change of the gear ratio

[Happy_Cloud]

Happy cloud. Welcome. It looks like English is not your first language so I will try to use simple words that a translation program will understand.

No one makes different gear ratios for the gears in the hubs. There are some gearing options where the gear teeth are angled (herring boned) for less noise and increased strength, but hub gears are always 1.92-1 ratio.

The only gear ratios you can easily and readily affect is the differential gearing, (unless you custom gear a transfer case or use transmissions of differing makes and gears such as Allison transmissions and Atlas transfer cases).

The easiest thing to do is purchase two sets of 2.56-1 gears for your front and rear differentials. You need to change front and rear crown gears and pinion gears with new gears of 2.56 ratio.

Hi Tobash, thank you for the welcome
Yes indeed you are right, english is not my first language. Here in Switzerland we usualy speak swiss german, raetoromansh, italian and french. But on my work as a mechanic for helicopter parts we speak more or less english because all the documents are in english and also most of my working colleagues are international.

Well i just wrote with springer1981 about the gear hubs with a different gear set (see conversation above)

Yes i understand the solution with 2.56 : 1 ratio differentials.

By the way: is there a formula or excel table to calculate the engine rpm - axle ratio - gear hubs ratio - vehicle speed? Because at the end i like to know how the engine rpm's are at a certain vehicle speed before i invest loads of money to change the ratios.

 

[Mogman]

Well that depends on what you start with, if you go from a 3.07 (turbo) to a 2.56 differential it would be somewhere around an 18% gain, to get to where you want to be it would take both a differential and a hub gear set change, quite allot of money, if the aftermarket gear sets are of the same quality as the factory ones the dependability would be the same.
I would highly suggest you borrow a HMMWV and drive it, you may realize it does not have enough power for what you think you want, I am under the impression Switzerland is not a flat country, even with the stock gearing they are miserable on hills.

 

[Mogman]

There are tons of calculators on the internet for tire/gear ratio calculations.

 

[springer1981]

Ok, interesting. So let's assume that this gear set really fits without modifications on the housing, would it be the better option to change the ratio there or better on the differential in terms of longevity?

I think it will come down to money however in your original post you said to assume you have a 6.5TD and 4L80. How fast are you trying to travel on the highway? I have 6.5 NA with a 4L80 with 2.73 differential. I can do 65 mph on the highway and wouldn't want to go any faster. In my opinion neither of the modifications are worth the costs and time involved.

 

[Mogman]

He specified 2000RPM@120KPH which is around 75MPH.
I have never owned a 4L80, certainly not my favorite transmission but even with 2.56 gears and a 6L80 which has a much higher top gear I am turning around 2300RPM@75MPH

 

[TOBASH]

You need to look up the specs on the transmission gears, transfer case gears, rear end gears and hub gears

If you have 2.56 diff gears and all hubs are 1.92, then you just need to google 4L80e transmission gears and then google the transfer case gears in your rig. Then factor in 37” diameter tires and you can make your own spread sheet.

As a helicopter mechanic, this should be well within your skill set.

 

[Coug]

I got bored so did a bunch of the math

so for engine at 2000 rpms, .75 overdrive and 37 inch tires, the below gearing will produce the listed speeds
2.56 gears is 60 mph (96.5 kph)
2.73 gears is 56mph (90 kph)
3.08 gears is 50 mph (80.5 kph)

Changing only the tires to 40 inch
2.56 gears is 65 mph (105 kph)
2.73 gears is 60 mph (96.5 kph)
3.08 gears is 54 mph (87 kph)



Changing to the 6l80 transmission with the 0.67 overdrive and 37 inch tires:
2.56 is 67mph (108 kph)
2.73 is 62mph (100 kph)
3.08 is 56mph (90 kph)

then increasing to 40 inch tires
2.56 gears is 72 mph (116 kph)
2.73 gears is 68 mph (109 kph)
3.08 gears is 60 mph (96.5 kph)




final gear ratio (ring/pinion and geared hub) (just included this for my reference as I was doing all the above math)
2.56 x 1.92 = 4.9152
2.73 x 1.92 = 5.2416
3.08 x 1.92 = 5.9136

basic thoughts:

Biggest benefit is changing from 3.07 to 2.56 gears. I've looked and can't find any gear ratio lower than 2.56, which is already pretty steep as most civilian applications of this differential use between 3.31 and 4.88 gearing. the HMMWV is the only application I can find for the 2.56, 2.73, and 3.08 gear sets.

you get about the same benefit for overdrive change to .67 from .75 as from going to 40" tires from 37" tires.

 

[Coug]

If you want to do a side by side comparison, this site does a pretty good job. Lets you play with lots of different numbers.
You can enter the geared hubs in either the transfer case or underdrive options on the form to give you accurate results without having to figure out the final ratio with hubs and pinion together.
It's meant more for extreme low ranges for rock crawlers and whatnot, but does all the speeds possible with all the ranges.

it does have an option at the top of the page for either SAE or Metric measurements.

Gear Ratio Calculator

 

[Happy_Cloud]

Well that depends on what you start with, if you go from a 3.07 (turbo) to a 2.56 differential it would be somewhere around an 18% gain, to get to where you want to be it would take both a differential and a hub gear set change, quite allot of money, if the aftermarket gear sets are of the same quality as the factory ones the dependability would be the same.
I would highly suggest you borrow a HMMWV and drive it, you may realize it does not have enough power for what you think you want, I am under the impression Switzerland is not a flat country, even with the stock gearing they are miserable on hills.

Ok thats an interesting input.

Yes you are right, Switzerland is located half in the alps (mountain chain) and the other half is flat with some smaller hills. But i live in the mountains where streets are usualy quite steep. So at the moment i'm driving with my previous big project i had the past 3 years. It's a Chevrolet K30 with a 4L80e and the 6.5l engine and a Banks sidewinder turbo. Boost is at 12 psi and it drives awesome in the mountains. The chevy is also 2.3 tons empty weight. So my next project, the hmmwv, should actualy drive similar because weight, engine and transmission are the same. But before i spend too much money i would like to plan a bit in advance.

 

[Happy_Cloud]

I think it will come down to money however in your original post you said to assume you have a 6.5TD and 4L80. How fast are you trying to travel on the highway? I have 6.5 NA with a 4L80 with 2.73 differential. I can do 65 mph on the highway and wouldn't want to go any faster. In my opinion neither of the modifications are worth the costs and time involved.

Well, here in Switzerland the max. speed on highways are 120 km/h. Therefore it would be cool to drive that speed in a range from 2000 - 2500 rpm's or so.

 

[Happy_Cloud]

He specified 2000RPM@120KPH which is around 75MPH.
I have never owned a 4L80, certainly not my favorite transmission but even with 2.56 gears and a 6L80 which has a much higher top gear I am turning around 2300RPM@75MPH

Interesting, that sounds good. I mean with 2300 rpm's @ 120 km/h i would be absolutely happy. (perhaps i should consider to put a 6L80 on the 6.5?)

 

[Happy_Cloud]

You need to look up the specs on the transmission gears, transfer case gears, rear end gears and hub gears

If you have 2.56 diff gears and all hubs are 1.92, then you just need to google 4L80e transmission gears and then google the transfer case gears in your rig. Then factor in 37” diameter tires and you can make your own spread sheet.

As a helicopter mechanic, this should be well within your skill set.

You got me. I admit that I'm a bit lazy at the moment and I don't have much time because I'm working a lot at the moment.

 

[Happy_Cloud]

I got bored so did a bunch of the math

so for engine at 2000 rpms, .75 overdrive and 37 inch tires, the below gearing will produce the listed speeds
2.56 gears is 60 mph (96.5 kph)
2.73 gears is 56mph (90 kph)
3.08 gears is 50 mph (80.5 kph)

Changing only the tires to 40 inch
2.56 gears is 65 mph (105 kph)
2.73 gears is 60 mph (96.5 kph)
3.08 gears is 54 mph (87 kph)



Changing to the 6l80 transmission with the 0.67 overdrive and 37 inch tires:
2.56 is 67mph (108 kph)
2.73 is 62mph (100 kph)
3.08 is 56mph (90 kph)

then increasing to 40 inch tires
2.56 gears is 72 mph (116 kph)
2.73 gears is 68 mph (109 kph)
3.08 gears is 60 mph (96.5 kph)




final gear ratio (ring/pinion and geared hub) (just included this for my reference as I was doing all the above math)
2.56 x 1.92 = 4.9152
2.73 x 1.92 = 5.2416
3.08 x 1.92 = 5.9136

basic thoughts:

Biggest benefit is changing from 3.07 to 2.56 gears. I've looked and can't find any gear ratio lower than 2.56, which is already pretty steep as most civilian applications of this differential use between 3.31 and 4.88 gearing. the HMMWV is the only application I can find for the 2.56, 2.73, and 3.08 gear sets.

you get about the same benefit for overdrive change to .67 from .75 as from going to 40" tires from 37" tires.

Wow! That's awesome. Good work! Great inputs.

 

[Mogman]

Interesting, that sounds good. I mean with 2300 rpm's @ 120 km/h i would be absolutely happy. (perhaps i should consider to put a 6L80 on the 6.5?)

Actually in my humble opinion you should try and borrow one first and see how it performs, as pointed out the difference between a 4L and a 6L is almost same as going to 40" tires, (the 6L has some distinct advantages) but tires are MUCH less work and money.
Besides you may want to spend some of that extra money trying to get it to run and ride decent first.

 

[Happy_Cloud]

If you want to do a side by side comparison, this site does a pretty good job. Lets you play with lots of different numbers.
You can enter the geared hubs in either the transfer case or underdrive options on the form to give you accurate results without having to figure out the final ratio with hubs and pinion together.
It's meant more for extreme low ranges for rock crawlers and whatnot, but does all the speeds possible with all the ranges.

it does have an option at the top of the page for either SAE or Metric measurements.

Gear Ratio Calculator

Cool. Thank you. I will try it on the weekend when i find some time.

 

[Happy_Cloud]

Actually in my humble opinion you should try and borrow one first and see how it performs, as pointed out the difference between a 4L and a 6L is almost same as going to 40" tires, (the 6L has some distinct advantages) but tires are MUCH less work and money.
Besides you may want to spend some of that extra money trying to get it to run and ride decent first.

Good input. Will think about it.

 

[AAVP7]

Sorry to chime in so late. Yes, Morlock Motors is indeed offering an alternative hub gear. I happened to be on their yard, when the prototype was ready, and since I´m admin of a large german HMMWV forum, they were so kind to offer me a test ride.

The Humvee with the changed ratio was a three-speed M998 with an 6.5 liter NA in softtop confuration, so comparatively lightweight. The ratio, as mentioned before, lowers engine rpm in all gears. However, such a "longer" ratio will also at the same rate reduce the torque available at the wheels .

Morlock couldn´t tell me the new hub ratio. We drove for about an hour over rural highways, and a few kilometers of Autobahn (in the very hilly Westerwald). The M998 topped out downhill with the speedometer needle straight down, but on that little even ground that was, the Humvee made perhaps 65-70 mph (indicated !). Reduction in rpm at that speed was noticeable, but as you all know, a Humvee ride at that speed feels like entering earth´s atmosphere with the space shuttle.
The drawback of the altered reduction was a marked sluggishness when accelerating in all gears.

I inquired about the production of the gears, who makes them, and from which material, but didn´t get an answer. Morlock is known to buy in China, so my personal guess is that the gears are made there. Since hub gears are very highly stressed, and even more so when you squeeze a smaller pinion gear into the same hub, the new gears would have to be made from superb materials, and somehow I´m sceptical whether Morlock would go that mile. A breaking pinion gear would probably freeze the hub and its wheel instantly, posing a real hazard on the road, so for me, I decided to pass on the offer. But that´s just my personal opinion.

 

[Retiredwarhorses]

Sorry to chime in so late. Yes, Morlock Motors is indeed offering an alternative hub gear. I happend to be on their yard, when the prototype was ready, and since I´m admin of a large german HMMWV forum, they were so kind to offer me a test ride.

The Humvee with the changed ratio was a three-speed M998 with an 6.5 liter NA in softtop confuration, so comparatively lightweight. The ratio, as mentioned before, lowers engine rpm in all gears. However, such a "longer" ratio will also at the same rate reduce the torque available at the wheels .

Morlock couldn´t tell me the new hub ratio. We drove for about an hour over rural highways, and a few kilometers of Autobahn (in the very hilly Westerwald). The M998 topped out downhill with the speedometer needle straight down, but on that little even ground that was, the Humvee made perhaps 65-70 mph (indicated !). Reduction in rpm at that speed was noticeable, but as you all know, a Humvee ride at that speed feels like entering earth´s atmosphere with the space shuttle.
The drawback of the altered reduction was a marked sluggishness when accelerating in all gears.

I inquired about the production of the gears, who makes them, and from which material, but didn´t get an answer. Morlock is known to buy in China, so my personal guess is that the gears are made there. Since hub gears are very highly stressed, and even more so when you squeeze a smaller pinion gear into the same hub, the new gears would have to be made from superb materials, and somehow I´m sceptical whether Morlock would go that mile. A breaking pinion gear would probably freeze the hub and its wheel instantly, posing a real hazard on the road, so for me, I decided to pass on the offer. But that´s just my personal opinion.

An M998 already has the best gear ratio of 2.56, making it even lower IMO would “as it appears you have found” make it a slug at low speeds. The absolute best thing for an m998 is a 4 speed transmission.

 

[Happy_Cloud]

Sorry to chime in so late. Yes, Morlock Motors is indeed offering an alternative hub gear. I happened to be on their yard, when the prototype was ready, and since I´m admin of a large german HMMWV forum, they were so kind to offer me a test ride.

The Humvee with the changed ratio was a three-speed M998 with an 6.5 liter NA in softtop confuration, so comparatively lightweight. The ratio, as mentioned before, lowers engine rpm in all gears. However, such a "longer" ratio will also at the same rate reduce the torque available at the wheels .

Morlock couldn´t tell me the new hub ratio. We drove for about an hour over rural highways, and a few kilometers of Autobahn (in the very hilly Westerwald). The M998 topped out downhill with the speedometer needle straight down, but on that little even ground that was, the Humvee made perhaps 65-70 mph (indicated !). Reduction in rpm at that speed was noticeable, but as you all know, a Humvee ride at that speed feels like entering earth´s atmosphere with the space shuttle.
The drawback of the altered reduction was a marked sluggishness when accelerating in all gears.

I inquired about the production of the gears, who makes them, and from which material, but didn´t get an answer. Morlock is known to buy in China, so my personal guess is that the gears are made there. Since hub gears are very highly stressed, and even more so when you squeeze a smaller pinion gear into the same hub, the new gears would have to be made from superb materials, and somehow I´m sceptical whether Morlock would go that mile. A breaking pinion gear would probably freeze the hub and its wheel instantly, posing a real hazard on the road, so for me, I decided to pass on the offer. But that´s just my personal opinion.

Ok cool, thats very interesting. Well, thats a special experience and also a huge luck that they offer you a test drive. So thank you to share that experience here. I was also one time on their yard, to buy 4 rims for my chevy K30. But i didn't had the luck for an offered test drive.

 

[AAVP7]

Ok cool, thats very interesting. Well, thats a special experience and also a huge luck that they offer you a test drive. So thank you to share that experience here. I was also one time on their yard, to buy 4 rims for my chevy K30. But i didn't had the luck for an offered test drive.

I guess I was just plain lucky. The boss wasn´t in town, and the employee wanted some fun instead of work, I guess . I think they mentioned that the Humvee was ready for delivery to a customer, so it was probably a one-time opportunity.