This may be an ignorant question, but I'm curious.

Does driving at the same speed in a higher gear always mean better MPG (just less power)? So say for example I'm driving down a road with cruise control set at 45 MPH. The manual suggests I shift at 46 MPH, so according to that I should be in 5th gear. If I do shift into 6th gear, will I get a little better MPG at the cost of power? Or say I'm going 35 MPH in 4th gear. Would shifting to 5th or even 6th get me a little more MPG? Would going up or down a hill affect this?

 

oh no.... oh nooo.... noooooooo.....

okae, enough of that, umm, actually, yeah it'll save you a little more gas due to your engine running at a lower rpm. lower rpm's are your friend for daily commuting

 

If you are just cruising, drive in the highest gear that you can for economy. You can easily drive an RX-8 around all day in 6th gear from as little as 35 mph.

 

so kind, so gentle...

i walked away from this hours ago..... ^^^^ are saints.

beers

 

Thanks

 

doesn't driving in low rpm cause carbon build up?

 

Actually, depending on the BSFC curve there can thereotically be a situation where you can get better economy in a lower gear. I can't tell you when that is for the RX-8, or even if it exists, but it is thereotically possible.

 

You don't want to bog down the engine. Personally, I've noticed it doesn't matter if I cruise at 2000 or 2500 or 3000 RPMs in city driving, the variance in gas mileage isn't that much. And look at highway mileage, your RPMs are usually at 3200-3500 RPMs and gas mileage is higher. Of course, you're not shifting or accelerating as much on the highway, but the point is that RPMs don't have a profound effect when city cruising in 4th/5th/6th, at least in my 8.

Meh, I just shift at 9200.

 

Your economy on the highway is higher because you never stop and loose that energy to heat in your brakes. It has nothing to do with the RPM of the engine.

And why don't you want to "bog down" the engine? At what RPM does this occur, and why is it bad?

 

-Easiest Rule of thumb:
Keep you revs over 2000 rpm

-Not so easy version :
If you are accelerating try to keep it over 2000 rpm
If you are maintaining the same speed 1500 rpm is ok maybe even lower
Under 1000 rpm is not a good idea,

If you are engine breaking or breaking then it doesn't matter.

-Once you are used to the car
2000 accelerating
1700 short dips before climbing above or gentle acceleration
1300 maintain speed

Note: I'm also a noob (have had car for 2 months or so) so if anyone counter says what I say, take their opinion.