Upgraded my tires over the weekend, went from a 265/70/17 to a 285/70/17..

Obviously the tires are bigger (and I like the look a lot more), but I also know this is going to alter the accuracy of my speedometer. can anyone give me an idea as to how far off I am? I know I could always just go haul ***, and let the cops give me their reading with the ol radar detector, but yeah I dont want a ticket.

I did look on the board, but found nothing of real help.

I will post pictures of the new look as soon as I give the filthy beast a bath.

Thanks for the help,

Matt

 

i would guess 2 miles over but a sure fire way to tell is use a gps

 

if you dont care about miles racking up slower just about your speedo being off then i just use my GPS for my speed. if you dont plan to regear and it bothers you you can swap the transmission speedo gear for about 25 bucks and itll be more accurate

 

97's and 98's require a change in the vss gear to correct the difference.

Lookie: https://www.f150online.com/forums/tr...ange-help.html

The difference in your tire size may not be enough to require a change in gear size. You may need to determine how much the speedo is off and keep an eye on it.

 

I did the gps thing with mine, turned out at 68-69 mph speedo, actual was 70. I wouldn't worry about it.

 

Agree with above 2-3 mph off that's about all. On another truck I had I increased the tire size by about 3.5 inches and was only 6 mph off at 70mph slower speeds is less though so don't sweat it.

 

Alrighty sounds good. Thanks fellas. My GPS wont display the speed, or at least I cant get it to pop up, may have to break down and read the manual, haha. I had read about getting a programmer to change it as well, but money is a little tight, and with christmas coming on, Ive got other purchases to make. Maybe santa will be good to me this year.

 

I read on another thread here that a programmer will not work on these trucks you actually have to replace the gear itself. Do a forum check for it they discuss how to do it on that thread seems easy enough. Anybody know the thread that it was?

 

Saw this a while ago.
type in your tire sizes, it will spit out the speed differences.

http://www.miata.net/garage/tirecalc.html

 

@60 mph you will be going 62 and @100 mph you will be going 103.5mph. The Instrument Cluster takes is speed reference from the sensor in the transmission. In 1999 that changed to taking its reference from the PCM. A programmer will not allow you to change the reference signal on a 97 or 98 truck.

 

i just put 285/75/16's on my 2000. im not too worried about the MH, more worried about the odometer seeing as im trying to track MG and will be going on a long trip soon. any suggestions or how far off should i be?

 

Check it against the mileposts on the highway.

 

Such a simple solution. Now I feel like an idiot, thanks

 

on my 97 I went to 285's and at lower speeds I'm off about 2mph at 60 and up I'm off 5mph per my gps. I also checked the odometer on a full tank of gas there is 47 miles less on the truck then the gps.

 

the amout its off will go up at higher speeds but 5mph off isnt bad thats what im at just the other way around. mines 5 mph faster at 70+