[python] Re: Geometry questions
- From: dirk.bonne@xxxxxxx
- To: python@xxxxxxxxxxxxx
- Date: Wed, 22 Aug 2007 09:16:39 +0200
Hi Dustin,
I currently ride a python with 406-50 wheels (it is code named "baby
python"). Look at my website for pictures for it (
http://dirkb.dnsalias.net/ ). Before that I rode a flevo racer (small
wheels too). Both of them are self built. I am experienced in riding
both, but the flevo has been in disuse for 3 years -the python is
clearly my favorit.
On my homepage you find some stuff on the "self centering effect" of the
negative trail, which might or might not be interesting. I worked out
the formulas for that and put them in a program. They only explain the
self centering, not the dynamics of the bike.
Together with a friend we tried to connect two flevos back to back to
see if it would work. It failed, because the pivot was at the standard
45degrees. When there was weight on the rear seat, it was impossible to
get the front part up again after swaying it left or right. That is why
I adviced you the large pivot angle. It is not about the dynamics of the
bike, but just the fact that the rear weight is going to pull the front
part down. The trail is much less important: the trail will determine
the feel of the bike, but you can get used to them all.
Experiences here on the mailing list differ wildly on max speed (50km/h
to 70km/h), which I find difficult to explain. My experience on the
python at speed is quite positive. Last vacation (2 weeks in Sweden) I
had the chance to test it out again, and the hills allowed me to coast
down beyond 60km/h. I found it was no problem and more could have been
done. I find it similar in feeling to my flevo. But honestly a "normal"
recumbent is certainly easier at high speed (I have had a challenge
twister 9 years ago, and never had a second thought about these speeds
at that time).
The Tom Taylor solution is quite different from a python or flevo,
because the pivot is located away from the hips. On a python/flevo, the
feet-steer dominates handlebar-steer, which makes it much more difficult
to learn. On a Tom Tayler the pivot is located further towards the feet,
so you can control the bike by handlebar steer, which makes it rideable
in short time for people with only "normal" bike experience.
If a Tom Taylor solution is okay for you, I would copy the data (pivot
angle, trail and pivot-BB distance) from his B2B tandem (I cannot find
his website right now, but I believe he made a B2B tandem). That way you
know the bike just works. If you on the other hand try a real
flevo/python solution then you might come in the dilemma where you
cannot pinpoint bad performance: is it because you didn't learn to ride
enough, or is something wrong with the geometry? The TT solution will
have the added advantage that people could try out your TT B2B tandem too.
groetjes,
Dirk
Dustin Anderson wrote:
> Hi Dirk,
>
> Thanks for you advice. It seems like that is more or less the same as
> the Tom Traylor head angle.
Tom Tazlors B2B is different as it has the pivot positioned so that zo
>
> May I ask what you are riding right now? and also what is your
> experience at speed on a center steering bike?
>
> Dustin
>
>
> On 21-Aug-07, at 1:23 PM, dirk.bonne@xxxxxxx wrote:
>
>> Hello Dustin,
>>
>> My guess is that the pivot angle should be choosen large, e.g. 70 or
>> more degrees, to prevent the weight at the rear to influence the
>> steering behaviour.
>>
>> I do not think that the trail matters so much as the angle, and you
>> probably can get away with taking a trail similar to existing projects.
>> So if you go flevo style, a positive trail of 9cm(?), then you will need
>> a steering damper to keep the front part upright. If you want a negative
>> trail (-14cm all up to -28cm), you won't need that as the bike will keep
>> itself upright as you sit on it.
>>
>> good luck with your project! I'de love to get my girlfriend on a
>> B2B-tandem!!
>>
>> best regards,
>> Dirk
>>
>> Dustin Anderson wrote:
>>> Hello,
>>>
>>> I am in the process of building a Flevo Back to Back and am wondering
>>> if anyone could offer any wisdom. Pivot angle, Trail, etc.
>>>
>>> My wife and I have toured Canada on a MIC WIC delta tandem twice and
>>> have since sold the bike and I am going to build a dual drive train
>>> B2B for 2008.
>>>
>>> Any advice would be most appreciated.
>>>
>>> Thanks.
>>>
>>> Dustin Anderson
>>> 5000 for health tour
>>> www.5000forhealth.com
>>>
>>>
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