Gear Ratio Chart for Different Tire Sizes...

[Dave]

http://www.offroaders.com/tech/gear-ratio-chart.htm

Dave

 

[J-Thompson]

It should be noted for the sake of this site that the KJ
came stock with 29" tall tires and with the auto it had
3.73 gears 6 speeds came with 3.55's

 

[tommudd]

Plus just so some know its not the RPM you would see driving down the road in overdrive

 

[ridenby]

Very informative,Thanks Dave.

 

[tjkj2002]

A better site that will give you much more info.

http://www.4lo.com/

 

[Conorren]

It is important to have gears according to the type and size of the tiers. you can get different gears based on different types of tires as to improve the flexibility of your vehicle.

 

[reflection]

how much does the gear ratio effect mpg in real life? (not theory) can anyone give an example?

thanks

caner

 

[tommudd]

how much does the gear ratio effect mpg in real life? (not theory) can anyone give an example?

thanks

caner

Installed 265-75-16s on mine after running 245-75s and 265-70s for quite q while
after installing them had to wait a week before I could regear
HATED driving the KJ, couldn't use over drive if I did mileage was 15 or so overall down from 20-21.
After regear went back up to 20-21 average with highs of 23 on long trips, could use over drive like it was stock. Around town way more fun light to light
Best single thing besides getting rid of the crappy suspension there is

 

[twowings]

Mileage is a function of RPM, not speed...so spinning the engine faster at any given speed is going to use more fuel and vice-versa...

 

[tommudd]

Mileage is a function of RPM, not speed...so spinning the engine faster at any given speed is going to use more fuel and vice-versa...

:shrug:
Depends on how you look at that
Given we are talking about Jeeps and installing taller tires etc then above could be taken the wrong way
For example with a fully loaded trailer in tow, using OD mine gets about 14-15, kick off the over drive which lets the RPMs go up and I now get 17-18

 

[twowings]

I agree...I should have added the caveat "as long as the engine is in its natural powerband"...
otherwise all bets are off...:gr_grin:

 

[Jbergun]

I got a question what if i put 4.10 gears in there with my stock sized 235-70-16 general grabber at2

 

[tommudd]

I got a question what if i put 4.10 gears in there with my stock sized 235-70-16 general grabber at2

Fun at the stop lights!

 

[Jbergun]

Fun at the stop lights!

Why is that better acceleration? cause i wouldnt mind that and for the cost its not outrageous

 

[Jbergun]

Fun at the stop lights!

I just dont understand it

 

[twowings]

I just dont understand it

Do you have access to a multi-speed bicycle? Accelerate from a dead stop to a quick pace and note the effort expended...now change gears to engage a larger-diameter gear on the rear wheel and perform the same test...notice the difference in effort and time-to-speed?

That's the miracle of gear ratios....:gr_grin:

 

[Jbergun]

Thank you for the analogy as i have experienced this first hand so my current gears is which i would be willing to do this now if i wouldnt lose alot of mpgs as sure as i wouldnt hurt my engine or trans i want a lift one day when i need new tires probably a year or two from now but can i do this now what will be the pros and cons

 

[twowings]

Well, once you regear and move the engine out of its powerband, then you've wasted your money and time...every engine has a rev range where it makes power (torque)...the factory engineers calculated the gear ratio that would give you the best compromise of power, economy, drivability (very important!), and reliability (VERY important!)...this calculation included tire size....if you study a gear ratio chart that lists speed and rpms at a given speed (say, 65 mph), you will see how different gear ratios in the differentials affect engine speed...old-time work trucks like pickups and farm trucks had gearing that let the engine make power at lower speeds which makes sense when you consider the kinds of work they were tasked with: heavy loads, bad roads, bad weather, etc...if you take one of those trucks on the highway, you would be hard-pressed to exceed 50 mph because of the very 'tall' gearing (like 4.88-5.13:1 or even higher) which had the engine screaming at high rpms at that speed...now let's look at race cars (not dragsters...they need higher ratios for quick acceleration)....they need very high speeds and have the luxury of great distances to reach high speeds...a race car is very hard to get rolling from a dead stop (lke a multi-geared bicycle in the highest gear) because their gear ratios are 'short' to enable taking advantage of high rpms (where race engines are tuned to make power) but once you get them rolling they are wicked fast...but their engines are tempermental (comparatively) to your street car and not suited for everyday driving, starting in all temperatures, conserving fuel, etc...all the things your street car does relatively well....you can modify your Jeep to your liking with bigger tires and higher gear ratios and all the toys we like to have but you have to make modifications in concert because changing one thing may cause needed changes in other areas...and you can reach a point where you don't really want to drive it every day because it no longer is suited to the street while being lots of fun on the trail....sorry for the long post....HTH

 

[Jbergun]

Well, once you regear and move the engine out of its powerband, then you've wasted your money and time...every engine has a rev range where it makes power (torque)...the factory engineers calculated the gear ratio that would give you the best compromise of power, economy, drivability (very important!), and reliability (VERY important!)...this calculation included tire size....if you study a gear ratio chart that lists speed and rpms at a given speed (say, 65 mph), you will see how different gear ratios in the differentials affect engine speed...old-time work trucks like pickups and farm trucks had gearing that let the engine make power at lower speeds which makes sense when you consider the kinds of work they were tasked with: heavy loads, bad roads, bad weather, etc...if you take one of those trucks on the highway, you would be hard-pressed to exceed 50 mph because of the very 'tall' gearing (like 4.88-5.13:1 or even higher) which had the engine screaming at high rpms at that speed...now let's look at race cars (not dragsters...they need higher ratios for quick acceleration)....they need very high speeds and have the luxury of great distances to reach high speeds...a race car is very hard to get rolling from a dead stop (lke a multi-geared bicycle in the highest gear) because their gear ratios are 'short' to enable taking advantage of high rpms (where race engines are tuned to make power) but once you get them rolling they are wicked fast...but their engines are tempermental (comparatively) to your street car and not suited for everyday driving, starting in all temperatures, conserving fuel, etc...all the things your street car does relatively well....you can modify your Jeep to your liking with bigger tires and higher gear ratios and all the toys we like to have but you have to make modifications in concert because changing one thing may cause needed changes in other areas...and you can reach a point where you don't really want to drive it every day because it no longer is suited to the street while being lots of fun on the trail....sorry for the long post....HTH

Never be sorry for providing someone with information thank you for taking the time to explain it in words i understand now i get it she is my daily driver for now one day she might be my toy but thanks again for helping me wrap my mind around that

 

[YP047]

So is it better to push the Over drive button in every time you highway drive or pushing it in (on an Automatic) does that shut it off?..my 02 seems to have a stall/flat spot if you stomp on the Gas..anyone else?Thanks