odd speedometer issue
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From: geary NB
odd speedometer issue
i noticed recently that my speedometer is reading 10-15 kph then actaully driving i tested few different ways to ensure i wasnt losing my mind on this one.
Recently bought a gps for a trip im gonna be going on and since it has a built in speedometer i used it to test my speed along with a friend in his own truck that i matched physical speed with and even a phone gps and all show the truck drives 10-15 lower then the speedometer is displaying . Now i know my truck has bigger then normal tires since 265 is factory and i have 285 on currently but from experience it should be opposite effect of the speedometer showing say 80 but actauly speed may be 85-90 my theory is th eold owner regeard the axels and didnt adjust the speedometer or had much bigger tires then currently on it and did adjust it but the removed the tires and didnt reset it any one have any ideas on this?
Recently bought a gps for a trip im gonna be going on and since it has a built in speedometer i used it to test my speed along with a friend in his own truck that i matched physical speed with and even a phone gps and all show the truck drives 10-15 lower then the speedometer is displaying . Now i know my truck has bigger then normal tires since 265 is factory and i have 285 on currently but from experience it should be opposite effect of the speedometer showing say 80 but actauly speed may be 85-90 my theory is th eold owner regeard the axels and didnt adjust the speedometer or had much bigger tires then currently on it and did adjust it but the removed the tires and didnt reset it any one have any ideas on this?
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From: Media PA
A gear change will not affect the speedo reading, I went from stock 3.73 to 4.88s and my speedo reading didn't change a bit. The speedo gets its reading from the ring gear, so only the tire diameter will affect the speedo reading. And yes, larger than stock tires should give a speed reading of less than actual.
I'm lazy, my 35" tires are 12% larger than stockers (figured both mathematically and verified by GPS) and I have not had my speedo recalibrated. So now I just know that a speedo reading of 60 MPH is really 66-ish and I factor everything by that 12% when figuring my MPGs. And I keep a small GPS unit mounted that displays my speed, Odometer and moving average speed.
I'm lazy, my 35" tires are 12% larger than stockers (figured both mathematically and verified by GPS) and I have not had my speedo recalibrated. So now I just know that a speedo reading of 60 MPH is really 66-ish and I factor everything by that 12% when figuring my MPGs. And I keep a small GPS unit mounted that displays my speed, Odometer and moving average speed.
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From: geary NB
darn and i was hoping it was just something not adjusted from previous owner since i know this truck has a small lift. Im using a gps to now to track my speeds. ill probably stop by ford to see if it can be adjusted while i check on getting any recalls related to safty done up too
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From: NoVA
Plug in your tire sizes in this calculator and it will show you the size, and speedometer errors. I've used it and it has been pretty accurate when comparing with 2 different GPS units and phone GPS.
https://tiresize.com/comparison/
https://tiresize.com/comparison/
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From: geary NB
but my issue is that my speedometer is reading 10-15 above actaul speed an i was wondering what could cause something like that to happen im already planning to program it to match current tires in hopes it fixes it and doesnt increase the difference gap
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