An unusual approach, perhaps, but it does have its merits. Not only does this save Mazda the cost of designing and installing a belt alternator/starter system, it also improves the response time for restart. According to the company, i-Stop can restart the engine in under four-tenths of a second, roughly half that of conventional belt-alternator-starter systems.
The Art of Start/Stop
On paper, triggering i-Stop to shut off the engine should have been as simple as coming to a halt, but the system is occasionally fickle in the real world. Mazda notes certain conditions, including low engine temperatures or high accessory loads (i.e. running the air conditioning at its highest settings) will preempt engine shutdown, but even in best-case scenarios, i-Stop exhibits a few quirks.
To prevent shutting the engine down during short or rolling stops, engineers have tuned i-Stop to activate once the car has come to a complete stop. As a result, drivers will need to be resting for quite some time with a steady, firm foot on the brake pedal. I-Stop's quick start-up is a boon when trying to drive in aggressive, fast-moving traffic patterns, but its tuning is a bit too aggressive. Any movement on the brake pedal, including wiggling a big toe, tricks the computer into thinking the driver is ready to go and fires the engine up once again.
Mazda claims the i-Stop system can increase fuel economy by up to ten percent, but such sizable improvements will only be noted if the car is extensively driven in stop-and-go traffic. In highway cycles or commutes with infrequent stops, including the route we put the Mazda3 through over the course of a weekend, i-Stop fails to return any notable fuel economy averages.