Linking forward and rear suspension



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Simon Brooke

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I was looking at a picture of a Whyte PRST1 earlier today, and musing as one does... The Whyte uses
quite similar suspension units for both front and rear suspesion: <URL:
http://www.whytebikes.com/whyte-2004/images/whyteprst1side72dpi.jpg >

and what I was musing about was the Citroen Deux Chevaux and the original Issigonis designed Austin
Mini. The 2cv had a single suspension unit on each side of the car which linked the front and rear
swing-arms; the original mini used 'hydrolastic' suspension units where the oil reservoir in the
forward suspension unit was linked with a pipe to the oil reervoir in the rear unit on the same
side. This was a conscious imitation of the principle of the 2cv system while avoiding the Citroen
patents. The hydropneumatic Citroens - DS, GS, SM, BX, CX, XM, Xantia and C5 - have of course more
complex hydraulic interconnection of the suspension units but that isn't what I'm thinking of here.

The point is that on both the 2cv (a car I love - in my opinion the world's most under-rated
sportscar) and the early minis the scheme worked extremely well to limit pitch, giving a perception
of a much smoother ride. When the front hit a bump and the front suspension compressed the rear
suspension would extend, keeping the body of the vehicle relatively level.

It struck me that this principal, if applied to mountain bikes, would possibly give a steadier and
more controllable ride particularly over fast rough sections, and that with modern air/oil
suspension struts it would not actually be that hard to rig up, and would add very little in weight.

So the question is, who has tried it and what were the results? I've done a quick web search but
haven't come up with anything... but the idea is so obvious _someone_ must have tried it, surely?

--
[email protected] (Simon Brooke) http://www.jasmine.org.uk/~simon/

;; this is not a .sig
 
Simon,

The original BMC mini used rubber for a suspension medium. The later ones, IIRC 1965 and later used
the Hydrolastic suspension setup. In rallying and racing any hydrospastic minis I have seen were
converted to a dry suspension.

The interlinking of suspension does have some merit to contol roll, dive
and squat in the automotive world. Such active systems do add complexity
and to work well need microprocessor control and a host of sensors.

I really don't see it being much use with the light weight, relatively short wheelbase and varying
conditions faced by an offroad bicycle.

That being said I'm sure somebody with time on their hands and some hose, double acting hydraulic
cylinders and a couple of diaphramed air/oil reservoirs could have hours of entertainment.

Marcus
 
On Tue, 25 Nov 2003 19:05:02 GMT, Simon Brooke <[email protected]> may have said:

>So the question is, who has tried it and what were the results? I've done a quick web search but
>haven't come up with anything... but the idea is so obvious _someone_ must have tried it, surely?

Maybe not, with good reason.

While it might seem logical to want the suspension to work that way, consider the effect in a
*downhill* situation. I think the problem will be immediately apparent. Then consider that unless
the system is disengaged during braking, it *accentuates* the forward weight transfer effect; this
is not desired behavior at all.

I had noticed the 2CV's tendency to exhibit unusual dive effects long before I knew why they were
present. When I looked at the design, I understood why it wasn't more widely used.

--
My email address is antispammed; pull WEEDS if replying via e-mail. Yes, I have a killfile. If I
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contains nuts.
 
In article <[email protected]>, stu wrote:
> http://www.whytebikes.com/whyte-2004/images/whyteprst1side72dpi.jpg Is it just me, or is there
> something not right about the lacing on these wheels?

They're the new VariCross(tm) wheels from VariSpoke, scheduled to be released in early April. Notice
the hubs are 100% hidden in the picture in accordance with the VariSpoke pre-release product rules.

Greg
--
Gregory S. Sutter "How do I read this file?" mailto:[email protected] "You uudecode it."
http://zer0.org/~gsutter/ "I I I decode it?"
 
On Wed, 26 Nov 2003 11:04:10 +1100, "stu" <[email protected]> wrote:
>http://www.whytebikes.com/whyte-2004/images/whyteprst1side72dpi.jpg Is it just me, or is there
>something not right about the lacing on these wheels?

Apart from there being something fundamentally wrong with the whole bike? It appears that it could
have been done better if they had thought even _more_ outside the box. Although I can't visualize it
at the moment, I imagine there must be a _much_ simpler solution to the idea of putting both shock
absorbers on the frame, rather than the front in the fork.

However, even so, doesn't the fork represent unsprung weight, which, IIRC, should be minimized for
better handling? Or is that not true of bikes?

Okay, back to the question: I'm no wheel expert, but the spoke lacing does appear a bit odd; I
seem to see parallel spokes where I shouldn't, and such pairs aren't evenly spaced from other such
pairs either.

It does appear to have very low gearing, though. I like that in a gnarly off-road bike...especially
if it also appears to weigh 50 pounds. ;) (The site says "Weight 27.8lbs fully built!")
--
Rick Onanian
 
> It's just you. That's conventional 23 x 3. How about exposing your doubts. What is it you
> find odd?
>
> Jobst Brandt [email protected]
Happy to take your word on it What I was looking at was how, on one half of the wheel you 3 places
where 4 spokes cross almost at the same spot, yet on the other half of the wheel it looks nothing
like that. I use 38 myself, so I guess I have just never noticed this before. thanks stu
 
stu wrote:

>>It's just you. That's conventional 23 x 3. How about exposing your doubts. What is it you
>>find odd?
>>
>>Jobst Brandt [email protected]
>
> Happy to take your word on it What I was looking at was how, on one half of the wheel you 3 places
> where 4 spokes cross almost at the same spot, yet on the other half of the wheel it looks nothing
> like that. I use 38 myself, so I guess I have just never noticed this before.

I certainly find it odd that Jobst considers 23 spokes to be conventional and that you use 38. :) I
think the appearance that's bothering you is just due to the perspective not being quite
perpendicular to the wheel and lining up some left-side and right-side spokes.
 
> I certainly find it odd that Jobst considers 23 spokes to be conventional and that you use 38. :)

lol oops I noticed Jobst's typo, lucky I didnt have a go at him about it hey lol

>I think the appearance that's bothering you is just due to the perspective not being quite
>perpendicular to the wheel and lining up some left-side and right-side spokes.
>

yes you are right, l went and had another look at my wheels and they do the same thing. l had
throught about that before l posted but l didnt find the right angel. thanks again stu (who must
look more carefully next time) and install his spell check
 
">
> I certainly find it odd that Jobst considers 23 spokes to be conventional and that you use 38. :)

lol oops I noticed Jobst's typo, lucky I didnt have a go at him about it hey lol

>I think the appearance that's bothering you is just due to the perspective not being quite
>perpendicular to the wheel and lining up some left-side and right-side spokes.
>

yes you are right, l went and had another look at my wheels and they do the same thing. l had
throught about that before l posted but l didnt find the right angel. thanks again stu (who must
look more carefully next time) and install his spell check
 
">
> I certainly find it odd that Jobst considers 23 spokes to be conventional and that you use 38. :)

lol oops I noticed Jobst's typo, lucky I didnt have a go at him about it hey lol

>I think the appearance that's bothering you is just due to the perspective not being quite
>perpendicular to the wheel and lining up some left-side and right-side spokes.
>

yes you are right, l went and had another look at my wheels and they do the same thing. l had
throught about that before l posted but l didnt find the right angel. thanks again stu (who must
look more carefully next time) and install his spell check
 
my posts have started not to appear????? l hope you arent all seeing this for the fourth time

> I certainly find it odd that Jobst considers 23 spokes to be conventional and that you use 38. :)

lol oops I noticed Jobst's typo, lucky I didnt have a go at him about it hey lol

>I think the appearance that's bothering you is just due to the perspective not being quite
>perpendicular to the wheel and lining up some left-side and right-side spokes.
>

yes you are right, l went and had another look at my wheels and they do the same thing. l had
throught about that before l posted but l didnt find the right angel. thanks again stu (who must
look more carefully next time) and install his spell check
 
Rick Onanian writes:

http://www.whytebikes.com/whyte-2004/images/whyteprst1side72dpi.jpg

>> Is it just me, or is there something not right about the lacing on these wheels?

It's just you. That's conventional 32 x 3.

> Apart from there being something fundamentally wrong with the whole bike? It appears that it could
> have been done better if they had thought even _more_ outside the box. Although I can't visualize
> it at the moment, I imagine there must be a _much_ simpler solution to the idea of putting both
> shock absorbers on the frame, rather than the front in the fork.

Ah, but you missed the feature. This bicycle uses the BMW patented anti-dive fork suspension
with unequal length leading links. I don't know how important the feature is for bicycling, not
having tried a suspension front end. It is a useful function for motorcycles that have large
suspension travel.

> However, even so, doesn't the fork represent unsprung weight, which, IIRC, should be minimized for
> better handling? Or is that not true of bikes?

It is probably untrue of bicycles about the same as wheel balancing. Weight of bicycle wheels and
forks is small compared to rider weight and poses no significant inertial dynamics.

> Okay, back to the question: I'm no wheel expert, but the spoke lacing does appear a bit odd; I
> seem to see parallel spokes where I shouldn't, and such pairs aren't evenly spaced from other such
> pairs either.

As was mentioned, it's perspective.

> It does appear to have very low gearing, though. I like that in a gnarly off-road bike...
> especially if it also appears to weigh 50 pounds. ;) (The site says "Weight 27.8lbs fully built!")
I he weight is probably correct.

Jobst Brandt [email protected]
 
Rick Onanian <[email protected]> wrote:

> >http://www.whytebikes.com/whyte-2004/images/whyteprst1side72dpi.jpg
>
> Although I can't visualize it at the moment, I imagine there must be a _much_ simpler solution to
> the idea of putting both shock absorbers on the frame, rather than the front in the fork.
>
> However, even so, doesn't the fork represent unsprung weight, which, IIRC, should be minimized for
> better handling? Or is that not true of bikes?

That fork looks like a variation on the BMW "Telelever" design, whose main virtue is to be
non-reactive to braking forces.

http://www.encycleopedia.com/index.cfm?pid=23&edID=260&thePage=photos

Chalo Colina
 
[email protected] wrote in message news:<[email protected]>...
> Rick Onanian writes:

[snip]

> > Okay, back to the question: I'm no wheel expert, but the spoke lacing does appear a bit odd; I
> > seem to see parallel spokes where I shouldn't, and such pairs aren't evenly spaced from other
> > such pairs either.
>
> As was mentioned, it's perspective.

[snip]

> Jobst Brandt [email protected]

Dear Jobst,

Yeah, perspective and smaller brains. I hate all you guys who didn't have to go out to the garage
and stare at a front wheel from different angles. I hate all optical illusions.

Time to go out in the back yard and pretend to throw the stick for the dog to make myself feel
smarter. Unfortunately, basset hounds lose interest in chasing sticks at about one year old, so I
may have to borrow the neighbor's dog to tease.

You guys should all be ashamed for trying to fool me.

Carl Fogel
 
On 26 Nov 2003 10:56:46 -0800, [email protected] (Carl Fogel) wrote:
>Unfortunately, basset hounds lose interest in chasing sticks at about one year old, so I may have
>to borrow the neighbor's dog to tease.

Just get a younger stick.

>Carl Fogel
--
Rick Onanian
 
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