GreenGrasshoppr

The only thing I can measure is my maximum speed at terminal velocity, coasting down the biggest hills around town

BlazingPedals

Coastdowns have been a mainstay of recumbents for years. The problems with them are, you have to normalize weight and there's always a difference of opinion on the validity of the details - what speed to start, do you measure acceleration, top speed, total roll-out, etc. When adding fairings, the weight thing can be important. And I'm not sure how any of them would be turned into a magical CdA number. Measuring power at the hub would seem to be more reliable, but few non-racers are willing to buy a PowerTap hub or similar equipment. (I know a few are, but they don't talk about it.)

Even 'aerodynamic' TT uprights seem to get more benefit from drafting than a typical lowracer. That tells me something, even without knowing numbers. I've been in a 5-bike lowracer paceline and the benefit is barely noticeable - certainly not the kind of help it gives the uprights.

RChung

Yeah, I've seen lots of references to coast downs but the protocols used vary tremendously, as you've observed. That's one of the things I was interested in: if you do coast downs, what protocol do you use. A common protocol is to try to control entry speed and mass and then to do either terminal rollouts, terminal (i.e., maximum) speed, or speed at the end of a known distance. In my experiments, all of these have limited precision. BTW, for some coast down protocols you don't actually need to control entry speed or mass -- in fact, you can improve precision by altering them. If you want precision (and not everyone needs or wants it) then the key isn't controlling speed, it's getting a precise measurement of it.

A lot of recumbents have unusual drivetrains that make something like a Power Tap inappropriate. It's true a Power Tap makes things faster but one of the alternatives I've been playing with doesn't actually use the PT hub--it uses a wired PT head and the old harness just as a way to record speed. Something like a GPS that had a wheel pickup for speed (rather than relying on the satellite positioning for speed) would also work.

[Edit:] BTW, someone just pointed me to this, which appeared today.

The Smokester

RC, Thanks for the info and the article (I will try to follow the series).

foxconner

You might be entertained by my efforts at measuring drag. Go to https://mysite.verizon.net/resob0n9/bicycle_performance/
If you wish you can email me at
foxconner@verizon.net

RChung

Interesting. I'm surprised that your estimate was so sensitive to speed, especially at less than 8m/s. I've tested at speeds roughly 50% higher and didn't see that *except* when there was wind.

RChung

I was searching for something and came across this thread from nearly a decade ago. Reading through it again was nostalgic. Man, you guys were suspicious back then.

BlazingPedals

I wasn't suspicious so much as I was unable to add anything useful.

Steamer

I retract my earlier suspicions. Robert is an ok guy.

I guess.

RChung

Um, thanks, but even I don't think I'm OK.

I'm just saying I didn't have ulterior motives.

Steamer

As I think I might have mentioned to you once, I suspected your ulterior motive was to put down recumbents. Not may non-recumbent folk show up in the places where recumbent folk hang out, so your mere presence made you guilty until proven innocent. Sorta like Mormon missionaries showing up at a biker bar. They aren't there to down some suds. Not there is anything wrong with Mormon missionaries, or biker bars. Ok, I'll stop now.

Although I do stand by my one old statement:

BlazingPedals

IIRC, weren't you doing something with leaning trikes a long time ago? I remember they looked pretty interesting, whoever was working with them.

Steamer

RChung

And I stand by my old statement:

RChung

Were you thinking of PurplePeople? He designed and built a tilting trike.

grayrest

In fairness, you did pretty much answer your own question.

JanMM

Still have not measured the CdA of my bikes.
But do have a general idea of what CdA means.