Autos vs Manual transmissions

+1. Left out the part about being able to shift while chain smoking, playing with phone, playing with self etc

 

Pulling a tanker with a auto sucks.
Especially when you have a product that weighs 12 pounds per gallon and you have 4000 gallons in a 6500 gallon trailer!

 

I run in a fleet of all Volvo I-shift 12 speeds running dedicated 150 mile runs loaded to 75-80k up and pulling empty back. Fleet has both midsize midroof sleepers and day cabs, oldest units are 2012. 405-435hp D13. Flat land all the way till we hit the rolling hills around Reading PA. We do have to contend with multiple traffic lights on 202. All this being said, I average 7.2 - 7.5 combined MPG on this 300-305 mile round trip. This is hand calculated MPG, not from the display. We have a few long term rentals that are Cascadias with 10 speed Eaton manual with unknown HP Detroits. I average 6.5-6.8 combined MPG on this set up. I agree with the other posters that mentioned the engine braking on the Volvos are superior to some other options. There are 5 settings (Off, Auto [engages w brake application], 1 [low], 2 [medium], 3 [high], D [3+forced downshift]). The trucks are the same specs that pull food grade tanks and do suck in the surge department. All in all, I feel that there are places that the autos and manuals have their place. I do part time drive for local farmers and an auto in the fields would be like teats on a boar hog. But as far as the fleet, it works well for the lanes they run.

 

Yes, everybody calculates fuel milage by 'hand' and we all show better fuel milage with an automatic.

If you reason this thing out, you know how stupid the claim that automatics get better fuel milage is. Most class 8 trucks spend 90-95% of their time in top gear not shifting gears. So 95% of the time, any efficiency that the automatic might have could not be realized; Automatics and manuals have the exact same efficiency in top gear.

For the other 5-10% of the time, when the truck is not in top gear, only a portion of that time could their be any difference in efficiency. And of all the fuel consuming inefficiencies in a truck, the transmission is a minutely small one.

Yet all these fools and lier's claim big efficiency gains with an automated manual. I read and hear 1,2,3 miles per gallon more with an automatic. 1mpg on a 6mpg truck 16% increase in efficiency. 3mpg is a 50% increase in overall truck efficiency! It is just not even possible that 16% of the fuel used in a truck is even used to turn the transmission.

The liars that sell these things say you can improve the MPG of a very poor driver by 5%. 5% of 6mpg is .3mpg. I think that is very optimistic conjecture. Really out of the realm of possibility when the transmission does not even consume that much energy (fuel) in the first place. But some drivers here are claiming much better then even the most optimistic salesmen. The only conclusion that justifies that: they are much worse drivers than anyone imagined.

 

I’d wager a good chunk of autos better fuel mileage is a result of other options ordered along with the trans that the older manual trucks don’t have. It’s a falacy

 

As I posted on another thread, the reason for automatics is that the majority of drivers and potential drivers cannot shift a manual transmission. And most have never even seen one in a car much less a truck.
It has nothing to do with performance, that's a salesman pitch.

 

We all know the reason for automatics. What I’m saying is, even with the same driver you can’t compare fuel mileage because in almost every case the trucks are specd different. Gear ratios, super singles, aero, oil weight......

 

We've had a dd12 auto for the last year and put just over 300,000 miles on it. It gets a tiny bit better fuel mileage than we got in a 10 speed manual, maybe 0.2 mpg.

I could kick the crap out of it city driving, can't compete at top speed though as it goes into "e-coast" on the slightest downhill dropping the rpms and oil pressure to nothing. That coasting is a nightmare driving mountains in winter, at our company I'm locked out of going into manual mode to keep it from coasting.

 

I think the only reason auto-shifts were introduced was to cut down on those with heavy right feet.

The funny thing is, put one of our Peterbilt 579's (aerocab) with the 435hp MX-13 and Auto 12 on a 100,000 lbs load heading west in Canada and it gets about 50-55 litres per 100 km (4.2-4.7 mpg). My truck, a Peterbilt 379 with 550 hp CAT and 18-speed Eaton, gets 45-55 (4.7-5.2) on the same load in the same region.

 

I think your math is off...
Is 55 l/100km = 4.2 or 4.7 in your book...

Also not really a fair comparison seeing as one has emissions other does not.