Balor
Zen MBB Master
Yea, *kind of*. Not exactly this level, but I do did castings of my feet and I'll have the uppers 'kind of' molded to those using intermediate thin insole.
AeroPod as CDA measurement
- Thread starter super slim
- Start date
Yea, *kind of*. Not exactly this level, but I do did castings of my feet and I'll have the uppers 'kind of' molded to those using intermediate thin insole.
Aerodynamic measurements are not really consumer level plug and play thingies. The attached link has a decent review of the current status. I have followed a bit because such a device with suitable software would theoretically save a lot of time. I don't think they are there yet.
If someone has an engineering or scientific background dealing with variation and experimental error and likes playing around, it could be fun to own one of these devices. There is an excellent blog post on the Cruz site about testing in the A2 wind tunnel and even in such an environment, testing is a challenge. To distinguish between a 0.220 m2 bent/rider combination and say 0.180, it is easy and these devices probably give you decent indications. But if you are trying to lower your CdA by small incremental values, I doubt instantaneous, absolute values can ever be valid unless one is inside a velodrome with all doors closed, no HVAC, and nobody moves. And you correct very carefully for temperature, pressure, and humidity. One needs to average over time or have replicates to lower error. The best way I have found to discern down to 0.003 m2 is to test using RChung method on a pipeline and only when there is no observable wind. I compare qualitatively. Better? Yes or no. Same day. If a car or even a lawn mover rides by, I have to ditch the entire run. I can detect joggers walking 6 dogs. I only ever make one change to configuration. For instance, I will run tests with a old tire and then compare to the new tire on the same day. Often, it is not clear. Then, I will also do ABBA runs up and down a 10 mile river road. It is extraordinarily time consuming to come to conclusion. Sometimes it is very clear like whether a 23mm tire is faster than a 25 mm tire but the extent varies from wheel to wheel. Anyway. If you look closely at Larry Oz's machines and especially the Frankenstine one, you can appreciate the amount of testing it takes to get there. I have read some people question how he can go 25 mph on such low power and laugh to myself because these same people cannot see the work it takes to find those speed improvements, when all it takes is looking at the photos of his bike.
https://forum.slowtwitch.com//Slfor.../Aero_sensors_for_dummies_thread__P7306234-2/
TransAm
Well-Known Member
So I may have some relevant experience. My other sport is flying cross country in sailplanes, where drag is also important. I tried to measure the CdA of my glider by measuring the glide ratio, which is the airspeed over the sink rate (about 40:1 for my glider). I tried using the Dick Johnson method for gliders, which is kind of the equivalent of the RChung method for bicycles.
He used a calibrated airspeed indicator to fly a constant known airspeed and timed the altitude loss with a calibrated altimeter and stopwatch. The altimeter was mechanical, so he had to tap it or use a vibrator to compensate for internal friction. But the flight test has to be done on a day with very light winds aloft, in perfectly still air. That means getting the glider ready for an high aerotow at sunrise.
Dick Johnson had published over 100 of these flight test reports, plotting sink rate at different speeds and fitting a curve by hand. I tried reproducing this without much luck. So I borrowed a differential GPS from work. This gave altitude every second with a precision of a few cm after differential post-processing against a ground receiver.
I did this on days that were so still that I could feel that I had run into my own wake after doing a 360 degree turn. One morning, it was so calm that fog formed in the valley just after takeoff, and the towplane and I had to land in the adjacent valley to wait for it to burn off. What I found is that even in the calmest conditions possible, the GPS showed that there was still too much air movement to get a precise measurement of the glide ratio in a reasonable time. I could plot the altitude every second, but a few hundred seconds of data was still too variable to get a solid straight line fit.
So I suspect it's similar with bicycle testing outdoors. Obviously testing right around sunrise when the air is still would help. But any air movement is going to introduce a big enough error to cover up small changes in CdA.
The aeropod device is relatively cheap. We await your review.
You are correct on early morning testing being the best. Even in the dog days of summer, testing before 10 am is essential.
Here is a picture of what I think is the fastest bent. It only took Larry Lem around 190 watts for 30 mph TT loops. Look under the seat and then the cardboard.
3bs
whereabouts unknown
@ed72 at a minimum, you do this so i can read these threads for which i am grateful.
i was in crowd of lycra weight weenies one day and for fun said to a guy i know who has both excess cash and excess body fat, i that i could make his cycling rig 10 pounds lighter. he said that was impossible because his bike was already 14 lbs, and no one could make a 4 lb bike. i pointed to his excess fat stores and said only one stop at McDonalds and two less beers a day, and your combined rig will be at least 10 lbs less, but you wont be as fast down the long hills.
i was in crowd of lycra weight weenies one day and for fun said to a guy i know who has both excess cash and excess body fat, i that i could make his cycling rig 10 pounds lighter. he said that was impossible because his bike was already 14 lbs, and no one could make a 4 lb bike. i pointed to his excess fat stores and said only one stop at McDonalds and two less beers a day, and your combined rig will be at least 10 lbs less, but you wont be as fast down the long hills.
if anyone is testing and wants some free speed, put some effort enclosing the area under and around the seat. I spent some time testing with that area, but not on V20. Very productive area for gains.....4 inch vinyl tape. even some sort of bag would help. See kent polk's railgun seat, Larry Oz' various reports, pretty much any john morciglio bent, the pseudo stock M5 hour record bent, etc. Cardboard works. The enclosed area under the seat could house your spare tire, tube, and pump.....very useful. Put water bottles behind the headrest. Some obvious stuff. Not sure how easy gunner handlebars are. This is one of the fastest ones ever
some of the helmets with shields are very fast compared to normal road helmets (for my recline angle). But sun gets in your eyes. One think I did was tape off the horizon on the visor and once confortable with that, I spray painted that clear part with white paint to match the helmet. Keeps sun out of eyes. Angle of eye shield can be important as is not wrestling the bike like an alligator when going very fast. esecially if air is messy.
if aeropod could let me determine which helmet and position is better with say an hour of testing, it would be gold. Transam.....buy one....let us know if it works as hoped
if aeropod could let me determine which helmet and position is better with say an hour of testing, it would be gold. Transam.....buy one....let us know if it works as hoped
MrSteve
Zen MBB Master
A seat angle closer to zero degrees will be much faster than any seat angle greater than zero degrees.
A zero-degree seat angle will reduce the frontal area. (So will short crank arms.)
Then, going faster, anything that produces turbulence before the slipstream is behind you will sap power and speed.
Then too, going faster, parasitic skin friction will also sap power and speed.
It's all a tradeoff, you know because a velomobile has a lot of skin surface and a slick recumbent bike has minimal frontal area.
My Sofrider, equipped with a rear disc wheel and a very reclined custom seat is faster than my Vendetta -also with a disc rear wheel.
This is my experience: Start with decreasing your frontal area!
A zero-degree seat angle will reduce the frontal area. (So will short crank arms.)
Then, going faster, anything that produces turbulence before the slipstream is behind you will sap power and speed.
Then too, going faster, parasitic skin friction will also sap power and speed.
It's all a tradeoff, you know because a velomobile has a lot of skin surface and a slick recumbent bike has minimal frontal area.
My Sofrider, equipped with a rear disc wheel and a very reclined custom seat is faster than my Vendetta -also with a disc rear wheel.
This is my experience: Start with decreasing your frontal area!
benphyr
Guru-me-not
All the factors come to play - don’t forget power decreasing if you get too close to zero. Handling and visibility and ability to see also.
But certainly the easiest to tweak ( as in without building or buying a new bike) is frontal area and closely related baggy clothing.
