Why do you Cummins guys want more gears

4x4ord wrote:

ShinerBock wrote:
Same reason why 18 speeds are better than 10 speeds in class 7-8 trucks. More gears give you more opportunities to be at the right rpm for power/efficiency at different driving speeds. When towing really heavy in a 10-speed semi going up hills, you are more limited on your speed because the large step down to the next gear may not put you in high enough rpm to make enough horsepower. In the same truck/engine towing heavy in an 18-speed, you are less limited since you have more gear options making the step to the next gear much less and therefore putting you at a better rpm to make enough horsepower for higher driving speeds.

It is just like the 6-speed F350 versus the 10-speed F350. Towing heavy up a hill with a 3.55 F350 6-speed, you may be limited to 55 mph in 3rd at 2,800 rpm because up shifting to 4th would put you down to 2,000 rpm where you are making much less horsepower. It may be too much of a step in this scenario and you start to lose speed every time you shift to 4th. Therefore you are limited to around 55-60 mph.

In the 10-speed, 5th gear is close to 3rd in the 6-speed and 7th gear is close to 4th in the 6-speed. This means that 6th in the 10-speed is right in the middle so instead of dropping 700 rpm in the 6-speed, you only drop 300 rpm in the 10-speed which puts at a higher rpm to make more power and are not as limited to certain speeds as you are with fewer gears.

It can be nice having more gears. With the Duramax what your aying is a big deal. The Cummins has a pretty flat power curve so bumping the rpm up is not going to buy you as much. Most RVers who tow, say a 16000 lb fiver, will seldom hit a hill that will pull them down below 60 mph which is 2350 rpm in 4th gear with 3.73 gears. But for the one or two times a year they hit an 8% grade they will spend a moment or two with the engine running between 2350 and 2150 before the transmission drops from 4th to 3rd. At 2150 the Cummins makes about 401 HP and at 2350 it can produce about 414 HP. So having a gear 1/2 way between 3rd and 4th would allow the engine to run in the range of 413 to 420 as compared to 401 to 420.... it does buy you something on the odd hill.

There is some things I like about the 10 speed. In my Ford with 3.31 final and 1st gear at 4.62 my truck can put more torque to the rear axle in 1st gear than could a 2019 F450 with 4.30 gears. So getting going from a stop is incredibly easy. On the top end of the scale I like having the ability to lock out 1 or 2 over drive gears depending on what I am towing. If I'm bucking a wind I might lock out 10th; windy and hills I can lock out 10th and 9th. With the 6 speed there were times you didn't know whether to lock out 6th or not.

True, while most will never tow enough to warrant needing an 8 or 10 with a Cummins, apparently Ike times matter to many who decide on which is the best truck based on the times in those tests. I will also add that I have a ZF 8HP in my diesel car and I love it. It is not a slush box like both 6-speed transmissions are in the Ram and it is lighting quick on its shifts. I have never pulled anything to need 8 or 10 gears especially with the truck being tuned, but I would still like to have it over the current 6-speed slush box options.