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#61
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On Sun, 20 Mar 2005 23:09:25 +0000, Simon Brooke
wrote: in message , Martin Wilson ') wrote: I've never seen a cheap bike with terrible alignment or substandard components. Then you haven't seen many cheap bikes. I've seen (and tried to adjust to some semblance of roadworthiness) several. I've seen at least one brand new 'Universal' brand bike in the past fortnight where the front dropouts were so far out of line that the front brake could not be made to work at all. Universal are an importer they don't make bikes. They are supplied with bikes by low cost factories in taiwan, china, vietnam, india etc. The same factories supply other brands including Raleigh, Falcon, concept etc. Some of the companies used are idealbikes, abeni, forever cycles, roadmaster (india) and quite a few others. What was the make and model of the universal bike in question ?(yes I realise it's imported by universal but many of their bikes are given other brand names) |
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#62
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In article ,
Ian Smith wrote: On Tue, 22 Mar 2005, Martin Wilson wrote: So your basically saying sheldon brown doesn't like them so the extra welded length of stays to the top tube has absolutely no improvement in strength at all. The fact the seat stays have two welded/anchor points does not add any strength what so ever. Absolutely. In fact, by adding local bending top teh tubes by loading them other than at teh node points of the truss, if anything, you'll weaken teh frame. They've taken a nice tidy shape that is intrinsically rigid without introducing local bending in teh elements of teh frame, then converted it to something that relies on local bending. real world users seem to accept GTs on this level and they have an excellent reputation for strength. After reading various postings So they make teh tubes thicker to compensate for poor design - doesn't make teh design good, and especially doesn't make it efficient. Spot on Ian. As another example of bad design... Consider this bike... http://www.dialledbikes.com/albert.htm To the uninformed, they'd think this hardtail which is meant for long travel suspension forks would be stronger because of the extra tube reinforcing the headtube area, but all the strut does is make the head area more rigid and concentrate the forces that would usually rip a head tube off into the weakest part of the bike - the thin walled main tubes so it's LESS strong than a normal diamond frame or one with well done side plates that transfer the head tube stress into the sides of the main tubes. The GT design is less of a problem as it's less stressed so is mostly cosmetic. And I can work this out without FEA software. ;-) Shaun |
#63
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In article ,
Martin Wilson wrote: Yeah right like I was suggesting there was about 3 inches of movement or something. You must surely realise that even a tiny amount of movement like 2mm or 3mm would still have a shock reducing effect and would be instantanously corrected. They don't even move that much with few exceptions - Ritchey Plexus being the obvious example, which you'd notice also has quite poor braking performance if you've ever ridden one. I don't know what your imagination is up to but I can assure you my seat and chain stays do not operate like some sort of elastic bands. Its well documented that the GT triple triangle frame design is more rigid because it supports the seat stays at both the seat tube and top tube with welds. It's also bunkem. There's no merit in the design at all. As a heavier rider I'm obviously going to get more movement there. If you sit on a brick do you expect it compress more than if I sit on it? Ok, perhaps it does at some sub-atomic level but like the forces in a bike rear triangle, it's negligible. What is your problem? Are you saying high tensile steel is not capable of flexing slightly under loads? Not saying that at all but in the context of a bicycle frame's rear triangle, it's irrelevant. What's more important is the quality of the welds joining everything together and on cheap Hi-Ten or for that matter cheap cromo or aluminium bikes, that's usually where they fail. Surely its aluminium frames which can be damaged by excessive constant flexing and they would have thicker seat/chain stays. But chain stays are usually built not to flex AT ALL no matter what you make them of. The exception being the Plexus and softtail bikes like Moots and the Ibis Ripley - both of which I've ridden. The Ripley was made entirely of aluminium and had about an inch of travel in the rear. It used a completely flat plate of aluminium, like a ruler, for a chainstay. Castellano, who designed the Ripley, is an ex-aircraft engineer. He went on to start his own bike company - http://www.castellanodesigns.com/ and still makes completely aluminium bikes with flexible chainstays. Read about it here - http://www.castellanodesigns.com/tech.html As I'm riding the bike its very difficult for me to judge technically why a frame is more comfortable all I know is it is and admittedly my guess is the seat and chain stays because when I've read about older bikes generally being often more comfortable using steel frames it seems to be flexing of the seat/chain stays which is the reason. Many older bikes use earlier possibly less advanced high tensile steel like my Raleigh Royal. It's a myth that has propagated down the years and still persists. It's got nothing to do with chainstays flexing. The comfort on a steel frame comes from the main tubes and a certain amount of splay in the wheelbase which dampens a lot of road vibration. It's even more of a myth on a mountain bike with big 2 inch wide tyres. Any splay at the fork is a bad thing if you're running a suspension fork - it just gets juddery for no reason and interferes with the forks small bump performance. Lateral splay also messes up the handling which isn't such a deal on a road bike but is offroad IMHO. I can't deny the possibility that its the seat post. It doesn't feel like the seatpost but its the only bike with a steel seatpost as far as I can tell. I don't see how it would absorb shocks though. Stick a ruler on a desk edge. Bend it up and down. That is what your seatpost is doing backwards and forwards. Now stick a pen on the edge of a desk and do the same. Bigger diameter, less flex. That's why oversize tubed bikes feel less comfortable. Aluminium seatposts generally flex more than steel ones too. Now stick a set square on your desk, one edge on the desk, pointy end in the air. Push down on the point - it doesn't flex vertically at all. It will eventually flex laterally with a side load, but that won't happen like that on a bike as a bike has two triangles joined at the points by the axle, bottom bracket, brake bridge, chainstay bridge (usually) and seat tube. Oddly, these same people whinge on about fatigue life too. Perhaps they should tell aeroplane designers that those big flexy wings need replacing with some nice heavy hi-ten steel ones? Yeah right like aeroplane wings flex about like the wings of bird, in fact you wonder why they have to fit jet engines or props at all. I'm pretty sure they design planes to minimise flexing/bending of the wings. Its a known fact that as a general rule steel can flex a lot more than aluminium without long term damage or structural problems. Its not that aluminium can't flex/bend its just you don't want it to because it would weaken it and shorten its lifespan. The wings on a 747 jet flex up and down 30 feet at the ends and are made out of aluminium, not steel. Jumbo jets fly thousands and thousands of miles every day without their wings falling off or being replaced. Shaun |
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Martin Wilson wrote:
So your basically saying sheldon brown doesn't like them so the extra welded length of stays to the top tube has absolutely no improvement in strength at all. The fact the seat stays have two welded/anchor points does not add any strength what so ever. No, I'm simply pointing out Sheldon's opinion. I haven't been able to find any authoritative rebuttal of it, and it would be extremely uncharacteristic of Sheldon to make such a statement in such absolute terms without being pretty sure of his ground. Admittedly the well documented statement is referring to mainly GT's own information but real world users seem to accept GTs on this level and they have an excellent reputation for strength. Marketing material then? I'd hardly describe that as "well documented". They may well be strong, but that could be just because they're over-built to compensate for the poor design. Maybe they would be stronger still with a conventional arrangement of the tubes. -- Dave... |
#65
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On Tue, 22 Mar 2005 22:51:05 +0000, JLB
wrote: Martin Wilson wrote: [snip several paragraphs about cheap bike frames, one of several posts in this thread on the same subject by Martin, and it's not the first thread where he's engaged on the subject]... I'm not sure I even care anyway ...[snip another couple of paragraphs] I can hardly wait to see what you'll do for a topic you really care about. I just made the point that of the bikes I've got the cheap bike seems very comfortable even with its greater weight. I don't see it as vastly inferior to my Kona, Gt or Giant. Its the bike that gets most used and abused. It goes out in all weathers and basically gets treated lke rubbish but I really can't fault it and don't know why people go on about how bad some of these cheap bikes are. Howver in the context of the posting you are referring too. I just mentioned that GT's triple triangle is meant to have a harsher ride as thats what I'd read and got the impression from reading over postings on mountain bike forums. As I've said I don't care if the GT does or doesn't have a more rigid frame. My point is simply the cheap bike is very comfortable and if anything seems to soften impacts more than the other bikes at the rear. This forum seems to be full of people with opinions that cheap bikes are; 1. Death traps 2. Unpleasant to ride 3. uncomfortable 4. incredibly heavy 5. have totally warped frames that you can't even fit wheels to or get the brakes to work etc. 6. the frames for these bikes are stored in the back of your local bike shop 7. The bikes are hidden away and never used. 8. They secretly enter your bedroom at night and will kill your whole family 9. They are special magnets that will cause airliners to crash into your house 10. Your family and anyone that goes near one will be jinxed for the rest of their life. 11. Your children will be born with terrible disfigurements and strange growths if you even think about buying one. 12. God himself is telling you not to buy one as its the 11th commandment but he forgot to mention it to moses at the time. Anyway I've sorted out a solution. I'm going to repaint the frame yellow and paint 'Cannondale' on it instead. So now on when I mention how much I enjoy riding my Cannondale or how good my Cannondale is it will be accepted. |
#66
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#67
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Martin Wilson wrote:
I just made the point that of the bikes I've got the cheap bike seems very comfortable even with its greater weight. I don't see it as vastly inferior to my Kona, Gt or Giant. Its the bike that gets most used and abused. It goes out in all weathers and basically gets treated lke rubbish but I really can't fault it So why bother with the others? This forum seems to be full of people with opinions that cheap bikes are; 1. Death traps Some are 2. Unpleasant to ride All the ones I've ridden have been. I've been in considerable discomfort after a few miles, though a lot of that would be correctable with a decent saddle. 3. uncomfortable Same thing as 2 in my book. 4. incredibly heavy If "incredibly heavy" bothered me in itself I wouldn't ride a couple of bikes that weighs 20 Kg. What is bad is excessively heavy for no good reason. The weight on my 20 Kg bikes all comes from useful stuff that makes the bikes better for my intended use. Things like fat steel tubes don't do that. 7. The bikes are hidden away and never used. Most of them are. For that matter, quite a few reasonable ones are too. Every now and then Trail mag exhorts its readers to "dig that bike out of the back of the garage and use it for walk ins" or similar. Why would it suggest this sort of thing if everyone's bikes were in regular use? Do some questioning around your friends and colleagues and see how many have bikes, and how many use them regularly. Pete. -- Peter Clinch Medical Physics IT Officer Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital Fax 44 1382 640177 Dundee DD1 9SY Scotland UK net http://www.dundee.ac.uk/~pjclinch/ |
#68
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On Thu, 24 Mar 2005 09:30:27 +0000, David Martin
wrote: 11. Your children will be born with terrible disfigurements and strange growths if you even think about buying one. Only if they are really made of Uranium. The quality of saddle provided will prevent this being a problem. |
#69
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On Thu, 24 Mar 2005 09:44:48 +0000, Peter Clinch
wrote: Martin Wilson wrote: I just made the point that of the bikes I've got the cheap bike seems very comfortable even with its greater weight. I don't see it as vastly inferior to my Kona, Gt or Giant. Its the bike that gets most used and abused. It goes out in all weathers and basically gets treated lke rubbish but I really can't fault it So why bother with the others? The variety of riding something different. For journeys where I don't have to worry about leaving it vulnerable to theft. Although it has to be said a big part was I simply wanted them. This forum seems to be full of people with opinions that cheap bikes are; 1. Death traps Some are Yes but which actual models? Normally if some item is unsafe it has a brand and model. If you hear that a washing machine can catch fire it might be a Candy 1100 or a tv that can catch fire it might be a wharfedale but what actual brand and models with regards bikes are actually unsafe. I assume its some sort of welding or material problem with them. |
#70
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Martin Wilson wrote:
Yes but which actual models? Normally if some item is unsafe it has a brand and model. But that isn't all there is to it. Often a cheap bike is unsafe because it's put together by someone Without A Clue and sold on to someone who doesn't know any better (case in point, a pal on a Halfwits Apollo MTB where the handlebars came off after a couple of days). I could make my /very/ expensive Streetmachine GT unsafe with some applied cluelessness, but that wouldn't make the brand and model inherently unsafe. I assume its some sort of welding or material problem with them. No, usually assembly, combined with components that don't encourage it to go together well. Bad welds happen but are unusual. OTOH, /any/ bolt or screw can come undone if it isn't done up properly to start with. Pete. -- Peter Clinch Medical Physics IT Officer Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital Fax 44 1382 640177 Dundee DD1 9SY Scotland UK net http://www.dundee.ac.uk/~pjclinch/ |
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