125CC sufficient (for aerodynamic custom tadpole trike)?
 

What speed/range/MPG can I expect from a 125cc/4 speed (Honda) reverse recumbent trike with a velo-like body on it?

I suppose we can estimate the weight ~500# or so, including myself, with a max weight limit of ~800#.

It's not built yet, so no, I don't have pics.

125cc 4 stroke? Lets say 11whp and 5ftlb torque?

Assuming its totally streamlined, you'd probably see around 150mpg and should be able to reach 65-70 with it.

Sweet, cuz I was hoping for 70+MPG and 55MPH tops!

Yeah, it's a 4 stroke, 4 speed. Not sure on power or torque figures, though.

I'm looking at the half tear drop profile, basically. I'd like to see a Cd of .2 or less (not likely, though, I don't think), and A of ~10-15 sq.ft. max. So assuming max figures, I want a CdA lower than 30. This should be completely doable with a tadpole, considering there is only one seat, and approx a 50" max width.

The way the engine is supposed to be setup, it won't idle at all. There's probably going to be a way to either human power the vehicle to very low speed from a stop, where the engine will take over.

If the Human Power part doesn't work out well, a recoil setup can be added to the braking system, I suppose. I want to make it so that I can continue to use the title to the original motorcycle, making it highway legal.

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.

Does it get 65-70 average, or can you still get that on a long drive through the country at speed?

I've tried to hypermile on it and failed, it's hard to coast with the wet clutch and I live in an area with alot of stop signs and stop lights that are poorly timed, so when I take it on longer trips my mileage tends to stay about the same.
The change in gearing didn't seem to hurt my mileage as far as I can tell, as running wide open with the old gearing pushed the engine RPM up to just over 10,000RPM and it has a 9,500 RPM red line, so the engine was much happier and seemed to run better.

If you want to head out on the interstate you legally are going to need a 250cc engine or larger, if you want to a larger engine like that I would look at one of the fuel injected 250cc motorcycles that just came out in the past year or so, or get a 250cc vespa engine that is fuel injected.

Thanks for mentioning this as i had forgotten to.

250cc engine..... from a ninja 250!!! :thumbup:

Actually, in most places the highway minimum is 125cc.

I will still +1 the 250 motor idea, though. 800# is going to be tough enough to pull along with a 250 from a stop, (you can forget about pedaling to speed unless you're Lance Armstrong), although 500# won't be quite as bad. My Ninja and I weigh in around 450-500# loaded, and I've cargo-carried in the 700# range before.

The pedaling to speed thing is more like pedaling to 5-6MPH where the engine can run sufficiently without lugging and take over in 1st gear, enabling it to autostop when the vehicle isn't moving, and restart without using the kicker or stater.

I'm fairly certain around here that a 125 is legal on the highway, but it's still considered a moped... even if it's not legal on the highway, I'm not really concerned, because I can get just about anywhere in the state without touching an interstate highway.

Rt 15 is an artery in this area, it can get you just about anywhere up or down the state, or to another highway to get where you're going... it also takes you clean to Canadia almost, and a few states southways as well, but I don't need to touch it to get anywhere, I just end up going slower and going a few extra miles. At 100+MPG, I don't think it'll make a difference, eh?

I have to check the bike... I'm not really sure at this point if it's a 125 or not, it may be a 90. Whichever it is, I'll do what I can with it. I don't mind if it can't reliably get on the highway, but I'd like to have it able to, at least, and be able to do 55-60 carrying light cargo, like groceries or materials for a new project.

I'm thinking that I might give up the partial human powered part, though... Logistically, it's going to be difficult to package something into the already small chassis that's showing up in my head. I may look into a small DC motor and capacitor that will get me moving, to be used only after braking, but that's probably not a viable option either.

I have decided that I won't bother with electric start, though, since the motor is so small, I can use the kick starter with my hand, given the proper leverage.