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The Passenger rides on a rigid frame

Monkeypants

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There is a lot of information in MPH and other sources about sizing the rear springs for the extra load of a passenger. Eddie Stevens has a table of recommendations for this in Chapter 22 of his great book "Know Thy Beast".
It occurred to me that all of this suspension/passenger info is wrong, at least in regard to the standard geometry of the A,Band C models.
I have one C Rapide which has the long struts in place to make the seat into the fully suspended type. This bike has heavier than stock rear springs and it needs them, it all works quite well when loaded up. It also carries a full set of luggage on a rack that connects to the seat and the pillion footrest support plate, so that load is on the rear springs as well.
The other Rapide is very softly sprung, has the standard C rear suspension, so the rear of the seat bobs up and down when going down the road. I always assumed that with it's very soft springs it would bottom out easily with a passenger on board. Even with it's much stronger springs, the fully suspended bike will bottom out on a really sharp bump, like when hitting a bridge deck that is 4" above the main road surface, that sort of thing.
To my amazement when I did try out the soft sprung bike with a passenger on board, it seemed to handle the bumps just fine, no easy bottoming at least. I was totally comfortable, however my passenger ,who normally rides on the fully sprung bike, was not so happy. Apparently it was a pretty jarring ride
For me, it seemed pretty much the same as when I ride it solo. The reason for this is that virtually none of the weight of the passenger is transmitted to the rear suspension. Other than the small amount of weight placed on the passenger footrests, all passenger weight is transferred directly thru the seat stays to the rigid top member of the rear frame and from there to the rear axle and ground. The only suspension for the passenger is the same as it was on my rigid framed 1949 Matchless G80, just whatever the tire and seat can provide.

To get an idea of how rigid the back end is on a standard non D Vincent, have someone hold the bike while you shove down on the seat in the area where the passenger's weight is centered. I could not get the rear suspension on the supple standard bike to budge when doing this. I have since tried this on another standard C, same result..
There is an easy fix however, and it is the already well known solution of the long struts or the fully suspended type seat/luggage carrier.

If you aren't going with either of these fully suspended routes and insist on the stock seat stays, you might as well keep some fairly soft springs in the back end, just whatever you and the luggage need, since virtually none of the passenger's weight enters into the equation.

Glen
 
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timetraveller

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And that is one reason the series 'D' was like it was. If you have never ridden one then the rear seat comfort is a revalation.
 

ossie

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my goodness me that was complicated.
its a bike her on the back don,t complain so whats the problem????
how many years riding has it taken to find out its not going up and down over bumps as YOU think it should.
[bramptons woodhead monroe front DAMPER... standard springs koni damper rear .
since 1966 still working ok.
OSSIE
 

Monkeypants

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VOC Member
My apologies if Imade that overly complicated, however the idea that some of the passenger's weight is on the springs seems to be pretty widespread and I believe, incorrect. There is lots of discussion of this in back issues of MPH. All the information comes with the assumption that rear springs pack some of the weight of the passenger and that the passenger is semi-suspended.
I am saying that nearly zero weight goes from the passenger to the springs and that the passenger might as well be on a rigid rear frame.So that is a different way of looking at it, I think?
Glen
 

ossie

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been up pub it was just in the best possible taste.
not pulling holes in your observations.
OSSIE
 

Monkeypants

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no problem, I don't mind if holes are poked in this observation. I just put the thought up for discussion because it seems to go against the common wisdom in MPH and also "Know ThyBeast"
Happy to hear other viewpoints on it
Glen
 

davidd

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VOC Member
Glen,

Having started out on an Egli, I was surprised at the lack of suspension when I rode on the back of Jim Young's Rapide in the 1970's. It was so rough I could not believe that Vincent owners could get their wives to sit on the back. Of course, that could be an answer. Jim told me the front was 75% sprung and the rear was 50% sprung, as I remember. I think what you are pointing out is correct. I suspect the rear may benefit from some springing, but it is more like 0-15%. In any event, I agree that struts are the way to go. I am always surprised that Vincent continued the oddly sprung seat considering none of the Grey Flash TT machines, or the prototype Flash used the seat stays. I have a feeling George Brown would have ridden anything with an engine, but from the racing photos, he is seen on the fully sprung Flash quite a lot. I would have thought they could have saved a bit of money by using the far superior struts and they were well tested.

David
 

clevtrev

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VOC Member
Don`t forget also that the pillion riders feet are going down when the rest of the body is going up.
 

Monkeypants

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True, I can see that a small amount of the riders weight is normally on the footrests. If the passenger can anticipate a large bump ahead, he/she can temporarily use leg muscles to have a similar effect to that of the long struts, that of transferring most or all of their weight onto the suspended part of the bike. To do that over a rough road on a long trip is hard work though and it would be impossible to forsee every bump. As the rider, I wouldn't want to ride a roadbike this way. I do this when riding a trials bike and after 30 minutes the leg muscles are screaming in pain.

Glen
 
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A-BCD

Well Known and Active Forum Website User
VOC Member
my goodness me that was complicated.
its a bike her on the back don,t complain so whats the problem????
how many years riding has it taken to find out its not going up and down over bumps as YOU think it should.
[bramptons woodhead monroe front DAMPER... standard springs koni damper rear .
since 1966 still working ok.
OSSIE
Ditto !!!!!!
 
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