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Originally Posted by fi3nd666
(Post 9037074)
i'm jacking this thread because this seems like a good place to ask my question. and i dont' want to starta new thread. . .
My rear tire is starting to wear down from the occasional skid. i'm a little broke a the moment and can't afford new tires just yet. would it be a bad idea to switch my front tire with my rear one to wear that one out first before i buy new tires? do any of you do this to save a couple bucks? http://www.sheldonbrown.com/tire-rotation.html don't worry, you're not the first to have it though, and at least you were smart enough to ask. Better than me the first time, front tires failing unexpectedly on descents can be very bad |
If you can see threads on your skidded out tire, don't do it. Get ye to the plasma center so you can buy an Innova Skyline, vittoria Zaffiro, Michelin dynamic, or the like. They're all under $15 'round here.
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Is that one of the Crank Brothers Eggbeaters? Did you show them that pic?
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Originally Posted by JackD
(Post 8969986)
Couple of principles. Skidding tires impart less resistance than rolling tires (basic physics).
The energy used to resist skidding is provided by your legs. Your legs also supply energy for accelerating your bike. The energy for pedaling forward strongly is the same as the energy available for resisting the motion. Thus no more force is put on the bike while skidding than while stomping on the pedals going forward. Further, chain tension created by typical FG is substantially lower than that generated by using a low gear on a mountain bike. Chain tension is inversely proportional to gear inches. Low gear inches mean higher potential for heavy stresses on chain - hub - bottom bracket. The chain tension required to skid a FG bike is less than half of what you would get hillclimbing in a granny gear. Seat stays on a fixed gear have only axial stress. Braking instead of skidding adds a load perpendicular to the seat stay. This stress is much tougher on the frame than an axial stress. So bottom bracket is experiencing lower forces than typical geared bikes and no different during skidding than when mashing hard. Seat stays have minimal stress. Chain tension on cog and chainring is lower than geared bikes and no different than when mashing. The only thing that is stressed more is your inseam as you stretch to impale your balls on your stem. This is basic physics people. Think about it.. |
Originally Posted by UCP
(Post 9038711)
Is that one of the Crank Brothers Eggbeaters? Did you show them that pic?
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tires and any thing in your drive train that is super cheap and nasty.. if you have nice parts hanging off your fixie the occasional loosing of your lock ring could be an issue
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Originally Posted by 2wheelsgood
(Post 8967138)
your bike will ooze machismo.
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Originally Posted by sugarkane
(Post 9046032)
tires and any thing in your drive train that is super cheap and nasty.. if you have nice parts hanging off your fixie the occasional loosing of your lock ring could be an issue
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I'm not really sure what he meant either.
Mazeav: I'm trying to figure out which clipless system I'd like to try, knowing that my purchase is a few months off. Eggbeaters never really looked all that stout to me. That pic is pretty much the axe in them for me. |
Originally Posted by UCP
(Post 9050927)
I'm not really sure what he meant either.
Mazeav: I'm trying to figure out which clipless system I'd like to try, knowing that my purchase is a few months off. Eggbeaters never really looked all that stout to me. That pic is pretty much the axe in them for me. |
ATAC seems to make the most people happy. Interesting Eggbeater photo. I have heard of many such failures, but not of the CB pedals that utilize some sort of platform, like the Candy or Quattro. Bearings seem to need frequent attention, and I have 3 rebuild kits sitting around waiting but haven't had to use them yet (I use Candys and Quattros and like them a lot).
If I was just starting to use clipless and was outfitting my bikes again, I would probably go ATAC. |
Originally Posted by JackD
(Post 8969986)
Couple of principles. Skidding tires impart less resistance than rolling tires (basic physics).
The energy used to resist skidding is provided by your legs. Your legs also supply energy for accelerating your bike. The energy for pedaling forward strongly is the same as the energy available for resisting the motion. Thus no more force is put on the bike while skidding than while stomping on the pedals going forward. Further, chain tension created by typical FG is substantially lower than that generated by using a low gear on a mountain bike. Chain tension is inversely proportional to gear inches. Low gear inches mean higher potential for heavy stresses on chain - hub - bottom bracket. The chain tension required to skid a FG bike is less than half of what you would get hillclimbing in a granny gear. Seat stays on a fixed gear have only axial stress. Braking instead of skidding adds a load perpendicular to the seat stay. This stress is much tougher on the frame than an axial stress. So bottom bracket is experiencing lower forces than typical geared bikes and no different during skidding than when mashing hard. Seat stays have minimal stress. Chain tension on cog and chainring is lower than geared bikes and no different than when mashing. The only thing that is stressed more is your inseam as you stretch to impale your balls on your stem. This is basic physics people. Think about it. You do it here again, "Low gear inches mean higher potential for heavy stresses on chain - hub - bottom bracket. The chain tension required to skid a FG bike is less than half of what you would get hillclimbing in a granny gear." Again please link to any kind of study done where this is proven and don't cop out like you and someone else did by telling me to take a physics lesson. |
precipitative awesomeness.
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It's raining lockrings?
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Originally Posted by Thetank
(Post 9051739)
I said it once and I'll say it again, PROVE IT! You can say all your "BASIC PHYSICS" but you're making claims like "chain tension created by typical FG is substantially lower than that generated by using a low gear on a mountain bike" where the hell do you get that info? Have you gone out and measured this yourself? Link to a study or article where this was tested?
You do it here again, "Low gear inches mean higher potential for heavy stresses on chain - hub - bottom bracket. The chain tension required to skid a FG bike is less than half of what you would get hillclimbing in a granny gear." Again please link to any kind of study done where this is proven and don't cop out like you and someone else did by telling me to take a physics lesson. Do you think a smaller chainring is easier to pedal than a big one? If yes, why do you think that is? There's your answer... |
Originally Posted by elTwitcho
(Post 9052649)
Dude, it's basic physics. If you don't understand how levers and pulleys work you need to learn rather than have someone else go through basic science lessons with you. You can't just sit here and demand proofs for things which are obviously true, it would be like someone demanding proof that a bicycle wheel has inertia or that a stiffer frame transfers power more efficiently. It's just obvious.
Do you think a smaller chainring is easier to pedal than a big one? If yes, why do you think that is? There's your answer... And I don't think it's out of line to want to see evidence of this. The statements made seem less obvious to me than the fact that a bicycle wheel has inertia. Also, if you asked someone to prove that a bicycle wheel has inertia, that person would be able to do that very easily. My entire high school geometry class consisted of proving things (that may be common knowledge to some) to be true. The thing that sketches me out about skidding is how sudden of a movement it is. Locking your wheel up into a skid happens really fast, as opposed to mashing up a hill which is a continuous, consistent movement (more or less). |
Because it increases your torque.
I'm taking physics in a week or two. |
Originally Posted by PedallingATX
(Post 9052748)
because it does less work.
So if you move the pedal a full rotation, the less chain you pull the more torque you put on the chain... |
Originally Posted by PedallingATX
(Post 9052748)
The thing that sketches me out about skidding is how sudden of a movement it is. Locking your wheel up into a skid happens really fast, as opposed to mashing up a hill which is a continuous, consistent movement (more or less).
Your leg exerts a force on the pedal which results in a force between the chainring and the chain. The tension in the chain is determined by the tangential force on the pedals and the difference between crank length and chainring radius. A smaller chainring means less chain pulled for each revolution of the cranks, therefore the chain tension will be greater for the same force on the pedals. If you've got a crank with a 44 tooth chainring, you'll have half the chain tension that you would if you put the same force on a crank with a 22 tooth chainring. Halve the tooth count again and you'll double the tension again. If you want proof, go out and try it. You'll have twice the acceleration with the halved tooth count, all else being equal, and the only thing that's changed is the force in the chain, and therefore the reaction forces in the rest of the bike. The "suddenness" of a wheel starting to skid isn't all that sudden. I can stop a wheel pretty damn suddenly just by spinning it in the stand and grabbing it with my hand, or by applying the brakes. Nothing explodes. |
If you've got a crank with a 44 tooth chainring, you'll have half the chain tension that you would if you put the same force on a crank with a 22 tooth chainring. Halve the tooth count again and you'll double the tension again. |
Originally Posted by Yellowbeard
(Post 9053929)
That's because you don't understand the physics.
Your leg exerts a force on the pedal which results in a force between the chainring and the chain. The tension in the chain is determined by the tangential force on the pedals and the difference between crank length and chainring radius. A smaller chainring means less chain pulled for each revolution of the cranks, therefore the chain tension will be greater for the same force on the pedals. If you've got a crank with a 44 tooth chainring, you'll have half the chain tension that you would if you put the same force on a crank with a 22 tooth chainring. Halve the tooth count again and you'll double the tension again. If you want proof, go out and try it. You'll have twice the acceleration with the halved tooth count, all else being equal, and the only thing that's changed is the force in the chain, and therefore the reaction forces in the rest of the bike. The "suddenness" of a wheel starting to skid isn't all that sudden. I can stop a wheel pretty damn suddenly just by spinning it in the stand and grabbing it with my hand, or by applying the brakes. Nothing explodes. I think it is a pretty sudden movement when your cranks are spinning at a certain RPM (along w/ your chain and rear wheel) and then you suddenly stop that entire motion in a split second. It's like those diagrams they used to show in drivers ed where a car hits something and the dummys keep going forward through the windshield (an object in motion will stay in motion). When I initiate a skid, I can't help but feel that I am forcibly restraining the entire drivetrain of my bicycle from continuing its forward motion. Explain to me why that is not jarring to all of the parts on said drivetrain. I just don't see it. There is a lot of momentum there in the cranks that is just suddenly stopped. A lone bicycle wheel in a truing stand does not have nearly the amount of momentum as a drive train that is carrying a heavy load going at a speed of, lets say, 17 m.p.h. |
A lone bicycle wheel in a truing stand does not have nearly the amount of momentum as a drive train that is carrying a heavy load going at a speed of, lets say, 17 m.p.h. |
Originally Posted by dtret7
(Post 9054410)
incorrect.
but i still don't see why that statement was incorrect |
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