+ ISM DRIVING IMPRESSIONS
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• The ISM promises better driveability than the M11 that it replaces, and our first drive would suggest that it delivers that promise. We took a Seddon Atkinson Strata 4x2 tractive unit fitted with the 405E variant around the Midlands to see what it was made of.
The ISM shares Cummins' idle torque system with its predecessor, so you don't have to mash the throttle when pulling away (if you do you'll simply lose drive). But you get used to it soon enough. Once it's rolling the engine is certainly more responsive than before. It feels a little more free-revving and throttle response seems smoother—as if a sticky mechanical throttle linkage had been lubricated. Cummins carefully avoids claiming better fuel economy, but good drivers may find that they can eke a little more from the ISM.
The revised Road Relay display is bigger and clearer than before, with a brighter fluorescent screen and more information visible. Instant and average fuel consumption information is available as before, but the latest version promises more, including a system to compare driver performance with fleet standards.
There's another bonus: the ISM actually sounds better than the M11. Whereas the cur
rent engine has a flat, metallic rasp which is rather uninspiring, the ISM has a slightly fruitier, old-fashioned burble. Oddly enough, despite the extra electronics it sounds more like a traditional mechanically fuelled engine. Who would have thought that computer control changes and relatively minor mechanical revisions could change the sound, and character, of an engine so much?