I’m hoping someone can show me where I’m going wrong but my truck seems to have self- calibrated the speedometer after I installed larger tires. I have a 2022 Ram 1500 Laramie 4X4 and added a 3.5” RC lift released the factory 275/55-20 wheels with 35/12.5-20 wheels. I assumed that the speedometer would need calibrated for the larger tires and made appt with the Ram dealer to do so. Before the 50 mile drive to the dealer, I downloaded a speedometer app just to see how much off the speedometer is. To my surprise, the speed on the app shows less than 1mph difference from the speedometer! From low speed up to 70mph, the app matched the speedometer. I pulled over and downloaded a separate speedometer app to compare against the other one and it also matches the speedometer display. Does anyone have an explanation for this? I need to mention the rest of the story; the Ram dealer told me that it was not possible for them to recalibrate the speedometer because their computer didn’t have a selection for 35” tires.
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2022 Ram 1500 Speedometer Calibration
- Thread starter Pumpdex
- Start date
Idahoktm
Spends too much time on here
Disconnect your phone from your truck next time you test the accuracy of your speedometer to a GPS. No, your truck will not self-calibrate your speedometer. This is how much error you will see with a 35" tire.
ramhouston
Well-Known Member
do the 35X12.50 rub with your setup out of curiosity?
They did have some slight rubbing but it was a fairly easy fix. On the front of the fender well, I used a heat gut to heat up the plastic and a wet towel to push and stretch the plastic for clearance. It was very easy to do. The wheel well plastic is very thin so keep the heat gun moving over a large area to keep from melting the plastic. I also had some slight contact on the back of the tire. This is a little more involved but still pretty easy to fix. You have to remove the little piece of black trim at the bottom of the wheel well. Once removed, there's a metal tab that sticks out that most people seem to cut off and use zip ties to pull the wheel well plastic away from the tire. Once you do this, the plastic trim that was removed is useless and can't reused. I opted to bend the metal tab up at a 90 degree angle instead of cutting off. I also took the black plastic trim piece and carefully cut a V notch out of the plastic on the bottom side. I then reinstalled the plastic trim and drilled a small hole through the trim and through the metal tab that I previously bent 90 degrees. I happen to find some automotive looking trim screws lying around so I screwed the trim piece to the metal tab. This pulled the plastic back about 3/8" and tire does not rub at all. The trim screw is a self tapping phiIlips rounded head with th washer mad onto it and is black so it looks like the rest of the screws. I wish I would have taken pictures as I went along because it is much easier to do than what I'm describing. It probably took an hour and a half to do both sides. Everything still looks completely factory. The only way that anyone could tell is if they laid on their back and crawled under the truck, you might see where I cut the V notch out of the plastic trim piece. When you snug up the screw, it closed the notch so it would only be detectable if you were looking for it. I hope this helps. If you have any mechanical ability, this is easy to do. Once you pop off the black plastic trim piece, it's easy to see what you need to do.
This must be the case but if so, even the service manager at the Ram dealership is unaware. I am now confident that it self-calibrated somehow. I've had a few people download different speedometer apps and ride in the truck and all match the truck speedo with 1 mph. I do have a RAM app for the truck that provides the mileage, fuel level, and allows for remote locking, starting, etc. I wonder if this is using GPS somehow to calibrate the speedometer? It's weird because I've not found any other threads where anyone has this happen after installing oversized tire.
That's exactly the results that I expected at first but now I'm confident that it is somehow self-calibrated. I don't know how it could do this unless the RAM app I have is using GPS? I've had friends download different speedometer apps to their phone that are not blue toothed to the truck every time I've tested, they are with 1 mph of the speedometer of the truck. Even the service manager at the RAM dealership says this is not possible. I've even done the mile marker test and where you drive 60 mph for 60 seconds and it's pretty much dead on. I'd love to find out how this is possible because I can't find any threads where anyone has installed oversized tires with this result. Maybe I have a unicorn?
Sal731
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I’m in the same boat. My phone and my truck match and the dealership is telling me that they can’t do it. FN ******** that the Speedo can’t be calculated. As far as your mile marker test. The couple of mph’s that your Speedo is off is why you say it’s almost dead on. Three to four mph in a one minute range is a few ft. Maybe 75 or so. I wish you were right but stop trying to convince yourself. The Speedo is off
