gear ratio

[wilson]

I recently put 31s on my pathy that originally came with 29s. I belive the original gear ratio is 4.3. I'd like to switch to the 4.6. I'm currently gettin about 18.8 MPG around town and like to keep or improve that. my question is how does change in ratio affect gas mileage?

[silverton]

The lower gearing will actually get you better gas mileage. Your 4.3's are now effectively 4.01's. If you switch up to the 4.6 gear set, with the 31's your gear ratio would be 4.29.

[KovemaN]

 

The mileage difference is only a trick. If you don't change the speedo gear you will actually be going faster and farther than your instruments are reading. If you change the actual gearing you can get back to more normal readings. I don't think a gear change will actually give you better mileage since the engine has to do the same amount of work either way. The bigger/heavier tires will drop your mileage some.

[SteeevO]

The lower gearing will actually get you better gas mileage. Your 4.3's are now effectively 4.01's. If you switch up to the 4.6 gear set, with the 31's your gear ratio would be 4.29.

 

 

How do you figure 4.3 are effectively 4.01's?

Edited August 31, 2010 by SteeevO

[MY1PATH]

MPG around town and like to keep or improve that. my question is how does change in ratio affect gas mileage?

The larger diameter tire requires more torque to turn but also gives more miles per revolution.

going to 4.6 (from 4.3) provides some extra torque and reduces miles per revolution.

 

The demand for troque is what brings down your MPGs

also, say your going 35mph with 31's in 3rd gear; your rpms are about 2500 with 3.3 gears and will be closer to 28~3000 with the 4.6.

2 things happen here, your vehcle produces more torqe at the higher range and the o2 sensor takes full control of Air Fuel Ratio when above 2800rpm (o2 when working properly is more accurate and efficent)

This is difficult to grasp because allot of people think that High rpms = poor mpg. The truth is that cruising 3500rpm and 10% throttle opening will use less gas than crusing 2500rpm and 100% throttle opening.

[silverton]

How do you figure 4.3 are effectively 4.01's?

 

 

this is what I'm talking about:

 

http://www.ehow.com/about_6591408_tire-size-effect-gear-ratio.html

[wilson]

The larger diameter tire requires more torque to turn but also gives more miles per revolution.

going to 4.6 (from 4.3) provides some extra torque and reduces miles per revolution.

 

The demand for troque is what brings down your MPGs

also, say your going 35mph with 31's in 3rd gear; your rpms are about 2500 with 3.3 gears and will be closer to 28~3000 with the 4.6.

2 things happen here, your vehcle produces more torqe at the higher range and the o2 sensor takes full control of Air Fuel Ratio when above 2800rpm (o2 when working properly is more accurate and efficent)

This is difficult to grasp because allot of people think that High rpms = poor mpg. The truth is that cruising 3500rpm and 10% throttle opening will use less gas than crusing 2500rpm and 100% throttle opening.

 

this is fascinating! as well as convincing. I can get an entire LSD rear axle for 250.00 @ the local JY. to upgrades at once.WOOT!

 

also, I figured changing the gear ratio would bring my speedometer back into calibration. kinda hard to wrap my head around eh?

[KovemaN]

You will need to swap the front diff as well if you go to 4.6s.

[silverton]

When changing differential gearing you have to change both front and rear diffs as they need to be the same, or VERY VERY close.

 

If you don't and engage 4wd the front and rear wheels will move at different speeds, and this is baaaaaddddd.

[wilson]

You will need to swap the front diff as well if you go to 4.6s.

yes, I am hip to this scene.

[flnl]

Or you can use a bigger tire in the slower speed axle