Motorcycling: Is 200 km/l possible?

About 19 years ago, I had my first fuel economy challenge. Mary Ann told me her Toyota Tercel got really good gas mileage, and asked my what kind of gas mileage I got on my Honda CBX. We did a trial run of about 300 km, and I lost. OK the CBX has 6 cylinders to the four on the Tercel, and I went faster because I can't drive as slow as Mary Ann (or at least I couldn't then - now I'm older, more mature, and I have a Kawasaki Vulcan).

In 1985, at Laguna Seca, California USA, the winner of the Craig Vetter Fuel Economy Challenge acheived 470 miles per gallon (US), with a motorcycle. Is this practical for the street? I want to go through some of the techniques and give my opinion on whether it is practical or not. I do not have the full explanation from the video, unfortunately which must be ordered on the web site, but some things are obvious from the rest of the web page.

First, although the web page talks about normal street speeds and conditions, this particular effort was a closed race track performance. Traffic and normal rules of the road would reduce this fuel efficiency. Speed was not mentioned on the web page, but probably reasonable, as streamlining was useful.

http://www.craigvetter.com/pages/470MPG/1985%20Fuel%20Economy-main.html

This was a relatively low budget effort, starting with normal street bikes. A manufactured design would do much better than this, but there would have to be a mass market for it, which there is not right now.

The motorcycle was a 1980 Honda XL125 displacing 185 cc. The engine was modified adding a neutral between 5th and 4th to allow the rider to drop into neutral and coast easily. Another modification was increasing the stroke to get 185 cc.

All grease and oil was removed and replaced with lightweight machine oil. This would not be good for long service life, though. This includes grease in the drive chain and wheel hubs. No wonder this guy won! Not because of this change alone, but just an example of the thoroughness of the preparation.

Lightweight valve springs were used to reduce internal friction, unfortunately this would permit the valve to float at high rpm and possibly cause engine trouble. At the very least to hamper performance.

Overall gearing was changed, I assume to reduce engine speed. Which of course would mean torque (or acceleration) at the rear wheel would also be reduced. High air pressure in the tires, makes a bit of a hard ride, but otherwise not difficult to put up with.

On a personal note, and you can judge the practicality of this for yourself, the rider's clothes were duct taped to stop power-robbing flapping.

The rider had to assume a low crouched position, which would be uncomfortable to hold for any length of time. I will do this on my CD175 just to get into a wind or go up a hill, but it's too uncomfortable to hold unless it was a serious competition.

One important modification was the addition of a streamlined body. I noticed some pretty small foot holes, meaning the average rider would fall down a lot at stop signs, unless there was training wheels. Which of course would add to the wind drag. In this competition, a pit crew could probably help you get started and stopped.

This winning machine was crushed by Honda in 2006, from that I assume they had something to do with building it.

That was the last official Vetter Fuel Economy run. Today, Craig is still working on fuel mileage. His latest challenge is a bike that gets 100 mpg at 70 mph into a 20 mph headwind, carrying three bags of groceries. To me, that seems like a high bar to set, maybe we could make do with 60 mph with no headwind? And a bag of Doritos? Anyway, streamlining is the answer. He is nowhere near 470 mpg though, more like 64 mpg. Although that is actually pretty good for a 20 mph headwind! One thing about a headwind is that it is much worse than doing (70+20) mph, because at 90 mph you are at least going somewhere at 90 mph. With a 20 mph headwind, you have the drag of 90 mph, but moving at only 70 mph, which really hurts your gas mileage. That's why I would suggest forget the headwind aspect of the challenge.

http://www.craigvetter.com/pages/470MPG/Last%20Vetter%20Fairing.html

So far, for a lot of reasons, 200 km/l seems out of reach, even for a motorcycle. But 50 may be possible if people were interested in going for streamlining, and a manufacturer would take the risk of mass production.

Picture: Matzu Matsuzawa Honda XL125

NOTE: This blog entry was recreated from a backup after Google lost the original