Downside of lower gears (why there not factory)
Thread Starter
JK Enthusiast
Joined: Aug 2009
Posts: 368
Likes: 1
From: Fort Worth, Texas
Downside of lower gears (why there not factory)
Hey yall,
I am wanting to do some lower gears with my 33's and 3.21's. All i ever hear is how great lower gears are and it makes me wonder what the downsides are other than cost of install? If they are such a godsent why does the factory sell some jk's with 32 inch tires and 3.21 gears? I drive from texas to florida often and was wanting some negatives to put up make sure I am not going to regret my decision.
Thanks yall!
I am wanting to do some lower gears with my 33's and 3.21's. All i ever hear is how great lower gears are and it makes me wonder what the downsides are other than cost of install? If they are such a godsent why does the factory sell some jk's with 32 inch tires and 3.21 gears? I drive from texas to florida often and was wanting some negatives to put up make sure I am not going to regret my decision.
Thanks yall!
JK Jedi Master
Joined: Jan 2008
Posts: 11,463
Likes: 165
From: Austin <--> Colorado Springs
I was running 295/75/16 Nitto Terra's (32" actual height) and 5.13 gears on my Auto for about 8 months before I moved to taller tires. The only downside for me was O/D Off towing on the freeways. (since you have a manual, you'll get more use out of 6th with taller gears)
3.21's and taller tires make it sluggish, lowering power and mileage. Gearing back into the proper ratio 'should' improve mileage as well as make it much more enjoyable to drive...
3.21's and taller tires make it sluggish, lowering power and mileage. Gearing back into the proper ratio 'should' improve mileage as well as make it much more enjoyable to drive...
Last edited by nthinuf; Mar 14, 2010 at 01:35 PM.
JK Super Freak
Joined: Mar 2008
Posts: 1,673
Likes: 3
From: Alberta
well yes and no for the 3.21's and 33's
definately 'performance' is reduced starting off the line, but mileage isn't necessarily going to improve unless your running on the highway all day...in town stop and go your going to burn more fuel trying to get those tires to turn
by regearing your trying to increase leverage on the tires so the engine can turn them easier at a lower RPM...of course it's all about balance because if you go to small your engine will be spinning ridiculously fast at higher speeds and you only have so many gear selections in the transmission....make sense?
If Jeep was producing the JK with factory 35's I'm sure the gearing would have been produced accordingly, but it's not so they don't.
definately 'performance' is reduced starting off the line, but mileage isn't necessarily going to improve unless your running on the highway all day...in town stop and go your going to burn more fuel trying to get those tires to turn
by regearing your trying to increase leverage on the tires so the engine can turn them easier at a lower RPM...of course it's all about balance because if you go to small your engine will be spinning ridiculously fast at higher speeds and you only have so many gear selections in the transmission....make sense?
If Jeep was producing the JK with factory 35's I'm sure the gearing would have been produced accordingly, but it's not so they don't.
Last edited by BlackNorthernJK; Mar 14, 2010 at 01:39 PM.
JK Enthusiast
Joined: Oct 2009
Posts: 206
Likes: 1
From: Littleton Colorado
Your jeep didn't come with 33's. . When you go 33's or higher in tires, rpm's drop, and engine works harder= worse gas mileage. If you put lower gears in bring it back to stock or little greater and makes the jeep mo better.
If rubicons came with 35in tires, maybe jeep would throw in a 4'88 R&P.
If rubicons came with 35in tires, maybe jeep would throw in a 4'88 R&P.
JK Junkie
Joined: Jul 2009
Posts: 2,343
Likes: 1
From: The San Andreas Fault
The 3.21s are designed to provide better fuel economy with the tire size they provide at the factory. The choice is driven by EPA and CAFE ratings, performance is secondary and ability to upgrade tire size isn't even a consideration.
If fuel economy is really important to you then forget about bigger tires, they are the cause of the "negatives" not the gears.
If fuel economy is really important to you then forget about bigger tires, they are the cause of the "negatives" not the gears.
Trending Topics
JK Freak
Joined: Jul 2009
Posts: 590
Likes: 1
From: State College, PA
More than likely increasing the gear ratio will increase your fuel economy with an auto transmission but decrease your fuel economy with a 6-speed.
The reason for this difference is because an auto only takes into account throttle position and speed to determine what gear to be in. What this means is when you are trying to go up hill on a highway and don't have the power to do so at a set speed in overdrive, your transmission will downshift (hence very much increasing engine speed at a set highway speed). With an increased gear ratio it will allow it to stay in OD more and hence get better fuel economy with an auto with higher gear ratios on the highway.
Higher gear ratios will likely increase fuel consumption with a 6-speed because of the fact that YOU choose which gear you are in. When I want to get good fuel economy at times instead of staying at a set speed of 70 mph on the highway, when I hit a hill I will leave it in 6th at full throttle. I will lose maybe 5 mph down to the 65 mph speed limit while climbing a hill but fuel consumption won't jump with the downshift from OD to a lower gear. Re-gearing may allow you to maintain speed better on the highway in 6th gear, but when you aren't climbing a hill, the vehicle won't travel as far per engine revolution. Therefore if I increased my gear ratio but all other things stayed equal (same shift points, driving habits, tire size, ect.) with a 6-speed the fuel consumption would actually go up.
So really if you have an auto, regearing is a good idea. If you have a 6-speed the two scenarios you will have are that you can increase performance at the cost of slightly increased fuel consumption or you can have higher fuel economy at the cost of less performance.
Hope this helps!
The reason for this difference is because an auto only takes into account throttle position and speed to determine what gear to be in. What this means is when you are trying to go up hill on a highway and don't have the power to do so at a set speed in overdrive, your transmission will downshift (hence very much increasing engine speed at a set highway speed). With an increased gear ratio it will allow it to stay in OD more and hence get better fuel economy with an auto with higher gear ratios on the highway.
Higher gear ratios will likely increase fuel consumption with a 6-speed because of the fact that YOU choose which gear you are in. When I want to get good fuel economy at times instead of staying at a set speed of 70 mph on the highway, when I hit a hill I will leave it in 6th at full throttle. I will lose maybe 5 mph down to the 65 mph speed limit while climbing a hill but fuel consumption won't jump with the downshift from OD to a lower gear. Re-gearing may allow you to maintain speed better on the highway in 6th gear, but when you aren't climbing a hill, the vehicle won't travel as far per engine revolution. Therefore if I increased my gear ratio but all other things stayed equal (same shift points, driving habits, tire size, ect.) with a 6-speed the fuel consumption would actually go up.
So really if you have an auto, regearing is a good idea. If you have a 6-speed the two scenarios you will have are that you can increase performance at the cost of slightly increased fuel consumption or you can have higher fuel economy at the cost of less performance.
Hope this helps!
Thread Starter
JK Enthusiast
Joined: Aug 2009
Posts: 368
Likes: 1
From: Fort Worth, Texas
More than likely increasing the gear ratio will increase your fuel economy with an auto transmission but decrease your fuel economy with a 6-speed.
The reason for this difference is because an auto only takes into account throttle position and speed to determine what gear to be in. What this means is when you are trying to go up hill on a highway and don't have the power to do so at a set speed in overdrive, your transmission will downshift (hence very much increasing engine speed at a set highway speed). With an increased gear ratio it will allow it to stay in OD more and hence get better fuel economy with an auto with higher gear ratios on the highway.
Higher gear ratios will likely increase fuel consumption with a 6-speed because of the fact that YOU choose which gear you are in. When I want to get good fuel economy at times instead of staying at a set speed of 70 mph on the highway, when I hit a hill I will leave it in 6th at full throttle. I will lose maybe 5 mph down to the 65 mph speed limit while climbing a hill but fuel consumption won't jump with the downshift from OD to a lower gear. Re-gearing may allow you to maintain speed better on the highway in 6th gear, but when you aren't climbing a hill, the vehicle won't travel as far per engine revolution. Therefore if I increased my gear ratio but all other things stayed equal (same shift points, driving habits, tire size, ect.) with a 6-speed the fuel consumption would actually go up.
So really if you have an auto, regearing is a good idea. If you have a 6-speed the two scenarios you will have are that you can increase performance at the cost of slightly increased fuel consumption or you can have higher fuel economy at the cost of less performance.
Hope this helps!
The reason for this difference is because an auto only takes into account throttle position and speed to determine what gear to be in. What this means is when you are trying to go up hill on a highway and don't have the power to do so at a set speed in overdrive, your transmission will downshift (hence very much increasing engine speed at a set highway speed). With an increased gear ratio it will allow it to stay in OD more and hence get better fuel economy with an auto with higher gear ratios on the highway.
Higher gear ratios will likely increase fuel consumption with a 6-speed because of the fact that YOU choose which gear you are in. When I want to get good fuel economy at times instead of staying at a set speed of 70 mph on the highway, when I hit a hill I will leave it in 6th at full throttle. I will lose maybe 5 mph down to the 65 mph speed limit while climbing a hill but fuel consumption won't jump with the downshift from OD to a lower gear. Re-gearing may allow you to maintain speed better on the highway in 6th gear, but when you aren't climbing a hill, the vehicle won't travel as far per engine revolution. Therefore if I increased my gear ratio but all other things stayed equal (same shift points, driving habits, tire size, ect.) with a 6-speed the fuel consumption would actually go up.
So really if you have an auto, regearing is a good idea. If you have a 6-speed the two scenarios you will have are that you can increase performance at the cost of slightly increased fuel consumption or you can have higher fuel economy at the cost of less performance.
Hope this helps!