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Old 04-25-2016, 07:55 PM
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Angry Dealer Can't Seem to program Tire Size Correctly

I put 315/75-16 tires on my JKUR in January. My speedo was reading about 3-4 miles slow at 65mph as expected. I asked the dealer to program the new size. Then the speedo was reading 6-7 miles slow at 65mph. Second trip to have it re-programmed had the error increase 9-10 miles low at 65mph. Today was the third time. They programmed it and told me if it is not right that I would need to buy a ProCal and do it myself. Well, it is still off by 9-10 miles.
Please, someone tell me the dealer should be capable of making this change!

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Old 04-25-2016, 08:01 PM   #2
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I put 315/75-16 tires on my JKUR in January. My speedo was reading about 3-4 miles slow at 65mph as expected. I asked the dealer to program the new size. Then the speedo was reading 6-7 miles slow at 65mph. Second trip to have it re-programmed had the error increase 9-10 miles low at 65mph. Today was the third time. They programmed it and told me if it is not right that I would need to buy a ProCal and do it myself. Well, it is still off by 9-10 miles.
Please, someone tell me the dealer should be capable of making this change!
The largest tire they can program is the stock Rubicon size. Believe me I tried myself. I work for a dealer.

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Old 04-25-2016, 08:04 PM   #3
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You will need to purchase an AEV Procal or Superchips Flashcal and do it yourself. It's what we all do. I recommend the Procal personally.
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Old 04-25-2016, 08:16 PM   #4
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My dealer told me to go to them when I get bigger tires to the program. He said anything I do with the computer voids the warranty
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Old 04-25-2016, 08:21 PM   #5
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My dealer told me to go to them when I get bigger tires to the program. He said anything I do with the computer voids the warranty

Find a new dealer. They aren't capable of making the adjustments. My dealer told me straight out to do it myself.
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Old 04-25-2016, 08:27 PM   #6
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I got a flashcal and for my 35" tires it is entered as 33.75" or so. Mine is off by 4mph I have adjusted it via trial and error about 6 times.


Point is you cant expect the dealer to get it perfect. To get it right you need to drive with gps, test, lower setting etc. Until you get it perfect. They entered the tire size and that is probably not the correct setting to get a 100% accurate speedo.
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Old 04-25-2016, 08:42 PM   #7
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My dealer told me to go to them when I get bigger tires to the program. He said anything I do with the computer voids the warranty
That's not true. And, as was previously indicated, they can't make that type of adjustment with their Starscan programmer. If whoever spoke to you doesn't know that they're doing you a disservice. Make your own adjustment with your own programmer.
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Old 04-25-2016, 09:13 PM   #8
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That's not true. And, as was previously indicated, they can't make that type of adjustment with their Starscan programmer. If whoever spoke to you doesn't know that they're doing you a disservice. Make your own adjustment with your own programmer.
Hmm thanks. I'll be anxious to see what he says when his shop guys tell him that. Kinda wish I would of ordered from another dealer but too late now. He just assured me they would reprogram
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Old 04-26-2016, 03:03 AM   #9
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I have 315/75r16 tires also. I used my procal and set it at 33 3/4 in tall and I'm within one mph against a gps.
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Old 04-26-2016, 07:00 AM   #10
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I have a tablet with the Torque App. https://torque-bhp.com/.

It has the ability to show you your speed both with the GPS (provided your tablet or phone has one) and what your Jeep is showing and will even show you the difference. It was very easy to set up the speedo to read correctly using both the procal and torque.
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Old 04-26-2016, 08:33 AM
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OK. Thanks everyone for the feedback. It must be that the dealers won't enter anything bigger than stock to protect themselves from litigation or something. I know that I can go buy a new Jeep off their lot with 35" tires right now. I would expect that the speedo would be correct, but maybe it would not be. If I can program the parameter but they can't, something is wrong.
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Old 04-26-2016, 11:22 AM   #12
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OK. Thanks everyone for the feedback. It must be that the dealers won't enter anything bigger than stock to protect themselves from litigation or something. I know that I can go buy a new Jeep off their lot with 35" tires right now. I would expect that the speedo would be correct, but maybe it would not be. If I can program the parameter but they can't, something is wrong.
You would think so. But they don't touch adjust anything. Just slap some tires and wheels on.

We use to be able to adjust to larger tires. I think up to 35s. But now with the new computers and WITECH there's only a few settings we can change it to. The largest optional size on my Jeep was 255/75r17. The stock size. Procals are cheap enough though and you get other functions you can adjust also.
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Old 04-26-2016, 02:30 PM   #13
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OK. Thanks everyone for the feedback. It must be that the dealers won't enter anything bigger than stock to protect themselves from litigation or something. I know that I can go buy a new Jeep off their lot with 35" tires right now. I would expect that the speedo would be correct, but maybe it would not be. If I can program the parameter but they can't, something is wrong.
A dealer that I know that sells JK's lifted and equipped with tires that are larger than stock uses a Procal to make adjustments and provides it to the customer. Of course the cost of the Procal is factored in.
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Old 04-26-2016, 03:22 PM   #14
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The new Red Rock Wrangers come with 35x12.5x17 so they CAN program for larger sizes and I do business with a few Jeep dealers who are happy to do so.

With that being said I purchased a Flash Cal and did it myself. I'm still off about 3mph which isn't a big deal at all but I love the other functions it offers.
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Old 04-26-2016, 03:53 PM   #15
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I put 315/75-16 tires on my JKUR in January. My speedo was reading about 3-4 miles slow at 65mph as expected. I asked the dealer to program the new size. Then the speedo was reading 6-7 miles slow at 65mph. Second trip to have it re-programmed had the error increase 9-10 miles low at 65mph. Today was the third time. They programmed it and told me if it is not right that I would need to buy a ProCal and do it myself. Well, it is still off by 9-10 miles.
Please, someone tell me the dealer should be capable of making this change!
Tell the technician to flash back to stock, then keep reversing the tire size in the other direction, twice...

If you want to do it yourself, Flashcal 3571, if your started with the pizza cutters, start with a new tire size of 32.75" in the flashcal, and don't worry, this is not exactly what the tires measures, it takes a little trial and error and GPS to get it right.

Have fun.
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Old 04-26-2016, 05:30 PM   #16
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The new Red Rock Wrangers come with 35x12.5x17 so they CAN program for larger sizes and I do business with a few Jeep dealers who are happy to do so.

With that being said I purchased a Flash Cal and did it myself. I'm still off about 3mph which isn't a big deal at all but I love the other functions it offers.
The Red Rock does not come with 35s. It comes with stock 32s. You can get mods done at Petty's Garage, one of them being 35s.
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Old 04-26-2016, 05:43 PM   #17
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Question for the guys who say that it CAN be done. Have you had it done personally? Because if it can then we must be doing something wrong.

Edit: I was curious. So I double checked mine. Hooked it up to Witech and It was not an option. Hmmm.
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Old 04-26-2016, 05:44 PM   #18
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ProCal it. Took me 5 minutes and it allows you to calibrate to the quarter inch.
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Old 04-27-2016, 03:00 PM
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OK. So I bit the bullet and bought an AEV ProCal from my local Jeep dealer for $183. I figure it is cheaper than getting a speeding ticket because the speedo was reading 10 mph low.
Took me about 30 seconds to get the right value set. I'll also be able to adjust the TPMS pressure lower so the light is not always on due to my running tire pressure at 28 psi.
Thanks everyone.
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Old 04-27-2016, 03:48 PM   #20
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The dealers here sell them with a lift, big tires, and the programmer goes with it. They acknowledge that using a programmer for the tires is the only way to do it, and it doesn't void the warranty to reprogram the tire size.

I'd look for a mod friendly dealer in your area, before they try to tell you the engine head is bad but because you reprogrammed the tire size they won't warranty it.
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Old 04-27-2016, 03:50 PM   #21
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I'd look for a mod friendly dealer in your area, before they try to tell you the engine head is bad because you reprogrammed the time size.
Wish I would have looked for mod friendly dealers before ordering.. My dealer says mod anything I want but DONT touch the computer. Can't wait to hear what he says about reprogramming my speedometer
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Old 04-27-2016, 04:36 PM   #22
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Wish I would have looked for mod friendly dealers before ordering.. My dealer says mod anything I want but DONT touch the computer. Can't wait to hear what he says about reprogramming my speedometer
Before ordering the Jeep? It does not matter what dealer you bought it from. You can take to any dealer you want for service.
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Old 04-28-2016, 12:49 PM   #23
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I put 315/75-16 tires on my JKUR in January. My speedo was reading about 3-4 miles slow at 65mph as expected. I asked the dealer to program the new size. Then the speedo was reading 6-7 miles slow at 65mph. Second trip to have it re-programmed had the error increase 9-10 miles low at 65mph. Today was the third time. They programmed it and told me if it is not right that I would need to buy a ProCal and do it myself. Well, it is still off by 9-10 miles. Please, someone tell me the dealer should be capable of making this change!
Just buy the procal and skip the dealer. Worth it
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Old 04-28-2016, 02:08 PM   #24
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My dealer says mod anything I want but DONT touch the computer. Can't wait to hear what he says about reprogramming my speedometer
I think they are trying to tell you not to do anything to the PCM (engine computer). However, the speedo calibration should be handled by the TIPM (body computer).

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