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What will happen when your feet/legs can no longer keep up?
I've been wondering about this for a while. Fixed gear bike, going down a long steep descent, feet attached to the pedals. No brakes or not using brakes. Bike and pedals keep speeding up, eventually the riders legs are not going to be able to keep up.
It seems to me that at some point a crash will be inevitable, but how exactly will it happen? Be specific if you can. |
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Unless the hill is very steep, terminal velocity is lower than you think. You've got to contend with wind resistance, rolling resistance, and the pedals trying to move your legs around as well. Unless you're applying power to the pedals, you're already slowing the bike down.
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If it is a very long, steep hill, your legs could take a real beating, even at terminal velocity. And this could conceivably result in a crash, as you might lose your balance from your legs spinning uncontrollably. Unless the hill is quite steep, you should be able to resist too much speed increase, although this may be difficult and tiring.
It's an interesting thought experiment, but the pragmatic answer is this: "If you plan on riding hills that big, install a brake on your bike. Then the point is moot." |
Put a brake on the front. I ride some fairly unpleasant hills, and feathering the front brake makes a world of difference.
Plus, you always want that on a less-controlled environment like the street. |
Speed control on descents is important. If you're running no brakes, it's essential that you've got enough strength in your legs to skid, skip, or slow the cranks to a manageable RPM. Going downhill on a fixed if you don't know the length & gradient can be unsafe and unpleasant.
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Most people start bouncing on the saddle when they hit uncomfortably high cadences. You'll start bouncing and either panic and lose control of the bike or get bucked off.
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@seau grateau gets and A+ because along with the correct answer, he actually answered the question asked.
The rest of you get an F minus. -Tim- |
actually, what happens is your legs will rip off and spin around like crazy arms, slapping the road and your torso for as long as you can hold on. true story, i've seen it happen.
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Originally Posted by TimothyH
(Post 21082630)
@seau grateau gets and A+ because along with the correct answer, he actually answered the question asked.
The rest of you get an F minus. -Tim- |
Don't write a check at the top of a hill that your legs can't cash at the bottom.
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Originally Posted by JCNeumann
(Post 21082546)
Put a brake on the front. I ride some fairly unpleasant hills, and feathering the front brake makes a world of difference.
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As OP I want to make it clear that I like my brakes (yep, both of 'em) and enjoy not crashing. Any post about adding a brake is misguided if directed at me.
Over speeding the legs downhill can end up causing a crash... even if a rider has brakes. I know I often try to increase my speed downhill by not braking, or braking as little as possible... but everyone has a limit. I'm interested in the specific details of what happens when one reaches that limit. No one can increase spin indefinitely.
Originally Posted by seau grateau
(Post 21082624)
Most people start bouncing on the saddle when they hit uncomfortably high cadences. You'll start bouncing and either panic and lose control of the bike or get bucked off.
I also think it also would be possible for a shoe to become ripped off of even the strongest clipless pedals (or foot pulled clean out of a shoe) once speeds get too high for the rider to manage. And then chopped up. First one, immediately followed by the other and a wicked crash! Have you ever crashed or had a close call while spinning at high speed down a hill? If so, please tell me about it. |
Originally Posted by AlmostTrick
(Post 21081528)
I've been wondering about this for a while. Fixed gear bike, going down a long steep descent, feet attached to the pedals. No brakes or not using brakes. Bike and pedals keep speeding up, eventually the riders legs are not going to be able to keep up.
It seems to me that at some point a crash will be inevitable, but how exactly will it happen? Be specific if you can. This is really should be a "why would you do this?" question, not "what would happen?" Edit: if you are planning to ride hills you cannot survive without brakes, it just might be smart to have two. Brakes have failed. Rims have gotten too hot. Fewer front brakes fail when a fair share of the routine braking is done with a rear and having both can go a long ways to keeping rim temperatures down below critical. (IQ required to figure this stuff out - not much.) Ben |
OP literally just said they ride with brakes.
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Originally Posted by AlmostTrick
(Post 21084822)
As OP I want to make it clear that I like my brakes (yep, both of 'em) and enjoy not crashing. Any post about adding a brake is misguided if directed at me.
Over speeding the legs downhill can end up causing a crash... even if a rider has brakes. I know I often try to increase my speed downhill by not braking, or braking as little as possible... but everyone has a limit. I'm interested in the specific details of what happens when one reaches that limit. No one can increase spin indefinitely. This makes sense to me. Add in some pavement ripples or bumps while at top spin and that would add to the risk of being launched off the bike. As would any emergency (like a motor vehicle pull out) that even momentarily causes one to attempt to let up on the spin. I also think it also would be possible for a shoe to become ripped off of even the strongest clipless pedals (or foot pulled clean out of a shoe) once speeds get too high for the rider to manage. And then chopped up. First one, immediately followed by the other and a wicked crash! Have you ever crashed or had a close call while spinning at high speed down a hill? If so, please tell me about it. And clipless pedals on fix gears and high speeds? You can have it. I will never. (I've unclpped at ~15 mph fixed. Bad! Promise you, hitting the road won't be the worst of your injuries. (Oh the blood and broken bones will get the medics attention, but the muscle/tendon/bone damage from being hit by that pedal will be lifetime.) With toestraps, you have that reliable leather strap. (It is in good condition, right? I have 1/2" high quality leather straps cut for me at a leather store and change them out regularly.) |
Some of you don't understand what the question is. He's not asking how to survive or whatever. He's not asking for advice. He's saying he knows that a person would wipe out, and the question is, how? In other words, in engineering terms, what is the failure mode?
Does that help? |
If you are taking about just riding down the hill, there is no need to put force. Just keep your legs loose and keep spinning without much if any pressure. That should not burn you out at all. However if you end up spinning faster than you can, you will probably start to bounce and from there if speed is still growing, you will probably crash.
Stopping is a different story. Keeping control from the start is mandatory. You can always use your foot to stop if you find your legs are too tired to brake. When I think back, we were riding brakeless bmx bikes in the 90's. Just used our foot to stop. |
if my calculations are correct when you hit 88 mph you're gonna see some serious s***.
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Some great and hilarious replies here. One thing to clarify is that we’re talking about cadence here more than speed. I have friends who ride brakeless track bikes here in Gatineau Park (Quebec), which has several climbs and descents. But they ride them on 50:16 or 49:15 or thereabouts and often hit 70km/h without spinning out. Not answering the question really so another F- for me. LOL
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Originally Posted by noglider
(Post 21084935)
Some of you don't understand what the question is. He's not asking how to survive or whatever. He's not asking for advice. He's saying he knows that a person would wipe out, and the question is, how? In other words, in engineering terms, what is the failure mode?
Does that help?
-Tim- |
@TimothyH, you get it. I see another person also doesn't get it. Oh well.
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I might also be accused of dancing around the actual question, but I think it depends on the rider and their bike fit. Assuming the feet don't detach from the pedals, it's a matter of what happens when the cadence goes above what they have experienced before*. I used to run my saddles higher, and noticed more bouncing then. When your knees are always slightly bent, I think they are better able to move with the pedals. I think this has also saved my bacon on a few occasions when I spaced out and tried to coast -- I might have been in trouble if my legs had been straight enough to lock my knees. ;)
* I think your question speaks to the importance of practicing high cadences so that you are physically and mentally prepared when they happen. Whether that's deliberately riding around on a really low gear, or seeing how fast you can take a spin bike at the gym. :thumb: |
Originally Posted by ThermionicScott
(Post 21085671)
* I think your question speaks to the importance of practicing high cadences so that you are physically and mentally prepared when they happen. Whether that's deliberately riding around on a really low gear, or seeing how fast you can take a spin bike at the gym. :thumb:
-Tim- |
When spinning very fast on a fixie, I've had the feeling that the pedals would throw me off the bike, but I'm not sure that that would happen. Maybe I would be thrown to the side, not over the bars. Or maybe I would start oscillating the handlebars left and right trying to get control back, and I would spill the bike on its side. I'm just guessing, though.
I once did an estimate that I hit 180 rpm. It's a challenge to keep your butt from bouncing, but I'm moderately decent at avoiding it. |
OP: Only one way to find out: Have at It!
Be sure to have a camera crew w/ a high frame rate available to document the experiment. Enjoy! -Bandera |
I did used to do the descent of Juaquim Miller Road from Skyline Blvd over Oakland, CA on a 42-17 with brakes but not using them. I was in my 20s, had raced two years before and had around 15,000 fix gear miles on my legs. I was also doing work that I knew had long term health issues I would eventually see. My post head-injury crazy years. To keep my sanity, I would ride up Juaquim Miller, turned around at Skyline and ride down. Fully crazy. Juaquim Miller is a parkway, two lanes either side of a planted meridian. Speed limit 50. I never got passed. (I doubt I hit 50 but I was close.)
42-17 has the nice feature that at 20 mph, one's cadence is 100 rpm. Easy math. 50 mph is 250 rpm. Been very close. But as a very experienced fix gear rider with recent race legs. Young and crazy. On a very funky Peugeot UO-8 that had been crashed many times and was as straight as a soggy noodle! (But newish Binda toestraps pulled tight! I wasn't all nuts.) Ben |
Originally Posted by ThermionicScott
(Post 21085671)
I might also be accused of dancing around the actual question, but I think it depends on the rider and their bike fit. Assuming the feet don't detach from the pedals, it's a matter of what happens when the cadence goes above what they have experienced before*. I used to run my saddles higher, and noticed more bouncing then. When your knees are always slightly bent, I think they are better able to move with the pedals. I think this has also saved my bacon on a few occasions when I spaced out and tried to coast -- I might have been in trouble if my legs had been straight enough to lock my knees. ;)
* I think your question speaks to the importance of practicing high cadences so that you are physically and mentally prepared when they happen. Whether that's deliberately riding around on a really low gear, or seeing how fast you can take a spin bike at the gym. :thumb: |
Originally Posted by seau grateau
(Post 21085848)
Bad bike fit definitely messes up your pedaling. Saddle too high leads to legs overextending and hips rocking back and forth to compensate, and the mechanics of it all are going to be really hard to control at high cadences.
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if you have brakes, just unclip and keep your feet out of the way of the pedals. then you can go as fast as you like and won't have to worry about your legs getting ripped off
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