Speedometer Calibration

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Xyleff

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Haaaaaa. Well it amazes me that some apparently can…i dont understand how it is even possible, but some say it happens for them.

U can also download a free speed app on your phone which is very accurate from what I can tell.
Thanks lol
 

CanRebel

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How are you checking it, with a speed app or something?

Check it at like 10 mph, then at 75 mph…there will be a difference. Changing from a stock 32” tire to a 35” tire is almost 9% larger tire, so thats how much your mph will be off (which the overall mpg number that it is off will change with different speed). Going to a 37” tire is like 13% larger.

Seems some people with the newer trucks are claiming all they had to do was drive it for a bit and it fixed itself….as in did not need a speedo recalibration tool.
Never heard of ram that would calibrate itself...

Anyways, I got this site from different member.


You put stock and whatever you purchased or what you want purchase. It will give you all specs/speed differences.
 

CanRebel

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I have read a few different guys on here claiming that their trucks did….all i know is my ‘16 didnt!
Guess those are special people ? :) Cause my 21 Rebel didn't :)
 

62Blazer

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First I have heard of speedometers automatically recalibrating. With GPS and computer controls it is definitely feasible for a vehicle to be able to do that. I guess the whole reason for having the speedo controlled by GPS is you don't have to worry about all of the other variables going on like gear ratio and tire size. It's also reasonable that they would use both GPS and some sort of traditional speedo along with it as a backup. Imagine driving through a long tunnel or down in a canyon and losing the GPS signal, which would than cause the speedo to stop working.

In regards to a previous post stating that GPS speedometers are always set 5-10% slow I'm not so sure about that. Those are some pretty big numbers. So if you are on a freeway with a 70 mph speed limit and you set the cruise to say you are going 70 mph, you are really only going 63 mph? Typically the speed and distance are directly related to each other, so if the speed was 10% off so would the miles travelled (odometer reading would be low, or at least the fuel mileage calculator would be off).
 

rgrbobbyedwards

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I just went to 35" BFG t/A KO2 tires from stock. I want to re-calibrate my speedometer.

My dealership told me they can't calibrate the speedometers on 2021 HD models yet. Procal devices seem to be sold out. Any thoughts here guys?

Thanks in advance.

Can the dealership do it on a 2020 model or do I still need something to fix it? I just ordered 35" Falken Wildpeaks earlier today....
 

Nick@GotExhaust

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Can the dealership do it on a 2020 model or do I still need something to fix it? I just ordered 35" Falken Wildpeaks earlier today....
This will calibrate your speedo and much more!



If anyone needs one for 09-18 4th gens we have it for yours as well!
 

rgrbobbyedwards

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This will calibrate your speedo and much more!



If anyone needs one for 09-18 4th gens we have it for yours as well!
*tire psi setting requires dealer trip, so the vehicle can recognize the change. Disabling TPMS system altogether and turning off the warning symbol does NOT require the dealer.

What does that mean...
 

Nick@GotExhaust

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*tire psi setting requires dealer trip, so the vehicle can recognize the change. Disabling TPMS system altogether and turning off the warning symbol does NOT require the dealer.

What does that mean...

so if you want to change the psi threshold that will trigger the psi warning light to turn on you would need to go to dealer to complete the change.
 

Tim7139

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"GPS speedometers are set five to 10 percent higher. This is the fact that the manufacturers can get sued for if they tell the users were under the speed limit when they are, in fact, over speeding. As a result, many drivers tend to drive slower than they think when they use GPS speedometers."

The same article also states it is accurate within 0.2 miles/hour, and provides no sources.

Both manned and road side radar have verified the GPS in my phone is accurate on staight and level roads, and the officer was all to eager to show his device was calibrated.
 

CombatWagon46

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If you have GPS it will automatically calibrate within a few hundred miles. I didn’t believe it either, but it did it both when I went to 35s and 37s. Confirmed it with 2 speedo apps before and after.
Can anyone else confirm if this worked for them?
 

spjackson772

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I can confirm that after putting 35" tires on my new truck that the speedo has adjusted accordingly. We took our first road trip thus weekend and at 75mph highway speeds we were within 1/2 mph confirmed with GPS satellites on phone. Dealers can not reprogram on the new trucks. It must be done with an aftermarket tuner. But to my surprise I do not need to change anything.
 

DrTron

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Be mindful that when your phone is connected to your truck (not sure about BT, but USB for sure) it doesn't use its GPS for speed but gets it from the truck. So it'll show what the truck's speedometer shows. Only way to check calibration is an independent GPS unit or disconnect your phone completely from the truck.
 

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