DIY Windtunnel for cyclists

[windcheeta]

Hi
Firstly, great site. Just stumbled upon it today
I have a question re Windtunnel design which is slightly off track - but hopefully not too far.

As a cyclist and Triathlete, I'm keen to get as aero as possible on the bike to minimise energy expenditure for a given speed (sound familiar?).

I know of plenty of wind tunnels that test cyclists to optimise their position and reduce drag most of which test at a wind speed of 30MPH using facilities designed for cars.

Could anyone hazzard a guess at what kind of size tunnel would be required to just study cyclists at windspeeds of around 30MPH yet still yield reasonable results in terms of accuracy? I'm thinking self build here.
Any advice gratefully appreciated!
windcheeta

[bikeracer]

there are lots of bike-specific tunnels designed for testing things like cyclists. just google low-speed wind tunnel and you'll get lots of results. Some in New England (MIT, some setup in CT), one in Colorado, and one in SoCal to name a few knowns.

Understanding the principals of how bikers get faster on their bikes is more efficient than wind tunnel time. You want to reduce your frontal area by getting a) narrower arms b) lower front end/shoulders/head c) legs closer to top tube d) an aero helmet.

Bike makes some difference, but being low and still able to pedal is the biggest thing. Talk with someone who knows about this stuff in person. There are plenty of wind tunnels that would be happy to take $1000 an hour to fit you and sell you wheels/helmets, but you can get 98% of the way there without the grams of drag feedback.

[thatguitarguy]

I've seen guys mount their bikes on cartop racks and get on them while the car drives around to do testing at whatever speed. Real world accuracy (whatever that is).

Don't try this without adult supervision, and check your local codes for legal questions.

[bikeracer]

Oh man. A scangauge and a roof-mounted cyclist? Great.

Wind will be acting differently at 50 where you might begin to be able to read a difference on a scangauge. But would it make a difference as to what position you'd end up in?

Some of the changes they're making are to lose a gram or two of drag.

[Bicycle Bob]

Rather than the scan guage, go for a force balance on the bike. For the easy version, pick a day when there's a nice crosswind blowing toward the highway, and ride along the shoulder, towed by a car, a rope, and a fish scale where you can see it. Tuck to minimize the pull, and pedal in too low a gear to keep the power off.

Do not run over the rope, or try this on a planet with lawyers.

[3-Wheeler]

Originally Posted by Bicycle Bob

...towed by a car, a rope, and a fish scale where you can see it...

Sort of along the same lines as Bicycle Bob, you could easily justify the price of one of those kits that measure your applied force to the pedals in real time.

One of the better one's has piezo sensor's mounted to the crank set and wirelessly transmits the data to a computer, which then calculates your pedaling wattage. With this setup, you would know exactly how aero efficient your riding posture is.

The systems I looked at (SRM) will take your breath away at $2000 though!!

Jim.

[Zyzzyx]

Mmm... SRM crankset. Very nice. There's also the Powertap rear hub setup. Still expensive at ~$1500 new, but available fairly often as used.


Personally, I just skipped all the problems of getting an aero profile and had one built instead. I picked up a Quest velomobile instead. Granted, doesn't work for triathlons and other competitions, but is great fun for time trials. Also wonderful for staying warm and riding through the winter.

[Sorrow Six Star]

wow how cool

this one is even attractive..

[Christ]

Re: Rider wind tunnel

If you really wanted to butt-dyno the wind resistance on a bike, you can get a large barn fan (~48" diameter) and build a tube around it with whatever. (PVC and plastic sheeting would work) Sit inside the tube with a controller switch to turn the fan on, on your bike, and get into whatever position, and turn the fan on high. Some of those fans have available wind speeds up to 20+ MPH.

[3-Wheeler]

Originally Posted by Christ

...If you really wanted to butt-dyno the wind resistance on a bike, you can get a large barn fan (~48" diameter) and build a tube around it with whatever...

And make sure to pull the air through the tube with the fan, rather than push it.

Many years ago, I built a small wind tunnel for 1/8th scale plastic models using a 21" window fan and found out very quickly that the air is much more stable when pulled through, and not turbulated by the fan blades.

Jim.