change of the gear ratio

[Happy_Cloud]

Hello all,
if i would like to change the gear ratio, would it be wiser to change it on the 4 geared hubs or on the axle differential or both? Let's assume i have to do it on a M1165, year 2005, turbo diesel and 4L80e. Goal would be to drive the vehicle with low rpm on the highway.
Does someone has a formula or excel table to calculate the rpm - ratio - speed? I would like to know which ratio i need at a speed of 120 km/h @ 2000 rpm in 4th gear.

Is there the possibility to manufacture a gear set for axel diff. or geared hubs without major change on the chassis, breaks or whatever with the above mentioned wish ratio? Or is there already something existing?

The other question is: i searched the ratio specs. Unfortunately i didn't find all. Interesting would be the following infos:

As far i could find out:

GVWR (lb)​	Ratio: axle differential for HMMWV​	Ratio: axle differential for H1​	Ratio: geared hubs for HMMWV​	Ratio: geared hubs for H1​	overall gear ratio for HMMWV​	overall gear ratio for H1​
10'300 and 10'800​	2.56 : 1​	2.56 : 1​	1.92 : 1​	1.92 : 1​		5.24 : 1​
​	2.73 : 1​	2.73 : 1​		​
12'100​	3.08 : 1​	3.08 : 1​

Thank you very much for your help.

Greetings from Switzerland

Benjamin

 

[Mogman]

Welcome to the forum!!
There is only one ratio for the hubs that I know of.
you could swap out the 307s for 273s or 256s
That list looks completely wrong, HMMWVs do not have 4:1 hubs

 

[Coug]

I've never heard of any of the geared hubs in either HMMWV OR H1 being anything other than 1.92-1 ratio.
No way a 4-1 ratio gearset would fit in the hubs.

Also, the 2.56 geared trucks should be 7.7k or 10.3k GVWR, and the 2.73 trucks are 10.3k rated. I haven't heard of a 10.8k rated truck.

 

[Happy_Cloud]

I've never heard of any of the geared hubs in either HMMWV OR H1 being anything other than 1.92-1 ratio.
No way a 4-1 ratio gearset would fit in the hubs.

Also, the 2.56 geared trucks should be 7.7k or 10.3k GVWR, and the 2.73 trucks are 10.3k rated. I haven't heard of a 10.8k rated truck.

Hi Coug,
thanks for the answer.
Well, i had several sources where i found those infos. One of this sources is the Hummer H1 Service Manual. I also read somewhere (i don't remember where) that there is a company in Germany who sells a gear set for the geared hubs with a different ratio. But i don't remember the ratio.

 

[Happy_Cloud]

Welcome to the forum!!
There is only one ratio for the hubs that I know of.
you could swap out the 307s for 273s or 256s
That list looks completely wrong, HMMWVs do not have 4:1 hubs

Hello Mogman,
thank you for the welcome.
I'm afraid that 2.56 : 1 is not enough to drive it in low rpm's with higher speeds. The info from the 4.0 : 1 ratio i found here: https://www.flashoffroad.com/hmmwv/HummervsHMMWV.htm
Let's see if we can gather all the correct infos to complete the list above.

 

[springer1981]

Hi Coug,
thanks for the answer.
Well, i had several sources where i found those infos. One of this sources is the Hummer H1 Service Manual. I also read somewhere (i don't remember where) that there is a company in Germany who sells a gear set for the geared hubs with a different ratio. But i don't remember the ratio.

In your attached document it states 1.92:1 ratio for the geared hubs, I can only assume that is what you are talking about since I can't find anything else in that document that applies. If I am wrong please point it out.

 

[springer1981]

Hello Mogman,
thank you for the welcome.
I'm afraid that 2.56 : 1 is not enough to drive it in low rpm's with higher speeds. The info from the 4.0 : 1 ratio i found here: https://www.flashoffroad.com/hmmwv/HummervsHMMWV.htm
Let's see if we can gather all the correct infos to complete the list above.

I don't see anything about 4.0:1 ratio geared hubs anywhere in there but did find this " *Add 1.92 to get total drive ratio (from geared hubs) "

I also found this statement "Torque Sensing differentials (Torsen) 4.0:1 ratio" and that does not refer to the geared hubs but clearly states the Differential and specifically Torsen Differentials which is what the HMMWV and Hummer H1 have. Those are NOT geared hubs. Also I am not sure what they mean by "4.0:1 ratio" because the differentials are either 2.56, 3.73 or 3.07 ratios so that 4.0:1 doesn't make sense to me. See EDIT below, I understand now.

"TT4 equipped Hummers have Torsen 1.7:1 ratio differentials (others are the same as military)" Again, this refers to the Differentials and NOT the geared hubs. There is no 1.7:1 ratio Differentials that I am aware of. I don't know what they mean by that. Again see EDIT below.

In your original post you talk about Geared Hubs having 1.92, 1.7 and 4.0 ratios but in the documentation you provided none of it say geared hub but rather talks about the differentials. There is no differential in the geared hubs.

I have actually looked at making a different gear ratio for the geared hubs and after doing a bunch of measurement it would be very difficult to increase the size of the smaller gear in the space provided to obtain a smaller gear ratio such as 1.7 or 1.5 for example. Also I don't think you could increase the size of the larger gear to obtain a 4.0:1 ratio and I can see no reason to want to do that. at 1.92:1 it already has plenty of torque not to mention you could also switch the transfer case to low gear.

I have never heard of a geared hub ratio other than 1.92:1.

EDIT: Upon further research the TT4 ratios of 1.7 and 4.0 refer to the torque bias of the Torsen Diff. If I understand it correctly that has to do with how much difference between wheel rotation before the differential locks up applying power to the other wheel. I did find this tidbit of information ... "T1 bias ratio is 3.2 and the t2 is half of that or 1.6" and that those ratio's are only valid when the diff is new - at it get's broken in, the ratio's go down. ". This seems to have been down due to ABS and driving on the road causing the lower ratio to lock up (apply torque to the other wheel) too easily.

 

[Mogman]

Hello Mogman,
thank you for the welcome.
I'm afraid that 2.56 : 1 is not enough to drive it in low rpm's with higher speeds. The info from the 4.0 : 1 ratio i found here: https://www.flashoffroad.com/hmmwv/HummervsHMMWV.htm
Let's see if we can gather all the correct infos to complete the list above.

I am not sure what you mean, 2.56 will give the highest speed for the lowest RPM of any available combination, there is only one hub ratio and that is 1.92:1
Unless there is someone making custom gear sets which I would assume this community would know about. and as pointed out above there is not much room for anything different.

 

[Mogman]

No differential would ever be produced with a 4:1 ratio, if you do some looking you will never find a modern automotive differential with an even ratio.
That is because with a 4:1 ratio for example the same pinion tooth would only come into contact with the same 4 teeth on the ring gear, this would lead to uneven wear and cause the diff. to be noisy, they all have an odd ratios that way every tooth on the pinion contacts every tooth on the ring gear.
this applies to just about every high speed gear set out there including the hub gears.
EDIT, OK some things like an engine gear train gears have to have an even ratio because that is the only way they can work, one reason cam chains are so popular.

 

[patracy]

The only way you could even package a 4:1 reduction in a hub would be in a planetary setup. Which would kinda defeat the entire HMMWV setup for suspension.

 

[springer1981]

The only way you could even package a 4:1 reduction in a hub would be in a planetary setup. Which would kinda defeat the entire HMMWV setup for suspension.

Unless you replaced the large gear in the portal hub with the planetary then we could have an 8:1 ratio with a top speed near 12 mph. LOL

 

[Retiredwarhorses]

Geared hubs are 2:1 IIRC

 

[Mogman]

Geared hubs are 2:1 IIRC

13X25=1.923076923076923:1 as stated above unless necessary no competent engineer would design a high speed gear set for an even ratio.

 

[Happy_Cloud]

I don't see anything about 4.0:1 ratio geared hubs anywhere in there but did find this " *Add 1.92 to get total drive ratio (from geared hubs) "

I also found this statement "Torque Sensing differentials (Torsen) 4.0:1 ratio" and that does not refer to the geared hubs but clearly states the Differential and specifically Torsen Differentials which is what the HMMWV and Hummer H1 have. Those are NOT geared hubs. Also I am not sure what they mean by "4.0:1 ratio" because the differentials are either 2.56, 3.73 or 3.07 ratios so that 4.0:1 doesn't make sense to me. See EDIT below, I understand now.

Yes i saw exact this statement but read too fast and thought about geared hubs. My mistake, sorry about that!

"TT4 equipped Hummers have Torsen 1.7:1 ratio differentials (others are the same as military)" Again, this refers to the Differentials and NOT the geared hubs. There is no 1.7:1 ratio Differentials that I am aware of. I don't know what they mean by that. Again see EDIT below.

Yes i see my reading mistake. By the way: what is TT4?

In your original post you talk about Geared Hubs having 1.92, 1.7 and 4.0 ratios but in the documentation you provided none of it say geared hub but rather talks about the differentials. There is no differential in the geared hubs.

Thats because i read in several sources and somehow i made a chaos with the ratios.

I have actually looked at making a different gear ratio for the geared hubs and after doing a bunch of measurement it would be very difficult to increase the size of the smaller gear in the space provided to obtain a smaller gear ratio such as 1.7 or 1.5 for example. Also I don't think you could increase the size of the larger gear to obtain a 4.0:1 ratio and I can see no reason to want to do that. at 1.92:1 it already has plenty of torque not to mention you could also switch the transfer case to low gear.

Ok, interesting. I actualy found the website where they sell a hub gearset that has a 17% longer gear ratio.

BEISPIELFAHRZEUGE AM General Hummer H1 M998 HMMWV, 42.500,00 €

BEISPIELFAHRZEUGE Am Genaral Hummer H1 M998 HMMWV ab 42500€

shop.morlock-motors.de

I have never heard of a geared hub ratio other than 1.92:1.

I think you are right.

EDIT: Upon further research the TT4 ratios of 1.7 and 4.0 refer to the torque bias of the Torsen Diff. If I understand it correctly that has to do with how much difference between wheel rotation before the differential locks up applying power to the other wheel. I did find this tidbit of information ... "T1 bias ratio is 3.2 and the t2 is half of that or 1.6" and that those ratio's are only valid when the diff is new - at it get's broken in, the ratio's go down. ". This seems to have been down due to ABS and driving on the road causing the lower ratio to lock up (apply torque to the other wheel) too easily.

Interesting. I found some infos here:
torsen-vs-plated-limited-slip-differential

BTM with TT4-Equipped Hummers

 

[Happy_Cloud]

I am not sure what you mean, 2.56 will give the highest speed for the lowest RPM of any available combination, there is only one hub ratio and that is 1.92:1
Unless there is someone making custom gear sets which I would assume this community would know about. and as pointed out above there is not much room for anything different.

About a custom gear set i found something here: BEISPIELFAHRZEUGE-AM-General-Hummer-H1-M998-HMMWV

Ok, let's assume i would like to drive with the hmmwv on the highway 120 km/h @ 2000 rpm's in the 4th gear, what would be theoretical differential ratio by calculation?

 

[Happy_Cloud]

No differential would ever be produced with a 4:1 ratio, if you do some looking you will never find a modern automotive differential with an even ratio.
That is because with a 4:1 ratio for example the same pinion tooth would only come into contact with the same 4 teeth on the ring gear, this would lead to uneven wear and cause the diff. to be noisy, they all have an odd ratios that way every tooth on the pinion contacts every tooth on the ring gear.
this applies to just about every high speed gear set out there including the hub gears.
EDIT, OK some things like an engine gear train gears have to have an even ratio because that is the only way they can work, one reason cam chains are so popular.

Ok yes you are right, i understand. The 4:1 ratio was anyway a reading mistake by me. (see answer to "springer1981")

 

[Happy_Cloud]

Geared hubs are 2:1 IIRC

That menas with other words?

 

[TOBASH]

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.

 

[springer1981]

About a custom gear set i found something here: BEISPIELFAHRZEUGE-AM-General-Hummer-H1-M998-HMMWV

Ok, let's assume i would like to drive with the hmmwv on the highway 120 km/h @ 2000 rpm's in the 4th gear, what would be theoretical differential ratio by calculation?

Based on the claims on that page, to achieve 17% gain the hub gear ratio would be 1.6:1. Doing the math shows a 24 large and 15 tooth small would give a 1.6:1 ratio and a 17% increase in speed. The question is if it bolts in or requires modifications to the hubs to fit the larger 15 tooth gear. It is very doable. I tried to do exactly this but the cost to do one off gears was too much for me to continue. I'm guessing the company you found has a lot more money than me. And they are charging 3000 for a set.

 

[Happy_Cloud]

Based on the claims on that page, to achieve 17% gain the hub gear ratio would be 1.6:1. Doing the math shows a 24 large and 15 tooth small would give a 1.6:1 ratio and a 17% increase in speed. The question is if it bolts in or requires modifications to the hubs to fit the larger 15 tooth gear. It is very doable. I tried to do exactly this but the cost to do one off gears was too much for me to continue. I'm guessing the company you found has a lot more money than me. And they are charging 3000 for a set.

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?

Yeah, this company has indeed lots of money. They are also very famous here in europe because they got famous on TV with their junkyard of military vehicles. They got an own tv series called "steel buddies" on dmax. They are also quite funny because they are so chaotic and always swearing.

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In der finalen Staffel ✓suchen die „Steel Buddies“✓ in Serbien nach einem Helikopter, in Spanien bringt ein alter Kran die Mechanik-Experten✓ zur Verzweiflung und in den USA hat der Firmenboss von „Morlock Motors“✓ ein besonderes Flugzeug im Visier. Aber damit ist Michael Manousakis✓ noch am...

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