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Old 06-26-2013, 03:00 PM   #1
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Will I Need to Re-Gear?? New Jeep Guy...

Just bought my first jeep, a 2013 Unlimited...funnest car I've ever owned!! After driving it for 3 months, I just dropped it off for a 2" spring lift, some Pro Comp 7069 wheels, and 33" GY Duratracs. However, after reading some of these posts, I'm concerned that the 3.21 axle is not enough for the tires and wheels I've chosen. It is an automatic, and had the stock 18" wheels and 32" tires before the change. I drive about 150 miles per day on the highway and am wondering if I'm going to see a serious drop off in pickup and MPH. Should I consider re-gearing at this point, or is the drop off going to be minimal? Any insights would be appreciated!

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Old 06-26-2013, 03:06 PM   #2
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33s are good to go. I have 285/70/17 on my 2012 manual and power loss was very minimal compared to the 16'steelies.

There are others that have 33's and regeared due to additional weight. It's just preference.

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Old 06-26-2013, 03:06 PM   #3
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Originally Posted by Jeep Bit View Post
Just bought my first jeep, a 2013 Unlimited...funnest car I've ever owned!! After driving it for 3 months, I just dropped it off for a 2" spring lift, some Pro Comp 7069 wheels, and 33" GY Duratracs. However, after reading some of these posts, I'm concerned that the 3.21 axle is not enough for the tires and wheels I've chosen. It is an automatic, and had the stock 18" wheels and 32" tires before the change. I drive about 150 miles per day on the highway and am wondering if I'm going to see a serious drop off in pickup and MPH. Should I consider re-gearing at this point, or is the drop off going to be minimal? Any insights would be appreciated!
Unless you go to 35's you won't have to regear. Just make sure to use an AEV Procal or similar device to correct your speedo with the new tire size.

And post some pics up when you get it back!
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Old 06-26-2013, 03:07 PM   #4
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With the auto you wont notice much change at all with the 33" tires. The Procal will indeed help correct the speedo but more important will correct shift points and make it shift better.
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Old 06-26-2013, 03:15 PM   #5
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You'll be fine. Just stop calling it a car. LOL
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Old 06-26-2013, 03:25 PM   #6
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Thanks everyone!
Duly noted on the "car"
I did add on an AEV Pro Cal. I will post before and after pictures when I get it back on Friday!! I appreciate the help.
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Old 06-26-2013, 04:26 PM   #7
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I added 275/70/18 (33.4") duratracs a few weeks ago on my 2012 jku with 3.21s and have noticed a drop in mpg from 18-19 down to 16-17. I drive about 60 miles daily. I had the stock 255/70/18 (32.1) tires and my speedometer is still dead on according to the nav. Im not sure how much a procal would help considering my speedo is still accurate at 70 mph.

In addition to the drop in mileage, i have also noticed a slight lack of power. I went with 33s instead of 35s to avoid regearing, but im now contemplating 4.10s or 4.56s.
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Old 06-26-2013, 04:31 PM   #8
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Your mileage dropped because your odometer is off .Your taller tire is covering more miles than your odometer thinks it is.Get a procal and measure your tires from ground to top of tire and put that measurement into procal and you will get most of your mileage back.
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Old 06-26-2013, 04:40 PM   #9
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^^ what he said. You can recalc your mileage by using your speedo as a guage. It goes in percentages, so if you're speedo says 60 and your gps says 66, you're off by 10%. Add 10% to your 16-17mpg and you're at 17.6 - 18.7, not bad.

To answer the original question, you'll be fine. I'm running a 2012 on 35's at 3.21, do a little rock crawling and managed some good hill climbs. It's my daily driver and when I take it really easy I average around 18 mpg. That being said, I bought it set up that way, I do take it off road, and I don't want to tear this thing up. I also plan on towing a small camper, so I'll be regearing to 4.88s or 5.13s soon (in support of future 37's).
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Old 06-27-2013, 10:34 AM   #10
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But my speedometer doesn't seem off. When it says i'm going 70, the gps nav says im going exactly 70.
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Old 06-27-2013, 10:45 AM   #11
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Quote:
Originally Posted by Jeep Bit View Post
Just bought my first jeep, a 2013 Unlimited...funnest car I've ever owned!! After driving it for 3 months, I just dropped it off for a 2" spring lift, some Pro Comp 7069 wheels, and 33" GY Duratracs. However, after reading some of these posts, I'm concerned that the 3.21 axle is not enough for the tires and wheels I've chosen. It is an automatic, and had the stock 18" wheels and 32" tires before the change. I drive about 150 miles per day on the highway and am wondering if I'm going to see a serious drop off in pickup and MPH. Should I consider re-gearing at this point, or is the drop off going to be minimal? Any insights would be appreciated!
Where do you live? Unless in Colorado or Northern California, with 3.21s and 33s you will be fine on the highway with a 150mile commute. If the speed limit is 65mph, stay in 4th.
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Old 06-27-2013, 10:46 AM   #12
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I added 275/70/18 (33.4") duratracs a few weeks ago on my 2012 jku with 3.21s and have noticed a drop in mpg from 18-19 down to 16-17. I drive about 60 miles daily. I had the stock 255/70/18 (32.1) tires and my speedometer is still dead on according to the nav. Im not sure how much a procal would help considering my speedo is still accurate at 70 mph.

In addition to the drop in mileage, i have also noticed a slight lack of power. I went with 33s instead of 35s to avoid regearing, but im now contemplating 4.10s or 4.56s.
Get the 4.56s, because you will want 35s next, and you'll be ready to go. You are in the same exact boat as I am.
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Old 06-27-2013, 11:07 AM   #13
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I just returned a few hours ago from Moab my "car" is also a 2013 JKU with auto, 321's and 33". I drove 75-80mph there and back and did about 500 miles of trails while I was there. I was loaded down with 3 adults and a ton of gear while on the road (when there and trail riding only had the humans loaded up) not once did I think my 3.21's were a detriment. I did not do the difficult trails and stuck to the moderate rated trails. If I lived closer to an area like Moab I might want to get 35-37" tires so I would need higher gearing (numerically) but for 99% of the off roading I am going to do the 33" and 3.21 are perfect. Between Missoula Mt and Moab Ut there are plenty of long grades and while at times I would shift to 3rd or 4th I never had to slow down due to being under powered. I hand figured every tank full of gas and was between 21mpg and 16.6mpg while on the road. Coming back I had a major head wind for much of the way and mpg dropped. off road mpg was worse as lots of sand washes and 4lo etc.

I have mine set with the procal and both odometer and speedo are dead on accurate according to 3 different gps and android phone speedo app.
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Old 06-27-2013, 11:18 AM   #14
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Originally Posted by msubrave View Post
I added 275/70/18 (33.4") duratracs a few weeks ago on my 2012 jku with 3.21s and have noticed a drop in mpg from 18-19 down to 16-17. I drive about 60 miles daily. I had the stock 255/70/18 (32.1) tires and my speedometer is still dead on according to the nav. Im not sure how much a procal would help considering my speedo is still accurate at 70 mph.

In addition to the drop in mileage, i have also noticed a slight lack of power. I went with 33s instead of 35s to avoid regearing, but im now contemplating 4.10s or 4.56s.
How is the ride with that size duratrac? I'm looking into those but concerned that the ride will be more "rough" than stock because of the "e" rating (thicker tire I'm assuming). Thanks.
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Old 06-27-2013, 11:45 AM   #15
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But my speedometer doesn't seem off. When it says i'm going 70, the gps nav says im going exactly 70.
I think some were saying the nav gets its speed from the speedo and not the sats but I cant confirm that. I know mine was off going from the stock 255/75/17 to 33/12.50/15 my speedo was off about 5 mph which made my mpg drop a good bit.
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Old 06-27-2013, 11:49 AM   #16
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I think some were saying the nav gets its speed from the speedo and not the sats but I cant confirm that. I know mine was off going from the stock 255/75/17 to 33/12.50/15 my speedo was off about 5 mph which made my mpg drop a good bit.
Im not sure either, I use a completely separate device (iphone) to check against the speedo. At 65 indicated GPS says 63, and I'm procaled. I need to adjust the tire, just not sure by how much . I suppose .1 lower?
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Old 06-27-2013, 11:58 AM   #17
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Im not sure either, I use a completely separate device (iphone) to check against the speedo. At 65 indicated GPS says 63, and I'm procaled. I need to adjust the tire, just not sure by how much . I suppose .1 lower?
I found in order to get mine dead nuts on I had to be .25" under what they actually measured not what the manufacturer said they were. I used a carpenters level and with my jeep parked on a level cement garage floor I layed the level on the top of the tire making sure it was level and measured from the floor to the bottom of the level. the procal goes in .25" increments so drop tire size .25" using the dip switches.
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Old 06-27-2013, 02:38 PM   #18
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How is the ride with that size duratrac? I'm looking into those but concerned that the ride will be more "rough" than stock because of the "e" rating (thicker tire I'm assuming). Thanks.
I was concerned it might be stiff too but so far i cant notice any difference from stock duelers. I also have a TF level kit and spidertrax spacers. Rides good just wish i had at least 3.73s but 3.21 are fine for the most part.
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Old 06-27-2013, 02:41 PM   #19
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I think some were saying the nav gets its speed from the speedo and not the sats but I cant confirm that. I know mine was off going from the stock 255/75/17 to 33/12.50/15 my speedo was off about 5 mph which made my mpg drop a good bit.
Well that could be interesting.. Anyone know if this is true? I have a portable gps that i will hook up next time to see what it says.
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Old 06-27-2013, 02:46 PM   #20
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Get the 4.56s, because you will want 35s next, and you'll be ready to go. You are in the same exact boat as I am.
RPMs will be fairly high with 33s and 4.56s until i get 35s... I was thinking 4.10s would be good with 33s and then just upgrade to a 34 like the 315/70/17 dt next and should still be fine with 4.10s.
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Old 06-27-2013, 03:29 PM   #21
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Well that could be interesting.. Anyone know if this is true? I have a portable gps that i will hook up next time to see what it says.
Lift the rear axle, drive jeep. If the GPS says 0mph, then it's reading satellites. If it gets a speed reading, it's reading from the sender unit on the jeep itself.
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Old 06-27-2013, 03:31 PM   #22
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RPMs will be fairly high with 33s and 4.56s until i get 35s... I was thinking 4.10s would be good with 33s and then just upgrade to a 34 like the 315/70/17 dt next and should still be fine with 4.10s.
Thats up to you. My personal opinion is that 4.56s seem to be perfect for the 3.6 and 35s. Don't forget that the chart people always use doesn't account for weight.

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