Gear Ratio MPH

1985 - Present, Questions, discussions, regarding anything related to the Humvee. (NO AUCTION or EBAY)

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Re: Gear Ratio MPH

Post by Retired War Horses » Fri Mar 23, 2018 7:48 am

Why do people buy these trucks and then attempt to make them drive like an F150.
Mr.Carrol I don’t know you, but why would you buy an M1123 HMMWV “high maintenance money wasting vehicle”to be a daily driver? And at the same time attempt to save money?
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Re: Gear Ratio MPH

Post by dilvoy » Fri Mar 23, 2018 10:08 am

johncarrol wrote:
Fri Mar 23, 2018 4:46 am
I did not state or imply I was looking for or happy with a 50RPM drop from what I have now. Running down the road at 1900RPM at 55MPH is not a 50RPM drop from 2175RPM.
OH, I misread your post. You might try talking to people who have Hummers, because I think they used the 2.56 gear ratio for some years along with the 4L80E. I don't know of any Humvees that used that ratio from the factory with the four speed trans.
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Re: Gear Ratio MPH

Post by Retired War Horses » Fri Mar 23, 2018 10:36 am

Your correct George, H1 used 2:56 for better top end, later they went to 2:73
The military used 2:73 on the A2 on up till 3:08 on the heavy trucks to get them off the line better, because military trucks don’t need to do 80mph
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Re: Gear Ratio MPH

Post by johncarrol » Fri Mar 23, 2018 1:22 pm

First I'd like to apologize. I gave the wrong RPM I was running at 55MPH when I had my 4L80E in the drive gear. I checked it today, and it was 2850RPM instead of 2350RPM. Thanks so much to those of you hopefully in the future who are willing to help me out on this forum, and thanks so much to the ones who have already. you know who you are. I will try in the future to just ask a question, not explain why I am asking it. I only tried to explain my reason in the past on this website to avoid replies like "Why do you want to do that!" I started this post. it reads Gear Ratio MPH My main question and others I asked on this topic were answered. Thank you. I will answer the question "WHY"? In as few words I can because I can't type and I have other things to do. I was given and took the opportunity to purchase a vehicle that I was able to afford by selling my daily driven vehicle, that I was able to license and insure to replace my daily driven vehicle that is equipped with an engine and transmission that I have knowledge about as far as maintenance and repair. I've loved to tinker with vehicles all my life and while driving it the first time, I believed I could tame it down in so many ways without changing the way it looks, that it will be close to as much a pleasure for me to drive, even on a long trip, as any other vehicle. And be safer on public roads than the untouched military version of it. While at the same time, spending the least amount of money. Right now, I'm about 3/4 there, from what I have already had done and the help I get here. If anyone is interested, I have a very long list of things I have done that I have proven to myself, and will share and explain. Why does it seem that some people do not want me to succeed? Are there any other people members of this forum who like to save money and accomplish what they want with their HMMWV besides me?

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Re: Gear Ratio MPH

Post by Action » Fri Mar 23, 2018 2:10 pm

johncarrol wrote:
Fri Mar 23, 2018 1:22 pm
First I'd like to apologize. I gave the wrong RPM I was running at 55MPH when I had my 4L80E in the drive gear. I checked it today, and it was 2850RPM instead of 2350RPM. ........
What do you mean by "drive gear"? Is it just in D? You should have it on the D with a circle around it.

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Re: Gear Ratio MPH

Post by Hell On Wheels » Thu Jul 29, 2021 5:03 pm

This is a good read and answered my curiosity on gear ratio. It all depends on top end or bottom end ok I got it. I just own a hmmwv to have my military flash backs. If I can save money I will try so that I can spend more for my money pit vehicle. :D thanks for the good topic. I just changed out my 3 speed transmission to a 4 speed and during the process blew my rear diff 2.56 and replaced both front and rea with 2.73. Reading through this gives me an idea what I should expect. BTW I have one good take out 2.56 real cheap, 3 speed with transfer really cheap. Thought to mention. Always got to remember everyone has an opinion good or bad but never intended to hate. Its a military forum of military vehicles.

Did I miss it, What is the calculations for
37" Tires, 4L80e in 4th (Overdrive), 2.73:1 diffs, 242 TC in high
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Re: Gear Ratio MPH

Post by SinDiesel » Tue Aug 03, 2021 8:48 pm

I had to pull up that old calc as I haven't used it in years. Guess I'm just getting old and driving slower these days.

To answer your question: 37" Tires, 4L80e in 4th (Overdrive), 2.73:1 diffs, 242 TC in high (assuming convertor is locked):

1900 rpm = 52.9 mph
2000 rpm = 55.7 mph
2100 rpm = 58.4 mph
2200 rpm = 61.2 mph
2300 rpm = 64.0 mph
2400 rpm = 50.1 mph
2500 rpm = 69.6 mph
2600 rpm = 72.3 mph
2700 rpm = 75.1 mph
2800 rpm = 77.9 mph
2900 rpm = 80.7 mph
3000 rpm = 83.5 mph
3100 rpm = 86.3 mph
3200 rpm = 86.3 mph
3300 rpm = 91.8 mph
3400 rpm = 94.6 mph
3500 rpm = 97.4 mph

Hope this helps. I had also set up this calc to compare the 3L80, 4L80E, and a allison 6speed. The allison 6 speed has some nice ratio's, including a steeper 1st for acceleration & crawling.

gear 3L80 4L80E Allison_ 6spd
1 2.48 2.48 3.10
2 1.48 1.48 1.81
3 1.00 1.00 1.41
4 N/A .75 1.00
5 N/A N/A 0.71
6 N/A N/A 0.61

With an Allison 6 speed and similar criteria, 37" Tires, Allison in 6th (Overdrive), 2.73:1 diffs, 242 TC in high (assuming convertor is locked):
2046 rpm = 70 mph (which is cruising close to the 6.5 peak torque curve @ ≈ 1,800 rpm if I remember correctly.

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Re: Gear Ratio MPH

Post by Hell On Wheels » Wed Aug 04, 2021 5:50 am

Thanks for the information really great data
Robert

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