6 Sep 2010

Higgins with differential

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The new owner of this Higgins 'Ultralite' trike has kindly sent me some excellent pictures of his rebuild progress. I have downsized the images slightly to avoid large downloads for my blog readers. Some images have been slightly cropped to emphasise some details. Steve is a competent and very experienced restorer of period bicycles, tandems, and now trikes. He already enjoys riding fixed wheel on his superb, classical track bikes.


His Higgins 'Ultralite' trike now road worthy and very tasty it looks too! Raring to go!


Here we see the Higgins differential. Suitable threads are provided on each side of the casing for a fixed sprocket or a threaded freewheel. The owner then has a choice to reverse the differential to taste. Albeit with some work involved in dismantling the rear axle. I must admit to a certain respect for anybody willing to learn to ride a trike from scratch with a fixed wheel.  Rather you than me! ;-)

I've just remembered that my first trike was fixed wheel to start with. On the first real ride into town I nearly ended up in a posh hotel via the revolving doors! Ouch! Fortunately I was fended off by the burly, uniformed doorman as I snaked across the road,  jumped onto the pavement, all on two wheels and completely out of control! Ah, the overconfidence of (idiot) youth. :-)


The view from the sprocket side. Note how the axle extends right through what is normally the idler side to provide drive to the offside wheel as well.


The overall rear end view. The Higgins Differential is a remarkably neat and compact unit. 


A posh, new, lightweight, alloy, eccentric, bottom bracket assembly has been installed in the bottom bracket shell. Presumably sourced from Chris Hewitt Cycles. A handy device to have for precise chain tension adjustment with a single speed drive. Particularly with fixed wheel where the chain is tensioned one way under power and then the other way by braking with reverse pressure on the pedals. This effectively doubles the effect of any chain slop.

Real trikes lack adjustable rear drop-outs. Though my first trike had telescoping, adjustable chainstays with nickel-plated, screwed sleeves for altering chain tension. Small clamps underneath the stays then kept everything tight and secure. I can still remember the struggle to keep the clamps tight with rather small and poor screws of the day. Today they would be fitted with much tougher Allen, hex socket screws. Back then these screws weren't yet in the public domain. Though specialist Allen screws were certainly being used on alloy chainsets.


 A very pretty Campag Record chainset has been fitted. I think it wise not to learn to ride a trike with toe-clips or even clip-in pedals. You rarely has time to remove a foot to save yourself if the trike should tip over. Not even when at a complete standstill! This is when it usually happens in my own experience.


Detail of the wonderful artistry of the Campagnolo Record single speed chainset. The new, eccentric bottom bracket assembly can be seen peeking through the chainwheel.


The period "cockpit" is fully in keeping with the age of the Higgins frameset. When this trike was built I was a 17 year-old, bike-mad teenager but still a couple of years short of a trike of my own.

It was a time of great change. With teenagers suddenly being recognised as a new economic species. To be catered for with wage increases to match their new-found needs and responsibilities. Bikes and British motorbikes were being scrapped in vast numbers. Everybody wanted the newly affordable, family cars. Hire purchase (credit) was a new phenomenon. Completely bypassing the former tyranny of the local bank manager. He who would only lend to those who already had money and property. Nobody realised it at the time but many manual skills would soon become only a very, distant memory. The computer had already arrived. Albeit in a space the size of warehouse. I worked on the peripherals of a couple of these monsters myself. Only the "boffins" in white coats could actually touch the machine itself.


Detail of the dual front brakes. Which are a typical combination of cantilevers on the brazed-on, fork bosses. With a centre-pull brake mounted on the hexagonal extension bar in front. The extension bar is essential to keep the brake blocks from overlapping when using two brakes in front of the forks. It is internally threaded for the brake fixing screw.


An unusual view of the brake arrangements with the forks turned sideways. I note that Steve chose to use the beautiful Campag Record headset bearings. Another real touch of high class cycle componentry.

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 Further updates: Steve, The new owner of the Higgins is enjoying his trike even more now he has fitted a freewheel block. He is now building some mileage but wondering how to proceed when confronted with stationary traffic. It is more difficult to wriggle through the traffic queues on a trike as I remember from my youth commuting between cities in England. Fortunately Denmark has bicycle lanes marked out almost everywhere so the problem rarely arises. 

Cornering on a trike at high speed with fixed wheel is a very difficult matter indeed. It takes a lot of the fun out of "hanging off the side" of the trike and drifting at high speed if one must keep pedalling. One learns to take a corner fast by free-wheeling and then start pedalling as soon as possible. Small roundabouts are enormous fun and one can get 3/4 of the way round without pedalling or losing speed. The trick is to use one's body weight well inboard on every corner. It feels strange an d dangerous at first but soon becomes the most enjoyable par of triking. IMO.

Here are some new images of the Higgins differential:


The Higgins half axles, without the differential, showing the actual distance between them in use. The trike is inverted here nicely showing the Higgins gear hanger boss. A small, right angle bracket is fitted here with a suitable thread to take the gear changer pivot directly.


Now with the trike the correct way up with the diff. carrying a five speed, screw-on, sprocket block. Only a single gear being used at present due to a lack of gear hanger. (Chris Hewitt usually has a choice of three different hangers)



The Higgins differential in close-up. Now fitted with a five speed, screw-on, sprocket block.

Note the two opposed threads are now on the other end of the diff. casing. The main thread is the same as any other screw-on sprocket. (but shorter) There is also a short left hand thread for the locking ring. If the locking ring had the same thread as the sprocket it would loosen as one back-pedalled to slow down. Reversing the thread ensures that the ring self-tightens. Safely holding a fixed sprocket firmly against any amount of reverse toque. If a fixed sprocket came loose the rider would lose all braking power on a track bike. And easily lose control on a road fixie!

From memory, it pays to tighten the sprocket well before tightening the locking ring. This avoids any free play in the sprocket which is very undesirable. The fixed sprocket can be tightened by standing on the pedals with the front wheel pushing against a wall. Or with the front brake(s) applied hard. Only then should the locking ring be tightened really well.

Do not try to use a fixed sprocket on a normal threaded hub designed for gears. The fixed sprocket  will fit the thread perfectly. This is not the problem. The problem is that even a pair of bottom bracket locking rings (if there is room on the thread) will suddenly undo themselves without warning! I tried this in my youth and was extremely grateful for my single front brake! It all came badly undone at the bottom of a long hill when a car in front braked suddenly. No fun at all and it required very quick reactions to avoid a nasty rear-end collision.


The bare Higgins Differential. Note the two different types of thread on either end of the casing. Long, continuous, gear thread on the right. Shorter fixed wheel thread on the left.  Opposite hand,  locking ring thread on the extreme left.



Higgins differential end view. Note the hexagon socket to fit the half axle. This hole will probably be in the back of a large bevel gear. The large headed screws on the outside of the casing no doubt support the four, small, bevel gears within.


The Higgins differential showing the opposite end of the casing. Note the grease nipple for lubricating the differential without the need for dismantling.

Here we see the other hexagon socket to fit the axle stub. Being completely reversible both end sockets must be identical.  Only the sprocket threads differ. Thereby offering the lucky trike owner a choice of fixed wheel or gears. This shows remarkable flexibility of thinking by the maker. Though admittedly fixed wheel was considerably more commonplace/popular at that time than it has been ever since. The fixie craze is only very recent. Though there were always those who preferred to ride fixed.

Riding a 72inch fixed gear was once considered the best way to get fit again after a winter lay-off. The gear was low enough to force rapid pedal rpm. (twiddling) Yet not too high for steep hill climbing. (Often out of the saddle) Nor was the gear too low to allow reasonable speeds downhill or with a tailwind. Time trials were once held for 72" fixed gear. I tried everything from 40" to 153" fixed in my youth. The latter with a 68T TA chainring was for pacing intercity buses but proved totally impractical. Particularly on the very long hills where I lived. I had a silly habit of trying to go as fast as possible downhill on these long drags. Which is where the (borrowed) 68T chairing came in. Not a good idea at all. :-) 

Note the large flats on the casing ends to take a very large spanner or vice jaws. (the latter used carefully and preferably fitted with protective slips on the jaws)  These flats hold the casing still as one unscrews sprockets or gear blocks from the other end. Often requiring considerable toque and a long chain wrench! The use of a common machinist's vice with typically rough jaws will probably damage the casing permanently if only cosmetically. A couple of small lengths of angle iron, brass angle, alloy angle or even strip steel bent at right angles, will protect the diff. casing from the roughest of vice jaws.

Yet again my thanks go to Steve, the Higgin's owner, for providing all of these excellent images.


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8 comments:

  1. How do I purchase one of these differentials? how much are they? Please let me know how to get one already made. rodney9872003@yahoo.com

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  2. I want to know how I can purchase one of these differentials and what is the cost? Thank you.

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  3. Hi Rodney

    Higgins differentials are no longer made. You have a number of choices: Buy another trike with one fitted already. Try and find a differential through the Tricycle Association. Or try asking Chris Hewitt Cycles in the UK. (address and Tel.No on the TA website under Higgins spares)

    The problem is that you also need the special axles to match the differential *and* the exact axle width of your own trike. This is difficult!

    Finally, and probably best IMO, is to buy a Trykit 2WD (Two Wheel Drive) double freehub and new axles. These will be made to exactly match your own trike. (if you have one)

    I am assuming here that you want to fit a diff to an existing trike and not just looking for a differential for another project. If you only want a cheap diff for a project then try and find a wrecked invalid trike already fitted with a diff. This is not going to be easy either!

    Good luck.
    Chris

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  4. Thank you, I will give it a try

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  5. - for tricycles i suggest to use with two electromotors, one in the left, one other in the right!

    :)

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    1. Hi VV2

      An interesting suggestion. (and I did see your smiley :-)) However, such a project would be fraught with difficulty. Any variation in power and/or speed between the two motors would send the trike into uncontrollable circles. While a single motor, driving the differential would avoid all such problems.

      In real life one might simply add a commercial electric motor hub to the front wheel and enjoy the best of both worlds: A pedal driven trike with independent electric power. A useful aid to help the rider climb hills or maintain a higher speed than which he he is normally capable. Handy when tired after a long ride. Or when age catches up with you. Or even worse, overtakes you. ;-)

      Thanks for your input.
      Chris

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  6. Dear Chrisbee,
    I find your post very interesting! I'm looking for information about differentials, do you know a good place to read more about 2WD double freehub and how it affects the driving of the trike?
    In another comment you write that the Higgings Diff aren't produced any more. Do you know how robust a differential is? Or is it a very sensitive part?
    I hope to hear from you!
    OliviaF

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  7. Hi Olivia

    Thanks for your comment and questions.

    Unfortunately I have zero experience of riding a trike with a differential. I have only illustrated them on my blog when owners have sent me images or they have come up on eBay.

    Higgins trikes haven't been made for years and differentials were only fitted to order. They needed special axles so cannot be retro-fitted to any other trike. Not even a Higgins.

    There is a thread on how diffs perform on the triking forum: http://on3wheels.myfastforum.org/about306.html

    If you don't find the information you are looking for in this thread you could ask further questions or I could do so for you.

    Regards
    Chris

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