125CC sufficient (for aerodynamic custom tadpole trike)?

[roflwaffle]

100+mpg should be easy, but acceleration and gradeability, or whatever it's called, will be lacking. I think investing in a 250cc motor and a taller sprocket at some point would be a better bet in terms of an acceptable trade-off between acceleration/climbing ability and mileage. I wouldn't be surprised if you could manage better mileage and acceleration w/ a larger engine and taller gearing.

[Christ]

I was thinking about upgrading later if the project turns out to be "unworthy" in terms of acceptable performance, but for now, I'd just like to get it built and tested, and put some miles on it. Unfortunately, it's hard to get started with limited work area and a very disapproving home owner looking over your shoulder all the time, so the bike still sits at my Father's barn, waiting for me to rob some parts off it for my CM185T project bike, which I haven't updated in awhile, because the cost of just the piece of exhaust I need for it is prohibitive, and I'm still undecided what direction it needs to end up going.

I'm hoping that I'll have more free time by the time my Wife gets out of school, so I can actually start laying out all these things I have in my brain and getting to work on them some.

[bondvagabond]

One solution to the problem of tall gears at low speed, or with big cargo in a little bike motor is the old school trail 90's. Before they had the cool sub tranny, they had two rear sprockets, and a chain with two master links. one length for big sprocket, then pop both master links and use one to put it back together on the little sprocket.

You could have one optimized for runnin' light, just you and the base weight.
The other one would be for the extra 300lbs cargo you were talking about, crappy roads, hills, passenger if you ever go that route, whatev!

my old one took about 3 seconds to change with no tools too.

Quicker than putting your passenger seat back in :-)

[Christ]

Originally Posted by bondvagabond

One solution to the problem of tall gears at low speed, or with big cargo in a little bike motor is the old school trail 90's. Before they had the cool sub tranny, they had two rear sprockets, and a chain with two master links. one length for big sprocket, then pop both master links and use one to put it back together on the little sprocket.

You could have one optimized for runnin' light, just you and the base weight.
The other one would be for the extra 300lbs cargo you were talking about, crappy roads, hills, passenger if you ever go that route, whatev!

my old one took about 3 seconds to change with no tools too.

Quicker than putting your passenger seat back in :-)

Great idea!

You've got to consider the fact that I'm not likely to even break 500# curb weight with a full fairing on this setup, cuz I don't even think the whole bike weighs in at like 200#, and I'm only ~150 most of the time, ~180 with my pockets full.

The max 800# limit was extremely pessimistic, and included me, my wife, possibly my kid, and groceries or something.

[bondvagabond]

Originally Posted by Christ

Great idea!

You've got to consider the fact that I'm not likely to even break 500# curb weight with a full fairing on this setup, cuz I don't even think the whole bike weighs in at like 200#, and I'm only ~150 most of the time, ~180 with my pockets full.

The max 800# limit was extremely pessimistic, and included me, my wife, possibly my kid, and groceries or something.

Given multiple solutions to a problem, my votes for the one that you can fix with a rock. heck, you could have a spare double sprocket and chain, and essentially role around with a spare sub tranny for like a 2lb penalty.

Give me reliability and ease of repair, anything else is bad engineering, and we all know what happens to naughty engineers...

[Christ]

I've still got a CVT pulley I could play with... too bad it's belt driven, and probably as lossy as... a jar with a hole in it.

Although I have a ~95% efficient CVT transmission design in my head that can't slip at all... Ah, but where is the money to produce it? LOL.

[Ryland]

It seems like if you look hard enough you should be able to find a very small turbocharger that will work on a 125cc engine, the engine in it's stock form is around 12hp at 9,500rpm but it sees like a turbo would help with climbing hills and those other times when a little more power is needed while giving you the advantage of the small engine the rest of the time.

[thatguitarguy]

Originally Posted by Ryland

I have a 1975 Honda CB125 that gets 65-70mpg and tops out at around 60mph, it has one tooth larger then stock front sprocket to get the higher speed, if I want to get the top speed out of it I need to tuck my knees in and duck down.
A simple rear faring would help alot, alloy wheels would help too.

My BMW R1100RT will go 50 MPG at 80 MPH all day without even trying. I've never tried to hypermile it because it's fun to just ride it, and the riding season is short high in the mountains. It does have what I'm guessing is a pretty efficient fairing on the front. It would be interesting to experiment with a boattail. It's nice to have the combination of efficiency and power when I need it for maneuvering in traffic. You already put yourself at risk by getting out from behind the airbags and safety equipment. This bike has fuel injection, and I think that really makes a difference with all the changes in elevation I encounter on a ride. Easily between 5000 ft and 11,000 ft. Not feasible do do jetting changes in a carb. If you're in a flatter area it might be OK, but a later model bike with FI might be a better starting point if you can afford it.

[Christ]

How much does your R1100 weigh? How's the aero on it? about 17 HP is all that's really needed to go 70+ comfortably in most all situations.. ask Craig Vetter.

I'm not looking to build it to "have fun", in the sense that everyone else thinks. It'll be fun enough tooling around in it just knowing that my hands built it, and how many people can say that?

I've got a GL1000 sitting in the yard, if it's old enough that I can get a title for it, I'll use it for a highway trike, then I'll have one for tooling around, and one for really "getting on it", as it were.

A boat tail would help by a few MPG, but true streamlining is necessary to really see any gains, because you bike has a very high Cd. I believe I read that there was approx 80% of the engine's power wasted just to keep the bike going 80+ MPH on some bikes. Yours probably isn't that bad, I think that was for cruisers and unfaired bikes.

[thatguitarguy]

Originally Posted by Christ

How much does your R1100 weigh? How's the aero on it?

Don't know, but it's lighter than other smaller bikes I've had. Don't know Cd, just going by seat of the pants, but the wind goes by pretty smooth and quiet till you lift your head above the windshield, or hold your arm out.

Originally Posted by Christ

I'm not looking to build it to "have fun", in the sense that everyone else thinks. It'll be fun enough tooling around in it just knowing that my hands built it, and how many people can say that?

That's cool, but if you're riding and not having fun, you're doing it wrong and ought to try something else.

Originally Posted by Christ

A boat tail would help by a few MPG, but true streamlining is necessary to really see any gains, because you bike has a very high Cd. I believe I read that there was approx 80% of the engine's power wasted just to keep the bike going 80+ MPH on some bikes.

It's not like an AeroCivic, but I don't know that the Cd is all that high, and the frontal area is pretty small compared to power at the rear wheel.

I ride recumbent bicycles and a tadpole trike, and people that have been streamlining those vehicles for years concentrate more on cleaning up behind the rider rather than in front. With your feet out in front of you, the air is dirty, but the area is small, and it's easier and more effective to put something behind you that you don't have to look over or through.

It's different on a motorcycle. You're not pushing through the air under your own power, and it's more comfortable pushing a wall of air out of the way with a plastic fairing than with your face. The challenge at the back of the bike has a lot more to do with crosswind aerodynamics and stability. Slicing through the air at Bonneville for a couple of runs is a lot different than slicing through traffic on I-70 during rush hour. I think some Kammback style touring cases could be really effective, but I think it's easier to experiment with Coroplast on low speed bicycles, or cars that have 4 wheels on the ground and more attachment points.

I'm looking forward to seeing how your vehicle develops!