Nov 3

Nov 3, 2004

Another try

This time at RaceCity Speedway - a half mile oval protected from evil semi trailers but not the wind. And boy was it windy! When I unloaded the streamliner from my car, the wind blew the 63 pound trike sideways across the pavement!

Getting high speed watts data was the plan, but unfortunately in this kind of wind, that wasn't going to happen. Just averaging 30 kph is fast enough when you round a corner from a tail wind to a instant side wind. I did get some more watts data, but I'm not sure how useful it is aside from confirming yesterdays low speed test. Basically, I was averaging about 32.5 kph on 88 watts (similar to yesterdays Hwy 22 test). I was able to do one higher speed loop, but it was a bit sporadic and probably included some acceleration power that shouldn't be included in this kind of test. I'm glad my buddy John Mackay was there to help, as the wind blew off my canopy cover and it needed to be duct tapped back on to continue the battle.

Let me explain the relationship between rolling resistance and drag: rolling resistance basically stops the wheel from turning around in circles. It's mostly a function of the size of the contact patch (the exact shape of the rubber on the pavement) and weight on the wheel. A round contact patch is more efficient than an oval one which is why fatter tires with higher pressure outperform narrow tires. Narrow tires are only more efficient because they are more Aerodynamically efficient, but when you can hide the tire in a fairing, you might as well go for the lowest rr you can get. Drag, (CdA) reflects how slippery your bike is through the wind. Low drag would be a thin plate turned sideways and high drag would be the same plate turned to face the wind like a fan. The power (amount of watts) required to overcome rolling resistance is the same at any speed. Once you have overcome the rolling resistance, all of your power goes to overcoming aero drag (producing speed). Therefore, at low speeds, rr is a higher percentage of your total power output and at higher speeds rr is a lower percentage. Using speed and power data from two runs (a high speed and a low speed) enables us to estimate what the rr is, and what the CdA is. That's basically what pwrdrag2.xls does.

Using the pwrdrag2.xls calculator, I played with the high speed values until I came up with some results that made some sense. It seems that my low speeds are fairly efficient, but I become less efficient at higher speeds. This means low Crr (rolling resistance) and high drag. I came up with a values for CdA and Crr that best fit most of the data I have to date.

Crr (rolling resistance) .046 This seems like it should be about right according to other rr values of similar tires and wheels

CdA (aero drag) 1.1 or so. This is poor, as I was hoping for around .7 or better.

I'll head back out to the track on the next CALM day and hopefully answer this nagging question once and for all. And the next question: If my drag really is over 1, then how come????

TCR2 (track) 2Do LIST:

1. Make a platform for the wind trainer (mini-rollers)
2. Add front caliper brake
3. Mount first fairing and all the work required with that
4. Make CF front wheel fairing
5. Make CF rear wheel discs
6. Make a new steering bar that rises up a bit higher - also takes up less room on the sides so fairing can be tighter
7. Adjustable seat height
8. Make fiberglass canopy top with acrylic bubble and tailbox
9. Paint this puppy!

TCR1 (cross country) 2Do LIST:

1 Add front derailleur
2 Run road, roll-over and watts tests for new suspension system
3 Worm gear steer prototype (Waiting for final design and parts list from Ben)

TOTAL distance on TCR1
756 km

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