Retrobike Forum Index

It is currently Thu Dec 08, 2016 7:25 pm

* Login   * Register * Search  * FAQ



Post new topic Reply to topic  [ 182 posts ]  Go to page Previous  1 ... 4, 5, 6, 7, 8, 9, 10 ... 19  Next
Author Message
 Post subject: Re: 1979 and all that
PostPosted: Fri Nov 21, 2008 9:12 pm 
retrobike rider
retrobike rider
User avatar

Joined: Tue Sep 30, 2008 6:25 pm
Posts: 924
Location: Near Wendover Bucks
GeoffApps wrote:
And now for the 1980 Range Rider....
...Anyway, any questions, anyone?


This brings me to the subject of cross braced frames. The phase 1 (1979) Cleland was unbraced. The Phase 2 (1980) Cleland had two.
I know that the cross braces are a geometric means of triangulating the frame by preventing fork induced bending forces from breaking it. (These can induce flex which can lead to metal fatigue and result in sudden failure).

What I would like to know is the story behind these being added to the 1980 bike.

Most framebuilders waited for oversize tripple or quadruple butted tubesets to be introduced. It seems to me that yours is a more elegant engineering solution when compared to simply adding more metal where the tubes flex.

In theory, triangulated braces should convert bending forces into the less destructive forces of compression and tension.

The technique, of replacing bending,sheer,and tortional forces, within structures, with the less destructive compression and tension, has been at the centre of structural engineering for centuries. Why do so many bike designers ignore this?

Maybe it's all about looks.


Last edited by GrahamJohnWallace on Sat Nov 22, 2008 11:52 am, edited 1 time in total.

Top
 Profile  
 
PostPosted: Sat Nov 22, 2008 1:13 am 
retrobike rider
retrobike rider
User avatar

Joined: Tue Sep 30, 2008 6:25 pm
Posts: 924
Location: Near Wendover Bucks
Triangulated forks and braced frame

This is the Phase 3 Cleland Dingbat in October 1988. Fitted with extra low trials gearing and braced (triangulated) forks.

:?: Which part of this Highpath Engineering built frameset will break first :?:

I don't know. But I wouldn't like to be a headset ball bearing if this bike collided with a solid object. :shock:


Attachments:
Cleland Dingbat1988.jpg
Cleland Dingbat1988.jpg [ 175.23 KiB | Viewed 1542 times ]
Top
 Profile  
 
 Post subject: 1979 and all that ...
PostPosted: Sat Nov 22, 2008 9:41 pm 
MacRetro rider
MacRetro rider
User avatar

Joined: Mon Nov 10, 2008 10:39 pm
Posts: 170
Location: SE Scotland
Graham:
I don't know why cross-bracing didn't catch-on. I think what you say applied in the days when cycle frames where restricted to tube construction. These days we have a whole range of monocoque style fabrications, computer generated, and suspension has demanded all kinds of struts and sub-frames. However, bracing isn't used on hardtail machines, where they could be made lighter with strategic use of smaller tubes. However, I'm not that bothered about cross-bracing, provided the frame is strong enough and of a suitable design, I don't worry too much about the minutia.
The frame in the photograph on page 2 did eventually break ~ below where the downtube meets the headstock ~ Billy Whitcomb had made that section too long ~ it should not have extended much beyond the downtube mitre.

Here's a photo of Tony Silver's production Aventura from 1982 ~ He was the first person to place an order, and paid the full price of £415, a vast sum to fork out for a bicycle in those days, it was the most costly bicycle on the market at that time!
The headstock on this machine, frame built by Jeremy Torr, and inevitably repaired by Dave Wrath-Sharman, also extends too far from the mitre, but this one has a reinforcing collar.


Attachments:
TonySilversAventura1982.jpg
TonySilversAventura1982.jpg [ 195.33 KiB | Viewed 1514 times ]
Top
 Profile  
 
 Post subject:
PostPosted: Sat Nov 22, 2008 10:55 pm 
East Midlands AEC
East Midlands AEC
User avatar

Joined: Thu Oct 05, 2006 7:45 pm
Posts: 15067
Location: Derby, UK
I may be way off the mark but noticed this on Ebay today and how similar it seemed in principle...


Attachments:
e4e8_3.jpg
e4e8_3.jpg [ 117.9 KiB | Viewed 1506 times ]
Top
 Profile  
 
 Post subject: 1979 and all that . . .
PostPosted: Sat Nov 22, 2008 11:44 pm 
MacRetro rider
MacRetro rider
User avatar

Joined: Mon Nov 10, 2008 10:39 pm
Posts: 170
Location: SE Scotland
Similar in appearance, but not in principle.

Look at the long rear end, and the forward slung handlebar. Those two factors neutralise the weight bias, as described in one of my earlier posts.

Mudguards have very little clearance and are fitted with stays, bad news off-road where twigs and sticks can catch up in them, and they do!

Other non-Cleland factors are:
lowish (by Cleland standards) bottom bracket and ground clearance
rim brakes
lack of a guard between the tyre and chain
MTB size 522 wheels.

Nice bike, but it doesn't fit the Cleland mould.


Top
 Profile  
 
 Post subject:
PostPosted: Sun Nov 23, 2008 12:30 am 
Old School Grand Master
User avatar

Joined: Wed Feb 20, 2008 12:21 pm
Posts: 5785
Location: Lost in Translation
One thing that strikes me from the Cleland design is that the high bottom bracket, high front end, and relatively short (in MTB terms) seatpost combine - even with the dropped top tube - to give quite a high standover height. A lot of the early mountain bike designs were constrained by the parts that were available for contemporary road bikes - 1" quill stems, short seatposts, etc - but long seatposts were available from small-wheeled bikes. For example, the Raleigh Twenty and Moulton Mk3 had a long 28.6mm post. With the parts that are available now - long seatposts and threadless riser stems, for example - would you have designed the bike for more standover clearance?


Top
 Profile  
 
PostPosted: Sun Nov 23, 2008 1:02 am 
retrobike rider
retrobike rider
User avatar

Joined: Tue Sep 30, 2008 6:25 pm
Posts: 924
Location: Near Wendover Bucks
Turning Mountain Bikes, into Clelands?

I have had reasonable amount of success in modifying Mountain bikes to give them more Cleland like handling characteristics. The bikes were modified for my two daughters to use, as they intuitively don’t like stretched out riding positions.

The original bikes were a 24 inch wheeled Marin Bayview Trail and a 26 inch wheeled Giant NRS3. Both have which have high bottom brackets, short chain stays and top tubes. The main modification is to that handle bar stem now rises over 8 inches directly above the top of the steering tube. I also had to design and make effective mudguards. I fitted rigid forks to the front of the NRS as no body weight placed on the handlebars, means that there is not enough rider induced inertia to compress the suspension forks.

They are similar to Clelands but differ in that they don't have as much mudguard clearance, their brakes are not as progressive and they require much more, post-muddy ride, maintenance. The tyres that the Clelands use have unique low-pressure shock absorbing characteristics, which the modern bikes lack. However, these properties come with a price as each Cleland heavy-duty 650B tyre and inner tube weighs 3lbs.


Top
 Profile  
 
 Post subject: 1979 and all that . . .
PostPosted: Sun Nov 23, 2008 7:23 am 
MacRetro rider
MacRetro rider
User avatar

Joined: Mon Nov 10, 2008 10:39 pm
Posts: 170
Location: SE Scotland
Hello One-eyed Jim ~

I spent a lot of my time tracking down parts, and having bits made by engineers, all very expensive and time-consuming.

My aim was to get the stand-over as low as possible without compromising the strength of the frame.

There are a number of ways this could be achieved and I felt the way the Aventura turned out was the best, most achieveable and most economical solution. Dave Wrath-Sharman came up with a design which took the down-tube to the top of the headstock and down to the bottom bracket, and the duplex cross-braces remained as per the Cleland on page two of this thread which has a duplex cross-brace (replaced by a single brace in 1981 design).

I wonder if anyone has a photo of Dave's cross-frame design ~ I'm sure I have somewhere . . .

Stand-over is a distinct problem with the Cleland design. This is because the saddle is so high that the rider cannot easily reach the ground without coming forward off the saddle, not always possible in a tight situation. This is a compromise I am very much prepared to make, developing a riding technique learned in motorcyle trials riding; often discovering that by resisting the temptation to take a dab, finding the dab is not really necessary; if I 'hang in there' I can get through a particularly difficult section with feet remaining on the pedals.

Not everyone who has ridden a Cleland is happy with this characteristic, although I sometimes wonder if they fully understood the advantages offered by the design would make a difference.


Top
 Profile  
 
PostPosted: Sun Nov 23, 2008 9:04 am 
Old School Grand Master
User avatar

Joined: Wed Feb 20, 2008 12:21 pm
Posts: 5785
Location: Lost in Translation
Thanks for the reply Geoff.

After I posted my question, I realised that the various wheel sizes and unfamiliar geometry make it hard for me to estimate dimensions from the photographs posted to this thread. Could you put some numbers on things? The bottom bracket is high, but how high? The chainstays and wheelbase are short, but how short? Are those TA cranks as long as they look?

GeoffApps wrote:
I wonder if anyone has a photo of Dave's cross-frame design ~ I'm sure I have somewhere . . .

I think this must be it:

http://www.63xc.com/dws/hubbrake.htm


Top
 Profile  
 
 Post subject: 1979 and all that . . .
PostPosted: Sun Nov 23, 2008 9:30 am 
MacRetro rider
MacRetro rider
User avatar

Joined: Mon Nov 10, 2008 10:39 pm
Posts: 170
Location: SE Scotland
Hello One-eyed Jim ~

The Range Riders and Aventuras all have 650B wheels.
These measure about 27 1/2" overall diameter.
The Dingbats have two wheel sizes: 531 front and 422 rear. However, the tyre sizes are different, therefore the overall diameter is the same for front and rear wheels, in this case, just over 24"

Bottom bracket height is usually 12 to 12 1/2 inches from the ground to the axis.

Does anyone remember the Deore drop-pedal?

I've designed a new version which will be made in the next few weeks, and can go some way to overcoming the high-ride issues. Also useful for very tall riders.

Chainstay length was as short as I could persuade an engineer/frame builder to make it. High bottom bracket facilitated a shorter chainstay in the days when we were restricted to tube construction.

TA cranks were, indeed, long at 190mm. These gave some extra torque when you needed it most, on a perilous tight turn, about to stall. When combined with my (quite radical) eggrings, the make a formidable rotary drive system.

I've had some debate with Mike Burrows on the use of short cranks and I think his case is very strong. One of these days I'm going to give it a try.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 182 posts ]  Go to page Previous  1 ... 4, 5, 6, 7, 8, 9, 10 ... 19  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: longun, shawnb and 53 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  

About Us

Follow Retrobike

Other cool stuff

All content © 2005-2015 Retrobike unless otherwise stated.
Cookies Policy.
bikedeals - the best bike deals in one place
FatCOGS - Fat Chance Owner's Group

Powered by phpBB® Forum Software © phpBB Group