Mark W Posted February 23, 2005 Report Share Posted February 23, 2005 That's what I was trying to point out; the fact that there needs to be a long period of testing, as opposed to just a few months. Quote Link to comment Share on other sites More sharing options...
andyroo Posted February 23, 2005 Report Share Posted February 23, 2005 Its all about fatigue though, also different forces being put on the forks. Braking forces, sharp braking forces in trials. Backwards stress from hooks, lots of instant stress coming from the front with bumps. The only way to test all these is with riders... ← But the forks will only fatigue and get stressed if they are taken passed their elastic limit, which can also be found out using the method i was talking about in my previous post. Its a much quicker, safer way of testing the forks limits, and knowing them for sure. applying an increasing pressure would suficently test the strength of the forks. Quote Link to comment Share on other sites More sharing options...
Tartridge Posted February 23, 2005 Report Share Posted February 23, 2005 How much force does the average rider put through a set of forks though? And in which direction? How do disc/rim brake forces add to/oppose this? And how many cycles at each level of stress do forks go through during their lifespan? All these questions are impossible to answer (at the moment), so the best way of testing forks is to give them to Rossi and have him ride them for a few months (Y) Quote Link to comment Share on other sites More sharing options...
andyroo Posted February 23, 2005 Report Share Posted February 23, 2005 How much force does the average rider put through a set of forks though? And in which direction? How do disc/rim brake forces add to/oppose this? And how many cycles at each level of stress do forks go through during their lifespan? All these questions are impossible to answer (at the moment), so the best way of testing forks is to give them to Rossi and have him ride them for a few months (Y) ← The only forces that will affect the steerer bond are the ones adjacent to it. And for the forces on the forks applied by the rider, you use a worse case scenario, taking the speed the bike approaches something, the mass of rider and bike, then you can work out the force applied onto the forks by the surface pushing against them. and then times it all by 1.4 just to be safe! that should be the greatest force the the forks would need to take, and then you can test the forks, by applying that amount of force on them, and seeing if they stand up to it. Not oo difficult with a company with a budget for r+d Quote Link to comment Share on other sites More sharing options...
Mark W Posted February 23, 2005 Report Share Posted February 23, 2005 Yes, but how can you work out what the force is anyway? Even for something as simple as a nosehop, you've got the fork legs being splayed outwards by the brake mount if a rim brake is used, the fork legs being bent by the force of the weight on them, if a disc is being used there'll be additional force there - there's just too much going on for them to be calculated even half-way accurately, or at least accurately enough to test them. However, a rider can test them perfectly well. Plus you can just get so many random forces being applied unexpected ways and so on. Edit: Not to mention there'll be different forces on the legs if the brake isn't set up correctly (or perfectly symmetrically), the wheel build isn't right, etc. Quote Link to comment Share on other sites More sharing options...
andyroo Posted February 23, 2005 Report Share Posted February 23, 2005 Yes, but how can you work out what the force is anyway? Even for something as simple as a nosehop, you've got the fork legs being splayed outwards by the brake mount if a rim brake is used, the fork legs being bent by the force of the weight on them, if a disc is being used there'll be additional force there - there's just too much going on for them to be calculated even half-way accurately, or at least accurately enough to test them. However, a rider can test them perfectly well. Plus you can just get so many random forces being applied unexpected ways and so on. ← im talking about the force on the steerer here- disk mount and rim brake mounts have ben tryed and tested to get strength, but the bond seems to be the big problem on these forks, and im talking about testing that. Any splay in the legs caused by braking will have little effect on the steere bond, and would be taken into account by a safty margin of 1.4 anyway. (1.4 because thats what the britich standards use for dead loads on beams and columns, and if its good enough for them, its good enough for me) Quote Link to comment Share on other sites More sharing options...
Tartridge Posted February 23, 2005 Report Share Posted February 23, 2005 Safety factor varies from 1.1 for aircraft, to 13 for civil engineering type structures, as im sure you know, but which one should you use? Where did 1.4 come from? Bike parts arent subject to dead loads. Also, its all very well testing these forks for failure - but we know they will take that. Fatigue is what destroys undamaged aluminium bicycle parts though (mostly). 'The only forces that will affect the steerer bond are the ones adjacent to it' What about direct tension? Torsion? None of these companies can be bothered to work all this out, its much easier to just slightly overbuild the fork, and then give it to a street basher for a few months. Another thing - why not just sack the bond off altogether? Its obviously crap! Quote Link to comment Share on other sites More sharing options...
boon racoon Posted February 23, 2005 Report Share Posted February 23, 2005 dan lend 'em me... then we'll see wat's a REAL fork (Y) pashley forks = 2 weeks Quote Link to comment Share on other sites More sharing options...
Tartridge Posted February 23, 2005 Report Share Posted February 23, 2005 dan lend 'em me... then we'll see wat's a REAL fork :) ← See, street basher :P" :P Just messin (Y) Thats the best way to test things :D Quote Link to comment Share on other sites More sharing options...
andyroo Posted February 23, 2005 Report Share Posted February 23, 2005 Safety factor varies from 1.1 for aircraft, to 13 for civil engineering type structures, as im sure you know, but which one should you use? Where did 1.4 come from? Bike parts arent subject to dead loads. Also, its all very well testing these forks for failure - but we know they will take that. Fatigue is what destroys undamaged aluminium bicycle parts (mostly). 'The only forces that will affect the steerer bond are the ones adjacent to it' What about direct tension? Torsion? None of these companies can be bothered to work all this out, its much easier to just slightly overbuild the fork, and then give it to a street basher for a few months. Another thing - why not just sack the bond off altogether? Its obviously crap! ← I am a civil engineer, civils dont build structures, structural engineers do. And the 1.4 factor for dead loads is taken from the BS handbook in the section for structural engineering with steel. Im not saying a bike is subject to dead loads, its just a used factor for safety. The point I am getting at, is if you really want to make a stiffer fork using a bonded steerer, it would be safer to apply an increasing force adjacent to the forks on the legs with the steerer clamped in place, so at least then you can say "Aha, the bonded steerer will withstand a direct force of however much, meaning trials riders who only exert so much force will not be able to break the bond." And then I was saying it would be a better pay off, to design the forks to withstand an adjacent force of a factor of the max force a trials rider could put on the steerer, thus eliminating all this hoo haa about the strength of the bonded steerer, meaning quicker release and quicker return in profit. Quote Link to comment Share on other sites More sharing options...
Mark W Posted February 23, 2005 Report Share Posted February 23, 2005 But the steerer is going to be moved by more than one plane of force? Quote Link to comment Share on other sites More sharing options...
Tartridge Posted February 23, 2005 Report Share Posted February 23, 2005 I am a civil engineer, civils dont build structures, structural engineers do. And the 1.4 factor for dead loads is taken from the BS handbook in the section for structural engineering with steel. Im not saying a bike is subject to dead loads, its just a used factor for safety. The point I am getting at, is if you really want to make a stiffer fork using a bonded steerer, it would be safer to apply an increasing force adjacent to the forks on the legs with the steerer clamped in place, so at least then you can say "Aha, the bonded steerer will withstand a direct force of however much, meaning trials riders who only exert so much force will not be able to break the bond." And then I was saying it would be a better pay off, to design the forks to withstand an adjacent force of a factor of the max force a trials rider could put on the steerer, thus eliminating all this hoo haa about the strength of the bonded steerer, meaning quicker release and quicker return in profit. ← I know that - i was probably wrong there, sorry, what do civils build? Cakes? Bike parts are aluminum and steel, and not subject to dead loads - so its totally pointless to use that factor? The point here is making a stronger fork, not a stiffer one? We cant quanfity the max force yet though, so its also useless. It could be done, but theres not enough money in trials to justify it. But the steerer is going to be moved by more than one plane of force? ← That too (Y) Quote Link to comment Share on other sites More sharing options...
andyroo Posted February 23, 2005 Report Share Posted February 23, 2005 The most force on the steerer will be that adjacent to it. If you really want to, you could use the live load factor for structures (which is the same whatever material you use in a structure) of 1.6. What your saying is that if i measured the force of someone punching me in the face, that force would cover the amount of force if someone poked me in the eye, because it is a lot greater. So when the force is coming at 90 degrees to the steerer, that will be the position that will have the most affect on the steerer, and will cover the smaller forces applied in other directions (like braking). I said before the max force would be simple to work out with mechanics (time to dig out those old A level books when i get home) using speed, weight and the formula for a collision against a still object. this will give you the force acting onto the object at the point of collision, which is equal to the force acting on the steerer. The only reason you use a steel bond over all alu, is to make the forks stiffer, but still not too heavy, like you said, so you need to make sure the bond is strong enough to make the extra stiffness created by the steel steerer worth it. Although civils do eat a lot of cakes, they dont build them. We do infrastructure ie roads and drainage Quote Link to comment Share on other sites More sharing options...
Heatsink Posted February 23, 2005 Report Share Posted February 23, 2005 On the fatigue point - Just to clear up the definition: Fatigue is the failure of a component due to loads below the material's breaking stress. This occurs because these loads are applied many times. Of course the higher the stress then the less number of cycles required to break the component. The beauty of steel and titanium is that you can eliminate fatigue failures if the stresses in the component go below a certain value, i.e. a proportion of the breaking stress. For aluminium it's possible to break the component no matter how low the stress if you apply it enough times, although the figures may be so high that they are outside the reasonable life of the component and so not a problem. From my own work with designing steel components for non-bike application with fatigue in mind, I've found that a factor of safety of 1.4/1.5 is a bit of a magic figure, because from the data I found, then you'll safely fall under the "Endurance limit" for steel and so sidestep any failures due to fatigue. Steve Quote Link to comment Share on other sites More sharing options...
Mark W Posted February 23, 2005 Report Share Posted February 23, 2005 The most force on the steerer will be that adjacent to it. If you really want to, you could use the live load factor for structures (which is the same whatever material you use in a structure) of 1.6. What your saying is that if i measured the force of someone punching me in the face, that force would cover the amount of force if someone poked me in the eye, because it is a lot greater. So when the force is coming at 90 degrees to the steerer, that will be the position that will have the most affect on the steerer, and will cover the smaller forces applied in other directions (like braking). I said before the max force would be simple to work out with mechanics (time to dig out those old A level books when i get home) using speed, weight and the formula for a collision against a still object.← But what does the last bit prove? It's not just the hitting still objects that's the problem? When someone lands a drop flat, for example, the force goes into pushing the fork leg upwards, twisting it from the pivot point which would be the bottom of the steerer. This means the force is going to be effectively tearing the steerer away from the legs from the back to the front. Your plane of movement won't cover this. If you're doing a 360 spin off something, you're going to land and you'll have the force of the landing pushing the forks up as before, but with the shitload of additional forces putting a torsional strain on the steerer, too. Either way, how strong the forks are won't just be about the steerer, will it? Quote Link to comment Share on other sites More sharing options...
Tartridge Posted February 23, 2005 Report Share Posted February 23, 2005 All very nice, but the head and tail of it is that current bonded steerers still break easily (Y) Quote Link to comment Share on other sites More sharing options...
andyroo Posted February 23, 2005 Report Share Posted February 23, 2005 (edited) Does the alu have a much lower elastic limit than steel then? So that steel can flex a lot more and return to its original shape without effect before actually becoming plastic? EDIT: Using Ads website, I answer my own question by saying yes, steel is a lot more flexable than alu, by a considerable amount! (4 times) Edited February 23, 2005 by andyroo Quote Link to comment Share on other sites More sharing options...
Tartridge Posted February 23, 2005 Report Share Posted February 23, 2005 http://www.matweb.com (Y) Quote Link to comment Share on other sites More sharing options...
andyroo Posted February 23, 2005 Report Share Posted February 23, 2005 All very nice, but the head and tail of it is that current bonded steerers still break easily (Y) ← Especially if they dont take the time to design them with safety factors. I think weve poo pooed these forks enough now! Oh well... Quote Link to comment Share on other sites More sharing options...
Dan@Trials-uk Posted February 23, 2005 Report Share Posted February 23, 2005 Hey All I can say to people who's wondering what these forks are like for strength, is to wait until they have been on the street for abit(Y), I mean I have been using my pair for about 6 months now, and they was the prototype ones aswell!, these forks has been in :python 04, team 05, python 05, and its still going strong now (Y) Best regards Dan@vizbikes. P.s stop with the massive argument, there is no need. Quote Link to comment Share on other sites More sharing options...
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