How bad do 285 75 r16 throw off you speedometer? Also I have no programmers or chips on the truck to recalibrate. Just wondering if any of you guys could give me some answers. Thanks in advance

Quick google search found this one. Not the one I was thinking but should work for you.
http://www.csgnetwork.com/speedocalibcalc.html

Brian

Maybe not reliable but those things the cops put up on the side of the road that tells your speed. It showed 3 mph faster than my speedo with the 285/16. On the 285/17's i have now it is about 4 mph difference

ive had 285's and now 295's and it does throw the speedo off quite a bit the faster you go the more off it is

at 55mph by speedo edge says 61mph and at 60mph edge says 68 mph by the time the speedo says 75mph edge says im at 85 mph

So if You were trying to figure up your mpg it would be off right?

So if You were trying to figure up your mpg it would be off right?

For the most part, 285-75-16's will affect your speedo this way: You will be traveling 7.8% faster than your speedo indicates. For example, if your speedo says 65 mph, you'll actually be going 70 mph. If speedo indicates 60, you'll be traveling about 64.7 mph. You can verify this if you have a GPS.

Thanks guys for all of your input