The case for motorcycles. Why not use one?

[Mighty Mira]

Originally Posted by SD26

I think it's a cost issue with smaller bikes.

I think you misunderstand me. The postie bike is made especially for Australia Post, but is similar to the cheap bikes produced for the Asian market. I'm not saying it would be cheap to fair it. I was saying that it was cheap for Honda to make for the Australian market as is, unfaired.

Although, it wouldn't cost them much, they just don't perceive any demand (and there won't be, until enough consumers are educated).

[GasSavers_SD26]

I'd equate it to specific market segments.

I had to look up a Postie.. . I almost got one of those about fifteen years ago used. In a lot of ways, I wish I did...

Anyway, a manufacture has several models in a line up. Honda already offers small displacement bikes with full fairings like the CBR125.

Would probably be hard to justify making an aero version of an existing utility bike. Might be more economical for an aftermarket company to develop, manufacturer, and market such an item.

That would be my take from my work inside the MC industry.

[GasSavers_Ryland]

Originally Posted by SD26

A lot of bikes have the speedo pick up coming off the countershaft sprocket. So, yeah, you'd need a "Speedohealer" to correct it after making changes to the overall gearing. The gearing changes are relatively easy to do.

In all of the motorcycles that I've seen in working at a friends motorcycle shop, I've never seen the speedo pickup coming off the countershaft, it alwas connects to the front wheel hub, you can even get induction pickups for digital speedometers that simply count the speed of the passing gear teeth without any mecanical connection.

I really like having a motorcycle in the summer, they are easyer to park, use less gas, are cheaper to regester, and in the case of mine, it's over 20 years old so I have collector plates that will never expire.
Last time I did a cost per mile comparison, my motorcycle was less then 11 cents per mile, and my car was over 25 cents per mile to operate.

[GasSavers_SD26]

Originally Posted by Ryland

In all of the motorcycles that I've seen in working at a friends motorcycle shop, I've never seen the speedo pickup coming off the countershaft, it alwas connects to the front wheel hub, you can even get induction pickups for digital speedometers that simply count the speed of the passing gear teeth without any mecanical connection.

We gotta get you into some newer production stuff...LOL!

It's pretty simple. A little rotor gets placed on the end of the counter shaft outside the front sprocket, and there's a pick up on the front sprocket cover. It's electronic, not cable driven. Every production bike that I've had since 1998 has had that style. I didn't race my own bikes for a few years, so I can't tell you when the transition was, but anything produced more recently has it.

With fuel injected bikes, speed is part of the ECM. Some bikes are even fly by wire in that the throttle does not connect to the FI butterflies at all. That's all controlled by the ECM. Basically, it's the furthering of traction control in bikes. In the late 80's GSXR1100's had a different ignition map for first gear to keep people from looping out. In fuel injected bikes, each gear, generally, has a different map.

[QDM]

I would think something like this would get very good mileage. Somewhat aerodynamic, small displacement, single cylinder, sport bike. Cheap too, about $1300.


Q

[Mighty Mira]

Originally Posted by theclencher

the problem is the dustbin moves the center of pressure forward to the point where a good xwind will blow it off the road. seriously.

I'm not saying the dustbin (as in the Cx) is the best way to design a fairing. As you can see from my designs, the center of pressure would be hardly moved. Although most likely not necessary, you could fair a bit more of the back to make up.

I strongly suspect that there are three main things you can do on a motorcycle to reduce drag.

1. Enclose wheels, because these get air rotating around with them, effectively having much larger area than they do. This couldn't get worse than with a bike, where the wheels are totally exposed (but don't have to be).

2. Smooth the airflow at the front, like a bullet. This gets the air flowing to the maximal area with as little resistance as possible. After this there is a wake, which you can either hide stuff in (like a rider and the rest of the motorcycle), or eliminate via a smooth, gradual taper.

3. Reduce the pressure drag at the back via said taper.

A dustbin fairing has no substantial taper back, and contributes a reasonable amount of side area. I suspect that 90% of the job it does could be done by fairing the front wheel and the handlebar to top of driver region, in something with relatively small side area.

well, yes there is. bikes are light. conventional bikes don't enjoy as big a break on frontal area as you'd think vs cars. and of course the Cd sux. unless you get radical with enclosed or nearly enclosed fairings.

Well, let have a look, shall we? Figures of around 0.56 square metres are bandied around for the hayabusa. So lets say that a more upright bike like the Honda CT110 has something like a frontal area of 0.8m^2. My Mira has a frontal area of 1.79m^2, and that is very small for a car. Which is less than half of mine. Something in a sport bike or recumbent style would be in fact less than 1/3.

Now, the initial drag coefficient is close to 1. A flat plate would be just as bad. I suspect that properly fairing the wheels and doing what I did in my Gimped version of the postie bike, you'd get it down to at least 0.5. At that stage, the CdA would be a bit less than my car. Maybe more, because not many people understand why unenclosed, rolling wheels are so bad for drag.

Going further, what you describe as radically faired need not be impractical. It's more a matter of fashion. And fashion is fickle - back a few hundred years ago the height of fashion was the codpiece. What "people won't do" is not constant.

The practical HPV I linked to earlier seems to indeed be practical.

So quantifiably, coast time is proportional to m/CdA.v^2.

Ignoring velocity, my m/CdA = 765/.46=1675 kg/m^2

Typical postie bike = 200/(.9* .8) = 277 kg/m^2, so coast time would be 16% of my car.

Modified with front shield and wheel fairings, I'm estimating 0.5 for Cd. So m/CdA = 500, or 30% of my coast down time.

I'm estimating 0.2 for the Cd of a practical HPV style modified postie bike.
m/CdA = 200/.8/.2 = 1250, or 75% the length of my coasts. Which is close enough not to worry about. Recumbent or sport bike style would probably beat my coast down times. Remember that there are many people here who are P&Ging with m/CdA worse than my car.

The other thing to consider is velocity. A 10 kph coast down in my car is about 8.5 seconds at 100kph. I happily do that. The modified postie bike would have a 10kph coastdown time of 8.5 seconds at about 55kph. I do a lot of my driving at 60kph or less, so this would certainly be worthwhile doing from my perspective.

I haven't ridden a motorcycle in a long time, but do they have a similar mechanism to a regular bike, where it automatically coasts if you do not provide peddle power? Is it easy to do?

"Really, without a fairing, there's not a lot of frontal area on a bike." You'd be surprised... especially when you stick the rider on it.

You are right, thanks for making me double check my figures, although I don't believe it is an insurmountable problem.

if posties are used the way i speculate they're used, they never get going fast enough for a fairing to matter anyway. then the fairing is just extra cost and weight and gets in the way of functionality.

Actually you'd be surprised. Remember that the force of rolling resistance is proportional to mass. Since mass is at LEAST a 1/4 of that of a normal car, drag takes over at a much smaller velocity. My calculations have it at about 18kph for the unmodified postie bike. That's tiny!

[GasSavers_SD26]

Mr Munro's set up.

[GasSavers_SD26]

Originally Posted by Mighty Mira

I haven't ridden a motorcycle in a long time, but do they have a similar mechanism to a regular bike, where it automatically coasts if you do not provide peddle power? Is it easy to do?

It won't automatically coast. A regular motorcycle has a gear box. Not like a car where one can put it into neutral from any gear, but current production bikes have neutral between first and second gear.

Originally Posted by Mighty Mira

Actually you'd be surprised. Remember that the force of rolling resistance is proportional to mass. Since mass is at LEAST a 1/4 of that of a normal car, drag takes over at a much smaller velocity. My calculations have it at about 18kph for the unmodified postie bike. That's tiny!

What are you assuming for a weight? My 600cc production race bikes weighed about 378 to 388 pounds after a race, depending upon how much fuel I wanted to have in the tank, still not being empty with the smaller number. Yes, there are heavier bikes, but production practices have continued to yield lighter bikes. I'm not sure what one would call average, but the Postie dry weight, no gas & no oil, is about 200#.

[Mighty Mira]

What are you assuming for a weight? My 600cc production race bikes weighed about 378 to 388 pounds after a race, depending upon how much fuel I wanted to have in the tank, still not being empty with the smaller number. Yes, there are heavier bikes, but production practices have continued to yield lighter bikes. I'm not sure what one would call average, but the Postie dry weight, no gas & no oil, is about 200#.

That's exactly what I figured. I'm using 100kg for rider and gear, being near enough to 200kg for rider + gear + bike as a round figure.

[StorminMatt]

I think that besides obvious resons such as ssfety and protection from the elements, there are other reasons why more people don't ride motorcycles.

1. Price/Value - Okay, so a motorcycle is going to be cheaper than MANY new cars. But this is not always the case with ANY motorcycle vs ANY car. This is particularly the case if we are considering the cheap end of the used market. You can find a decent running used car for MUCH less money than a running motorcycle. Also, at ANY level, you obviously get more for your money from a car.

2. Ability to carry stuff. This is another obvious one that maybe many might not think of. Anyone ever try to go on a $100 grocery shopping trip on a motorcycle? For that matter, how does one go shopping if a motorcycle is all they have?

3. Carrying passengers. This is, of course directly related to the last problem. You just can't carry a family on a motorcycle.

4. Theft. Not many people think of this one. But I know several people who have lost their bikes. All it takes is for three or our motivated guys to drive aroud in a pickup.

For all of these reasons, as well as ones mentioned above, motorcycles are just not practical as a primary vehicle for most people.