bsut

I commute on 700x25 Conti Ultra Gatorskins, at around 100psi (30+lb bike and 210lb rider). The fenders are SKS Race Blades because that's all that fits on this bike. I try to keep the panniers snugged down so they're not too bulky. I wear tight cycling clothing, except if it's raining hard enough to get out the floppy jacket, in which case it slows me down.

RChung

In that case I think my estimate is in the right ballpark: you'd need a new bike with a CdA of around .12 or .13 m^2.

BTW, I'm also guessing your "commuting" output at around 2 W/kg (which isn't out of line for commuting).

purplepeople

"A watched pot never boils." and "Time flies when you're having fun."

Losing 10 secs at an intersection always seems longer for the person doing than the person observing. Just as with all the car drivers that speed up and pass other cars to reach the next red light, cyclists dislike stopping, especially when they have to unclip and put their foot down. I also think that the more someone likes speed, the more they will be frustrated at any delay. I hate to admit it, but I fit this stereotype, even though I know the difference over my typical commute might be only a minute or two.

:)ensen.

RChung

That cyclists dislike losing 10 seconds doesn't explain why they're more likely to obey traffic signs once they get off the bike and into their cars. You're saying they don't like losing 10 seconds when they're on a bike but they don't mind when they're in a car? What does explain that behavior is that on a bike acceleration even to modest speeds requires a fair amount of effort. My city has a network of bicycle boulevards, ostensibly to promote cycling. Unfortunately, the city insisted on installing stop signs at almost every intersection. I did a comparison of the power required to ride both a neighborhood bike boulevard and a parallel arterial, so I have lots of data on how much power it takes to accelerate to modest, moderate, and high speeds. Even accelerating from a stop to a modest commute speed typically requires a power spike in excess of FTP. Because of that riding a bike boulevard is not only slower but it also takes more Joules of work than riding an arterial. It's really no wonder that cyclists who aren't running experiments don't stop at stop signs: the re-accelerations are substantial.

Having a way to measure speed and power can be pretty handy, eh?

purplepeople

Actually, no. I think that someone who is impatient on their bike will be impatient in their car and if I were to guess, I'd say a large majority of people don't like stopping when they are moving from A to B, including me. For instance, with good regularity, I see a number of car drivers that slowly roll through a stop sign when it is clear. The drivers have slowed enough to make a good decision on the safety of going through the intersection. If there is traffic, safety and rules requires a stop, but in the absence of traffic or pedestrians, it's fair to say that stopping is merely blind obedience. Just because there is a law and it is civilized to comply does not mean it is smart.


Yes... depending on your needs. My needs don't run there yet.

In my case, being able to put a number on my energy demands does not make the effort any less painful. Since I continuously look for the flattest, straightest route with the least number of stops and intersections, it is only after optimizing my route that I might look for another way of lowering my energy requirements. And before I get into power measurement, I'd be looking optimizing the vehicle... better engine, basic fairing, disk wheels, then lighter components.

:)ensen.

RChung

My observations (and, as you may have guessed from my pattern in other posts, I've collected data on this) is that when crossing arterials, car drivers and cyclists don't differ in their stopping behavior but in low traffic areas (such as on these bike boulevards) they do -- and that when cyclists get behind the wheel of their cars their behavior changes. Same person, same street, same stop sign, different vehicle and different behavior. When combined with the info from the power data, the picture is clearer: top speed may be nice but cyclists are sensitive to the additional effort it takes to accelerate from a stop.
Fair enough. Even though I find them useful, I've never said that everyone should have a power meter. That, btw, is the reason that (despite your beliefs) I don't promote my method: not a lot of people have the equipment it takes to measure their drag (though the equipment demands are actually quite low) so it doesn't make sense to advertise it to people who can't use it. People who already have the equipment and are interested in measuring their drag eventually find it on their own anyway. When I went over to recumbents.com, I thought that dedicated enthusiasts with technical know-how would already be measuring their drag -- what I didn't understand was that in this case it appears that the availability of measuring devices drives the demand for knowing drag.

OTOH, if one is interested in how much faster a recumbent is than a standard road bike (that was the OP's original question) it seems that quantifiable estimates of drag (both aero and rolling) would be on topic.

chucky

So what kind of bike has a CdA of .13? Correct me if I'm wrong, but my impression is that's about the lower limit for an unfaired bike/rider.

RChung

Hmmm. It's not easy getting CdA measurements on recumbents and, as I've said, the few measurements I've seen don't include low racers. I've tried to make clear that I don't know anything about recumbents but do know a bit about power and measuring rolling and aero drag -- so I can say 0.13 m^2 is pretty low but I can't say for sure what bike would attain that level. Maybe a very aggressive low racer, but I'm thinking you're getting into faired territory. John Tetz has estimated the CdA of his faired Zote foam trike at 0.11 m^2. https://www.liggecykelforeningen.dk/u...velomobile.pdf

bent eagle

My road bike is a Specialized Sequoia, and my bent is a Bacchetta Ti Aero. I'm about 20% faster on the bent.

Crash2Much

I have a 30 mile ride I like to do. If I ride my low racer I am 8 mph faster than my other bikes.

The Smokester

From this chart one might conclude that an upright bicycle is as aerodynamic as a recumbent which is a misleading and not particularly useful general conclusion. Maybe it's true for some recumbents since they come in some many shapes and sizes. But, I have a Bacchetta Ti-Aero (an unfaired SWB high racer) and on the rare times I ride it with my regular club I can easily outrun any upright (even hi-zoot racers with aero bars) on any downhills...And believe me many have tried to catch it. The most likely explanation for this is that the Aero has significantly lower aerodynamic drag.

One thing I have noticed is that there is some "missing" power when I ride my Aero. About 4%. Since I tend to ride uprights more frequently, perhaps it's due to lack of bent-specific conditioning.

RChung

There are some oddities about that chart that make me think one should be cautious about using it for many conclusions. I guess one could conclude that there is lots of variability in measured CdA across different kinds of bikes but I'm not sure what else could be said.
Perhaps, but what would that bent-specific conditioning be?

The Smokester

I don't know. I have pledged to ride the 'bent for at least a year before drawing conclusions.

jediphobic

I would not be surprised to find that the perceived increase in speed when moving from a DF to a bent is at least partly due to increased time spent riding. After all, no one disagrees that bents are more comfortable.
Also, the records and such do seem to indicate that as you approach the higher end of either style, the difference between them is very, very tiny. But the athletes who set the recumbent records were almost certainly in less pain after the effort. Hmmmm.... that might be why recumbent teams are starting to do better in RAAM, which is after all a very long ordeal.

BlazingPedals

I attribute my speed increase to the fact that I've gone from a standard road bike to ultra-fast recumbent models. When I hop on my hybrid, which was my commuting bike in my pre-bent days, I am the same speed on it as I have always been. In my case, it is my recumbents, not me, that are several mph faster than my old road bike.