Hello everyone!
For a few years i've know of the existance of recumbent bikes. I've always been interested in their aerodynamic advantages, but as I also race ocasionally, I can't use UCI illegal bikes for that. Since now I got all the upright racing bikes I wanted, I can think about a recumbent just for the fun of going faster, and this is a project I want to develop during this year. It's a quite lengthy post, but I hope some of you can help me with this project! Thanks in advance!
The thing is I live in Brazil and there are basically no recumbents around. Well, actually, there's a place near where I live that actually makes them in a very small scale. But they are not the kind that go fast. Seat above the wheels, 20 inch fat tires, not laid back, found a pic here:
http://3.bp.blogspot.com/-ESwzrc0ma4...0/P1020291.jpg
The company actually makes steel gates for houses and stuff like that. So I don't think they are the right people to build me a custom machine.
Since all my upright bikes are custom steel, I mentioned the idea of making a recumbent to the framebuilder (who is a friend) and he agreed we could do it. I can't find anything to buy, so custom it is. The thing is: which type of bike? Been thinking about pros and cons of each design but I need experienced opinions! Here are my considerations:
1) I want the aero benefits, so I'll at least add windshield and tail fairing to the thing, the tail fairing could also double as storage.
2) Low seat is more aero, and the fairing being close to the ground makes it more stable to cross winds I guess. But I think its a good idea to have my eyes above knees so I can see something without a camera. I also won't have to bother with aero wheels. Anyway, I have something low racer style in mind.
3) That probably means small front wheel is the practical choice. But are there good 20 inch tires? Is Schwalbe Pro One tubeless the best and only choice at the moment? Should I fear they cease production and I'm left without good tires? I have 700c wheels and tires at hand, but that would mean high seat and probably slower, or a highly unpractical very long bike.
4) The rear wheel being the same size would make it small and more practical, since I'd have to stock only one model of tire and inner tubes in case of flat (pro one is tubeless). I don't believe there's any measurable rolling resistance difference to justify bigger rear wheel with pneumatic tires, rolling resistance and wheel size has been tested as early as 19th century, and it only makes a difference for solid wheels. What could justify 700c rear wheel is if I get RWD so I don't need massive chainrings. And I can use a wheel I have, although that isn't the determining factor.
5) I'm thinking SWB with front wheel between legs makes for the fastest machine. But how practical is steering? For that I think cable operated steering is the ideal way, but I concern about loose or broken cables.
6) Front or rear wheel drive? FWD makes a shorter chain and no pulleys, but what about steering? And high power pedalling, will I have to counter-steer to hold a straight line if I build the drive on the fork? I've seen one FWD bike that the crank is on the frame, but I suppose steering is very limited since any turn twists the chain. How steep can I climb before loosing traction? I don't intend to hit serious hills on purpose, but you never know. Some hills around here peak above 20%, but can be avoided, and I'm really building a machine for the flats, so probably never above 10%max.
FWD is also the simpler to build for a low seat bike.
The "Performer" model has a twisting iddle pulley, but I guess that design only works for high seat. Ideas?
And rear drive... means some 3 chain lengths. Will it wear at the same rate and make for expensive maintenance, or does it last 3 times longer since each link sees the cassette 1/3 as often? Do the guide pulleys add much drag? How limited would steering be, since the tire can rub the chain..? Is it too hard to enclose the chain to protect from dirt, since it will probably travel close to the ground..?
7) 20 inch drive wheel means huge chainrings, short cranks, or both. I bought a 120mm crank to experiment on my upright, the idea being foot speed will be the same and the cadence 30% higher, so chainring can be 30% smaller, but I haven't tested them yet (need to swap the bb for square taper). That would make 53/36 ok to ride, and fits 110bcd. I'd spin out 52/11 at about 80km/h if my theories are correct. Anything bigger means some 165mm crank and massive chainrings. Probably then FD can't shift more than 18t so that would limit low range with something stupid like 78/60 that I don't even know if I can find. Unless I have a pulley to double the ratio, or a system with two rear derailleurs so i can have a close ratio at the wheel and wide range in some 7 speed in the middle, using the big cog to pull the second chain, and only have one chainring at front. But that means adapting a freewheel and hanger on top of the fork. It could solve tire-chain clearance issue though, but also suck some 5w of chain friction.
I don't really consider 1x(12) because I don't want big gaps in a machine meant to ride fast on the flats. And probably 50t cassette is almost the size of the rims.
8) Then comfort. Since I can't stand over bumps or holes (and there are lots of around here, we have this kind of stuff in Brazil too:
http://tinyurl.com/y4tt8c4b and
http://tinyurl.com/yylmkge3 ), I might add some kind of suspension besides running 28mm tires, if I go the Schwalbe Pro One path. My reasoning is since a laid back recumbent pedaling motion is nearly horizontal, I wouldn't loose meaningful power to suspension swing as you do on a MTB. Rear suspension is quite easy to add, even if it's just short travel elastomer. Not sure about the front wheel, specially with fwd. Ideas? I could instead make some kind of suspended seat, borrowing principles from a beach chair. That would probably be light too.
8) Finally, what kind of handlebar? Simply get a mtb riser handlebar with some angle and cut it narrow, in a moto-gp style?
If you know of bikes I should borrow inspiration, please link me.
I've made all my upright bike projects myself on BikeCAD, but I don't think I can get a recumbent made there. Will I have to do it by hand?
Thanks for the help!