Trucks tested in drag racing

That said, Allison was keen to conduct several races between trucks fitted with its automatic transmissions and rigs with manual shifters during a recent demonstration event at Queensland’s Mt Cotton driving centre.

While there is no prize from tearing away from the traffic lights in every day driving, Allison wanted to illustrate how much time can be saved using a traditional automatic with a torque convertor as opposed to a human operated manual or a computer controlled automated manual (AMT).

Allison performed several drag runs during its demonstration and even threw open the opportunity to journalists to have a crack at beating the Allison equipped truck by driving a manual transmission rig.

We elected two of our most experienced and best-shifting journos (not me) and they were still beaten. The only ‘victory’ for the manual truck came when a Chinese trucking journalist forgot to put the Allison automatic in Drive.

Allison reckons the difference between an AMT and a full automatic from 0-100km/h can be 18 seconds. That sounds a bit much, but the demonstrations certainly did prove the point that full automatics shift faster.

Allison engineering chief, Steve Spurling explains that the torque convertor smoothes the shifts, maintaining power delivery during changes. “With a manual or an AMT, each time these shifts occur vehicle momentum is lost and must be regained.”

So what about the extra fuel used by an automatic? Allison insists the fuel consumption of trucks running its automatics is “competitive” with manuals and AMTs but doesn’t go so far as saying the consumption matches or is better than them.

However, Allison marketing man, Larry Love (yes, that’s his real name), puts it another way. He concedes a full automatic Allison might use more fuel for the distance travelled, but gets the job done quicker.  “Fuel economy is important, but fuel efficiency is really what we see as the most important,” Love says. “Fuel efficiency is the measure of work done per litre of fuel burned, or the ability to deliver a higher average speed per litre of fuel.”

Driver comfort is another factor and Allison says a full automatic is easier on the driver than a crash box manual and a synchromesh manual because the driver does a lot less work. This writer can also attest that it’s also a lot less stressful to use than a crash box (non-synchro) for those not overly experienced in the complex art of driving a RoadRanger style gearbox that requires perfect timing, finesse and the ability to remember which gear (out of 18) you’re in.

Allison has also introduced a range of safety features. For instance, one feature ensures the truck or bus will not move forward unintentionally when dropped into drive. The transmission simply doesn’t select drive until the service brake is applied.

If a driver puts the park brake on and leaves the transmission in drive, the gearbox computer decides to select neutral instead. The smooth changes of automatic transmissions are known to reduce stress on driveline components and tyres during take off and changes, eliminating potential jerkiness, but they can also do damage if mistreated.

One issue is when a driver moves back and forward, perhaps when doing a multi-point turn, selecting drive and reverse without actually bringing the vehicle to a stop.

An optional Allison feature means the change can’t be performed without the vehicle stopping, avoiding harsh loads on the driveshafts.

Other features include a torque peak reduction system to spread out power delivery, which is a handy way of keeping lead-foot bus drivers from scaring passengers and optional transmission retarders, which slow the acceleration of vehicles so the driver can avoid over-using the brakes.