How do low gears lessen engine load?

[Gunfreak25]

Was wondering if anybody could explain how lower differential gears can lessen the load on engines and transmissions, effectively prolonging their life? Just curious is all.

 

[clinto]

Go get on a 10 speed bike.

Pedal for one mile, in first gear, at 20 mph

Wait, rest.

Now pedal for one mile, in tenth gear at 20 mph.

In this equation:

You = engine
10 speeds on bike = high and low gearing in vehicle

 

[hndrsonj]

Well 20 MPH in first might be a stretch, It makes it easier to run but the engine has to turn over faster. (remember lower gears are numerically higher)

 

[hndrsonj]

Another way to think is, when driving an old jeep; Start out in 1st then stop and start in 3rd. The jeep (and your clutch) will really bog down and struggle in 3rd.

 

[hoop]

It is just like some other things....Look for the sweet spot. Less wear and tear and gets the job done with ease.

 

[Ressoldier]

It is all about mechanical advantage, 4x4 enthusiasts do it all the time. There is a trade off at some point so you need to do the research. Basically you are dealing with % of load on the engine(how hard the engine has to work at a given RPM). Also remember that it takes Torque to get the vehicle moving and gears are torque multipliers. The main reason you would want to change gear ratios from factory is if you have done some of the following modifications, Larger heavier tires, lift or increased profile(putting higher in airstream increasing wind resistance/surface area), added a bunch of weight.

Will go with my 4 Runner since I can use first hand knowledge

Factory 4.10 gears 31" tires 3800lb vehicle 21mpg 2400rpm at 70mph
Now 4.10 gears 33" tires 4760lbs 4" lift increasing wind drag 15 mpg 2100rpm at 70pmh

What you notice is that even though my gears are the same and the RPM's are lower at freeway speeds the Load on my engine is much higher(has to work harder at a given RPM) which is evident by the lower MPG. Now if I re-gear to compensate for the additional weight of my larger tires, steel armor(bumpers, skids, rock sliders, roof rack) and increased surface area then I will reduce the strain on the drivetrain and regain mileage. However if I regear to low I will not be able to reach freeway speeds or will be turning to high an RPM and will loose mileage.

Another example is a pulley system or fulcrum. If you use one pulley you have made it easier to move an object but you add a second pulley and while making it even easier you are now having to use energy to move three times the distance. I think you get the idea from the examples.

 

[Gunfreak25]

That's all, great examples posted by everybody.

 

[bearboley]

I don't exactly agree with more engine rpms lessen engine wear. I think the multifuel spins to fast for its own good, too many harmonic vibrations that send things flying. Little motor made to move a big load. Every engine has its sweet spot or max torque at a certain rpm per its dyno results, you should aim to balance the torque curve peak to desired speed The duece loaded seems to like 35 to 40 miles per hr. If you have ever driven along a country road loaded with one you know what I mean. I don't think they where meant to even run 55. I think in todays world that those who collect and don't haul anything would be better off with a lot higher gear like a 4.56 ratio in a duece it would slow the motor down and work the turbo more I think the multi would like it better for cruisin. I like to think of it as a lever the long the lever the easier it is to move a load. Lowe gears=longer lever

 

[Gunfreak25]

The biggest issue is people using these trucks for things they were never intended to do. They were designed with 1 thing in mind. To move lots of weight over bad terrain at an average speed of 25mph. Plus, people forget that at that time there were still many unpaved roads across America where lower speeds were needed to keep dust down. If the designers of the M35 were alive today they'd probably have a hard time even fathoming how far we have come in diesel engine technology, let alone how many hard roads we have now.

Personally, I love the old school mentality of small engine and lots of gears. While not as effecient as todays technology it always got the job done and I think it's a testament to the way people did things back then.

With the above being said, I am making my M211 into a daily driver. Again, it falls down to intended purpose. It will see a maximum speed of 50mph and will rarely be used to haul heavy loads like it was designed to do. This will put me right in my engines powerband. I know people brag about putting in OD tranny's and turning the fuel up, but to me it just seems darn right stupid to push a 57 year old truck past it's design specifications, especially with a tire designed with 1920 technology.

Just my $02.

 

[bearboley]

I am gald you said it. I have always wanted to but never want to upset the heard. I don't think its smart too turn them up and put big tires in them and go fast. They are what there are and do a good job at it. i use mine for a farm truck it hauls fuel and tools and pumps up tires and pull stuck thing out. I like the 35mph speed my truck likes it to. I started driving a 1963 Chevy C60 when I was 16 it had a single master cly. system on it and you drove it like you did not have breaks even though it did but you never knew, and the hand brake is worthless. I hate to see people that have never drove anything bigger than a car get one of these trucks because they look cool. Its a military truck no more no less. With it comes great responsibilities. Insurance , operating cost , maintenance. These things are not toys and can kill in the wrong hands and when they do it makes it hard for guys like me that actully use them everyday. Sorry to get off subject and on a rant . I yeild the soapbox to the next guy

 

[swbradley1]

They were designed with 1 thing in mind. To move lots of weight over bad terrain at an average speed of 25mph.

Lots of weight over bad terrain at an avg speed of 25mph? I'd really like to see that.

Having been on bad terrain you are lucky to do 5mph, let alone with it fully loaded.

So ends another of my meaningless thoughts...........

 

[Flyingvan911]

Lots of weight over bad terrain at an avg speed of 25mph? I'd really like to see that.

You untie the load and at 25 mph it is a quick way to distibute it along the trail.

When it snows and I am in heavy, slow traffic I use low range. It lets the engine use the rpm instead of brute force to move the truck.

 

[Ressoldier]

I am gald you said it. I have always wanted to but never want to upset the heard. I don't think its smart too turn them up and put big tires in them and go fast. They are what there are and do a good job at it. i use mine for a farm truck it hauls fuel and tools and pumps up tires and pull stuck thing out. I like the 35mph speed my truck likes it to. I started driving a 1963 Chevy C60 when I was 16 it had a single master cly. system on it and you drove it like you did not have breaks even though it did but you never knew, and the hand brake is worthless. I hate to see people that have never drove anything bigger than a car get one of these trucks because they look cool. Its a military truck no more no less. With it comes great responsibilities. Insurance , operating cost , maintenance. These things are not toys and can kill in the wrong hands and when they do it makes it hard for guys like me that actully use them everyday. Sorry to get off subject and on a rant . I yeild the soapbox to the next guy

So based on this you feel that all vehicles are perfectly engineered and no need to find an improvement? Or that all vehicles are designed to meet everyones need or use and therefor no need to be modified to better meet ones needs or use? So the Jeep owner that puts a lift kit with larger tires, to go more remote or challenging places because it was designed with a certain level of capability is wrong? So that must also mean that Hot Rodders of the 30's-60's were idiotic because they wanted to go faster then the vehicle was designed to do. At least now we have technological advances that allow us to improve on a vehicle to make it suit our needs/ use better and in a safe manner. Those 30'-60's Hot rods and muscle cars can now have disc brakes, steering and suspension systems to make them safe. Just like the Deuce can have new gears, lockers and brake and steering systems to make them safe. If not then we wouldn't have the A1,A2,A3,A4,A5 versions of any vehicle. If the government is able to find room to improve a model is it not feasable for a MV hobbyist to find room for improvement as well? This is not to say that all modifications are done safely nor do I agree with all modifications but if done properly there is nothing wrong. While deployed I had to modify my vehicles to better meet the needs of the mission and safety of my soldiers. We added sheet steel(not armor, just scrap steel) to better protect our trucks and form a Gunners box in the back of my 923 Cargo trucks. We then had to turn up the boost to make up for weight and required driving. I also had to cut and move the smoke stacks since it was blowing in the face of the guys standing in the back of the "Gun Truck" and we had a few go down for Carbon Monoxide poison. In the end it is the user of the vehicle that ultimately determines how it is used and if there are modifications to make it better.

Rebutal Rant Off.

 

[bearboley]

Not at all, I have had my share of modified vehicles. But your comparing apples to oranges. In all reality Automotive companies spend million and millions on R&D and a Joe Blow of the street is not going to engineer anything better. Granted a jeep built to suit ones needs is fine with me I have one but its not engineered for anyone without Experience with this type of vehicle to drive. I am just saying its a tandem axle truck built to haul a relatively small load over rough terrain at slow speed. There is forces at play there that You or I can not fully understand, and If you make it go faster, ride higher, put on bigger tires it was not designed for that and not as safe as it once was that is just the facts. Keep in mind that the modified duece in the form of the A3 was a failure. Those guys in the 50's and 60's did there thing and it was great but the political climate was worlds apart from the way people act today. In this sue anybody over anything if I get in a wreck with my truck I better make **** sure the I got my sh*t together or they will flame me I'm just not willing to let that happen. I had a fellow hit my bumper with his mirror, I was stopped he was driving by me in the turning lane, the Osp called the Dot and they went over my duece with a fine toothed comb and there big question was Is it modified in any way he though my bumper was to high. Someone rear ends you without a rear bumper and your screwed Ever notice the ICC bumper on strait trucks? All im saying is have some sense and don't mess it up for all of us. Say you make your duece blow giant clouds of black smoke and your local law enforcement gets a hard on for MV's and starts writing tickets, well here I come minding my own business through your town and before I leave it lightens my billfold. Its just a uncomfortable slow underpowered truck if you wanna go fast and be comfortable buy a Petebilt

 

[Ressoldier]

Actually I can understand the forces at play large vehicles. I also have faith that most of the people that are taking the time to modify these trucks are educating themselves on them if not they woudnt be on this site seeking advice. I have been driving big trucks on and off-road for 22 years Military and 18 years with over 2 million miles civilian side. I can tell you that the ones pushing the black smoke are wasting their money as well. Black smoke is a sign of over fueling. Look at a Gale banks engineered system and you will find tons of HP and torque increase without any black smoke. I remember when they first came out with the M900 series cargo's. They ended up having a SOUM stating not to be operated over 35mph because the brake design was bad. Then they issued a MWO and did a retrofit with new brakes and was back to 55mph. You are 100% correct about being slow and uncomfortable but that doesnt mean we shouldnt try to come up with ways to make them more comfortable and a little better performance wise. The main thing is to realize the line between performance and safety and to maintain that balance.

In my first post I said not all modifications are safe and don't agree with all of them either. Anyone that is modifying their vehicle needs to research and educate themselves on all the ramifications of each modification. Yes sometimes those of us that do and are minding our business can get affected by someone elses actions but that is life.

 

[m16ty]

Higher RPMs cause more wear than lower RPMs. Just think about it, every time the engine makes a revolution there is some wear. The more times the crankshaft turns, the more wear.

You can go too far though and put too much strain on the engine. Like has been said above, you've got to find the sweet spot. Ideally, you want the vehicle at as low of RPMs as you can without straining the engine too much. There's always a tradeoff though because we are never driving in ideal conditions.