speedo recalibration

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Dec 12, 2006 | 04:15 PM

69ford99

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From: Paola

speedo recalibration

Superlift sells a speedometer recalibrator and I was wondering if I needed one since I have 33's now or can the dealership recalibrate it?

Dec 12, 2006 | 05:39 PM

95bogginbronco

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From: minnesota

What year is your truck. '92-'96 ford's have a PSOM. That stands for programmable speedometer odometer module. That superlift recalibrator will not work on this year of ford trucks. Instead have the dealer recalibrate your speedo. I put 31's on my truck and had a dealer fix my speedo for me. A couple guys on here now the process for doing this. Ask around and you'll get help. Good luck.

Dec 12, 2006 | 05:59 PM

69ford99

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From: Paola

The Superlift module says for ONLY '92-96.

Dec 12, 2006 | 06:09 PM

quicklook2

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From: Lakewood, Ohio

you can do it.

i think the articles/specs at the top of the page has an article on it.

it is not hard to do.

Dec 13, 2006 | 10:42 AM

wileec

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From: Western US

Ditto I rember seeing it in the FAQ for Broncos.

Dec 13, 2006 | 12:21 PM

b4hntn

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From: Longview, TX

The way I did it is down in this thread. Recalibrates both speedometer and odometer.

https://www.ford-trucks.com/forums/3...ht=speedometer

Dec 13, 2006 | 11:48 PM

benshere

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From: Longwood, Fl

Psom

I did that recalibration, easy to do, but be careful, there is a countdown clock for recalibrations and I think you only get 6 (been a while since I did it). Thats in the article.

Cant recall how I handled the tire size, but 32X1150X15 is supposed to be 32" tall, but it actually isnt. Really only about 31" if you measure. That will affect the revolutions per mile calculation.

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Dec 14, 2006 | 12:09 AM

benshere

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From: Longwood, Fl

Revs/mile

Mfgs do list revolutions per mile, but I would check that figure for accuracy. It may be based on what their target size was rather than the actual size of the tire. My old 31X1050X15's were also not 31", so I did my own measurements.

Dec 14, 2006 | 05:26 AM

#10

Torque1st

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The manufacturer's info would be much more accurate than a tape measure. The spec does vary with manufacturer tho. If that is not available then an average of the ones you can find might work.

Dec 14, 2006 | 10:45 AM

#11

benshere

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From: Longwood, Fl

Mfg's specs

I respectfully disagree with the accuracy of the Mfg's figures. The same mfg figures for tire height are provided for rev per mile. I have actually measured the rollout of numerous tires, and have found that the diameter of the tire is not actually accurate. The circumference of a circle (which is what we are dealing with) is a precice measurement and that is the figure used to calculate revolutions per mile of the tire. A tire mfg does not change those dynamics. Because there is no variation in the tread diamenter (very very small at best), only the sidewall can flex to any degree but the tread does not "compress" or "expand". If you measure the distance the tread travels in one revolution, you have the accurate figure for "revolutions per mile". It may be the mfg's figures for that are more realistic, to be honest (gawd I really hate that

) I have not checked that figure in all cases, so that may be accurate, but I prefer, when I really need accuracy, to check it myself.

My brother and I used to have this argument---while contributing to Anheiser-Bushes bottom line, so I am not trying to flame anyone, just a little disagreement

Dec 14, 2006 | 11:45 AM

#12

b4hntn

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From: Longview, TX

benshere, there is another variable....tire pressure changes the distance between the center of the axle and the road. i.e. lower pressure equals smaller radius giving more revolutions per mile. The following procedure was dead on for me and used only one try. All you need are mile markers, calculator and piece of wire. Nothing else. Again, as before see the thread for my calibration.
Merry Christmas to all. Please see my reply there.

https://www.ford-trucks.com/forums/3...ght=speedometer

Dec 14, 2006 | 12:45 PM

#13

benshere

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From: Longwood, Fl

Variable--PSI

Oh No !! b4htn

Not the old "rolling radius" argument. There is no such thing as "rolling radius". "Radius" & "Diameter" apply only to a circle. If all points on the circle are not equidistant from the center then it "aint" a circle and therefore "radius" or "diameter" do not apply and it becomes some other geometric figure (dont ask me what, I dont know). I think some forget about the fact that when PSI is lowered, the length of the footprint gets longer, thats where the extra inches for the circumference go. It does not change the length of tread that must hit the pavement for each revolution. If you calculate the Circumference of the tire based on the lower radius, then the tire must slide for the extra inches lost. Sure wouldnt last long-----. The amount of tread above the pavement plus the amount of tread on the pavement will equal the circumference of the tire---regardless. The distance a tire travels in one revolution is dependant on the diameter of the circle, not a fluctuating radius----which dosnt exist for a circle.

Thats my story and I'm stickin to it---

but I will listen!

Dec 14, 2006 | 01:40 PM

#14

b4hntn

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From: Longview, TX

Yep, I have been thinking about it. If the axle rotates one rev the the tread does also. You are correct. BUT, you knew this was coming, why bother with measurements, charts, etc? Mile marker, watch, wire, and calculator are easy. Who cares how you do it as long as long as the speedometer/odometer are accurate? You only get 6 changes per vehicle.

Dec 14, 2006 | 01:59 PM

#15

benshere

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From: Longwood, Fl

calibrations

Yep, I agree, whatever works

I have used them all. I used to like to use a 10 mile test on the turnpikes, seems like a little variance in milemarkers, but 10 miles evens it all out. I did the PSOM thing for my 31X1050X15's, dont recall how much the constant figure was off by, but wasnt much. Have not done the 32X1150X15's yet. Funny thing is that the neighborhood roadside speed radars show me about 1 MPH slow----go figure. Have not tried a time (on interstate) trial yet, but the odometer seems dead on-----for the 31's.