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Unread 03-01-2011, 10:35 AM   #1
mikevella00
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Need Gear Ratio help

Hi, I have an 09 Wrangler X. I have stock tires P225/75R BSW on/off road tires and I just got some Hankook Dynapro AT RF 10 265/70R17T. The guy said I need to change the gear ratio, but I have no idea how to find out what gear I need. Please help, or lead me in the right direction

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Unread 03-01-2011, 11:01 AM   #2
aristobrat
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First off, you only change gears if you don't like the way your JK performs with the new tires. It's not like you're "required" to change gears just because you got new tires.

There's an entry in the FAQ at the top of the forum that leads to a chart that should help in regards to gearing. Take the physical measurement of your tires (really, go measure them -- they're often different from what you'd think), pick your transmission (gears differ greatly between autos and manuals), and then look at what the chart recommends.

Also consider what you're going to be doing in the future. Doesn't make sense (to most) to pay $1500 to regear for your current tires when you know 3-4 years down the road, you're probably going to be running 35s.

Also, if you think that the chart is crazy because the RPMs that it shows are way too high, remember that the JK's power band is between 2K and 3K. You may think (esp if you have an auto) that running lower RPMs is a very good thing, but if they're so low that your transmission is constantly shifting out of over drive, then running them that low is way more likely killing your MPG and performance vs. if you ran steady RPMs more close to the JK's power band.
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Unread 03-01-2011, 01:09 PM   #3
mikevella00
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Re:

Hi Aris,

Thanks for the advice. However is was referring to recalibration the odometer and speedometer as the wheels and tires with be significantly larger than what I'm running now. Is this an entirely computerized system that needs to be reprogrammed or do I have to make and mechanical changes in the cluster for me to get a true readings?

Thanks,

Mike
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Unread 03-01-2011, 01:58 PM   #4
RockyClymer
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You only have to recalibrate for tires if you change from stock size and if you have an auto for gearing (it will help change the shift points). I would only gear if you go to larger tires, say a 35, and then if you do not like the way the vehicles runs...it will put it out of the 3.8 power range and that is the reason most regear at that time.
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Unread 03-01-2011, 02:11 PM   #5
aristobrat
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Quote:
Originally Posted by mikevella00 View Post
Is this an entirely computerized system that needs to be reprogrammed
Yes. On the JKs, you program in the correct size tires, and the computer (PCM) will automatically adjust the speedometer/odometer for you.

To program it yourself, check out the AEV ProCal Module or the Superchips Flashpaq.

It looks like your new tires are under 32". I had read somewhere that Jeep dealers can program in tires that are 32" or less.
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Unread 03-01-2011, 02:38 PM   #6
mikevella00
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Yes, I believe they are just under 32", so that is a big help if it can just be programmed and to see if the dealer can do it if I can't figure it out myself.

I guess one last thing, I am going from 16" wheels to 17" wheels, should have mentioned that earlier, does that change the previous responses?

Thanks a lot guys.
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Unread 03-01-2011, 02:44 PM   #7
aristobrat
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Quote:
Originally Posted by mikevella00 View Post
I guess one last thing, I am going from 16" wheels to 17" wheels, should have mentioned that earlier, does that change the previous responses?
That shouldn't matter. You just need the overall height of the tire.
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Unread 03-01-2011, 02:50 PM   #8
mikevella00
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Excellent, thanks so much.
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Unread 03-01-2011, 02:55 PM   #9
RockyClymer
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And, the only way you do it yourself is with a programmer such as the AEV Procal, no way to do it otherwise as it needs to be entered into the OBDII port.
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Unread 03-01-2011, 03:24 PM   #10
Mol
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Most dealers will charge you about $100 to reprogram for larger tires....pay the extra $50 for the Procal, and you can change as many times as you change tires, not to mention the several other benefits of the Procal...reprogram for gears if you go that route down the road and have an auto, headlight functions, steering wheel centering, and a few others that I'm currently blanking on
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