I've been driving manual transmissions for 40 years. My wife and I currently have a 2016 Mazda3 with SkyActiv technology. They put a 6mt in the car...and it's ridiculous. For one thing, a 6-speed gearbox is only necessary for a supercar with top speeds over 170-180, and secondly, the gearing isn't designed properly. 3rd is too close to 2nd, and mostly useless. The final drive ratio in 6th is fine, but what would be most useful is to eliminate 3rd, and move 4th and 5th somewhere lower than the points where they are now.

The only reason for the current popularity in 6mt gearboxes is purely a marketing thing.

After driving the car for a year, I've learned that most of the time, accelerating to a point between 45 and 55 at a comfortable, fuel-efficient rate goes like this: 1-2-4-6. If I'm accelerating to highway speeds more quickly, then: 1-2-3-6. Every time I shift like this I find it annoying!

If you're driving in a 30-35 zone without your foot in it, just basically idling along, I wouldn't recommend anything higher than 5th. You're not going to hurt the engine without any engine load, and you're not going to be driving far enough to start carboning issues. At that speed, the difference in fuel economy between 4th and 5th would be negligible. In a 30mph zone I'm in 4th, and 35mph is generally where I move into 5th. I realize this is meaningless without RPMs, but you get the idea. There isn't that much difference in gearing ratios from the Mazda3 and the Z.

The Mazda3 is designed for fuel economy, and I've learned how to tweak the accelerator to squeeze out better mileage than the 5-door version is rated for, by watching the mpg computer. (I don't rely on the computer for final tallies, however.) Even though the Z is a completely different animal, the same principles apply.

My two cents...

I generally try to keep it no lower than ~1300 rpm unless slowing down. Even then, if I'm too lazy to shift, I'll accelerate very slowly (~5% throttle if that). Here in chicago it's all flatland so very easy to get away with this. Around 2K rpm is when I start to be more assertive with the throttle. No flooring until closer to 3K or higher.

Putting around town at any thing over 35 is usually 5th gear. 45+ is 6th gear. For reasons unknown, this car (370z/g37 6mt) is geared very short. 6Th gear is really more like a 5th gear. At 60 mph, engine is turning around 2500 rpm. Should be more like 1800-2K rpm. A 7th cog would be welcome.

I've done the 1st to 6th shift before :eekdance:

But seriously though, it's stupid to go that slow in 6th gear - it's an overdrive gear for higher speeds. You're getting worse gas trying to accelerate from 35 mph in 6th gear than if you were in 3rd or 4th gear.

I'll also point out that my Fast Intentions exhaust is deeper and louder when you bog the car with throttle at low RPMs. I've found the perfect RPMs for stealth is right around 3000 in the appropriate gear for your speed with just enough throttle to maintain speed on level ground. Plus much closer to the power band than 1500 RPMs :rolleyes: