[python] Re: PC2 rideable - and test results
- From: "25hz" <25hz@xxxxxxxxxx>
- To: <python@xxxxxxxxxxxxx>
- Date: Fri, 7 Oct 2005 20:32:24 -0400
Not all that productive, as I always seem to find time to sit on my butt,
according to my wife :) You can call me "Jim" if you like, but most call me
Tim, as that's actually my name :) Then again, many have also call me much
worse that doesn't bear repeating in a public forum. As for my epics, I
have always had a problem with brevity. When learning something (or trying
to) I hate loose ends that are unexplained, so I tend to write the same way
to leave as few things as possible that can be misunderstood. Varying
success on that. I'll apologize now for another epic.
But, to the tests on the PC2 . . (trying to be brief)
Subjects:
- 5 test subjects. 1 rider can only ride for a minute or so without having
a wipe-out. 2 others are more accomplished beginners than can ride for
minutes (3 minutes to 10 minutes or so) at a time without wiping out. Last
2 are Marcel and myself with about 400km each of road riding on a python.
- rider weight varied from about 165lbs(75kg) up to 225lbs(113kg), and
heights of 1.6m to 1.9m.
Technical settings:
- initial settings were 42"(107cm) wheelbase and 65 degree PA(pivot angle).
This was to confirm that the test riders could ride it, which they all
could.
- the rod ends were changed to maximum adjustment of 72 degrees, and then
incrementally adjusted to their maximum adjustment in the other direction
(with a condition) to 57 degrees. The "condition" was that we couldn't go
lower than 57 degrees because there wasn't enough ground clearance to go
further. The rod ends could be adjusted to 52 degrees at the pivot's
lowest.
- after the angle adjustments were optimized, the wheelbase was adjusted
from the minimum of 42"(107cm) to the max extension of 48.5"(123cm).
- pivot angle changed to a maximum of 4.5 to 5 degrees when the suspension
was fully compressed, but this was accounted for in the angle details.
- max speed attained (with the python set in single speed mode) was ~25 to
27 kph on flat ground. Hill testing will be done when the brakes and
gearing are completed.
Results:
The results tended to fall into an area that is easily generalized and the
specific numbers turn out to be un-necessary to mention. The trends were as
follows:
- the closer the angle to 72 degrees, the "lighter" the steering felt and it
was difficult to feel the "weight" that keeps you going straight. The
"lightness" was not associated with how stiff the pivot was to turn, but it
refers to a lack of feedback from the bike itself. It was difficult to be
stable in a straight line because there was little sensory input, it seemed,
to tell you if you were balancing ok or not. As the pivot angle was reduced
and approached 57 degrees, the ride became more stable and easier to control
and ride straight, smoothly. The increased "weight" to the steering motion
allowed all the riders to agree that they felt more relaxed and in control
while riding straight and turning. We wanted to see how far down towards 50
degrees we could go, but were limited by the python's design. All the
riders were unanimous in the opinion that the lower angle made the python
easier to ride, and we were also all unanimous in agreeing that there was no
problem with "wheel flop" at 57 degrees while trying to turn. These results
mirror the remarks of other python riders on the list, aside from the lack
of problem with wheel flop at low pivot angles. All the riders liked the 57
degrees and we would have liked to go to 55 or lower.
- the wheelbase results were more determined by rider experience. The less
experienced/skilled/confident, the rider was, the more they favoured the
longer wheelbase, and the more visibly unstable they were trying to balance
as teh wheelbase shortened. The more experienced/skilled/confident the
rider, the less important the wheelbase was. With all riders though, the
favoured wheelbase for control and the "speed" of the steering corrections
was the 48"(123mm) setting.
- the final variable was how "stiff" the pivot was. The pod ends could be
tightened up to the point that the pivot would not turn at all, or it could
be loosened so that it felt as free as regular ball bearings would feel.
All the riders preferred to have the pivot a little tighter than free ball
bearings would feel like. The more confident the rider and/or the more
physically strong they were, the slightly tighter they liked it. The less
skilled the rider, the more loose they liked the pivot. Unfortunately, it's
hard to quantify the tightness without some more equipment besides a
measuring tape and a protractor, so suffice it to say, the level of
tightness was pretty much up to the feel of the rider.
Conclusion:
After going through the pivot angles, and then through the wheelbase
adjustments, we all were aware of how difficult it was to detect what effect
the subtle adjustments had on the python's handling, but everyone sort of
agreed on the general feel of where the adjustments were going. In the end,
we went from max angle to minimum angle, and then the change was easy to
both notice and confirm. We also did the same with wheelbase going from max
to min settings to confirm our opinions.
The final tally was as follows:
- 57 degrees was the preferred angle by all. An angle like this should also
help on downhill speed stability - to be confirmed later.
- 48.5"(123mm) wheelbase was also preferred by all (yes, me too :))
- all the riders preferred a pivot that had a little stiffness or drag to
it. I don't think spring loaded dampners would produce the same feel, but
could be wrong.
During the adjustments, the BB was 17.5"(45cm) at it's highest while at the
same time the seat height was 10"(25cm). This is interesting because it
took the seat being about 12" to 13" before the python felt easy to balance
at angles of 65 to 70 degrees. None of the riders mentioned any problem
balancing and none of the riders looked like they had a problem balancing,
even with the low seat height. Also, none of the riders had any complaint
about the BB to seat height until AFTER I measured it, when all the riding
and testing was done after a little more than an hour. Power of suggestion?
:)
Lastly, I noticed that all the riders would adapt fairly quickly to the
changes and while discussing the ride characteristics, everyone became aware
of what certain changes might produce as far as handling is concerned. In
hind sight, I should have made the adjustments while the riders didn't
watch, and then they just tell me how it felt. Also, it got to the point
where even fairly major config changes were difficult to specifically
describe the handling changes. Case in point is everyone's final ride.
While the other 4 were discussing our findings, I adjusted the wheelbase
4"(~10cm) to about 45"(114cm) and told everyone to take a final ride for
confirmation and any last remarks. The first two riders didn't even notice
that I had changed the wheelbase, the third rider noticed a "slight change"
in the "feel" of the python, and the 4th rider commented on it as well, but
likely only because he heard the third rider mention it. I think the 45"
setting is a good compromise between straight line stability and trying to
keep the python compact. 3 of us remember how it felt like trying to turn a
battleship when my BHP had a 51" wheelbase, so I think we were in the right
area for length, but I still would have liked to tried the sub 40"
wheelbases, just for the record. While wheel flop wasn't a problem on the
flat, even at very low speeds, it might be a problem at low speed, with high
effort, on a steep hill.
My next python will use rod ends again, start with a pivot angle of 60
degrees, and have a wheelbase of about 45" with the front wheel mounted
under the chain stays. This configuration will give me the ground clearance
needed to experiment with mid 50s pivot angles.
> Hi 25hz,
>
> Wowie, you are really productive!
> Hard for me to follow. Also the amount of info on your
> website. Not to mention the s.th. "epic" mails you write.
>
> But I find everything VERY interesting and I am pleased
> that you joined the "investigation team". I will work out
> a more detailed reply in the next few days...
>
> Keep up the good work,
> Jürgen.
>
> PS: May I call you Jim?
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