26inch Posted February 11, 2007 Report Share Posted February 11, 2007 Hi, this may sound like an odd question but basically im trying to find reasons why the rear tiangle of a frame would be unlikely bend form breing droped/bailed. Im looking for reasonably tech answers (not just. 'should be strong enough not to be dropped') Thanks Quote Link to comment Share on other sites More sharing options...
Ash-Kennard Posted February 11, 2007 Report Share Posted February 11, 2007 think about it, if we dropped and landed on our wheels say on the spokes, then it probably would bend, but they are reinforced enough to prevent this when normally landed, if you think about the design, it is generally two triangles, with triangles being the strongest shape, it just seems logical.thats my 15 year old input for you Quote Link to comment Share on other sites More sharing options...
Walleee Posted February 11, 2007 Report Share Posted February 11, 2007 (edited) The material will bend permananetly once the material passes it's 'Eastic Limit' the material will bend before reaching this point, but it will bend back to it's original shape.If the loading continues past the elastic limit, the material will eventually fail resulting in a crack or snap of some sort.http://www.uoregon.edu/~struct/courseware/..._lecture24.htmlandhttp://en.wikipedia.org/wiki/Stress-strain_curveWill be particurily useful for you.^^ could almost bee seen as a comparison for steel and aluminium, aluminium is more brittle and doesn't have as much resistance to fatigue as steel, so tends to snap rather than bending.....Edit: havn't really answered you, the reason it's unlikely to bend is because there are two chain stays, when you drop from a height the chainstays pull away from the BB, without the seatstays, the rear wheel would move up(like a motor bike swing arm sorta thing) but because the seatstays are there, they transfer the force pushing the rear wheel up to the top of your seattube/toptube.i'll try and throw together acrude paint diagram for you.....Red arrow is the direction the force is pushing the back wheel, the blue's are the forces put upon the rear triangle.That any better for you than what I originally wrote? Edited February 11, 2007 by jake1516 Quote Link to comment Share on other sites More sharing options...
ogre Posted February 11, 2007 Report Share Posted February 11, 2007 wouldn't that make the frame crumple on the toptube? or am i being silly? Quote Link to comment Share on other sites More sharing options...
Walleee Posted February 11, 2007 Report Share Posted February 11, 2007 (edited) wouldn't that make the frame crumple on the toptube? or am i being silly?well, depending on the force, possibly, but it's rare. the transfer of the force from one tube to another creates a loss in energy, therefore reducing the stress as the force's go around the frame. Frame are usually designed in such a way that the chainstay's will snap before the top tube would, that and the fact that the chainstays are were most of the force is acting upon (remember your feet are allways on the pedals, something I neglected to include on the paint drawing)in theorey it could happe as you've said, but in practise by the time the stress get's there it's negligable.Edit: also consider how the tubes are placed, they are stronger under compression(which is what the top tube is under) than tension(what the chainstays are under) Edited February 11, 2007 by jake1516 Quote Link to comment Share on other sites More sharing options...
26inch Posted February 11, 2007 Author Report Share Posted February 11, 2007 Thanks for your help, its sort of helpful. Basically its for a warrenty claim, i'm trying to prove that the frame bent through manufacurers poor design/riding while they are saying bends happen from crashes/bails Quote Link to comment Share on other sites More sharing options...
Walleee Posted February 11, 2007 Report Share Posted February 11, 2007 Thanks for your help, its sort of helpful. Basically its for a warrenty claim, i'm trying to prove that the frame bent through manufacurers poor design/riding while they are saying bends happen from crashes/bailsWhat sort of frame is it?Where did it break?Generally manufacturer's will have a get out clause where it may only be manufacturing errors that are covered, if for example some chinaman forget's to finish off a welding program and your frame is only spot welded or something crazy, they would be responsible, but the frame wouldn't get out of the factory in that state ever.who is it that's giving you hassle bout replacing/compensating for it. Quote Link to comment Share on other sites More sharing options...
ogre Posted February 11, 2007 Report Share Posted February 11, 2007 dinting would make a differnce to it bending, because wouldn't the forces focus there? Quote Link to comment Share on other sites More sharing options...
26inch Posted February 11, 2007 Author Report Share Posted February 11, 2007 Its a dmr. Ive had them crack before and theyve been fine about it, Really im just trying to prove that a frame would not bend from a crash /bail Quote Link to comment Share on other sites More sharing options...
ogre Posted February 11, 2007 Report Share Posted February 11, 2007 why wouldn't it though? 'cause you'd be weakening it surely when yuo dent a fram the metal is stretched thiner to make the extra surface area from the dent Quote Link to comment Share on other sites More sharing options...
Simpson Posted February 11, 2007 Report Share Posted February 11, 2007 (edited) edited.... cba with the agro sorry for cluttering up the thread Edited February 11, 2007 by Simpson Quote Link to comment Share on other sites More sharing options...
Krisboats Posted February 11, 2007 Report Share Posted February 11, 2007 Its a dmr. Ive had them crack before and theyve been fine about it, Really im just trying to prove that a frame would not bend from a crash /bailYeah it blatantly could. Say your doing a 720 over a double, and land sideways on the top of the landing ramp with all the force being absorbed by your rear triangle.Thats enough to bend it. Hell i've seen a frame bend when someone failed to bunnyhop onto a bin, the rear triangle was all misalligned and so the frame got scrapped. Quote Link to comment Share on other sites More sharing options...
downhill_rob2@hotmail.com Posted February 12, 2007 Report Share Posted February 12, 2007 wouldn't that make the frame crumple on the toptube? or am i being silly?No, not really, you cant crush a a straight pipe lengthways...Like, you can stand on a empty coke can, when its standing up, and it wont crush...But do it on its side, and it crushes really easily... Its a dmr. Ive had them crack before and theyve been fine about it, Really im just trying to prove that a frame would not bend from a crash /bailThere needs to be alot of presure for a frame to bend, the weight of the bike itself isnt enough for the frame to bend... but it enough for it to dent... Quote Link to comment Share on other sites More sharing options...
Walleee Posted February 12, 2007 Report Share Posted February 12, 2007 Your fighting a loosing battle, of course frames can get broken from bails/crashes/ghosties, you'd like to think that they won't break, as if they can't handle the stress without a rider how will it handle it with an extra 10-15 stone bouncing about? Quote Link to comment Share on other sites More sharing options...
Fixed Pants™ Posted February 12, 2007 Report Share Posted February 12, 2007 Pics would help? Quote Link to comment Share on other sites More sharing options...
nmt_oli Posted February 12, 2007 Report Share Posted February 12, 2007 About to say, any pics of what your tryig to argue would def help us help you.A bike frame is effectively a pin jointed framework, very structually strong in some directions, and not others. If i wasnt about to go to bed id get more involved and start drawing diagrams, ect. As people have said, a heavy bail on the side of the bike is enough to twist a frame, they are weakest side on. Quote Link to comment Share on other sites More sharing options...
26inch Posted February 13, 2007 Author Report Share Posted February 13, 2007 HaFor all you non believers if you spend enough time on the phone you can get somewhere. I ended up getting a new frame with headset for £50 Quote Link to comment Share on other sites More sharing options...
Waynio Posted February 13, 2007 Report Share Posted February 13, 2007 (edited) a wheel is like an egg, and i have found some frames are just like eggs, you can land on them all days long from pressure hitting them in a line (from drop offs and gaps etc) BUT knock them from the side and they have more of a tendancy to bend. its purely the impact that is put on the bike, you wouldnt stop something bending as there in theory has to be some degree of flex in things, or it would literally do damage to the person riding it, it would be like a bucking bronco!!!if i was more scientific i would have guessed and looked into it being something to do with the grade of the aluminium material used and if the "grade" of alloy goes along tubes as opposed to around tubes or vice versa, it may have something to do with that. (but god knows it might be totally irrelevant )it is quite an interesting thing. are you trying to get the point across that things WILL always bend? or are you trying to come up with an idea to STOP things bending?Waynio.......................JUST one thing for you to consider, watch Evolve when Ryan Leech dents the top tube of his Ti Norco frame???? that is totally accidental and HAPPENED it is fact that things will bend and break from Crashes (Terror-error has a very valid point on it literally how i look at it) Edited February 13, 2007 by Waynio Quote Link to comment Share on other sites More sharing options...
Walleee Posted February 13, 2007 Report Share Posted February 13, 2007 (edited) a wheel is like an egg, and i have found some frames are just like eggs, you can land on them all days long from pressure hitting them in a line (from drop offs and gaps etc) BUT knock them from the side and they have more of a tendancy to bend. its purely the impact that is put on the bike, you wouldnt stop something bending as there in theory has to be some degree of flex in things, or it would literally do damage to the person riding it, it would be like a bucking bronco!!!if i was more scientific i would have guessed and looked into it being something to do with the grade of the aluminium material used and if the "grade" of alloy goes along tubes as opposed to around tubes or vice versa, it may have something to do with that. (but god knows it might be totally irrelevant )it is quite an interesting thing. are you trying to get the point across that things WILL always bend? or are you trying to come up with an idea to STOP things bending?Waynio.......................JUST one thing for you to consider, watch Evolve when Ryan Leech dents the top tube of his Ti Norco frame???? that is totally accidental and HAPPENED it is fact that things will bend and break from Crashes (Terror-error has a very valid point on it literally how i look at it)The heat treatment of the metal once the frame has been welded allows the material to soften up to a degree. In the material there are microscopic 'dislocations' which are the causes of weakness in materials. When heated to the right temperature for the right length of time the metal softens to a point where it basically sort itself out, the dislocations reduce in size/disappear and the ideal grain structure of the material takes form, try to imagine loads of diamonds in a 'crystal lattice' type structure??(like what climbing plant's use to grow up walls?)But yeh, that's pretty irrelavent seeing as I think it's a steel frame being a DMR, and they generally don't under go heat treatment as welding doesn't soften them up as much. Edited February 13, 2007 by jake1516 Quote Link to comment Share on other sites More sharing options...
Bionic Balls Posted February 14, 2007 Report Share Posted February 14, 2007 jake my son...i think a little too much wikipedia is going on here.. Quote Link to comment Share on other sites More sharing options...
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