Page 1 of 2 1 2 LastLast
Results 1 to 25 of 37

Thread: 1st Frame

  1. #1
    mtbr member
    Reputation:
    Join Date
    Aug 2008
    Posts
    34

    1st Frame

    I've been reading this forum for the better part of a year now, and as a senior in high school, I'm building a rigid 29er for my CADD project. I'm basing my jig off of an extrusion I-beam design. I've haven't had access to my drawing at school, so I've attached a scan of a previous printout. I know the 2nd top tube doesn't do anything, but from what I read as long as the down-tube is ample it won't hurt. For the miters I was planning on using a hole-saw to get close, and then hand filing. I'll be riding it for cross-country trails here at Bootleg Canyon and in the Golden/Denver area when I go up to school. I'm about 6'5" and 240lbs.(without gear).
    I rode various 29ers at Interbike, so I based the geometry somewhat off of what I liked about those and with what I have and like, a demo 7 and a 24" bmx bike(that'd I've been using for the cross country trails). It will mostly be used for cross country but also messing around(doing wheelies around campus and what not). So what I came up with:
    Head tube:130mm(68/69 angle)
    Effective Top Tube: 635mm
    Seattube:500mm(74 angle)
    Chainstay length: 450mm
    Bottom bracket drop:66mm
    Wheelbase: 1160mm
    I plan on using a 470mm atc fork with 38mm rake
    The thing I might want to change is the chainstay length. I think it would probably be better for me shorter, but I'd like to use straight gauge 7/8" with a single bend, so I'm not sure how short I can get them like that to still have clearance for a larger tire. I plan on running a 1x9 gear setup. It will most likely be TIG welded by a professional that has been welding for a long time and has done a few bike frames in the past(the founder of Redline actually worked for him for a while) so I'm not worried about heat control but I'm not sure about tube thicknesses and changes to geometry I may want to make.
    Thanks,
    Aaron
    Attached Thumbnails Attached Thumbnails 1st Frame-frame-jig-4.jpg  

    I hope your car has a big trunk because I am going to put my bike in it.

  2. #2
    mtbr member
    Reputation:
    Join Date
    Dec 2012
    Posts
    35
    You should go with shorter chainstays if you plan to do wheelies or even lift the front wheel at all. Its going to be very hard to lift the front on a bike with 450mm stays. I'm at 425mm on my 650B and I wish I had gone about 10mm shorter. You can offset your seat tube forward on the bottom bracket to get a little more tire clearance. I'm sure your professional welder can give you some advice if he has done bikes before.

  3. #3
    mtbr member
    Reputation:
    Join Date
    Jan 2011
    Posts
    745
    440mm stays are just fine. Going shorter will be hard to manage in terms of tire clearance. If you like wheelies a 29er might not be your cup of tea. People get way hung up on short chainstays but 430mm to 445mm will ride just fine.

    Wheelies are silly but it's not just about chainstay length...
    Chad Cottom's Mundo Wheelie - YouTube

    You don't need the small brace on the chainstays especially with TIG welded 7/8" stays. The little bridge does not add much strength or stiffness and is a pain to TIG. The extra top tube is also sort of silly because it makes the bike heavier and gets in the way of water bottles so I am not sure what the point is.

    Good luck and have fun with the build!
    Mark Farnsworth, Raleigh, NC
    http://farnsworthbikes.com

  4. #4
    mtbr member
    Reputation:
    Join Date
    Aug 2008
    Posts
    34
    Well he's a welder, not a bike frame builder so I'm not sure if he'll have much advice in that area. I'm not sure if I'm just taking your comment the wrong way Dsaul or if my statement of "professional welder" rubbed you the wrong way, but I wasn't saying that I'm getting my frame welded better than anybody else, I just meant I know the person is a proficient welder and its not a friend of a friend of a friend who may or may not be able to do this.
    To febikes, should I remove only the chainstay bridge or the seatstay bridge also? I'm considering removing the 2nd top tube, but I do really like how the bike looks with in(sorta like some of Coconino cycles) and I figure if I'm making my own frame might as well make it different.
    I hope your car has a big trunk because I am going to put my bike in it.

  5. #5
    mtbr member
    Reputation:
    Join Date
    Jan 2011
    Posts
    745
    Quote Originally Posted by mtnbikinggolfer View Post
    To febikes, should I remove only the chainstay bridge or the seatstay bridge also? I'm considering removing the 2nd top tube, but I do really like how the bike looks with in(sorta like some of Coconino cycles) and I figure if I'm making my own frame might as well make it different.
    Loose the chainstay bridge but keep the seat stay bridge.

    Also, use 5/8" round for seat stays or 16mm tapered. Use 7/8", 3/4", or bicycle specfic oval tubes for the chain stays.
    Mark Farnsworth, Raleigh, NC
    http://farnsworthbikes.com

  6. #6
    mtbr member
    Reputation:
    Join Date
    Dec 2012
    Posts
    55
    Move the chainstay brace to the area between the rear brake boss and the chainstay.

  7. #7
    Nemophilist
    Reputation: TrailMaker's Avatar
    Join Date
    Sep 2007
    Posts
    1,708
    Aaron;

    - I think you are reading DSaul wrong. He just thought your guy might have some ability to help you with the mods he suggested re; offset ST/BB, and other things to make the build easier and more successful.

    - The 2nd TT is redundant, but of course you know that. Adding a pure style piece is just fine as long as you can rationalize the extra weight. You might get a piece of .028 straight gauge to pare the weight down a touch, or even thinner if you can find it.

    - 17.5-ish CS is just fine. You can go shorter of course, but at the possible expense of some ultimate climbing traction. A 74* ST would shift your weight forward more, and that with the "longish" stays might make it harder to loft the front. However, I am the same size as you. I've got a 20mm longer TT, 454mm CS, and a 40mm longer WB, and I can still loft the front pretty much at will. I'll give you a traction for-instance; even riding my Kroozer in 6-8" of snow, I can climb a pretty steep grade, feel the front wheel floating off the ground a bit, and not lose traction at the back. Impressive.

    - I think .875 is overkill for the CS. I use .750 and it seems to work just fine. You can probably also use .625 for the SS without trouble, and save a bit more weight to offset your 2nd TT. Smaller tubes will also free up some tire space for you!

    - I wish that I had ditched the CS bridge on my Kroozer. It really catches a lot of muck. While it did add a noticeable amount of stiffening, that is when bending stays together with no wheel attached, and I'm not sure that is a valid test for any realistic action. My next frame will not have one.

    This from a two-frame-wonder with about 25% of a clue on any of this, so...
    Last edited by TrailMaker; 04-16-2013 at 09:58 AM. Reason: Spellung. ;)
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
    - John Hajny, a.k.a. TrailMaker

  8. #8
    mtbr member
    Reputation:
    Join Date
    Dec 2012
    Posts
    35
    TM is correct. I was just thinking your guy might have some experience that could help you figure out whether you should make changes to your design. With regard to chainstay length, I'm just sharing my experience. My frame also has a slack 69 degree head tube angle that lengthens the front center and puts the weight of the front wheel further forward. I ride fairly aggressively and like to lean back and loft my front wheel over obstacles while descending. I found that very difficult with the sliding dropouts at 435 and considerably easier at 425. I think it would be perfect for me at about 420.

  9. #9
    Moderator Moderator
    Reputation:
    Join Date
    Jan 2004
    Posts
    4,015
    Dude, he's 6'5"! I think he can probably lift the front wheel.

    Sheesh.

    -Walt
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  10. #10
    Most Delicious
    Reputation: dr.welby's Avatar
    Join Date
    Jan 2004
    Posts
    1,010
    Why the 74 seat angle?

  11. #11
    mtbr member
    Reputation:
    Join Date
    Apr 2012
    Posts
    204
    The second TT will be welded into a thinner section of the down tube. No biggie, just harder to tig thin stuff but do it for the look if you'd like.
    cheers
    andy walker

  12. #12
    mtbr member
    Reputation:
    Join Date
    Aug 2008
    Posts
    34

    tubing

    I'm dropping the chainstay bridge, and I didn't realize this printout didn't include the disc brake bridge. The second top tube will go for now, and if its all done and I decide I still want it, it can be added on without much trouble. I don't think I'll need to offset the bottom bracket for this one. The things I was unsure about were the effects of the seat tube angle and the fork trail.
    As far as tubing goes, I think it'll be;
    Head Tube:
    1.625" x .156" 4130 tube (Aircraft spruce), turned down to 1.6-1.7mm wall
    Top Tube
    31.8 x .7 / .6 OX Plat (BikeLugs)
    28.6 - 8/5/8 Ox Plat (Bike Lugs)
    31.8 x .9 Stress Relieved(VERHT1?)(Bike Lugs)
    Downtube
    34.9 x 1.2 / .8 x Stress Relieved 4130(Bike Lugs)
    Seattube:
    28.6 1.2/0.6/0.9 4130(NovaCyclesSupply)
    Bottom Bracket:
    1.5" x 73.5mm 4130(Paragon)
    Chainstays:
    3/4" x .035" 4130 tube(Aircraft spruce)
    Dropouts:
    Boomerang plate dropouts HD(Naked Bicycles)
    Seatstays:
    5/8" x .035" 4130(Aircraft spruce)

    Thanks for the tips and help everyone,
    Aaron
    I hope your car has a big trunk because I am going to put my bike in it.

  13. #13
    Most Delicious
    Reputation: dr.welby's Avatar
    Join Date
    Jan 2004
    Posts
    1,010
    Why a disc bridge with the Boomerang dropouts?

    Why not buy a head tube?

  14. #14
    mtbr member
    Reputation:
    Join Date
    Aug 2008
    Posts
    34
    Didn't come across the Boomerang dropouts until just now, so I didn't realize I wouldn't need the bridge(correct?). As for buying a head tube, I don't want the 44mm Paragon one and I don't mind making one.
    I hope your car has a big trunk because I am going to put my bike in it.

  15. #15
    Moderator Moderator
    Reputation:
    Join Date
    Jan 2004
    Posts
    4,015
    No way would I use a .7mm toptube if I weighed two-fiddy. Supertherm the toptube. Supertherm the downtube and go 38mm - 35 is way too wimpy. Use whatever the thinnest thing you can find is for the kicker tube (or whatever you call it).

    Otherwise I'd say you're good.

    -Walt
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  16. #16
    mtbr member
    Reputation:
    Join Date
    Aug 2008
    Posts
    34
    Where should I look for supertherm tubing?
    I hope your car has a big trunk because I am going to put my bike in it.

  17. #17
    Moderator Moderator
    Reputation:
    Join Date
    Jan 2004
    Posts
    4,015
    Henry James has it.

    -Walt
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  18. #18
    mtbr member
    Reputation: Eric Malcolm's Avatar
    Join Date
    Dec 2011
    Posts
    472
    I find it interesting that big Riders keep shelling for smaller Dia downtubes. If you are spidery like me, I can get away with it, but boy!! 250 pounders....38mm min, if you like to play, 42mm. The strength increase of a couple of mm is huge for little weight gain when, now that the redundant tube is out of the picture, won't add diddly squat to the big picture weight wise. The riding quality reward for the bigger tube is just too much to compromise on. Top tube = 31.8mm with a .9mm butt. No problem with turning a head tube, its not mythical, Paragons are turned. 74* ST = about 10mm at the seat for a longer leg over 73*. Its tuneable for seat adjustment, but if a more aggressive ride position is adopted, it uses the riders leg power better, though compromises the ability to wheelie. Also, that 635mm TT will keep the wheelie balance firmly planted at the front end. Big bikes will always be a challenge to get all the ticks of the boxes. Looks good otherwise.

    Eric
    If I don't make an attempt, how will I know if it will work?

  19. #19
    mtbr member
    Reputation:
    Join Date
    Aug 2008
    Posts
    34
    So would a 38.1mm 1/.7/1 ST downtube and 34.9mm 1/.7/1 ST top tube work? And would it be worth getting a .9/.6/1.22 S3 seattube too than? Or is it not worth the extra trouble for reaming it?
    Thanks for helping me
    I hope your car has a big trunk because I am going to put my bike in it.

  20. #20
    Most Delicious
    Reputation: dr.welby's Avatar
    Join Date
    Jan 2004
    Posts
    1,010
    74 seat angle is a little odd for a guy your height - is there a reason you picked that?

  21. #21
    mtbr member
    Reputation:
    Join Date
    Aug 2008
    Posts
    34
    Thought I addressed it, must've forgot. No reason really, just sort of based it off what I had ridden since I don't really know anything else. I'll be more than happy to hear if you have any advice about that.
    I hope your car has a big trunk because I am going to put my bike in it.

  22. #22
    mtbr member
    Reputation:
    Join Date
    Aug 2008
    Posts
    34
    I wasn't aiming for smaller tubes, I just forgot about Henry James. Would a 44.5mm 1/.7/1 ST be better for the downtube then, or is that pushing it too large? I'm not too concerned about weight. As far as seat tube angle, that was more so an arbitrary number and I welcome suggestions. I may considering shortening the front end too.
    Thanks,
    Aaron
    I hope your car has a big trunk because I am going to put my bike in it.

  23. #23
    mtbr member
    Reputation: Eric Malcolm's Avatar
    Join Date
    Dec 2011
    Posts
    472
    SuperTherm, where's Walt, this is his area.
    If I don't make an attempt, how will I know if it will work?

  24. #24
    mtbr member
    Reputation:
    Join Date
    Aug 2008
    Posts
    34
    He gave me suggestions for the Supertherm, and said 38 for the downtube. I didn't notice there was a 44 Supertherm downtube. I don't really care about the extra weight, but was unsure if there would be a reason not to use that.
    I hope your car has a big trunk because I am going to put my bike in it.

  25. #25
    Most Delicious
    Reputation: dr.welby's Avatar
    Join Date
    Jan 2004
    Posts
    1,010
    Since crank arms don't scale proportionately to the range of frame sizes, you often see bigger guys on slacker seat angles to account for it. But without knowing your proportions and seeing what you ride now we can't say whether it will or won't work for you. You won't run into any mechanical problems with it, like you would if you were trying to do a really slack seat angle with really short stays.

    Same goes for the front end - hard to say without more information. It's long, but you're tall, and the long back end would probably balance it out.

Page 1 of 2 1 2 LastLast

Similar Threads

  1. Replies: 0
    Last Post: 03-03-2013, 02:18 PM
  2. Replies: 0
    Last Post: 12-04-2011, 02:02 PM
  3. Replies: 5
    Last Post: 03-10-2011, 07:25 AM

Posting Permissions

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