[python] Re: The Python genisis

  • From: George Durbridge <gdurbrid@xxxxxxxxxxxxxx>
  • To: python@xxxxxxxxxxxxx
  • Date: Fri, 12 Oct 2007 06:24:50 +1000

On Thu, 2007-10-11 at 07:54 +1000, Henry Thomas wrote:

<snip>

> In my experience, I would have expected that my Jetrike despite its low 
> profile would have a reasonably large frontal area because of its high 
> seat angle and rear wheels sticking out. Yet on the flat, in gusty head 
> winds I pass stronger riders on mountain bikes by a significant margin. 
> The only way I can explain it is that seated at 30cm above the ground 
> there must less wind pushing against me than other diamond frame riders 
> seated at say 70cm above the ground.
> 
<snip>
> In 15-20 knot winds I can still cruise at about 28-30kph these days, and 
> the other cyclists despite trying to draft off my rear, simply can't 
> keep up. Its rather entertaining :)

I don't follow this. Your seat angle looks to be no more than 45 degrees
from the horizontal, so the effective frontal area of your torso should
be 30% less than if you sat bolt upright, on the British Policeman's
Bike. But then, roadies also hunch down, leaning forwards instead of
backwards.  What is probably more relevant, your legs occupy the same
patch of frontal area as your torso, which must cut your frontal area by
nearly half, compared with both a roadie and the British Policeman's
Bike.

> I have also recently found that a tire pressure of about 65psi seems to 
> be optimal on my maxis hookworm tires. I tried higher, but the front 
> wheel gets so springy that I loose efficiency due to some tire scrub. 
> Much lower and the rolling resistance becomes more noticeable.


Can you say a bit more about the effects of too much pressure?  What I
find is that if the tyres are at too high a pressure to suit a
particular road, the trike bounces over stones and other small bumps
which softer tyres would have absorbed, leading to rapid loss of energy.
But I've never been much bothered by tyre scrub.

BTW the mk3 link on your website seems to be broken.

-- 
George Durbridge
+61 3 9481 3500
+61 409 413 945

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