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Discussion Starter · #1 ·
I finally put the lift and 35's on the jeep. I noticed I lost some house power. Not complaining, I guess if I wanted horse power I would have kept the 650i. My question is why? Are the tires heavier?
 

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Did you reprogram the computer with a Procal or Superchips? Next issue is gearing. What is your ratio? Next question is what motor? 3.6 or 3.8? Next question is what transmission? Auto or stick.

Sure the tires are heavier but my guess is your gear ratio is 3.21 or 3.73. You will surely notice a difference.
 

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Discussion Starter · #5 ·
Eh....ok.....I thought I would have to change the gear ratio if I went to 37's. Ok well I'm not a mechanic so I don't have any of the answers to your questions. But, it looks as though I should be asking. Thanks alot guys. Still love it! I don't care I'm putting around.
 

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Eh....ok.....I thought I would have to change the gear ratio if I went to 37's. Ok well I'm not a mechanic so I don't have any of the answers to your questions. But, it looks as though I should be asking. Thanks alot guys. Still love it! I don't care I'm putting around.
:) That's the great thing about driving a Jeep!
 

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I suggest a great place to start with these answers is to go get the factory build sheet for your jeep. It was suggested by another WF member and is wealth of information about your jeep. Of course if you bought it already modded, hopefully you purchased from the owner and not a dealer , as the owner would have chewed your ear off for an hour about the mods.
Jeep - Contact Us
hopefully this helps. Get a print out and have all those answers in hand.:)
 

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Three reasons you feel like you lost power:

1) Heavier/larger tires have a higher moment of inertia, which requires more torque to accelerate them. When accelerating, more of the engine's torque/power is now "lost" to accelerating the tires themselves rather than being transferred to the road. This is only relevant when accelerating. When maintaining a steady speed, this has zero impact.

2) Larger tires reduce the mechanical advantage (leverage) the engine has against the ground. It's a similar effect as shifting into a higher transmission gear, or being in 4HI vs 4LO. If you ignore the effects of #1 above (such as driving at a steady speed so there's no acceleration involved), you haven't actually lost any power or torque. The torque is divided by the radius of the tire to determine the linear force against the road. Larger tire = less linear force against the road = less acceleration.

3) Big lift and big tires is less aerodynamic. At higher speeds (highway speeds and above), aerodynamic drag is quite substantial, especially with a brick on wheels (Jeep). Make the Jeep less aerodynamic, and now more power is "lost" to simply pushing the brick through the air, and less power is available to be transmitted to the ground.
 

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You can negate the effects on item #2 in my previous post by re-gearing the axles to increase the mechanical advantage, offsetting the decrease in mechanical advantage caused by the larger tires.

There's nothing you can do to directly regain the losses from #1 and #3 though (well, except for increasing power with a supercharger, turbo, or a bigger engine). The best you can do is over-compensate with the re-gearing for additional mechanical advantage. This does not give you more power, but in most normal street driving and off-road situations, it gives you easier access to the power that you do have available more quickly at lower speeds. It will feel more powerful, throttle will be more responsive in general, but you won't technically have more power.
 

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Triple post! Last one, I promise...

Reasons #1 and #2 also explain why the brakes may feel weaker too. With bigger tires, the brakes have less mechanical advantage against the ground to slow the Jeep, and more braking power is "lost" to slowing down the rotation of the tires themselves, with less power available for slowing down the linear motion of the Jeep.
 

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Discussion Starter · #12 ·
Three reasons you feel like you lost power:

1) Heavier/larger tires have a higher moment of inertia, which requires more torque to accelerate them. When accelerating, more of the engine's torque/power is now "lost" to accelerating the tires themselves rather than being transferred to the road. This is only relevant when accelerating. When maintaining a steady speed, this has zero impact.

2) Larger tires reduce the mechanical advantage (leverage) the engine has against the ground. It's a similar effect as shifting into a higher transmission gear, or being in 4HI vs 4LO. If you ignore the effects of #1 above (such as driving at a steady speed so there's no acceleration involved), you haven't actually lost any power or torque. The torque is divided by the radius of the tire to determine the linear force against the road. Larger tire = less linear force against the road = less acceleration.

3) Big lift and big tires is less aerodynamic. At higher speeds (highway speeds and above), aerodynamic drag is quite substantial, especially with a brick on wheels (Jeep). Make the Jeep less aerodynamic, and now more power is "lost" to simply pushing the brick through the air, and less power is available to be transmitted to the ground.
I actually understood that. Thank you.
 

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Discussion Starter · #13 ·
ok, makes alot of sense, but would it be worth going thru all that, or just say it's ok the way it is? I guess what I mean, would it hurt if I don't make any changes to it and leave as is?
You can negate the effects on item #2 in my previous post by re-gearing the axles to increase the mechanical advantage, offsetting the decrease in mechanical advantage caused by the larger tires.

There's nothing you can do to directly regain the losses from #1 and #3 though (well, except for increasing power with a supercharger, turbo, or a bigger engine). The best you can do is over-compensate with the re-gearing for additional mechanical advantage. This does not give you more power, but in most normal street driving and off-road situations, it gives you easier access to the power that you do have available more quickly at lower speeds. It will feel more powerful, throttle will be more responsive in general, but you won't technically have more power.
 

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Discussion Starter · #14 ·
Triple post! Last one, I promise...

Reasons #1 and #2 also explain why the brakes may feel weaker too. With bigger tires, the brakes have less mechanical advantage against the ground to slow the Jeep, and more braking power is "lost" to slowing down the rotation of the tires themselves, with less power available for slowing down the linear motion of the Jeep.
Yes I noticed they as well, so I drove it slower than normal.
 

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Discussion Starter · #15 ·
I suggest a great place to start with these answers is to go get the factory build sheet for your jeep. It was suggested by another WF member and is wealth of information about your jeep. Of course if you bought it already modded, hopefully you purchased from the owner and not a dealer , as the owner would have chewed your ear off for an hour about the mods.
Jeep - Contact Us
hopefully this helps. Get a print out and have all those answers in hand.:)
no I bought the jeep from a dealership, no modifications were on it. Thank you ill look into that.
 

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Discussion Starter · #16 ·
Did you reprogram the computer with a Procal or Superchips? Next issue is gearing. What is your ratio? Next question is what motor? 3.6 or 3.8? Next question is what transmission? Auto or stick.

Sure the tires are heavier but my guess is your gear ratio is 3.21 or 3.73. You will surely notice a difference.
eh....lol....the only answer I can give ys, it's an automatic
 

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I saw your post in another thread, looks like you have a newer Oscar Mike JKU. I just lifted mine about a month ago, no difference in power until I got the tires (35") last week. I noticed a difference. But after calibrating the ECU with my ProCal (a device you plug into your OBD port, which is by your left foot on the bottom of the dash), it was much better.

Tire and wheel size and weight will greatly impact your performance as well. For example, I went with BFG KO2's 35" that run on the smaller size. But the tire weighs in at 63lbs. Versus a General Grabber which weighs 82lbs. That extra 20lbs will make a age difference. Then you have to factor the wheel weight. The larger diameter the wheel, the heavier it's going to weigh.

But first item you check off the box is calibrating the ECU. I think once you do that, you'll notice a big difference, plus it will put your speedometer where it should be.

Hope all these posts help out!
 

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Lol, that font.
 

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Discussion Starter · #19 ·
I saw your post in another thread, looks like you have a newer Oscar Mike JKU. I just lifted mine about a month ago, no difference in power until I got the tires (35") last week. I noticed a difference. But after calibrating the ECU with my ProCal (a device you plug into your OBD port, which is by your left foot on the bottom of the dash), it was much better.

Tire and wheel size and weight will greatly impact your performance as well. For example, I went with BFG KO2's 35" that run on the smaller size. But the tire weighs in at 63lbs. Versus a General Grabber which weighs 82lbs. That extra 20lbs will make a age difference. Then you have to factor the wheel weight. The larger diameter the wheel, the heavier it's going to weigh.

But first item you check off the box is calibrating the ECU. I think once you do that, you'll notice a big difference, plus it will put your speedometer where it should be.

Hope all these posts help out!
thank you I screened shot your comment, and sent it via text to the person who did the work. Waiting to hear what he says.
 

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thank you I screened shot your comment, and sent it via text to the person who did the work. Waiting to hear what he says.
Great! I think you live in Tucson? I live in Phoenix. If you lived closer I would hook my ProCal up and set it up for you. They cast $150 and have some additional options besides calibrating tire size. But unless you would ever use the other options, it's a one time deal and your out the $150. Hope it helps!
 
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