TEST bench results have a habit of surprising even the best prepared engineers.
And a comparison on paper, or even a sophisticated computer model, can miss the real-life performance of vehicles in service.
There's simply no substitute for in-field testing under practical work conditions. Particularly with trucks, where a failure is not just an inconvenience, but can break the bank.
The take-up rate of automated manual transmissions in Australia has been particularly strong.
Fleets are recognising the advantages of drivers keeping focused on road conditions and enjoying savings on clutch maintenance and replacement costs.
But there still remains some resistance to a full automatic, with additional cost usually cited as the reason.
Allison is the undisputed leader in truck automatics, and operators using the transmissions, even in the most rugged applications, commonly report zero downtime.
But one of the most compelling reasons for making a full automatic choice when ordering your next truck has been difficult to quantify.
It's easiest to recognise on a long hill under load, where a manual gearbox truck will lose momentum at every change, using additional fuel to get back up to speed again.
The impact on fuel is less so with an AMT, but even the best of them still have a delay on the change that costs more as the GCM increases.
Earlier this year a French company, STAF Transports decided to establish exactly how much revenue the company could save on choice of transmissions. It completed a comparison trial of automated manual and Allison fully automatic transmission-equipped Renault Premiums, conducted over a 12-month period.
The trial was designed to establish the fuel economy benefits of eliminating power loss during gear changing.
The company operates a fleet of more than 350 vehicles and supplies major supermarkets in Paris along with many other stores.
STAF started introducing Allison transmissions to the fleet in 2008 as part of its plan to renew the distribution fleet, specifically Allison's 3000 Series in its 19-tonne Renaults. There are now 20 trucks on the fleet equipped with the transmission.
Between June 2009 and 2010, the Allison equipped vehicles were operated alongside identical Renaults fitted with automated manual transmissions (AMTs).
Data on fuel consumption and productivity were collected electronically.
Because the specifications suggested that a torque converter was more efficient than a clutch, the 370hp 11-litre engines used in the AMT equipped trucks were downgraded to seven-litre 320hp engines in the Allison-equipped trucks. The comparison tests on the daily duty cycles around Paris resulted in an average fuel consumption of 28l/100km for the Allison versus 36.4l/100km for the AMT, without sacrificing productivity or performance.
That's a whopping 23 per cent reduction in fuel consumption.
The weight saving of the lighter engine in the Allison-equipped vehicle contributed 16 per cent to the total fuel savings, while an additional seven per cent was achieved through Allison's optimisation package including Load Based Shift Scheduling (LBSS) technology.
Allison's LBSS automatically selects between economy and performance shift schedules based on the actual vehicle payload (which the transmission calculates from throttle, torque and gear ratio calculations), and route topography.
No longer does a driver have to select "Eco" mode after delivering a 20-30-tonne load.
The technology will adjust shift patterns to maximise the torque characteristics of the engine it is bolted to, at whatever weight the truck is running.
"The savings we have seen over the test period amount to an 8.5l/100 km fuel saving in favour of the Allison," says Kara Mendjel, CEO of STAF Transports. "The trucks that we have fitted with Allison automatics not only deliver better fuel economy when compared to trucks we have with automated manual transmissions, but maintain or even improve productivity when it comes to payload transported."
Manlio Alvaro, Allison's European marketing manager said: "Mating an Allison transmission to smaller, more affordable and economical engines can return better productivity while reducing emissions and lowering fuel costs."
Downsizing the engine spec of fleet replacement trucks is the next step in maximising the returns and savings available from automatic transmissions. Now there are some hard statistics based on real operations to back that argument up.