tech answer is to use a gps unit. low tech is to get on a flat road with mile markers. 60 mph will cover the 1 mile in exactly 60 sec. I saw a similar post somewhere that suggested tweaking your tire size setting in the programmer. If you find out let us (me) know. I was thinking about buying a programmer to correct for my 285/75's, but I hate spending that much money, especially if it doesn't work right.

 

I used my gps to find mph and miles traveled. I checked the speeds at all speeds and it is always 10 mph faster than my speedo with the stock program. And always 5 mph off with the hypertech program. My door sticker does say 245/75/16 but they would look very small for the truck. It is a 2001 sport. It was built in canada I don't know if this makes any difference or not. The only thing I know that is different is the daytime driving lights. Anybody know how to get a build list for your truck?

 

Yup ...

http://www.dodge.com/wccsapp/univers...ull&category=U