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  1. #1
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    Homebuild Lowracer or Highracer?

    After months of drooling over dozens of recumbents, I think it's time to start building! I've built a couple fun bikes (a tall bike and chopper) to get enough bike building experience that it shouldn't be a complete disaster.

    I just need to decide what type of recumbent to build! I've narrowed it down to two basic designs, the lowracer (M5, Optima Baron, etc.) and highracer (Bacchetta, Volae, etc.)

    What would you suggest I go for? I'm looking for something simple, efficient, aerodynamic, stable, comfortable, and fast. The lowracer design appears to be the fastest, but I'm concerned about chain interference with the wheel - I need something I can ride around the city and do tight corners with. The highracer eliminates this problem, but is it as aerodynamic? Also, I like how on a lowracer I could stop and balance with my hands - on a highracer I'd have to clip out. The position is quite similar on both, with comfort maybe being a little better on a highracer. For ride quality, would the highracer's large front wheel be a big advantage?

    Any tips on building a recumbent in general? Is it best to have the seat slide forward/backward, or build an adjustable boom for the cranks? What should I build the seat out of?

    Thanks!
    Mike

  2. #2
    hmBldr
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    Check out the Marauder on the atomic zombie web page:

    http://www.atomiczombie.com/books.htm

    Buy the book, it is a relatively easy bike to build, adjustable seat, some frame flex for comfort, fast, and no chainline issues.

    Darren

  3. #3
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    I do have that book (highly recommended) and was planning to build the Marauder for a while, but it concerns me that no recumbent company uses a similar design. I like that it is low and with no chain issues, but it's also more complicated (steer linkage instead of direct) and much longer than most.

    I'm considering the Marauder as an option, but would trust a design by a company like M5, Optima, or Bacchetta because they've been around for years and a lot of design revisions.

    I just came across a bike that's no longer in production, the Flevobike Rapido. Here's a picture. Any thoughts on this design? I like that it's quite simple and with box tubing (easy to weld and align), but there's still the issue of chain overlap.

    I'm starting to lean more toward the highracer design, like the Bacchetta or Volae. It's simple, has little or no chain overlap, and would have better visibility in traffic. On the downside, it's probably not as aerodynamic as a lowracer design... and doesn't look as cool.

    Either way, the seat is important and will be a large project in itself. Has anyone here ever built a recumbent seat? I could do plywood with padding, but I'd really like a "proper" recumbent seat... something curvy and lightweight. Should I try and build one from fiberglass? Bent steel rails with fabric stretched across? Any ideas would be great!

    Mike

  4. #4
    hmBldr
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    The chain overlap problem is a major one, I've tried various methods to get around it with swb lowracer designs and haven't found a good solution. Apparently neither have the manufactures. Remember, these lowracers were originally designed for track racing, so u-turns were not on the requirements list. Zox like fwd works, but is pretty radical for most. The marauder is actually pretty easy to build, the remote steering is not complicated, just a tube or rod with two tie-rod ends bolted between metal tabs welded onto the fork and head piece. Cheap, easy and reliable. Getting the wheel in front of the crank takes care of many issues like the chain overlap and heel strike.
    About the seat, foam over plywood works very well, and is actually pretty light, you can drill holes in the plywood to lighten further. I've also found surplus roll-end neoprene for sale on ebay for $5 - $10 a yard to give it a nicer finished look. If you want to go curvy, you can still use wood. Make a jig with sturdy dowels at the curve locations. Then laminate very thin sheets of wood together using epoxy or urethane glue, arching the wood in your jig. You can also buy precast fiberglass seat shells from some of the manufactures if you don't mind spending some cash. You can also make a custom seat shell with some help from your friends. You make a plaster-of-paris mold of your back, then use it to cast a fiberglass shell into the mold. This works great but takes much more time and effort.

    Darren

  5. #5
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    Thanks for the info... I think I've decided against a SWB lowracer because of these chain issues. So now it's highracer, Marauder, or a front wheel drive design.

    Have you ever tried a Zox? I see they have a dual 26" model that looks really interesting. It seems like the chain would be pulled sideways as the front wheel turns. I see some chain guide tubes... maybe these are held rigid to keep the chain straight?

    Most likely, it's a highracer (Bacchetta, Volae) or the Marauder LWB lowracer.

    I'm leaning towards the highracer because of its simplicity; it's basically one main boom. Would the Marauder actually be a lot faster than a highracer? It's lower, but the body position is very similar, and it would have a larger front wheel which should roll smoother.

    Mike

  6. #6
    hmBldr
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    check out this bike:

    http://homepage.mac.com/john4bho/Menu3.html

    He makes great looking carbon bikes, 23 lb Bacchetta clone, SWEET!

    Also nice guy, has helped several others with tech advice and sources.

    Darren

  7. #7
    hmBldr
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    I've seen a Zox, never ridden, I heard the price and got too scared. They use a special flex twisting chain.

    Darren

  8. #8
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    That's perfect! He's done a magnificent job with that bike... especially with those rear chainstays. I like how the monotube is actually shaped to surround the rear tire, with the brake mounted directly to it - simple and slick.

    I'm thinking of using square tubing for easier alignment, mounting to a jig, and possibly more stiffness. If the square tubing was sliced down the middle and bent outwards into a rear chainstay, would it still be strong enough? Seems like a simple way to form the stays that would look great too.

    Possible problem with square stays... would the front adjustable boom clamp as tightly? With round tubing it's being clamped all the way around, but square tubing might put most of the pressure on the corners. Does this make sense?

    Thanks,
    Mike

  9. #9
    meb
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    Square frame tubing sleeved inside a round or square boom might actually reduce boom flex during pedalling-giing you an unexpected benefit. There are squre tubed manufactured bents, including a couple of swb bents. Even George Reynolds has ventured in this area.

    LWB lowracer willl be fast & stable, but difficult to transport and store. Lowracer is less practical around cars since you are less visible and your own view would be lesser than a taller bike.

    But its rarity among bent makers is not a reason to avoid the genre.

  10. #10
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    I'd imagine that square tubing is stiffer (provided it has the same wall thickness) - I'm just wondering if clamping square tubes would give uneven pressure or something... should this be a concern?

    I think I'm set on the highracer setup... should be nice and fast, but still visible in traffic and with no chainline issues - easy to build too.

    Thanks!
    Mike

  11. #11
    meb
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    Round tubing is stiffer torsionally. Square tubing is stiffer along the tube's axis.

  12. #12
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    I've been wondering about the properties of different shaped tubing; thanks for the tip meb.

    Now I'm off to build the seat, which I'd like to have done first so that I can sit on it and take measurements to determine approxiamate BB position, seat angle, etc. Without a real recumbent seat to copy, I don't know the proper shape and size. So I went out in the backyard and started digging in a pile of a dirt. After a lot of careful sculpting, packing, and sitting in this dirt... I've got a "seat" that fits me perfectly.

    What should I do from here? I could put a layer of fiberglass directly on this dirt mold, but I'm concerned about little problems that might be in the shape... it's hard to tell if everything is symmetrical. Should I be shaping it in one dimension (like a ribbon) or curving up the edges for more of a bucket shape?

    Thanks!
    Mike

  13. #13
    hmBldr
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    I'd make a plaster cast of the female (negative) dirt mold you've made, to make a new male (positive). Line the cavity with trashbag or food wrap plastic to keep the dirt from sticking. You can then use a file or Shurform to clean up the high spots and wrinkles, or body filler paste to fill in any holes and low spots. The smoother the make it, the better the cast will come out. Once you get a clean positive, wax it up real well and use it to cast your seat.

    Darren

  14. #14
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    Thanks, Darren - I used paper mache (no plaster available) and it's drying in the yard now. That dirt pile sure is comfortable.

    Mike

  15. #15
    hmBldr
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    The paper mache will be pretty rough, so you'll need to use some body putty (bondo) to fill and smooth it out. You may want to put a surface coat of epoxy or polyester resin on the surface to harden it, I don't know if you'll be able to get it hard and smooth enough for a fiberglass cast to release. I've had trouble with fiberglass cast on a plaster mold not wanting to release even with several coats of wax. You may be forced to destroy the mold to get the cast, not the end of the world, but it would be better if you can get several casts off the same mold. Epoxy/carbon casts want a REALLY smooth and waxed mold.

    Check out this site for some excellent info on casting curved motorcycle parts in carbon. Very informative and fully applicable to bike seats.

    http://www.mci.i12.com/carbon/

    Darren

  16. #16
    hmBldr
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    Here's a similar thread on another board with additional links.

    http://www.bentrideronline.com/messa...ead.php?t=5359

    Darren

  17. #17
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    Has anyone worked on one of these? The photos make it look easy. I realize this is an illusion but I bet they sell a lot of plan sets.

    http://www.rqriley.com/xr2.html

    tom o.

  18. #18
    meb
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    Quote Originally Posted by tom o
    Has anyone worked on one of these? The photos make it look easy. I realize this is an illusion but I bet they sell a lot of plan sets.

    http://www.rqriley.com/xr2.html

    tom o.
    I've heard of three problems with the Groundhugger XR2.
    1) midrive chainring hitting ground-remedied by use of smaller middrive cogs.
    2) lack of an adjustable seat-pedal position.
    3) Excessive play with the U-joint steering-remedied by a traditional linkage bar in leu of the U-joint.

  19. #19
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    My favorite is the F'lowroller http://www.rohorn.com/ It has a really clean design and though not necessarily fast it is so cool that I think it would make a great project. No problems with the chain on turns. Fat tires for a smooth ride. Though it may look like one it is not a lowracer as the sitting position is more upright. It is a cruizer.

    Bob is not producing the bike or the trike right now but if there was enough demand he might be pursuaded to sell copies of the plans.

    tom o.

  20. #20
    hmBldr
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    Hey Meltable,

    How did the seat mold come out?

    Darren

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