Friday, September 11, 2015

Duomatic

Behold! Mr. Larrington is gone to our colony of Canadia on the way to his annual Visitation to examine the most sophisticated of bicycles, and this reminds me that I have just built the least.

A while ago there came into my possession a Raleigh Twenty, one of the foulest vehicles perpetrated on the cycling public, but after languishing on the bike heap where the swallows twitt'ring from the straw-built shed coated it with fertiliser I chanced to look more closely and found in the middle of the back wheel a Fitchel and Sachs Torpedo Duomatic 36-hole hub. This is a rare fish: most of them were 28-hole hubs because in the European view, a 20" wheel doesn't need 36 spokes.

Mr. Knight regards this hub with disfavour but it intrigues me. If you pedal backwards gently it changes gear from a 1:1 to a 1: 1.36 ratio, and if you then pedal backwards gently again, it changes back. If you pedal backward hard, it operates a coaster-brake. Accordingly you can build a simple bicycle with two gears and the only control lever you need is for your front brake. My daily ride does not involve serious hills and I can manage with two gears. It occurred to me that if I fit a 22 tooth cog to the hub and a 36 tooth chainring, I can have a practical 60" and a 44" gear.

I removed said wheel. Couldn't get the tyre off. Tried lashing tyre to one-half-of-the-rim so's to push the bead into the central rim well and force it proud on t'other side of the wheel. Still wouldn't move. Made a few pertinent observations to relieve feelings using words of medieval emotion into which Mr. Larrington's sister (probably) could offer some insight, and got out tyre levers. Three of them. Got all three under the bead, and gently prised the tyre up onto the edge of the rim. Still couldn't get it off. Unscrewed four, five, six spokes to allow more room for tyre levers to go all the way through the wheel.

Success! Tyre unseated.

Examined interior to see what the problem was.

Previous owner - moron - had felt the rim tape inadequate to the task of sealing all the rust inside the rim, and had entirely filled the rim well with duck tape. - And yes, duck tape is correct even though those who programmed this computer think it should be duct tape, but it shouldn't, because you don't tape ducts, and duck tape comes from its development during WWII as a form of sticky tape made from duck cotton. - Moreover the inner tube was from a 24" wheel, concertinaed at the valve to cram it in.

I rebuilt the wheel as a 700c using a discarded pringled rim which I'd been saving for some such purpose - the joint now sufficiently prominent as to preclude rim brakes for ever - and some 27 x 1 ΒΌ three-cross spokes which had come off the pringled wheel. - This is a common ploy. They are the right length as four-cross in a 700c, and out in the bush the bike shops used whatever was to hand.

All then that was needed was a frame and nearly-matching front fork from the Bike Heap, and a retired saddle and Dutch handlebar turned upside down etc. Here it is.



22 tooth back sprocket, 36 tooth chainring, and it gives a 44 inch and a 60 inch gear. Civilised and useful rather than fast.

There remains the Raleigh Twenty frame, and we must address what to do with that but I am reminded of the period of about a million years ago when everyone busied themselves with Raleigh Twenties and found they made 'stremely good short wheelbase recumbents.



Probably Mr. Tweddle's.


Probably Mr. Adcock's.


Probably mine.




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2 Comments:

Blogger Daisee Fransisco said...

Thanks for sharing this great article! That is very interesting I love reading and I am always searching for informative information like this.
carbon cycling wheels

October 30, 2015 at 3:08 AM  
Blogger Mr Larrington said...

Dr Larrington is indeed my Big Sis and you must all go to a suitable emporium and buy her books.

December 5, 2015 at 11:05 PM  

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