fuel

[btm24]

with all this talk about gears, i was wondering what are yall getting mpg wise with your gears? I'm looking if updating to 4:10 gears would make a big diff in mpg (because of the more work it takes) compared with what I'm getting now. ill let yall know what my gear rating is after i mow the grass ill check. Thanks

 

Brandon

[wannabeMJ]

http://www.google.ca/images?hl=fr&sourc ... =&gs_rfai=

 

go there youll see just pick one and do your calculation

[Pete M]

it's not a gear "rating", it's a gear ratio. :thumbsup: as in the ratio of teeth between the ring and pinion gears. 4 to 1, 3.5 to 1, etc.

 

if you add big tires but keep the same gear ratio, the mpgs will go down. upgrading the gear ratio will pick that back up. the gear ratio is literally the leverage that your engine gets over the tires. think of upgrading to 4.10s as putting a pipe extension on a wrench. takes less effort to accomplish the same task (undoing a bolt in this example).

[btm24]

http://www.google.ca/images?hl=fr&source=imghp&biw=1436&bih=706&q=gear+ratio+chart&gbv=2&aq=f&aqi=&aql=&oq=&gs_rfai=

 

go there youll see just pick one and do your calculation

 

:doh: i should have thought about that thanks you big help :yes:

 

and yeah thanks you pete for helping out with my rate compared to ratio now i know :dunno: and yeah i know that about the gears but i was thinking that since having the the moder work harder to move the at the same speed it would burn more fuel. however being this would be a good thing when it comes to wheeling but not so much at highway speeds. right?

 

Brandon

[Pete M]

do not associate rpms directly with fuel consumption. it's far more complex than that. the basic goal is to keep your engine in its optimum torque range because that's where the best fuel economy happens. Lets assume that your current setup was ideal (it's likely already running at a bit lower rpm than ideal). when you install 33s, in order to maintain a given speed the engine will now be at a much lower rpm which is now lower than optimum and now the engine is working extra hard to maintain that same speed (meaning it's consuming more fuel). adding in lower gears (higher number) brings that back up to the optimum. keep in mind that bigger tires are, well, bigger. they weigh more and have more friction with the ground and mpgs can suffer num matter what you do. the key is to get the best bang for the buck.

 

tire diameter and gear ratio are directly related to each other when it comes to both engine performance and mpgs. when you change one, you need to change the other. :thumbsup:

[btm24]

tire diameter and gear ratio are directly related to each other when it comes to both engine performance and mpgs. when you change one, you need to change the other. :thumbsup:

 

I knew most of the other stuff already its that last part that rly got me, Big tire/higher gear ratio. Thank you yet again pete :bowdown:

 

Brandon

[Pete M]

just make sure you keep it straight. higher number = lower gears :thumbsup:

[btm24]

i sure will :D Thanks

 

Brandon

[Comanche County]

FWIW, here's what I've gotten with different tire sizes and gear ratios on my rig.

 

All are +/- 1-2MPGs w/ mostly highway driving and some city miles. I used to check my MPGs every time I filled up.

 

3.07 and 30" tires - 18 mpg average (firestone ATs, stock steel wheels)

3.73 and 30" tires - 20 mpg average (firestone ATs, stock steel wheels. Same MPG with 30" BFT ATs on XJ aluminum wheels)

3.73 and 31" tires - 17 mpg average (BFG MT 31s, steel D window wheels)

3.73 and 33" tires - 16 mpg average (After having the head rebuilt that jumped up a bit to 17 mpg. That was with 33" Mud Brutes, 33" BFG MTs on Soft 8 Steelies. MT Baja Claws on Soft 8s was a little worse.)

4.56 and 35" tires - 17-18 mpg (current set up, I need to do some more driving but that's my rough estimate for now)

 

More rotating mass and resistance of off road tires and heavier wheels kill MPGs.