Please register to participate in our discussions with 2 million other members - it's free and quick! Some forums can only be seen by registered members. After you create your account, you'll be able to customize options and access all our 15,000 new posts/day with fewer ads.
Location: We_tside PNW (Columbia Gorge) / CO / SA TX / Thailand
34,690 posts, read 57,994,855 times
Reputation: 46171
a lot of Semi trucks do have automatics, or the new 'manual automatic' Shifts for you, but is just like a clutched manual, not a TC 'slippery' auto.
Trucks often need their trannies for SLOWING down / exhaust brakes, and for additional ranges for getting loads moving / inclines / driving conditions. Automatics can generate a LOT of heat under load / between gears / i.e. slipping. Trucks nor trannies do not like HEAT. Automatics the HUGE size required for trucks are HEAVY and could reduce cargo capacity AND reduce mileage / economy. Trucking is a VERY narrow profit business, don't complicate it! But yes... many OTR trucks and Firetrucks have automatics. Dump trucks, log trucks (offroad) are less likely to have automatic, but some do.
Buses are not LIGHT, but their cargo is pretty light considering a TRUCK / HEAVY... so ezr to make it up grades and frequent stops.
in a City Bus... Service life of a manual tranny, and a driver's left leg would be rough on budgets and bodies.
When HHV (Hydraulic Hybrids) make it into more trucks, automatics would be easier to integrate / benefit from that technology.
There are a wide range of auto shifting transmissions for heavy duty trucks that cover a wide range of technologies but passenger and luxury coaches are generally not as cost or weight sensitive as truck tractors are. Plus it would be difficult if not impossible to put a manual gearbox into a coach that has the powertrain sitting in the back far away from the driver's seat. In a truck tractor the shift lever comes straight out of the top of the transmission through the floor of the cab. Manual gearboxes are simpler and cheaper and considered more reliable than auto shifting units, although that is changing.
If buses like greyhounds amd double deckers and city buses can have automatics why not semi trucks?
For one, automatics are better for passenger comfort. For another, the load variance is a lot narrower for a bus versus a semi tractor whose load can vary by more than a hundred thousand pounds so you need more gears and more control over which gears are selected when, depending on load and conditions. But as others have said, modern semi tractors are often equipped with manu-matics that take the clutch pedal out of the equation.
To add to this, I believe a lot of truckers, especially the ones that have been doing it a while prefer manuals and won't buy/drive an automatic.
And conversely, many of those recruited to drive urban and school buses grew up in environments where manual transmissions were not as readily encountered.
The maximum weight of a fully loaded passenger bus is about 30,000 lbs. A semi with a fully loaded 40' trailer can be up to 80,000 lbs, almost 3 times the weight. As such, the gearing needs to be very short to get that weight moving. A typical semi transmission has 10 gears, new ones have 18 gears and even higher. I don't think any automatics even exist with that many gears.
Back into the 60's, all or nearly all buses and trucks had manuals. The school buses I rode on were all manuals.
To answer the original question, most 18-wheel trucks spend a good bit of time on the highway, where you get into a gear and stay there. So the driver of a manual is not working any harder than if the truck was automatic, and not wearing the clutch. Most city buses operate in, well, an urban environment with a lot of stop and go. I think Greyhound and Trailways buses were manuals for a while after most city buses had gone to automatics. In those days an automatic would use more fuel, with locking torque converters and etc. this is not true anymore.
Location: We_tside PNW (Columbia Gorge) / CO / SA TX / Thailand
34,690 posts, read 57,994,855 times
Reputation: 46171
(automatic transmission truck... centric discussion, not to be inferred as divisive) Women are excellent candidates for HD truck drivers, they CAN be very skilled at shifting and 'leading' a HD truck through it's complex course. School Bus drivers, and handicap bus / van drivers are often women, due to their more perceptive attitudes toward clients. BUT... I find them to be easier on my equipment and less apt to STRETCH the performance capability of commercial vehicles. Men and women can each contribute unique value as drivers. I use both. (where they each shine)
FYI for future: HHV (automatic tranny adaptable) (too bad we (USA) have used CHEAP (under market price) fuel to AVOID a comprehensive energy policy / alternate technology developments. This could seriously benefit our engineering / economy / manufacturing / contribution to technology / environment.. too bad politicians allocate efficiency / intellectual manufacturing growth in USA), or... we could be sequestered to 3rd / 10th - 50th place in alternative energy technology and implementation.
been about 10 yrs since the 're-emphasis on HHV's', but for HD vehicles and trains (less sensitive to the additional weight, and already equipped with HYD and easy to convert). Garbage trucks are ideal candidates, as are metro buses (usually running under cargo capacity and frequent need for regen braking). Australia was leading the last research I saw.
The main difference between hydraulic hybrids and electric hybrids is that hydraulic hybrids recover a vehicle's kinetic energy during braking and decelerating significantly more efficiently than electric systems; hydraulic hybrids are able to capture and reuse 70%-80% of the vehicle's braking energy compared to 25% for electric hybrids. For trucks and buses, hydraulic systems can also be less expensive than electric systems
I have considered a few HHV applications to my econo diesel cars to push them over 75 mpg, but... not as simple on a manual tranny 'light weight' automobile, and I can't get an automatic tranny LOW HP diesel car to get within 20% economy of a manual tranny econo car. In fact my 4spds are more economical than my 5 spds, so these are VERY sensitive to acceleration / weight / friction drag. My MACK truck OTOH... would LOVE to host a HHV system!, a few thousand # is of little concern to it.
Last edited by StealthRabbit; 10-31-2016 at 03:44 PM..
Please register to post and access all features of our very popular forum. It is free and quick. Over $68,000 in prizes has already been given out to active posters on our forum. Additional giveaways are planned.
Detailed information about all U.S. cities, counties, and zip codes on our site: City-data.com.
Please register to participate in our discussions with 2 million other members - it's free and quick! Some forums can only be seen by registered members. After you create your account, you'll be able to customize options and access all our 15,000 new posts/day with fewer ads.
