How important is B.B. height?

Discussion in 'Recumbent bicycles' started by freewilly, Nov 22, 2003.

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  1. freewilly

    freewilly New Member

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    Hi everyone! Just found this forum today & have spent a few (enjoyable) hours going through some of the old posts. I figured that I'd pose a question I've been mulling on for a while..but first a bit of background info.
    I was hanging around at my buddy Oran's school bus between the cherry & apple picking seasons when I decided, on the spur of the moment, to build myself a clwb recumbent from a couple of mtb's I had lying about. So, out came the hacksaw & chainsaw file. Well, considering that it was all seat-of-the-pants construction with no in-depth knowledge & no jig (neither for assembly or welding), it turned out pretty decent. Against all probability the frame came out straight when my brother-in-law welded it up in the garage. Unfortunately I'd made a pretty basic mistake when making the initial measurements & had measured inseam, not x-seam. This little error then required having the seating position raised quite a bit when I ran out of rearward travel room. The end result of this is that the B.B. is now rather low (15" B.B. & 30" seat height w. a wheelbase of 63"). The bike isn't quite finished yet 'cause I'm debating whether to hack it apart..and all this depends on the B.B.
    Going through various forums & reading the posts, I'm given the impression that B.B. height relative to the seat is a rather important issue with many, seeming to have a direct correlation with performance. I plan to take whatever I build touring around B.C. and, if it's a decent ride, off continent. Now I've come to the stage where some actual money will have to be put into the bike (the two mtb's came from the dump) for the purchase of handlebars & aluminum tubing/c-channel for the seat. Having to lay out some cold cash now has me wondering if, because the B.B. is so low, it will be a slug & therefor a waste of cash. On the other hand, it is definitely a recumbent style bike & rather comfortable to ride; I made a few test runs using some bodged together stuff (seat & handlebars). In real world long distance self-supported touring, how critical are such things as B.B. height, weight, & seating position. I'm not only concerned about the raw speed issue, but also safety, comfort, & pure enjoyment.
    I'll close this post by admitting that I've never rode a recumbent & don't have access to one, therefor all these concerns. Anyway, any comments, anecdotes, etc. will be appreciated. Thanks..Willy.
     
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  2. "freewilly" <[email protected]> wrote in message
    >In real world long distance self-supported touring, how critical are such things as B.B. height,
    >weight, & seating position. I'm not only concerned about the raw speed issue, but also safety,
    >comfort, & pure enjoyment. I'll close this post by admitting that I've never rode a recumbent &
    >don't have access to one, therefor all these concerns. Anyway, any comments, anecdotes, etc. will
    >be appreciated.

    Willy, I'm neither a designer or a builder (I just ride em). I've ben riding Lightfoot Cycles trikes
    for the last 3 years for self-supported touring and the bottom bracket is 15" with seat height 22".
    This position is so comfortable I've been able to ride 12 hours in a day. Mind you the seat makes a
    difference also. For touring IMHO; comfort,carrying ability, stability under load, and low enough
    gears is what matters most. With a 15" BB and 30" seat, you will be exposing more frontal, so more
    wind resistance, but a front fairing (like ZZipper) could look after that. Here's some pics from my
    latest tour: http://community.webshots.com/user/barrydavidson

    Barry Davidson

    --
    Cyclotec HPV: human powered sport/utility vehicles Peterborough, Ontario, Canada ph.705 749 2859 We
    sell: Lightfoot Cycles, http://www.lightfootcycles.com Heinzmann Hub Motor, http://www.heinzmann.de
    ZZipper Road Fairings http://www.zzipper.com Freddy Fenders http://www.planetbike.com
     
  3. I have found that the overridding issue for a high bottom bracket is foot numbness. The tendency for
    this to happen depends on the individual and also on riding style ( some people spin faster than
    others). I have two Bentechs and a Rans Tailwind. The tailwind has the lowest BB relative to the
    seat. I have never had foot numbness on the Tailwind. However, when the crank rpm goes down under
    long duration climbs (e.g., 30 minutes in mountains) I can experience numbness on the SWB Bentech.
    The solution is to ease up, unclip and change foot position, spin more, etc.

    Note that BB position is a performance issue. The Bacchetta bikes have high BB's and this minimizes
    frontal area. However, the TourEasy has a low BB, but the fairing more than compensates for the
    increase in frontal area. It is a fast bike in my opinion.

    "freewilly" <[email protected]> wrote in message news:[email protected]...
    > Hi everyone! Just found this forum today & have spent a few (enjoyable) hours going through some
    > of the old posts. I figured that I'd pose a question I've been mulling on for a while..but first a
    > bit of background info. I was hanging around at my buddy Oran's school bus between the cherry &
    > apple picking seasons when I decided, on the spur of the moment, to build myself a clwb recumbent
    > from a couple of mtb's I had lying about. So, out came the hacksaw & chainsaw file. Well,
    > considering that it was all seat-of-the-pants construction with no in-depth knowledge & no jig
    > (neither for assembly or welding), it turned out pretty decent. Against all probability the frame
    > came out straight when my brother-in-law welded it up in the garage. Unfortunately I'd made a
    > pretty basic mistake when making the initial measurements & had measured inseam, not x-seam. This
    > little error then required having the seating position raised quite a bit when I ran out of
    > rearward travel room. The end result of this is that the B.B. is now rather low (15" B.B. & 30"
    > seat height w. a wheelbase of 63"). The bike isn't quite finished yet 'cause I'm debating whether
    > to hack it apart..and all this depends on the B.B. Going through various forums & reading the
    > posts, I'm given the impression that B.B. height relative to the seat is a rather important issue
    > with many, seeming to have a direct correlation with performance. I plan to take whatever I build
    > touring around B.C. and, if it's a decent ride, off continent. Now I've come to the stage where
    > some actual money will have to be put into the bike (the two mtb's came from the dump) for the
    > purchase of handlebars & aluminum tubing/c-channel for the seat. Having to lay out some cold cash
    > now has me wondering if, because the B.B. is so low, it will be a slug & therefor a waste of cash.
    > On the other hand, it is definitely a recumbent style bike & rather comfortable to ride; I made a
    > few test runs using some bodged together stuff (seat & handlebars). In real world long distance
    > self-supported touring, how critical are such things as B.B. height, weight, & seating position.
    > I'm not only concerned about the raw speed issue, but also safety, comfort, & pure enjoyment. I'll
    > close this post by admitting that I've never rode a recumbent & don't have access to one, therefor
    > all these concerns. Anyway, any comments, anecdotes, etc. will be appreciated. Thanks..Willy.
    >
    >
    >
    > --
    > >--------------------------<
    > Posted via cyclingforums.com http://www.cyclingforums.com
     
  4. freewilly

    freewilly New Member

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    Hi Barry. I like your trike setup. Was also thinking about cobbling up one for touring, but I'm still weighing the pros & cons. One idea that I find kinda appealing is a dual function bike.
    Looking at pics of trikes like yours & the EZ I noticed that there's little difference between the main frame of the 2-wheeler vs. the 3-wheeler (I think the Lightfoot IS the same). I have an idea for a very simple elastomeric suspension system that *might* work nicely on a trike & allow for the rear to be unbolted & a conventional rear triangle to be substituted, thereby making it into a 2-wheel suspended recumbent.
    Another possibility is a breakdown frame for traveling. Unfortunately, S&S will only sell their couplers to a legit bike shop & they have to do the insallation. No way in hell I'm gonna pay $700 for that little job. I'll just do the nesting tube 'n clamp bit & learn how to braze or....seems to me that a nesting tube joint, which has to be bonded for half its length to one of a larger diameter, would be an ideal candidate for epoxy (JB Weld or other). The main criteria is to have something that fits in a container of around 40"x26"x12" for hauling around on a bus & has an overall weight, including box, of less than 50 lbs.
    So, aside from all that, how do you think the trike stacks up against a 2 wheeler for touring? I'm thinking that they might be rather close performance wise, for heavyweight touring, insofar as hauling a trailer behind a 2 w. would give it the same (or greater ) rolling resistance & probably even out the weight disparity. Another thing for me to think about is that the Coast Mtns. & the Rockies both have loooooooong steeeeep climbs & plenty of them. This could be a situation wherein a trike would excel. Also, I'm kinda curious about the high speed stability, going through turns, of a delta such as yours. A tadpole would pobably be inappropriate for the type of touring I'd be engaging in, so delta (or LWB 2 w.) it would have to be.
    Well, that's a whole buncha stuff to consider. Maybe I'd be better off hacking & lengthening the bike (to bring down the seat height & CG) and turning it into a breakdown trike/bike? Mmmmm..decisions, decisions. Catch ya later...Willy.
     
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