R. Chung

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	3,583 reputation	bio	website		visits	member for	1 year, 9 months
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Jun 18	comment	How can one estimate drag for a bicycle? The "tow rope" method is discussed in the Debraux et al. article linked elsewhere. It doesn't have good precision. The deceleration method works well if you have a way to record moment-by-moment speed, such as with one of the increasingly popular Garmin bike computers. A method for doing this is discussed at forum.slowtwitch.com/cgi-bin/gforum.cgi?post=3590389#3590389 and, when done on a calm day without passing cars or other traffic, it has produced results in agreement with wind tunnel estimates.
Jun 18	comment	How can one estimate drag for a bicycle? Sadly, that article focuses only on one component of drag that cyclists experience (viz., aerodynamic drag) and answers the question "how can one estimate drag?" with "in a wind tunnel."
Jun 18	comment	Are there devices to moderate speed on mountain descents without braking? @Reid, Basically, ask something like this: "I want to estimate either the amount of drag force when coasting down a hill at a certain speed, or the amount of power needed to ride on the flat or up a hill at a certain speed. All of the online calculators either assume coefficients of rolling resistance or aerodynamic drag or assume that I have estimates for them. How do they make those assumptions, or how can I make those estimates myself?"
Jun 17	comment	Are there devices to moderate speed on mountain descents without braking? Well, the short answer to your question is how to convert drag force into power, and that's simple. Convert the drag force into Newtons, then multiply by speed in meters/sec. A watt is a Newton-meter/sec, so if you're traveling at 10 m/s and experiencing, say, 3 kg of drag "force", you'll just convert to Newtons then multiply by speed. That's 3 * 9.8 m/sec^2 * 10 m/s = ~ 300 watts. The longer question is how to estimate drag area on a bike. The answer is long (and I have fewer than 10 characters of explanation left) so that probably deserves its own question. Ask it and I'll answer.
Jun 17	comment	Why is the rear wheel of my tandem bike skidding? What kind of brakes do you have on this tandem? In particular, do you happen to have a rear drum drag brake?
Apr 22	comment	Performing on long and tiring tour There's not quite enough information in your question to give a targeted answer. Was this a typical distance for you, or had you not previously attempted a ride like this? How steep were the climbs? How often did you stop, what did you eat and how often, were you riding alone at your own pace (like a randonee) or riding with a group that set your pace (like an audax)?
Apr 20	comment	Setting up a bicycle for someone with restricted knee articulation Here's a similar product.
Apr 20	comment	Why such a dramatic drop in power when the handlebars are lower than the seat? @heltonbiker: Fair enough. I'd upvote your answer if it were modified to explain that you're giving an explanation about "typical" reasons why power drops with lowered position but that in this particular case the loss is atypical and may be the result of a different cause.
Apr 19	comment	Why such a dramatic drop in power when the handlebars are lower than the seat? @heltonbiker: exactly, it appears to be atypical, which is why I would think that a "typical" answer (that is, closing of the hip angle) isn't the issue, especially since he's seeing it with a 0.5 cm change not only in bar height but also in reach. That's why I haven't been able (yet) to upvote your answer.
Apr 19	comment	Why such a dramatic drop in power when the handlebars are lower than the seat? There's a current thread over on the timetriallingforum which includes more "typical" losses with drop; the post author is reporting something like 30% for .5 - 1.0 cm change in drop.
Apr 19	comment	Why such a dramatic drop in power when the handlebars are lower than the seat? What about the change in reach?
Apr 19	comment	Why such a dramatic drop in power when the handlebars are lower than the seat? I don't think the hip-torso angles explain it. He says a 5 - 10 mm change in height or in reach has a large effect on speed. I've seen small changes in height or reach affect aero drag and power -- but never as large as observed here.
Apr 19	comment	Why such a dramatic drop in power when the handlebars are lower than the seat? To clarify, are you saying that you can climb a 10% grade at, say, 10 kph while if you lower your bars by a quarter inch you climb the same hill at 7 kph? Without knowing your exact weight or that of your bike it's impossible to make an exact calculation but that would probably be in the neighborhood of 1 watt/kg difference (like, from 3.3 watts/kg to 2.3 watts/kg). That's a huge difference for a change in bar height of that size.
Apr 19	comment	Why such a dramatic drop in power when the handlebars are lower than the seat? 3+ kph slower up a 10% grade from a 5-10 mm change in bar height is pretty extreme. What is your "base" speed from which this 3+ kph loss is observed?
Apr 17	comment	Why can't Yellow Jersey change hands on last day of Tour De France? In 1947, the first post-WWII Tour, Jean Robic started the final stage in 3rd place on GC, about 3 minutes down on the Italian rider Brambila. The stage was long and flat, from Caen in Normandy to Paris, but the absence of race radios meant that Brambila lost track of Robic. Robic finished about 13 minutes ahead of Brambila.
Apr 17	comment	Why is it safer to bike with traffic, instead of facing oncoming cars? Oh, I'm pretty happy with what I wrote. The original question did not make any mention of presence or absence of cycling infrastructure, I linked to a report from a governmental research institute that discusses the exact reasons and conditions under which riding against traffic is a safe activity, I mentioned the NHTSA/FARS data in other situations, and I showed that the real world is actually quite complex. I'm willing to take downvotes on this.
Apr 16	comment	Is a recumbent trike faster than a non-recumbent bicycle? I should clarify that among trikes, the ICE Vortex is considered to be fairly low, reclined, and aerodynamic; this means that the "typical" trike will have higher CdA than measured for the Vortex.
Apr 16	comment	Is a recumbent trike faster than a non-recumbent bicycle? Here are some actual test data: bentrideronline.com/messageboard/… These data show that a (tadpole) trike (the Vortex) has roughly the same CdA as a rider on a standard road bike with hands on the brake hoods -- that is, more aero drag than a rider on a TT bike or in the drops on a road bike, but less than a rider with hands on the bar tops, or on a MTB or a city bike. However, this particular trike has much higher rolling resistance.
Feb 23	comment	Crosswind effect on an aerodynamic front wheel vs a rear wheel A wind tunnel would tell you about drag force but it wouldn't (easily) tell you how it affects handling. In particular, wind tunnels don't measure the effect of "gusts" very well since it takes some time to increase the wind speed and most wind tunnels are not designed to measure torque forces around the mount point (which is what you'd need to determine differential drag at non-zero yaw between the front and rear of the bike).
Jan 29	comment	Difference between 650c and 700c wheels? Compared to 700c tires/wheels of equivalent width and structure, 650c tires/wheels have been measured to have less aerodynamic drag but more rolling drag.