Speedo is off
 

Just griping here.

My town has a portable speed limit sign, so it tells you how fast you are going. My mustang and my windstar are right on according to this sign. But my F-150's speedo reads about 3 to 4 miles per hour faster than the sign. I contacted my local Ford dealer and they told me that Ford considered up to 7 miles per hour off to be acceptable. Wow.

Other than that, I love my truck.

Your truck was probaly made for bigger tires, but didn't get them. On my stock '89 Bronco, with my 32" tires, it read just right, but now with the smaller temp. tires I have on, it reads fast.

Actually, my truck came with a special V6 option package that included a 6-disk CD changer and larger (P255) tires. It does have those tires on it.

Well then, thats odd.-lol

oops

Hey, u could always put bigger tires on:D

Hmm. I assume that it being a 2002 that the speedo is an electronic unit driven off of the rear end.. If so, tire size wont affect speedometer ratio readings. When you put bigger or smaller tires on the truck, the wheel, axle and rear end compnents turn slower or faster accordingly.. If the speedo is triggered off of the ring gear tire size should have no bearing what so ever..

Bradley

Brad,

Maybe you should explain that to me again, I don't follow you. I would think that if you changed something before the point at which the speed is taken then the speedo would not be off (such as tranny gearing). But if you change something after the point in which the speed is registered, then it would affect the speedo. In this case, if I were to put bigger tires on my truck, the tires would move the truck a little further with each revolution and thus the speedo would be reading a little slower.

Make sense?

This should be true, thus it be off the tranny, or off the rear end, changing the tires would still change the reading, but if u changed the rear gears, in a older car, it would still change, but in yours, the speed would be the same.

Make sense now??

Bradley

Nope, still confused.

I agree that changing gear ratios will throw off the speedo on an older car. But if you take your readings at the rear end, changing gears won't throw it off. But no matter where you take the reading, if you change tire size, then it has to throw off your speedo, right????

Harry

Okay. First of all, changing tire size will affect the speedo accuracy on any vehicle. So will changing the rear gears. Older vehicles corrected a rear gear swap by changing the speedo cable gear, but digital speedos have no cable or gear. As mentioned, they are run via the VSS (Vehicle Speed Sensor) in the rear end and the PSOM (Programmable Speedometer/Odometer Module). If the rear gears are changed, the PSOM needs to be reprogrammed, or the speedo will be off. This is extremely difficult in the 2002 vehicles, and to my knowledge can only be done at the dealer.

Take care,
~Chris