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PostPosted: Sun Sep 12, 2010 10:04 am 
retrobike rider
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Yep!

It sure is ! :oops:

The use of a drum brake or RollerBrake could easily sort that out.

Prototypes often have teething troubles. And especially so with a design of this complexity. I am surprised that this bike works at all, as half of the mechanism is only there to sort out the problems thrown up by fact that the frame is free to articulate. :shock:


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PostPosted: Sun Sep 12, 2010 5:09 pm 
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Are you sure Rube Goldberg didn't design that bike? :D :D


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PostPosted: Sun Sep 12, 2010 5:58 pm 
retrobike rider
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Since a similar effect can be achieved by standing upright on a full suspension Cleland and letting the bike rotate underneath you, this does at first appear to be a Rube Goldberg style, overcomplicated solution.

However, standing upright whilst pedaling at the same time is tiring and only works at slow cadences. Also articulation on ordinary bikes only works when the centre of mass of the rider is directly above the pedals as it is essential that there is no weight on the arms. The TopTrail allows for a wide range of riding postures. This is because the handlebars and saddle are isolated from shocks and so remain relatively still.

However, I do find it hard to believe that there is not be a simpler way to allow the bike to articulate whilst the rider remains in the saddle? :?


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PostPosted: Sun Sep 12, 2010 6:10 pm 
MacRetro rider
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It reminds me of a crazy looking Danish bike I saw recently that instead of a toptube had a long leather "belt" that the saddle was directly attached to.

I can't remember what the hell it was called though but looked like a huge upright Moulton.


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PostPosted: Sun Sep 12, 2010 6:13 pm 
Gold Trader / PoTM Winner / RB Rider
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reminds me of the ATZ prototype bike rideen by P Perakis in the early 90s .

I see what you mean now when you said at the OWC you had to drop the weight a bit .


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PostPosted: Sun Sep 12, 2010 6:39 pm 
retrobike rider
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Hi Tazio.

Yes I am sure there are some Pedersen genes in there somewhere 8)

Hi Chris.

The bike that Geoff Apps and I are trying to make lighter is the Cleland TT shown below.

The TopTrail is not a Geoff Apps design but was designed by Adrian Griffiths and made by David Wrath-Sharman at Highpath Engineering.


Attachments:
File comment: Cleland Aventura TT Prototype
Cleland TT.jpg
Cleland TT.jpg [ 233.78 KiB | Viewed 1520 times ]
File comment: Pedersen Bicycle
Pedersen.jpg
Pedersen.jpg [ 136.5 KiB | Viewed 1520 times ]
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PostPosted: Sun Sep 12, 2010 6:42 pm 
MacRetro rider
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Pedersen!!

I've been trying to remember that for over a month now. There's a rather eccentric character rides one around Edinburgh whilst wearing a striped blazer and a straw boater.

I had a good look at it last month and it's a fascinating device.


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PostPosted: Mon Sep 13, 2010 12:29 am 
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Tazio wrote:
Pedersen!!

They're now made in Denmark, but the originals were built in Dursley, Gloucestershire by Danish engineer Mikael Pedersen who'd moved to Britain towards the end of the 19th century.

If you're ever in Gloucester, look for the transport annex of the Gloucester Museum. They've got three Dursley Pedersens (lady, gent, and child) in the window.

http://www.livinggloucester.co.uk/histo ... en_cycles/

http://dursley.dk/galleri/thumbnails.php?album=7


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PostPosted: Mon Sep 13, 2010 9:08 am 
MacRetro rider
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Going back to an earlier post about tyre pressures: I recently bought a low-pressure gauge and discovered that the pressures I currently use on the AventuraTT, now equipped with WTB Dissent 2.5" tyres and motorcycle weight 25" (effectively 28" or 700C) innertubes, are:
Rear - 11psi
Front - 7 psi
I'm not sure a tubeless system could reliably contain such low pressures.
The tyres seem to function a bit like tank caterpillar tracks; getting places, but not very fast. The tyres are gripped by the nut at the base of the valve stem, which must be aligned with the rim flanges. I have not experienced any pinchies or rim-creep. A certain amount of wallow is inevitable, but the stout construction of the Dissents minimises this.
This makes the AventuraTT a bit of a slug on-road, but I'm not in any hurry.
Pedersen: not dissimilar the Cleland in riding posture.


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PostPosted: Mon Sep 13, 2010 6:05 pm 
retrobike rider
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GrahamJohnWallace wrote:
But why carry around the extra weight of a heavy duty inner-tube?
On smooth surfaces it only makes sense in terms of increasing tyre contact patch and so the grip. On rough surfaces, like cobble stones, the low pressure tyres can absorb all the vibration and so reduce the rolling resistance. Tyre design is important in that an inflexible tyre will have a very high rolling resistance when run at low pressure. The original Cleland tyres are thick but flexible, and are remarkably quick off-road.


Since writing the above I have had time to experiment with low pressure inner-tube and tyre combinations.

Here are my conclusions so far:

1/Using ordinary "tubed" tyres on tubeless rims stops rim creep and the resulting valve rip out.

2/ Some tyres have a reasonable rolling resistance when run at low pressures. However some that have good high pressure rolling resistances are very bad when run low.

3/It is by matching the width of the tyre with the width of the tube that allows the use of very low pressures. Wide lightweight tubes appear to work just as well as heavy duty tubes. (Too wide and the tube will chaff and eventually puncture. Too narrow and too much pressure is wasted on expanding the tube to contact the tyre).

So a heavy-duty, thick walled tube, is only useful in that it can prevent pinch punctures and reduce the risk of ordinery punctures. (It should be possible to redesign rims so they are less likely to pinch puncture the tubes. Also, some modern cars are designed to run flat for short distances).


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