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Old 06-27-2010, 11:15 AM   #1
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Question Question re: new wheels and tires

Just had Khumo 33x12.5R17 AT tires on Rev 50 Caliber Black Machined Face Wheels insalled on my 2010 Jeep Wrangler Sport. Fully expected the MPG to go down but it also feels like I have lost power as well especially in 5th and 6th gears. Am I imagining this or is this normal when you go to bigger tires?

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Old 06-27-2010, 11:22 AM   #2
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Normal to lose power with bigger tires, engine has to work harder to spin them. To correct, change your gears to a lower(higher number) set.

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Old 06-27-2010, 11:35 AM   #3
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4Jeepn: Can you explain the changing gears a little more. How is this done?
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Old 06-27-2010, 12:00 PM   #4
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Old 06-27-2010, 01:17 PM   #5
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Everyone is correct. This is normal behavior.

You can either buy new gears, or try a programmer. Programmers are great if you're "just outside the reccomended gear ratio" and it's a bonus if you have an automatic transmission.

Since your complaining of power with 33's I'm sure you've got 3.21 gears. 3.73 is good for 33's and a manual, 4.10 is the best.

Programmers are $300. Gears are at least $1000. Try the programmer first. If you don't like it, get gears. The programmer isn't a waste either. It eliminated that throttle lag, and corrected the speedo. With 4.10's, a programmer, and 33's...you'll be in great shape
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Old 06-27-2010, 02:57 PM   #6
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Listen, At LEAST 4.56 or 4.88's and do your lockers now. Two sets of gears,install kit,and labor @ $1500.
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Old 06-27-2010, 05:01 PM   #7
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^ Woah- a bit of overkill. And you don't lose power due to having to spin bigger tires- yes, this is SOMEWHAT true, but the REAL reason is:
Tires are gears!
Yep. In the power equation, the diameter of your tires helps determine what is known as the final drive ratio. Bigger tires lower than, reducing torque multiplication to the ground, causing the vehicle to feel, and be, slower to accelerate, same as if you re-geared from 3.73 to 3.21, for instance. The bigger the tire size increase, the lower the final drive gets. This is why you re-gear a vehicle for bigger tires.
As for re-gearing, if you have OEM 3.21 gears, try adding a Superchips programmer to re-gain some of your power, and also to adjust the speedo/odometer back to being accurate. I would recommend re-gearing as a last resort, as the 3.21's can handle 33's (it'll never be a rocket off the line, however, and you may lose ~1 MPG). Re-gearing will void your warranty with MOST dealerships for your entire axle at each end, and costs a LOT to do- it's up to you to determine if it's worth the $1K+ it'll run you, parts and labor.
If you REALLY want to re-gear, you can find a set of OEM 4.10 gears for not a ton of coin- NOT Rubicon gears, but '07/8 D30/D44 gears (I'm assuming you're not in a Rubi, by the way). They're uncommonish, but out there. Check Craigslist, and the forums.
Class dismissed Mark W.
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Old 06-27-2010, 07:10 PM   #8
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Quote:
Originally Posted by fan45acp View Post
Listen, At LEAST 4.56 or 4.88's and do your lockers now. Two sets of gears,install kit,and labor @ $1500.
for 33's?

dude i'm on 35's, 4.10's, AND an automatic...a superchip covered it just fine. i'm not buying any gears.

when my jeep was stock the 4.10's with 32's were perfect. unless you live on a damn mountain, 33's with a chip and 3.73 will be fine.
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Old 06-27-2010, 08:13 PM   #9
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Yeah- 4.56's would be massive overkill- that'd leave you over 3K RPM's at 70 MPH on the highway- not cool. As I said, I'd recommend re-gearing only if you wheel frequently, or really feel the need to, and even then, 3.73's or 4.10's max- Mark W.

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