Odometer/Speedometer calibration

[J 2]

I had no idea this was so widespread for new stock vehicles. Now a days it seems like most cars & trucks have GPS built in, why not link the computer to the GPS on occasion to calibrate? If I understand correctly the tire size is input into the computer for the speedometer now, at least that is how my 2019 F150 was explained to me, they just didn't have access to adjust and I didn't want to play around with Forscan.

 

[J 2]

I just noticed 4 pages of posts then started at the beginning wondering what the ???? Looks like this was moved to a really old thread, um ok.

 

[J 2]

I know what you mean. These trucks can't correct for 38s (hopefully someday) so mine's off about 2-3%. Drives my closet OCD nuts sometimes

PS props to those that saw the selloff coming and got out in time. Buying opportunities await those with the testicular fortitude (or lack of intelligence in my case)

I didn't actually get out, I have 2 ex-wives They left me with nothing to invest so I worked on paying everything off early. Recovered

 

[J 2]

GPS isn't really feasible due to reception issues. Correct on the truck calculating based on tire size. I've been correcting speedometers since they were gear-driven cables off the transmission

I remember those, I started working on cars around 1979 or so. Wish I could remember what I saw these on first. Pretty sure I had a motorcycle with a cable to the speedo, or maybe a VW Baja Bug.

 

[Modman]

I just noticed 4 pages of posts then started at the beginning wondering what the ???? Looks like this was moved to a really old thread, um ok.

I merged the two since there was quite a bit of overlap including discussion of the 1 mph delta. I didn't see any logic/benefit in keeping them separate. While the original thread was started in '23 there was activity in December of '24 so I would consider that still fairly recent.

 

[Godzilla/Tremornator]

Damnit, I know that, man...fixed my post above. Been driving lifted trucks all my life. We'll chalk that one up to a lack of sleep (I'm actually mildly retarded)

Gotta rizz 'em with the 'tism

get a nap !!!!!

I'm sure that'll fix you right up!!!

 

[J 2]

You guys pretty much called it. Dealer states it's working properly within the PCM, +/- 1 mph. They had to replace the leaking oil filter so it was worth a shot while it was there.

 

[Godzilla/Tremornator]

lot on your plate

enjoy it all you can, while you got it.


they'll all be grown & gone before ya know it

 

[HeavyAssault]

Now a days it seems like most cars & trucks have GPS built in, why not link the computer to the GPS on occasion to calibrate?

Technically speaking the GPS cannot be "calibrated" or interfaced at a low enough cost to be used as the speed input source to qualify as a "certified speed".

Spot on : @McE expressed the problem with GPS reception....hence...your ability to use the satellites to bring down the error probability to say the "speed" is exact.
Think of you sitting there looking up at one satellite directly overhead chances are that will NOT be accurate at all for speed. Now think of seeing 100 satellites all at different positions overhead, towards the horizon, half way up the horizon...now you can get a MUCH lower error probability to detect your speed.

I run a stand alone Garmin GPS unit in a cradle (hand held unit) which shows the GPS position error and device speed. GPS position error tends to run about 6 feet. Meaning the position is accurate to within 6 feet.
For speed and miles : I've long seen that the highest is about 3% off in miles driven, with 1-2 MPH off for speed. Now it doesn't seem like a big deal until you use it along with Total Miles Driven to see what your MPGs turn into....wow...an added .5+ MPG (if not better) in most instances as a average.

Use your phone....get a GPS app....use the speed and see what's the difference.
Otherwise you need to get your speedo checked/certified at a specific shop that does that work. In VA they do that kind of thing....funny part.....courts only accept the "certification" if it's been done in the last 6 months...before you got your speeding ticket ming you.
So....who's really calibrating their speedo every 6 months.....no one I know.

 

[Optimus🤖]

So....who's really calibrating their speedo every 6 months.....no one I know.

Please tell me you won't wear speedos.

 

[HeavyAssault]

Please tell me you won't wear speedos.

Never ever say never....cause it's all about how much, for how long, and where.
I learned that from your book....Chapter 20 Making milk money.