F150tony85

Hi all so I bought a F250 light duty 2 months ago. It is a 1997 F250 Light Duty 4x4 supercab XLT 5.4L with E4OD trans. It has 170,000 miles. I noticed that my truck seems pretty slow going 45 mph according to the speedometer, and when my brother got in I didn’t tell him about the problem I suspected it has and instantly he told me “dang are you sure that speedometer is right?” So yes yesterday I downloaded a speedometer app on my phone and when Im supposedly going 45 it says Im doing about 38mph on my phone. Also yes it has factory wheels BUT the tires are 265 75 R16, which according to a bunch of tire websites isn’t factory size. The factory tire size is 245 70 r16 or 255 70 r16. Anyways, do trucks this old simply need to have the speedometer recalibrated every once in a while? Or is it due to the tires size? I have tried doing research but people say it can be several different sensors, tire size, or it needs calibration. It has no check engine lights and from my knowledge the speedometer seems to be the only mechanical problem it has. Thanks for the info!!

16IngotFX4

Either of the 2 optional sizes you listed as possible stock would both have you between 41 and 42mph with a 45 reading.
No need to have a speedometer calibrated on any vehicle routinely.
You can learn the factory size by looking at the driver door jamb, there is a tire information sticker there.

The discrepancy would likely be off based on the tire size, pretty much exclusively.

Efarmer

A speedometer app is probably off by its self, have the dash lights been changed? Could have places the needle back in the wrong position accidently. Maybe by you or PO. Has it had a tuner or programmer? Could put a backyard tune on it and tried to calibrate for larger tires and went the wrong direction. Again, this could be a PO induced problem that you may not know happened

Johnny Paycheck

The tire size difference would account for some speedo difference, but if my ‘03 is any indicator, that’s a built-in 3-4 MPH high right there.

No matter which roadside radar I may pass, my speedometer is a flat 3 mph over. My tires are factory issued size and I’ve never pulled needles on the gauges or any other theoretical mess.

Edit: with a bigger tire, your speedometer should be reading slower. If the 97 models still used a speedo gear going into the transmission, it’s possible it was replaced with one with the wrong gear tooth count.

F150tony85

Thank you and everybody else for the replies. I kinda asked this for no reason really, as in I should’ve just realized that theres a chance a free app on my dumb iPhone is not gonna be 100% accurate itself lol. But yeah this is my first heavy truck I have owned, (if you can even call it heavy.) Or I guess heaviest I have owned. It’s probably just not geared the same as modern Civics, Camrys and what have you. Or it’s not as peppy as other types of vehicles lol. I came to a realization that my truck shouldn’t be compared to 4 cyl modern cars with drivers that all seemingly are 30 min late to work, and want to accelerate to whatever the speed limit is in 1.2 seconds. It’s funny because I’m sure everybody says this about their cities, but we have some of the worst and most aggressive drivers out here in SoCal. I say this because I noticed since I bought my truck whenever Im next to someone and the light turns green they accelerate like 10X faster than me lol.

F150tony85

Actually yeah I listened to yall and passed by a Speeder Radar thing and it says im going 5 under, I’ll have some experts calibrate it as soon as possible

akdoggie

97-98s are actually very simple systems. The only ways you can be off speed is, either the needles have been removed and reinstalled (in the wrong positions) or your tires are way off to the original sizes or a rear end gear change. This system is a simple gear (in the trans output shaft) a VSS sender, and the cluster. Nothing is adjustable by a scan tool in these years. 99 up yes.

F150tony85

Thanks for the help, yeah I’m gonna wait until the weather stops being 118 degrees to open the cluster cover and try to adjust the needle, in the mean time I’ll drive about 5 over. Y’all are a big help. 1 mechanic I took my truck to never heard of a speedometer calibration, and 2 other ones didn’t have the time but said to bring it in on a certain day and they were gonna spend the entire day calibrating it with their fancy tools.