tkjode

iTrader: (1)

Always use the highest gear that makes sense for cruising. Keep those RPMs as low as possible and you see some decent gas savings. Any city road moving at a normal pace you should be able to cruise just fine in 5th gear.

Some people tried to convince me of some nonsense that running 4th gear @ 3000RPM in the city is more fuel efficient than running 5th gear @ 2100 RPM or so. They made some point that the torque curve of the engine is lower, thus more fuel to maintain speed blah blah blah. I decided to see if it was nonsense or not and plugged my OBD-II diag tool in and did some data logging. My injector duty cycle was MAYBE 2-3% higher on average in 5th gear than 4th to maintain an identical cruising speed.... but the RPM difference is much bigger than that. So, less fuel burned per revolution, but almost 30% more revolutions per second, so more fuel burned in a lower gear.

BlitzSix

Personally I say that's a little hardcore. There is no way in hell I would put it in 5th when I'm doing 40. In the city you're rarely going a steady speed for an extended period, so that's way too unreasonable. If you're cruising 70-80 though I would put it in 5th, but it depends like always on traffic, the grade of the road, etc..

MPR

If you're doing a steady 40kph (not accelerating, very little or no load on the engine) you will burn more fuel in 4th than in 5th. It's when you try to accelerate in 5th (with more than 25% throttle or so) at 40kph that you will burn more fuel because the engine is not operating near it's optimal torque range.

Honestly it's your own discretion. If you're going slightly up hill, or its a short distance to when you will need to accelerate, then by all means keep it in 4th.