AlmostTrick

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.

20t

..

DrIsotope

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.

Broctoon

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."

JCNeumann

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.

Stracknasty

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.

seau grateau

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.

TimothyH

@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-

t_e_r_r_y

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.

seau grateau

I'm losing my snarky edge. Just got back from a vacation down south and I think it rubbed off on me.

bmwjoe

Don't write a check at the top of a hill that your legs can't cash at the bottom.

JohnDThompson 

+1 this. Especially toward the end of, say, a hundred mile fixed gear ride. Legs want to take a bit of a break on the downhills by then.

AlmostTrick

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.

79pmooney

Do you climb into barrels and roll down hills? Why no brakes? I ride with quality leather toestraps in good condition and pulled tight. Aluminum cleats with deep slots. My feet don't come out. But I am not willing to perform your test. Yes, I will ride that hill, but with brakes. (And quite likely with a cog small enough to be kind to my undercarriage.)

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

seau grateau

OP literally just said they ride with brakes.

79pmooney

No. There are crashes I never want to do. That's one. Right up there with that is pulling a foot off the pedal at high RPMs, hence toeclips and straps. I have uncleated a few times but I just brake a little with the rear brake, get my RPM down a touch, re-engage the cleat and continue on sobered up.

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.)

noglider 

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?

diff

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.

REDMASTA

if my calculations are correct when you hit 88 mph you're gonna see some serious s***.

Stracknasty

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

TimothyH

We had a guy who specialized in Failure Mode and Effect Analysis when I worked in manufacturing.

• Steps in the process
• Failure modes (What could go wrong?)
• Failure causes (Why would the failure happen?)
• Failure effects (What would be the consequences of each failure?)

Interesting work. Sadly, not all companies spend the money required to do this.


-Tim-

noglider 

@TimothyH, you get it. I see another person also doesn't get it. Oh well.

ThermionicScott 

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.

TimothyH

Or fixed gear on rollers.


-Tim-

noglider 

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.