aener Posted March 17, 2008 Report Share Posted March 17, 2008 (edited) I was talking to a guy at work, he knows a fair bit about bikes - rides a lot of XC.He'd never heard of trials before (he's oooooold, compared to most of us.... late 40's), but when I told him about it, he'd seen some clips.He raised an interesting point - one that I'd never thought about before.He said: "When you do that hop to the side, and especially the ones where you keep it at quite a vertical angle on just the back wheel - how do your feet not come off the pedals?"This got me thinking... How the hell DO we not come off the pedals?Is it purely the hold on the bars, and pulling it up with us? Surely that'd only work on quite steep angled hops... What about low down ones, where you don't raise the front wheel too much?A combo of friction between pedals and feet, pulling on the bars, and just general momentum?I'm sure one of the physicists on here is about to make me feel very silly indeed, but I'd rather feel silly and know the answer, than not Any ideas? Edited March 17, 2008 by Flipp Quote Link to comment Share on other sites More sharing options...
sidehop Posted March 17, 2008 Report Share Posted March 17, 2008 We do come off..Watch a video of sombody gapping, or sidehoping in slow mo. Watch their lead foot, When they return from the kick the foot leave the pedal Not really the answer to your question haha, Owell may interest you for 30 seconds. Quote Link to comment Share on other sites More sharing options...
aener Posted March 17, 2008 Author Report Share Posted March 17, 2008 Mine don't Quote Link to comment Share on other sites More sharing options...
sidehop Posted March 17, 2008 Report Share Posted March 17, 2008 You dont kick hard enough Haha....Sack my point then Quote Link to comment Share on other sites More sharing options...
Danny Kearns Posted March 17, 2008 Report Share Posted March 17, 2008 Gravity ?Danny. Quote Link to comment Share on other sites More sharing options...
Gavyn. Posted March 17, 2008 Report Share Posted March 17, 2008 it's to do with the fact that your heavier than the bike. so when you start going up the bike is traveling faster than you are and your knees are bending to compensate for that. try sidehopping without bending your knees at all. it's hard. Quote Link to comment Share on other sites More sharing options...
Captain Scarlet Posted March 17, 2008 Report Share Posted March 17, 2008 I'm assuming that its that your body has a greater mass than the bike, therefore the gravitaional pull on it is larger, keeping your feet on the pedals.An analagy of it would be to put a small circle of paper underneath a coin and drop it, that way they both move at the same rate. Quote Link to comment Share on other sites More sharing options...
aener Posted March 17, 2008 Author Report Share Posted March 17, 2008 Yeah - gravity keeps the bike down.You jump up.If you didn't grip the bars, you'd just come RIGHT off - so that must play a major role. But if you have the front end low down, why doesn't your body mass just pivot around your hands? Quote Link to comment Share on other sites More sharing options...
NileBrown™ Posted March 17, 2008 Report Share Posted March 17, 2008 Yeah its similar to skateboarding if you think about it, I've never been into skateing and always thought when trying stuff, ' How does the board stick to your feet'? Quote Link to comment Share on other sites More sharing options...
Gavyn. Posted March 17, 2008 Report Share Posted March 17, 2008 your mass does pivot around the bars if you have them low enough. Quote Link to comment Share on other sites More sharing options...
Luke Rainbird Posted March 17, 2008 Report Share Posted March 17, 2008 Sometime we do come off the pedals - usually when we've not got the technique right, or just generally balls it up!Consider a nice new set of pedals, big sticky out shin-munching pins, and another set of pedals, all pins removed.Soft rubber soles, deforming round these areas of higher pressure as you move your foot grip onto the pins (and as such the pedals), so provided you don't just move your foot perpendicular to the pedal surface (ie. taking your foot off!) it'll provide friction.Look at the old vids, and it breaks down the basics of lifting/unweighting the rear wheel. It's all about theDown, back and up Quote Link to comment Share on other sites More sharing options...
aener Posted March 17, 2008 Author Report Share Posted March 17, 2008 Thought it might be something along those lines Cheers. Quote Link to comment Share on other sites More sharing options...
Phil H Posted March 17, 2008 Report Share Posted March 17, 2008 Yeah its similar to skateboarding if you think about it, I've never been into skateing and always thought when trying stuff, ' How does the board stick to your feet'?Yeah friction with the pedals, especially as they are not flat when you are on them, so any pressure on them is at an angle creating more friction meaning they don't release from your feet. Make sense in my mind, probably explained poorly but im certain that is an important factor.Phil Quote Link to comment Share on other sites More sharing options...
Radfax Posted March 17, 2008 Report Share Posted March 17, 2008 i have also thought of this, and think its weird, even when you do something pretty slow my feet stay on the pedals pretty odd, my feet do some off when i give a good ard slap on the pedals for a gap! its because im magic i spose.... Quote Link to comment Share on other sites More sharing options...
steve@banbury-trials Posted March 17, 2008 Report Share Posted March 17, 2008 (edited) i reckon its all about being a special person,so since im not special my feet never stay on my pedals hence my shins have loads of pedal wounds Edited March 17, 2008 by banbury trials Quote Link to comment Share on other sites More sharing options...
Krisboats Posted March 18, 2008 Report Share Posted March 18, 2008 I'm assuming that its that your body has a greater mass than the bike, therefore the gravitaional pull on it is larger, keeping your feet on the pedals.An analagy of it would be to put a small circle of paper underneath a coin and drop it, that way they both move at the same rate.Not quite, it'd be the same as putting a piece of paper under a coin and flicking it up in the air, the coin would come off the paper. You'd need something like blue tac or a paper clip to replicate the idea of hanging on to the bars and you should find the paper stays attached, and whilst maybe not keeping full contact with the coin at all times, it will be attached for the important bits.Basically just holding the bars higher than your legs will allow keeps the feet on the pedals, along with pedal pins/shoes.Its EXACTLY the same principle behind the phone magic trick. Get a mobile phone in the palm of your open hand with your palm facing upwards. Accelerate your hand upwards and on the way up flip you hand over and continue moving it upwards. The phone will accelerate faster than your arm allows which gives the impression of it being "stuck" to your hand. Quote Link to comment Share on other sites More sharing options...
trials_pimp Posted March 18, 2008 Report Share Posted March 18, 2008 I dont think its as Scinetific as that.Its to do with how you pull the rear end of the bike up with your feet.If you notice it or not, when you pick the back end of your bike up, your using your feet to do so. What happens is you point your feet down, and push back and up on the pedals, like a scoop. Your feet wont fall off because they are being pushed into the pedals, and the grip on the pedals helps transfer that effort into lifting the bike.It was like the time someone I knew used to think to bunny hop you had to pull the bars up, then push them down really quickly to bring the back end up, wrong its all in the feet.Try any trials move whie keeping your feet straight (chances are you cant, its insticnt by now) and youll fall off the pedals. Quote Link to comment Share on other sites More sharing options...
max-t Posted March 18, 2008 Report Share Posted March 18, 2008 (edited) Edited, to stop arguing. Edited March 18, 2008 by max-t Quote Link to comment Share on other sites More sharing options...
psycholist Posted March 18, 2008 Report Share Posted March 18, 2008 I don't think its as Scientific as that.Its to do with how you pull the rear end of the bike up with your feet.If you notice it or not, when you pick the back end of your bike up, your using your feet to do so. What happens is you point your feet down, and push back and up on the pedals, like a scoop. Your feet wont fall off because they are being pushed into the pedals, and the grip on the pedals helps transfer that effort into lifting the bike.It was like the time someone I knew used to think to bunny hop you had to pull the bars up, then push them down really quickly to bring the back end up, wrong its all in the feet.Try any trials move while keeping your feet straight (chances are you cant, its instinct by now) and you'll fall off the pedals.A lot of the work to lift the back wheel in bunnyhops is done by the handlebars. The trick is to move your feet out of the way of the bike as it rises while still keeping it under control. Same as required with a skateboard where you can't really brace backwards into the board to add to the lift, so it's all about getting your feet out of the way to allow the board to come up rather than lifting it directly with your back foot.As a quick demo of the forces involved, stand in front of your bike and pull the handlebars upwards and towards you suddenly - you'll see the back wheel lift. If you pull them up higher and push them down very suddenly the back wheel will lift more (This is more like what you do bunnyhopping). By pushing back into the pedals (By pushing forward on the handlebars while on the bike), especially the one you keep to the back you can add more to this lift. Strangely as far as I can tell the front foot, which is your 'good' foot plays almost no part in hopping like this as force applied backwards to this pedal will try to turn the cranks.To demonstrate lifting the back of the bike with your feet, stand astride the bike, put on the back brake with the cranks level and with your front foot on the ground, push back into the pedal with your back foot and lift the bike up. You'll notice that there's a lot of strain in the back of the lifting leg and you can feel the tension between the handlebars and the pedal. This feels like a lot more than I'd notice while hopping, so this is the reason I would say the feet play less of a part than arms in getting the back wheel airborne. Your legs still provide the initial lift by pushing you into the ground before take-off begins at all though. Quote Link to comment Share on other sites More sharing options...
2sixstreet Posted March 19, 2008 Report Share Posted March 19, 2008 I dont think its as Scinetific as that.Its to do with how you pull the rear end of the bike up with your feet.If you notice it or not, when you pick the back end of your bike up, your using your feet to do so. What happens is you point your feet down, and push back and up on the pedals, like a scoop. Your feet wont fall off because they are being pushed into the pedals, and the grip on the pedals helps transfer that effort into lifting the bike.It was like the time someone I knew used to think to bunny hop you had to pull the bars up, then push them down really quickly to bring the back end up, wrong its all in the feet.Try any trials move whie keeping your feet straight (chances are you cant, its insticnt by now) and youll fall off the pedals.Agreed. I think thats why when you first attempt them you end up going backwards a little, you are gripping the pedals with your feet by rotating your feet forwards which is then pushing you back. After some time you learn to counteract this and go more or less straight up. Quote Link to comment Share on other sites More sharing options...
NVWOCI WVS Posted March 19, 2008 Report Share Posted March 19, 2008 it's to do with the fact that your heavier than the bike. so when you start going up the bike is traveling faster than you are and your knees are bending to compensate for that. try sidehopping without bending your knees at all. it's hard.That's completely wrong. gravity acts on all bodies of mass equally, pulling them towards the center of the earth at aprox 9.81 ms ^-2 You and the bike are being acted on by gravity equally. Quote Link to comment Share on other sites More sharing options...
Gavyn. Posted March 19, 2008 Report Share Posted March 19, 2008 That's completely wrong. gravity acts on all bodies of mass equally, pulling them towards the center of the earth at aprox 9.81 ms ^-2 You and the bike are being acted on by gravity equally.I never mentioned gravity? still works the same. you apply one force for you and the bike. The bike is much lighter than you so it still goes up faster. Quote Link to comment Share on other sites More sharing options...
Krisboats Posted March 19, 2008 Report Share Posted March 19, 2008 I dont think its as Scinetific as that.Its to do with how you pull the rear end of the bike up with your feet.If you notice it or not, when you pick the back end of your bike up, your using your feet to do so. What happens is you point your feet down, and push back and up on the pedals, like a scoop. Your feet wont fall off because they are being pushed into the pedals, and the grip on the pedals helps transfer that effort into lifting the bike.It was like the time someone I knew used to think to bunny hop you had to pull the bars up, then push them down really quickly to bring the back end up, wrong its all in the feet.Try any trials move whie keeping your feet straight (chances are you cant, its insticnt by now) and youll fall off the pedals.That's only a small part, the majority is being done by your arms/bars. Think of when your static upping something, your pushing the bike in front of you and you feet are angled in the opposite way to how you describe.... yet the bike still goes upwards. Its entirely possible to sidehop without angling your feet, which implies that you don't really use your feet at all to angle the pedals and suck the bike up. Quote Link to comment Share on other sites More sharing options...
Revolver Posted March 19, 2008 Report Share Posted March 19, 2008 ooh, the physics has come out! Quote Link to comment Share on other sites More sharing options...
aener Posted March 19, 2008 Author Report Share Posted March 19, 2008 inb4/war.Didn't mean to start one Quote Link to comment Share on other sites More sharing options...
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