bikenh

I know I'm getting lied to somewhere but I'm not even close to sure where the lying is coming from. Does anybody know a good formula/website for calculating cadence at a given rpm/gear ratio? Sheldon is crap and so is bikecalc. I wasn't pedaling 158 rpm today with room still to run. I was doing 37.8 mph in a 52x17 fixed gear. It was the second day in a row I've been over 37(37.4 yesterday) mph on a descent. I'm running 700x25 with 175 mm cranks.

Now the second question is a bit more intriguing. When on a descent that has speed to it, even when riding a big gear and your going to possibly hit point where you will have to reach for the brakes as you can't pedal any faster without losing control what is the way to most optimize your highest maximum cadence? What I mean from yesterday's 37.4 to todays 37.8 mph descent, different drops, yesterday I was still sitting fully upright, today I dropped onto the drops and got into a downhiller tuck style position. Today I did have a bit more wind to deal with that may have been playing with the mind. Today seemed closer to top end than yesterday(yeah, day to day effects could effect the way it will feel each day I realize this). What is optimal body position for reaching the highest cadence possible. I know you want to be as relaxed as possible. Do you want to be sitting upright or down on the drop in the lower body position? Which will let the legs spin faster?

Unkle Rico

37mph downhill on a fixed gear?

Are you sure you arent lying to yourself and us?

bikenh

It's what the cyclecomputer was showing. Pretty much the hill is one that anytime other than winter I can typically descend down it at 37-39 mph. Today was the first time this year I've been able to hit that fast thanks to mid to upper 40s for temps. Comparing with other peoples cyclecomputers I'm generally always within 1 mph of what they are showing.

MattoftheRocks

The numbers work out. There isn't an upper body position that I've found which yields significantly increased control, just aero and sight seer. You can get a more stable spin if you pedal with your ankles and minimize knee-bob.

cale

I generally steer from the drops on fast downhills. The control is better especially because it is easier to shift weight rearward for better stopping distances. I'm thinking also of the urban roads where I ride and the need to dodge traffic and bad roads.

bikenh

In the case of gravity propelled does it make more sense to free float the legs, aka not applying pressure to make the legs go around but just let them spin by force from being clipped into the pedals? I know the first couple of days I was free floating the legs but anymore I haven't been doing that to the same sensation in the legs as I was back a week or so ago. I would think the answer would be yes, since that would help you to be more relaxed and that helps to keep everything more stable.

bikenh

I generally on the nice downhills around here used to ride on homemade aero bars, aka resting the forearms on the top of the regular handlebars. Right now I'm still too chicken to even try that thanks to knowing what I've heard can happen if the chain pops off. I want my hands by the brakes

TejanoTrackie 

This is precisely what you DO NOT want to to do. It will just guarantee that you start hopping around and will make it much harder to ride smoothly and maintain control. You need to keep your legs spinning ahead of the pedals, instead of letting the pedals drive your legs. If you feel your cadence getting uncomfortably fast, ride the front brake (you do have a front brake, right ?) to keep your speed from increasing. You need to work on smooth pedaling with your legs moving straight up and down, and your hips motionless.

MattoftheRocks

No floating. Pedal with your ankles. If you're gonna float anything, maybe your underside if you've got enough of a headwind to push into.

bikenh

I'm glad I asked the question...I would have guessed just the opposite. Thank you. Definitely have the front brake. Around here I could mostly get away without it but there are a couple of must stop intersections where I don't have the leg strength for making the stop thanks to the gravity pulling me right into the stop. I also know there are one or two hills around the area where I might need brakes to slow down to keep it under control. After yesterday and today and looking at the conversion going up in gear which I'm waiting to do until the temps warm up more I know I will be close to being able to ride most anything downhill around here without needing to brake in a 52x15 during spring-fall months. I've ridden up the same hills in a 52x15 seated the entire way up them after having ridden 100 miles already for the day. That's the scenario I've been trying to set up for myself, where I can climb it and descend it without much worry about getting overwhelmed on the downhill and not being able to climb up it. 52x17 during the winter...been riding it all winter and I can go days, heck even two or three weeks at a time during the winter months without hitting 30 mph on any drops thanks to the cold effects on the bike. 52x15, I've already ridden one of the biggest drops/climbs that I see frequently during the summer months. So I figure that is going to be my gear choices. Granted with having spent all winter in 52x17 spring could be interesting. For the most part the 17 is quite easy around here anymore so once the winter effects leave the 15 might not be that much of an upgrade. I've typically been switching to a 52x15 right off the bat in the spring the past two years until I get ready to leave for the summer bike trip and then I switch down for the rest of the year. The upgear to the 15 might not seem like much once winter gets outta here. That may take another month though.

mihlbach

I hit 47 once on a steep hill with 49/16. It sucked and was seriously not fun after a few seconds. I did not wuss out and hit the brake. Fortunately the hill was not very tall.

klhada

damn, in my months riding fixed, I learned to just relax the legs, and to me it helped to stabilize myself. Trying to control the pedal movement, I just bounced like I'm riding a chariot

maybe I should try to improve my technique

Onfixiate

175 crank arms are kinda long; Your pedal velocity would be lower with shorter cranks. (Less flail factor)

bikenh

Okay, I'll bite on this one. Why would shorter crank arms give lower pedal velocity? Are you saying less energy to have to counteract or what? Actually I would think you have more energy since the same amount of power is going out with each pedal stroke if you have shorter cranks. I'm definitely ignorant here somewhere, maybe on what you mean by pedal velocity. As I'm typing this I'm thinking at the same time... You mean because of having the shorter crank your legs aren't having to go around such a big circle so their isn't as much of a chance to get the bouncing******************** I might be able to see the sense in that.

bikenh

What I think was meant above was that you still want a little positive pressure on the pedals versus letting the pedals control the legs. I think you can still 'relax' while maintaining that little bit of pedal pressure. I think it's what I've did the past two days in reality. You still need to be in control instead of the bike being in control.

The one thing I notice right now, being new may be the reason I'm noticing it, is I do seem to be a lot more focused when I'm pedaling crazily fast versus normal riding.

prooftheory

The pedal velocity is the speed that the pedal is going. The rotations are going to be constant for a given speed and so the velocity should be 2 x pi x crank arm length x rotations per second. Thus, increasing the crank arm length will proportionally increase the velocity. This has nothing to do with torque or power. In the situation of going down hill and trying to get the highest cadence you should probably assume that torque and power are not relevant.

Also 158 rpm for a couple seconds to hit a max speed doesn't really seem that incredible to me.

Answering your original question about posture, if the question is really how to get the maximum cadence rather than the maximum speed you would do the best to have a more upright position to allow more room for your legs and lungs. Most of the reason for getting lower has to do with air resistance but that isn't really a factor in cadence. You could probably improve your cadence if you geared down to 52x19 and sat up more even though you would also probably be going slower. If you look at rollapaluza videos you never see anybody trying to get real low although they do usually get in the drops.

SquidPuppet

Could you expand on that please. Thanks.

Onfixiate

Yep, that's pretty much it. Think about a turntable. for a given rpm (cadence), compare how fast a spot on the record disc near the center is moving, compared to a spot at the very edge of the disc ("pedal velocity).

I run longer cranks on my mtn bikes, compared to my road/fixed gears rides... You can put more torque into the rear wheel (power) with the longer crank arms, and "spin" easier with shorter cranks. Everybody talks about gear ratios, but much of the perceived effort is also a function of your crank arm length as well.

You may want to evaluate your saddle height as well; that is another variable affecting your "spin".