MetroMPG.com mailbag: details of 104 mpg fill-up?

[MetroMPG]

Received this message after someone had a look at the Flea's fuel log:

Just had a look at your fuel consumption chart and saw the 104 mpg tank. Cool!

You mentioned the average speed was 20 mph. Did you spend any appreciable time in top gear? What's the lowest speed you can use top gear in that car and hold throttle mostly open to maintain a load on engine?

I'm just curious about how it actually worked out. My own situation is very different - auto tranny car that weighs considerably more than yours.

The 104 mpg fill-up was a deliberate attempt to see what I could do if I used pulse & glide at ALL opportunities. (Normally, I don't P&G on highway trips if they're going to be longer than about 30-45 minutes; I just target drive (DWL) instead, to save wear & tear and raise my average speed.)

The fill was in ideal summer conditions, and while it was a mix of sub/urban & rural routes of medium length segments, and a good portion of the driving was on empty or near-empty secondary highways. All were real, "legitimate" trips (ie. didn't displace any bicycle use).

To answer your question: none of that driving was in top gear, and very little of it was in 4th gear. The P&G was mostly 2nd to 3rd gear, which is usually between 25-55 km/h.

Since installing the taller final drive transmission, the lowest speed I can cruise in top gear on level ground without lugging, is about 65 km/h (~40 mph).

Also note that the alternator would have been disconnected for the duration; I would have been running the 12v off a pair (130 lbs) of flooded batteries.