Results 1 to 32 of 32
  1. #1
    mtbr member
    Reputation:
    Join Date
    Aug 2010
    Posts
    180

    Plausibility of frames w/out top tubes

    When I ran across pics of the bixi rental bikes which are popular in urban areas in Canada, I thought, Why couldn't mountain bikes have those types of frames? It would shave some weight off the frame and make it a lot easier to mount and dismount (I've always wondered why the lowered top tubes are for women only). Am I missing some important physics/geometry info about the necessity of top tubes?
    Attached Thumbnails Attached Thumbnails Plausibility of frames w/out top tubes-bixibike.jpg  

    Granny gear lover

  2. #2
    mtbr member
    Reputation:
    Join Date
    Apr 2010
    Posts
    213
    what is the strongest shape? a triangle.

  3. #3
    Nouveau Retrogrouch SuperModerator
    Reputation: shiggy's Avatar
    Join Date
    Dec 1998
    Posts
    48,236
    Quote Originally Posted by John K.
    When I ran across pics of the bixi rental bikes which are popular in urban areas in Canada, I thought, Why couldn't mountain bikes have those types of frames? It would shave some weight off the frame and make it a lot easier to mount and dismount (I've always wondered why the lowered top tubes are for women only). Am I missing some important physics/geometry info about the necessity of top tubes?
    That is a street bike. Not subjected to the nearly the same stresses as an off road bike. Plus it must be heavier than a diamond frame to have the same strength. Even with the "light weight aluminum frame" the Bixi is about 40 pounds.
    mtbtires.com
    The trouble with common sense is it is no longer common

  4. #4
    It's about showing up.
    Reputation: Berkeley Mike's Avatar
    Join Date
    Jan 2004
    Posts
    12,737

    There is a bike

    with a cable downtube. Called a Slingshot.
    Attached Images Attached Images  
    Last edited by Berkeley Mike; 12-11-2010 at 09:48 PM.

  5. #5
    mtbr member
    Reputation: k1lluaA's Avatar
    Join Date
    Oct 2008
    Posts
    332
    god those things are ugly...
    2008 Kona Caldera

    "Today I saw my own son use a bicycle as a weapon....
    I seriously thought he was going to rape me"

  6. #6
    mtbr member
    Reputation: dkbikes4life's Avatar
    Join Date
    Nov 2010
    Posts
    406
    Imagine when the rear wheel takes a hard hit. There is nothing at the top of the seat tube to hold it and stop it from being pushed towards the front of the bike. You would constantly break frames at the bottom bracket area. Also if you were to jump the bike you would bend the downtube upwards over time. When I rode BMX I broke a trek Y issue frame down where the two tubes come together.

    This type of frame design works when your just sitting down and riding around town. But when riding a frame hard, a top tube is needed to keep the front and rear triangles from caving in on each other.

  7. #7
    mtbr member
    Reputation:
    Join Date
    Aug 2010
    Posts
    180
    Are you saying the bixi or the slingshot is ugly? I think the bixi actually looks pretty nice. Nice curve on the bottom tube.
    Granny gear lover

  8. #8
    Former Bike Wrench
    Reputation: mtnbiker72's Avatar
    Join Date
    Jan 2007
    Posts
    15,976
    Cannondale Super-V frames basically lacked a top tube


  9. #9
    mtbr member
    Reputation:
    Join Date
    Sep 2010
    Posts
    341
    Those c dales are the ugliest bikes ever produced along with the trek Y (YMMV). Like everyone else said a triangle is the strongest shape. It is also the easiest to make lightweight.

  10. #10
    mtbr member
    Reputation:
    Join Date
    Aug 2010
    Posts
    180
    The funny part is cheap brands like Next still use that frame design in their FS bikes. I see what you mean about triangles being the easiest to make lightweight. That's a thick ass bottom tube on the bixi, as well as some thick ass chainstays.
    Granny gear lover

  11. #11
    Former Bike Wrench
    Reputation: mtnbiker72's Avatar
    Join Date
    Jan 2007
    Posts
    15,976
    Quote Originally Posted by dust3313
    Those c dales are the ugliest bikes ever produced along with the trek Y (YMMV). Like everyone else said a triangle is the strongest shape. It is also the easiest to make lightweight.
    Didn't say it was good looking, but the main frame was durable (can't say as much for the headshox) and it lacks a top tube

  12. #12
    Nouveau Retrogrouch SuperModerator
    Reputation: shiggy's Avatar
    Join Date
    Dec 1998
    Posts
    48,236
    Quote Originally Posted by Berkeley Mike
    with a cable downtube. Called a Slingshot.
    I think you totally missed John's point.
    mtbtires.com
    The trouble with common sense is it is no longer common

  13. #13
    mtbr member
    Reputation: mtnbikerfred's Avatar
    Join Date
    Mar 2004
    Posts
    224
    Quote Originally Posted by mtnbiker72
    Cannondale Super-V frames basically lacked a top tube
    So did the Trek/Gary Fisher Y-bikes. Yup, we see lots of those around now don't we? =
    Giant Trance Advanced SL0
    Black Cat 26 " SS

  14. #14
    It's about showing up.
    Reputation: Berkeley Mike's Avatar
    Join Date
    Jan 2004
    Posts
    12,737

    Just revealing flexibility

    Quote Originally Posted by shiggy
    I think you totally missed John's point.
    in frame design assumptions.

  15. #15
    mtbr member
    Reputation: Mountain Cycle Shawn's Avatar
    Join Date
    Jan 2004
    Posts
    12,736
    Here's one:


    And another:

  16. #16
    mtbr member
    Reputation:
    Join Date
    Aug 2010
    Posts
    180
    mountain cycle shawn - which one is the 96 and which one is the 04?
    Granny gear lover

  17. #17
    mtbr member
    Reputation: Mountain Cycle Shawn's Avatar
    Join Date
    Jan 2004
    Posts
    12,736
    The first one is the '04. The frame now belongs to SanAnMAn. The polished one is the '96. I'm getting it a few new parts soon.

  18. #18
    mtbr member
    Reputation:
    Join Date
    Aug 2010
    Posts
    180
    Cool. I didn't know people used clipless pedals on FR/DH bikes. This is the exception rather than the rule right?
    Granny gear lover

  19. #19
    mtbr member
    Reputation: Mountain Cycle Shawn's Avatar
    Join Date
    Jan 2004
    Posts
    12,736
    Quote Originally Posted by John K.
    Cool. I didn't know people used clipless pedals on FR/DH bikes. This is the exception rather than the rule right?
    These are trail/all mountain bikes, clipless with this type of bike is perfectly normal.

  20. #20
    mtbr member
    Reputation:
    Join Date
    Aug 2010
    Posts
    180
    I see. I guess MC just makes super burly looking frames for all their bikes. How much do they weigh?
    Granny gear lover

  21. #21
    mtbr member
    Reputation: boomn's Avatar
    Join Date
    Jul 2007
    Posts
    9,961
    Quote Originally Posted by John K.
    Cool. I didn't know people used clipless pedals on FR/DH bikes. This is the exception rather than the rule right?
    a lot of DH riders, especially pro racers, use clipless for control and safety

  22. #22
    Hi.
    Reputation: jtmartino's Avatar
    Join Date
    Jul 2008
    Posts
    3,860
    Quote Originally Posted by mtnbiker72
    Didn't say it was good looking, but the main frame was durable (can't say as much for the headshox) and it lacks a top tube
    You don't think the HeadShoks were durable? I think their design resulted in superior stiffness and durability than their counterparts. There was greater surface area for bearing load during compression and in rebuilding a couple, I learned to appreciate their design far more than the standard friction bushing design of other forks. But I can't speak to their air cartridges, as I only had coil shocks. I was under the impression that they weren't as popular because most shops didn't have the capability to work on them and they were expensive to repair when sent in.

    And to all those stating that the triangle is the strongest shape, you must be omitting the shape of a circle due to limitations in framebuilding, right?

    And I'd be more inclined to believe that framebuilders make diamond-shaped bikes because it works and it's easy. Why screw up a good thing with new technology that may be difficult to manufacture or manipulate?

    But then again, there's guys like Jeff Jones who seem to bend the rules a bit, if you don't mind the pun.

  23. #23
    mtbr member
    Reputation:
    Join Date
    Aug 2010
    Posts
    180
    Quote Originally Posted by boomn
    a lot of DH riders, especially pro racers, use clipless for control and safety
    When you see riders doing gigantic jumps and flips, are they usually clipped in?
    Granny gear lover

  24. #24
    mtbr member
    Reputation: boomn's Avatar
    Join Date
    Jul 2007
    Posts
    9,961
    Quote Originally Posted by John K.
    When you see riders doing gigantic jumps and flips, are they usually clipped in?
    Doing flips and gigantic jumps over and over like at Red Bull Rampage would be FR, and in that case no, most are not clipped, they are using platform pedals so they can easily push away from the bike in mid-air. DH can involve a lot of jumping too but the focus is on getting down a trail at high speed without crashing (too much) so being clipped in is more common. In the real world there is some overlap between FR and DH though

  25. #25
    mtbr member
    Reputation: Mountain Cycle Shawn's Avatar
    Join Date
    Jan 2004
    Posts
    12,736
    Quote Originally Posted by John K.
    I see. I guess MC just makes super burly looking frames for all their bikes. How much do they weigh?
    29 pounds each.

  26. #26
    mtbr member
    Reputation:
    Join Date
    Apr 2010
    Posts
    84
    Quote Originally Posted by boomn
    a lot of DH riders, especially pro racers, use clipless for control and safety
    How, exactly, does being clipped in make it safer?

    And to the OP, not all bikes with dropped/angled/slanted top tubes are women specific. I'd venture to say that most new bikes have some sort of drop or angle going into the seat tube than not, and not many companies even have men/women specific models anymore.

  27. #27
    mtbr member
    Reputation: boomn's Avatar
    Join Date
    Jul 2007
    Posts
    9,961
    Quote Originally Posted by Philius413
    How, exactly, does being clipped in make it safer?
    Let me first clarify that "safety" here is a give and take thing; in some aspects clipless is safer and in other, different aspects platforms are safer. In other words, clipless isn't safer in every situation, but it is in some situations and it comes to down to the rider's personal preference of which situations are more important to them. Moving on...

    The ways that clipless can be safer are pretty much all matters of control, but at speed on rough trails control is safety.

    The biggest reason is that clipless keeps you from being bounced up off the pedals on rough sections of trail and big impacts. Proper technique of applying downward pressure on the pedals can help avoid this with platform pedals too, but it isn't as foolproof as clipless is, doesn't keep you from being surprised, and of course doesn't work if you simply forget. This problem was the thing that got me first considering clipless (esp after I had to ride to a stop with my junk on the top tube once) and my trails pale in comparison to the craziness of many DH courses and my speeds are slower too. Also, personally I feel like I ride "lighter" and less tense on my bike with clipless because I don't have to push down through rough sections and instead can float on the pedals or even lift a bit to help the bike float through smoother. That's not a safety issue though.

  28. #28
    mtbr member
    Reputation: Mountain Cycle Shawn's Avatar
    Join Date
    Jan 2004
    Posts
    12,736
    Quote Originally Posted by boomn
    Let me first clarify that "safety" here is a give and take thing; in some aspects clipless is safer and in other, different aspects platforms are safer. In other words, clipless isn't safer in every situation, but it is in some situations and it comes to down to the rider's personal preference of which situations are more important to them. Moving on...

    The ways that clipless can be safer are pretty much all matters of control, but at speed on rough trails control is safety.

    The biggest reason is that clipless keeps you from being bounced up off the pedals on rough sections of trail and big impacts. Proper technique of applying downward pressure on the pedals can help avoid this with platform pedals too, but it isn't as foolproof as clipless is, doesn't keep you from being surprised, and of course doesn't work if you simply forget. This problem was the thing that got me first considering clipless (esp after I had to ride to a stop with my junk on the top tube once) and my trails pale in comparison to the craziness of many DH courses and my speeds are slower too. Also, personally I feel like I ride "lighter" and less tense on my bike with clipless because I don't have to push down through rough sections and instead can float on the pedals or even lift a bit to help the bike float through smoother. That's not a safety issue though.
    You forget being clipped in?

    I have to agree, for all but the most extreme riding, clipless is safer, a lot easier and more fun to ride.

  29. #29
    mtbr member
    Reputation: boomn's Avatar
    Join Date
    Jul 2007
    Posts
    9,961
    Quote Originally Posted by Mountain Cycle Shawn
    You forget being clipped in?
    no, I was saying those are downsides to having to push down on platforms, that you can forget to apply enough pressure

  30. #30
    mtbr member
    Reputation: Mountain Cycle Shawn's Avatar
    Join Date
    Jan 2004
    Posts
    12,736
    Oh, I get it, sorry.

  31. #31
    mtbr member
    Reputation: boomn's Avatar
    Join Date
    Jul 2007
    Posts
    9,961
    Quote Originally Posted by Mountain Cycle Shawn
    Oh, I get it, sorry.
    no problem

  32. #32
    mtbr member
    Reputation:
    Join Date
    Nov 2007
    Posts
    59
    I like to compare being clipped in to wrapping your hands around the handlebar. Riding flat pedals is kind of like just resting your hands on top of the handlebars, it works in some situations, but in many you have more control by wrapping your hands/clipping in.
    And as pointed out it's lighter and stronger by having the triangle.

Members who have read this thread: 0

Posting Permissions

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

THE SITE

ABOUT MTBR

VISIT US AT

© Copyright 2019 VerticalScope Inc. All rights reserved.