Gear Change MPG Affect

[pdexta]

I have a Kiwi MPG, I'll give that a try. Excellent suggestion.

[MetroMPG]

32 miles round trip, eh?

Well, going 70 instead of 80 would add less than 2 minutes to each leg of the commute. Whether that creates "unnessary drive time" is your call. Slowing down is the fastest, easiest and cheapest solution.

[Piwoslaw]

Slowing down also proportionally reduces your rpms.

[pdexta]

I was simply trying to ask a physics question to people I thought might be knowledgable or have personal experience. If I wanted someone to tell me to drive slower I could have just asked my mom.

[MetroMPG]

No offense intended.

But "adjusting the nut behind the wheel" is often the first and most appropriate bit of advice given in many threads around here.

[Frank Lee]

Basjoos claims to have good fe at high speed using a combo of aero, lean burn, and gearing.

There are several gearing threads that the search function will find. There is an optimal rpm range for engines and I'm sure at 80 mph you are well past it with stock gears.

Tell your Mom "Hi" for me.

[Flakbadger]

Originally Posted by pdexta

I was simply trying to ask a physics question to people I thought might be knowledgable or have personal experience. If I wanted someone to tell me to drive slower I could have just asked my mom.

To be fair, advice like "drive slower" is a physics answer , as Wikipedia will tell you.

"Note that the power needed to push an object through a fluid increases as the cube of the velocity."

Maybe the reception was a bit harsh in your eyes, but you are asking a question that has been discussed a few times.

Will aero or gearing mods help? Definitely. But they'll help even more if you combine them with lower speeds.

[JRMichler]

Since few of us drive 80 MPH, the following experiment would be of interest to many of us:

1) Measure trip time (door to door, not just car moving time) and gas mileage for a week driving 80 MPH.

2) Repeat, only at 70 MPH for a week.

3) Go back to 80 MPH for a week.

This is an ABA test.

Report the results. I'm curious myself.

[basjoos]

Originally Posted by Frank Lee

Basjoos claims to have good fe at high speed using a combo of aero, lean burn, and gearing.

The Aerocivic gets low 60's mpg on 80mph interstate trips in the summer but to get that mileage requires a combo of exteme aero, tall gearing (2000 rpm @62mph), and the low Cd allowing me to run in lean burn at that speed.

[serialk11r]

Yea, 4000rpm is pretty high. If you ever look at the few BSFC charts out there you'll notice light vehicle engines tend to start losing efficiency above 3000rpm at any load, presumably because friction is getting pretty serious. For short geared cars people tend to report pretty big mpg changes with taller gears because of this; my MR2 runs a little under 4400rpm at 80mph (no, I never cruise at 80, I do 55 and let people blow past me at 70), people who swap the 5th gear to an 11% taller one have claimed pretty big improvement (like 9%ish) when doing 70mph.