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Discussion Starter #1
Ive got a JKUR and the speedometer reads fast at slow speeds, perfect around 55-60, and then slow at high speeds. At around 25 the speedometer reads 30ish, and at 70mph it reads 77. Ive got 4.10 axles, and running 255/70R17 Tires.

Ive got a superchips traildash 2 programmer Im using, and when I measured the tires I got around 31-31.25" diameter. I tried a few different settings, and each one adjusted the range a bit, but never got it to a place im happy with it. Any thoughts on what might be wrong here? Ive had tire size programming issues before and usually the speedometer will read more and more off the correct value the faster you go. This seems to be something of a curve.
 

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Park on flat ground. Use a ruler to measure from the ground to the top of one of your tires. That will give you your tire diameter. Use that measurement to program your Jeep.

255/70R17 should yield a 31.1 inch diameter. The stock JK 17 inch tire is 255/75/17, so you are running a slightly smaller tire.
 

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Discussion Starter #3
Park on flat ground. Use a ruler to measure from the ground to the top of one of your tires. That will give you your tire diameter. Use that measurement to program your Jeep.

255/70R17 should yield a 31.1 inch diameter. The stock JK 17 inch tire is 255/75/17, so you are running a slightly smaller tire.
My bad, that was a typo. Its the 255/75R17 BFG MTs. You can only program in .25" intervals into the programmer. It wasnt really close at either setting, I was thinking it might be a sensor issue...
 

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So you're running the stock tire? How are you checking that the speedo is not reading correctly?

If everything is stock, set your traildash back to the stock size and take the vehicle to be looked at by your dealer.
 

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Discussion Starter #5
This was an issue that I had before the traildash, I bought the traildash to do ECU modifications and be able to correct speedometer issues myself. I thought someone had used different tires previously and had set a different tire size into the computer, and that was the reason for the deviation. When the traildash obtained the tire size in the computer it was set to 30.75".

To measure speed I used 2 smartphone GPS's with live updates, and set cruise control on the jeep at certain speeds. I thought the phones werent being accurate enough, so I used my Garmin plug in unit that confirmed the phones were correct. Id used the Garmin previously on another stock vehicle and it perfectly matched the speedometer, so Im confident the GPS is accurate. The vehicle is originally from Canada, and because someone didnt file the paperwork when it was imported I dont have any warranty on the vehicle. Im hoping to fix the issue without getting the dealership involved. They're my last resort.
 

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Like Dave said, I would flash it back to stock. Then check it again. You said that the system was showing a tire size other than stock to begin with, and you suspected the previous owner may have had a different size tire.

When ever you are unsure, always go back to ground zero and start eliminating from there. If you take it to the dealer, they will re-flash it and do the same thing.
 

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Set your traildash back to the stock 17 inch wheel setting. If still off, go down .25" at a time to 30.50" and see what happens. Stock tire is 32", but depending on vehicle weight and air pressure will vary. Some have had success with a 30.75" setting and others with 30.50". Again, only do this if the stock setting doesn't work.
 

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I just put 315/75-16's, which measured out at 34 1/2" tall, on my 2014 Willys. The speedo was way off, of course, so I flashed it to 34 1/2" to start...still off. Went down to 34", and still off. Had to go all the way to 33" to get the speedo to read correctly!
 

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Discussion Starter #9
Ill try that and see where it gets me. I went to talk with the dealer yesterday to get their opinion, and I had gone in before and mentioned that the jeep was originally from Canada. They said that the gauges had been switched to miles where it would have originally been kilometers. They recommended checking the back of the gauge cluster to see if the part number was correct for the vehicle. That might not be for a while, but in the meantime ill set it back to stock and see if anything changes.
 

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Ill try that and see where it gets me. I went to talk with the dealer yesterday to get their opinion, and I had gone in before and mentioned that the jeep was originally from Canada. They said that the gauges had been switched to miles where it would have originally been kilometers. They recommended checking the back of the gauge cluster to see if the part number was correct for the vehicle. That might not be for a while, but in the meantime ill set it back to stock and see if anything changes.
Hold on a sec. You have a Canadian build? Please go and check your speedometer.

Does it look like this?:



Or does it look like this?:

 

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Discussion Starter #11
So, that speedometer didnt look familiar, and the dealer might have been correct... It appears my speedometer goes up to 120mph. According to the dealer it WAS in kilometers being Canadian, but at some point it was changed and the kilometers converted to miles.
 

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I asked you to check the speedo to see whether it was in MPH or KMH. If you look at your pic and the 2nd one I posted, you'll notice the dials are opposite. This leads me to believe that yes your speedo was changed (US speedos only read up to 100MPH), but your vehicle is still somehow setup for the metric system. I would set everything back to stock with your traildash and then head back to the dealer to have them sort everything out.
 

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Ok, Ive got my answer on this. The traildash has a MPH setting that I checked against my GPS, and the two are spot on. The Jeep thinks it's showing me the correct speed, but whoever swapped the gauge cluster put in the wrong cluster. I called the dealer and they told me the proper cluster goes up to 100mph, which is why the gauge is reading wrong. Both gauges move from the 9:00 position to the 3:00 position, but since mine goes up to 120mph it's the numbers on the speedometer responsible for the error, not the Jeep. They said if I brought the Jeep in they would ship the unit to Chrysler, where they would swap the unit for the correct one, and they would change the odometer over at the same time. Apparently the odometer reading is stored in the gauge cluster, and not just displaying it from the computer. Ill have to do that at some point. For now Ill use the traildash as my speedometer.
 

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Ok, Ive got my answer on this. The traildash has a MPH setting that I checked against my GPS, and the two are spot on. The Jeep thinks it's showing me the correct speed, but whoever swapped the gauge cluster put in the wrong cluster. I called the dealer and they told me the proper cluster goes up to 100mph, which is why the gauge is reading wrong. Both gauges move from the 9:00 position to the 3:00 position, but since mine goes up to 120mph it's the numbers on the speedometer responsible for the error, not the Jeep. They said if I brought the Jeep in they would ship the unit to Chrysler, where they would swap the unit for the correct one, and they would change the odometer over at the same time. Apparently the odometer reading is stored in the gauge cluster, and not just displaying it from the computer. Ill have to do that at some point. For now Ill use the traildash as my speedometer.
Have you gotten this swap done yet? I bought a JKU a few weeks ago and was having the exact same problem with my gauges. It has been at the dealer for a week now and I have still not heard back. just wondering if they replace the entire cluster or recalibrate the 120mph cluster
 

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really interested in this thread as i work at a dealer and got a 2015 wrangler that is Canadian. It is now in the US. Someone has changed the cluster and it reads as if is US. the part number on the back of the cluster is a Canadian part number. It is currently owned by a fleet dealer. They brought it in complaining that the vehicle info center was inop. this is the display on the left. Chrysler cant cant cover it under warranty as it is not the factory built part. I am not poiative that this is a cluster isssue but it is leading me that way. tomorrow i will check for accurate speed and chrysler is asking for photos of front and back.
Again, I am not sure yet that this is caused by converting from Canadian to US.
 

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I Just got my Jeep back from the dealer yesterday. It was originally was in KPH then someone converted to the MPH 125 plate which read correct at 60 but nowhere else. I took it back to the dealer I bought it at. They sent the cluster to US Speedo in Michigan. It took two weeks to get back and they changed it to the 100 us plate. When I picked it up it was perfect in town but as soon as I hit the interstate at 75 mph on the digital it was at 45 on the analog. So I went back and they sent the cluster back in and it was re-calibrated to US specs. I picked it up yesterday and it is working perfectly. Luckily the dealer covered all the cost so I don't know the cost of it.
 
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