Results 1 to 15 of 15
  1. #1
    mtbr member
    Reputation:
    Join Date
    Dec 2006
    Posts
    20

    Designing custom belt-driven singlespeed

    Hi all,

    I've been thinking about building up a belt-driven singlespeed frame for a while now and have finally decided to do something about it.

    I have spoken to several manufacturers about purchasing/modifying some sliding dropouts to allow them to split and let the belt through and am waiting to see how that progresses.

    In the meantime, I am looking at the overall geometry of the bike and trying to work out how I want it set up. I have very little experience of off-road singlespeed riding and thought that some of you may have ideas or insights that could be useful.

    Broadly, I am planning on quite an aggressive xc frame, not unlike the Scott Scale that I ride but made from titanium and set-up around around my old Pace RC31 rigid fork. Its intended use is for riding through the winter here in the UK on the sort of xc trails that I would ride on the Scott, the only difference being the amount of maintenance it would need after the ride. I may also use it for some marathon racing of things get very muddy!

    On the Scott I use low, narrow, flat barswith bar ends. Does anyone think it would be better to use a riser or make the geometry less race oriented? Would this make things a bit easier on the singlespeed? I'd rather keep it low and fast if possible but I'm open to all suggestions!

    Many thanks in advance,

    Ed

  2. #2
    mtbr member
    Reputation: Velobike's Avatar
    Join Date
    Jun 2007
    Posts
    4,578
    There's a bit more to building a belt-drive bike than splitting the rear dropout, so just make sure that whoever builds your frame has some experience with it.

    I have modified a few bikes and found that some frames do not have enough clearance for belt drive and others are much too flexy.

    When it works it's great.
    As little bike as possible, as silent as possible.
    Latitude: 5736' Highlands, Scotland

  3. #3
    mtbr member
    Reputation:
    Join Date
    Dec 2006
    Posts
    20
    That was quick!

    I know there's more to it than that but I was trying to keep it simple so that my post didn't read like War and Peace! Thanks for the heads up though

    Gates actually have a very good page with lots of info on potential pitfalls etc (http://www.carbondrivesystems.com/fo...s.php?lang=us). Neither I nor the frame builder have any experience of belt drives whatsoever so this is going to be quite a learning experience!

    Once I've got the dropout issue fully sorted I'll start work on checking chainstay lengths, clearance etc.

    My one concern is that flexible titanium might give a little too much. I'm hoping to run this one past Gates and see what they think.

    Thanks again,

    Ed

  4. #4
    mtbr member
    Reputation: Velobike's Avatar
    Join Date
    Jun 2007
    Posts
    4,578
    Quote Originally Posted by ejls2
    ...Once I've got the dropout issue fully sorted I'll start work on checking chainstay lengths, clearance etc.

    My one concern is that flexible titanium might give a little too much....
    Lynskey are offering a Ti belt drive frame, so hopefully it is not too flexy, but flex is your biggest enemy. One frame I used is too flexible at the BB so I get belt pop - doesn't come off, just rides up on the cog and snaps back down with a loud klaak. I sorted that by a bodge - butchered a Yess tensioner and fitted a pulley running just against the belt where it meets the cog.

    I think lateral flex on the chainstay is what to avoid because the belt can end up being fed into the rear cog at a slight angle. I don't think that vertical flex is the same problem.

    The best result was on a bike designed a single speed with track ends. Plenty stiffness in the BB and chainstay right from the start, easy to keep tensioned, and no belt pop yet.

    The dropout is actually the simplest issue, just a simple pin joint where the seatstay meets the dropout will do. I think some of the dropout solutions we are seeing are excessively complicated and have more to do with companies trying to make a proprietary solution rather than being the most efficient.
    As little bike as possible, as silent as possible.
    Latitude: 5736' Highlands, Scotland

  5. #5
    mtbr member
    Reputation:
    Join Date
    Dec 2006
    Posts
    20
    That makes sense. I think I might get the rear end built up with thick, plain gauge tubing to reduce flex problems. Certainly on the drive side chainstay. I wonder if I could get some box section tubing like the alu used on Nicolais...

    Will also build up the BB quite a lot. Thanks for the tip! Do you think a larger diameter down-tube help with BB stifness?

    I have actually just head back from Mark at Paragon. He has a slot dropout which has a simple break in it which looks like a good solution. May well try to get one of those.

    Any ideas about the geometry issue? Am I best off going with out-and-out XC or do you think it might be worth "softening" it a bit? I'm going to try to get some test rides in of other singlespeeds this weekend but any input would be welcome

    Cheers,

    Ed

  6. #6
    Off the back...
    Reputation: pinkrobe's Avatar
    Join Date
    Jan 2004
    Posts
    1,876
    I'm a big fan of 71/73 geometry for XC bikes, especially hardtails. Kona used to run 70.5 up front, and that might be better for messy winter riding.

  7. #7
    mtbr member
    Reputation:
    Join Date
    Dec 2006
    Posts
    20
    71/73 is what I run on my Scale. I take your point though about slackening it a bit for slippy winter riding. Will have a think!

    I have just emailed the builder and asked for a frame diagram. I've asked for it to be based on their standard 19" frame for now but may have a tweak when I see it.

    I have specified that:

    - it will be disc brake only so does not need v-brake bosses;
    - it will be singlespeed only so only needs hose guides for the rear brake hose;
    - sliding dropouts with the break in the chainstay for the belt drive;
    - front facing slot on the seat tube (to stop mud getting in);
    - crud catcher mounts on the downtube;
    - double butted tubing (but I may de-spec this if people think it might be too flexy); and
    - two bottle cage mounts.

    Can anyone think of anything that I may have forgotten? I just need to make sure that it's set up properly for my fork. I think I got the 440 mm version which should be correct for a 4" travel suspension fork.

  8. #8
    I am the owl
    Reputation: riderx's Avatar
    Join Date
    Jan 2004
    Posts
    1,705
    Quote Originally Posted by ejls2
    I have very little experience of off-road singlespeed riding and thought that some of you may have ideas or insights that could be useful.
    Before investing in a custom frame, especially one with a belt drive, it would be wise to get more experience so you know exactly what you want. There will be plenty of good (and bad) ideas that you can get from this forum, but only you will know your riding style and the things that feel good or bad that should go into your frame design. That will come from saddle time. Just my $.02
    SingleSpeedOutlaw .com
    Riding Bikes and Drinking Beer.

  9. #9
    mtbr member
    Reputation:
    Join Date
    Dec 2006
    Posts
    20
    I quite agree. I don't think I'll actually get it built up for a while yet, I'm still toying with ideas and designs but it never hurts to ask more experienced people what they think I've got the design now but it'll be a while before I actually order anything. I just find it helps me work out what issues I need to consider*.

    I'm fairly sure I want it to replicate my Scale as much as possible and so will try to try out singlespeeds with that sort of geometry but if everyone jumped on and said no, no, no you need more X or less Y or geometry Z then I would probably have tried that first.

    As it is, it seems that I can stick with the scale's geometry so I guess I can practice riding the scale without changing gear for a bit and see what happens!

    * - having seen the designs, I have realised that I need to consider rear brake cable routing. I'm in the UK so run a left hand rear brake. I also imagine that I will be carrying this bike up steep rocky sections quite often so having the cable under the top tube and on the left will lead to it getting kinked and hitting the frame. It looks like I'll have to go with it on the top right hand side and then cross it back down the left seat-stay behind the top of the seat tube.

    There is also an issue with the belt drive, in that the lengths of belt that are available don't seem to suit my standard 420mm chain-stays. I either need a longer one or a shorter one and that will compromise handling unless I can find a way of being clever

  10. #10
    mtbr member
    Reputation: Velobike's Avatar
    Join Date
    Jun 2007
    Posts
    4,578
    Quote Originally Posted by ejls2
    ...unless I can find a way of being clever...
    Excentriker or Forward Components EBBs could be used to move your crank thus allowing a little extra adjustment.
    As little bike as possible, as silent as possible.
    Latitude: 5736' Highlands, Scotland

  11. #11
    mtbr member
    Reputation:
    Join Date
    Dec 2006
    Posts
    20
    Nice idea! Though won't that end up altering the effective geometry?

  12. #12
    mtbr member
    Reputation: Velobike's Avatar
    Join Date
    Jun 2007
    Posts
    4,578
    Quote Originally Posted by ejls2
    Nice idea! Though won't that end up altering the effective geometry?
    No more than the variations you get using a SS with an EBB.

    If you have suspension you'll be seeing far bigger variations in geometry when you compare it at each end of the fork travel.
    As little bike as possible, as silent as possible.
    Latitude: 5736' Highlands, Scotland

  13. #13
    mtbr member
    Reputation:
    Join Date
    Dec 2006
    Posts
    20
    Thanks! I'm not going to have suspension on this one but I take your point! I'll have a look and see how much adjustability I can get between an eccentric BB and the sliding dropouts. My one concern would be that I've heard that belt drives can be quite hard on BBs due to the tension requirements and I imagine an EBB would be more susceptible to this than a regular one.

    It's a shame they don't have a belt that sits between 113 and 118 "links" though. Given the comparatively limited set of sprockets currently available, there doesn't seem to be a way to get a decent chainstay length, it either needs to be 415mm or 440mm. I'll try to do the maths and see what the maximum clearance I could get with 415mm stays would be.

  14. #14
    mtbr member
    Reputation: Velobike's Avatar
    Join Date
    Jun 2007
    Posts
    4,578
    Quote Originally Posted by ejls2
    ...It's a shame they don't have a belt that sits between 113 and 118 "links" though. Given the comparatively limited set of sprockets currently available, there doesn't seem to be a way to get a decent chainstay length, it either needs to be 415mm or 440mm...
    The big problem (in my opinion) is that the range of sprockets are aimed at hybrids rather than mountain bikes. A range that included smaller front sprockets would make it easier to fit with mountain bike chainstays.
    As little bike as possible, as silent as possible.
    Latitude: 5736' Highlands, Scotland

  15. #15
    mtbr member
    Reputation:
    Join Date
    Dec 2006
    Posts
    20
    From what I've seen, they seem to have been aiming them at 29ers as well. You still have the same issue with the chainstay clearance (which seems to be more of a factor of sprocket width than anything else) but the belts all seem to match up to to the slightly longer chainstays.

    The chainstay clearance is the next thing on my list of things to look at. Gates have a good manual on the correct alignment so I just need to work out the q factor of the chainset (Shimano XT) with the bottom brackets (Ecentric or Chris King) and try to see if it'll be clear.

    The good news is that the slotted dropouts result in slightly wider chainstays (as the inserts fit on the inside) so there is less chance of the rear sprocket fouling the chainstay as well.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •