Tri Axle loads and gear ratio

Trucks with as low as 2.26 run city work all the time, I have 2.74 with an 18spd and run mostly highway and get stuck in stop and go and all the other bs all the time. the trade off to going to 2.74 is I have to use my low gear to take off in when loaded, it handles grades fine and have pulled to 90,000 just fine, but you have to use low gear taking off with that much weight. And yes I have used it in off road situations and end dump work with this setup and it is fine. For whatever reason people can't wrap there head around the low gear ratio but its the same people that never use there low gear and can't wrap there mind around the fact that you rarely use od (17th and 18th gear on a 18 spd manual) On the highway unless I am empty or really light I am rarely in od. On the plus side I get way better fuel mileage and it pulls at highway speed ten times better in direct gear then any truck ever will in od. Its simple math the parasitic drag of your deep over drive gear (usually .72 on most manuals) far outweighs the parasitic drag on your lower gears in the rear ends of your truck, the low gears in your rear ends cause around 2% more parasitic drag while overdrive causes up to 25% parasitic drag, In other words you are way better off with low gears and staying in direct, which for me my direct gear at 70 mph puts me at around 1475 rpm's and right in the start of the good power band for my motor. The big downside is you have to be careful off road and especially taking off heavy off road. The good side is I get better fuel mileage and on the highway it drives ten times better and is easier on the truck, so for what I do for 90% of my work I will take the low gears every time.

 

The high ratio differential carriers are off set more where the ring bolts on. This is because the higher the ratio the more pinion teeth which makes the pinion itself larger diameter. Now the more you move that ring from center the more side load you’re applying. (None except the Mack bull gear type are in center) also the higher the ratio the more it takes to start it rolling. Once rolling those numbers drop drastically now with the right transmission yes 1st gear is stupid reduction which I’m a fan of. That helps you get it started without noticing the power applied to it. Where the rubber meets the road is the one spot you can’t change. The more torque multiplication it takes the harder on drivelines and differentials it will be. As a rule an OTR truck doesn’t go through that process as often as a local multiple loads a day rig.

 

Years ago, when someone said they had 2:something ratios, they had 600hp Cat motors and went 110 mph across the desert. I agree on hard on driveline. If all you did was get on a ramp and go 100 mph, high gears would be fine, but in trucking, one never knows when a rough start, or stuck, or in traffic, or backing in a tough spot, all real possibilities, and you see those trucks jumping and hopping, that's why. I just don't think high ratios work.

 

You’re talking about old engines and transmissions and high ratios and the original post is asking about newer Volvos with an auto and a high ratio. Not exactly the same thing.

 

2.64 direct drive is almost exactly the same start ability and highway rpm as a 3.55 double over unit which was the most common ratio for decades even with tri axle loads . A direct drive transmission has a different set of gears than a overdrive unit so they are comparable. In 2000 my boss had one of each both with a 500 series 60 I was surprised one day when I read door tag showing rear end ratio because I thought both were 3.55 ratio . The lifetime mpg on the 2.64 unit was about 3/10ths better .

 

I think I would ask someone that does the work Im looking to do rather than people on the internet that do not.

Doing something once or what sales literature says does not qualify anyone as an expert in anything.


I stayed at a holiday inn express one time.

 

I guess you didn't read @wore out 's post explain'n in detail what the higher geared ratio's due as far as torque stress . Now I don't have a college degree in Mathematics or geometry. But I do know that basic math & geometry have not changed over the years
JMO but torque is still torque the same as it was 50 years ago.. and side load & surface area are still determined in the same manor as it was 50 years ago
The only difference between now & 50 years ago is the same goals are try'n to be reached with less
But I also know your 1 of them guys that belive just because its newer it gota be better