People: Robin Thorn of Thorn Cycles – Interview

I came across this interview with Robin Thorn tonight. Interesting discussion ranging over many of the old chestnuts: aluminium or steel, Rohloff or derailler, panniers or trailer etc.  But added in were some good thoughts about value for money and expectations, and best of all why people are taking to touring more and more and where they go touring.  I enjoyed it.

I only spoke with Robin once myself, over the phone when specifying a Thorn Raven at the time.  I remember he was very patient and keen to understand what I wanted: even at the point when I took fright and decided not to go ahead!  He must have left a good impression, however, as I was back a couple of years later and the deal was done!

Maintenance: Adjusting the Chain Tension on a Thorn Rohloff Bicycle

These instructions are adapted from the advice provided in the Thorn Bicycle and Tandem Owners’ Guide.

When and how to adjust the eccentric bottom bracket

According to Thorn,  slack train will not do any damage whatsoever, if it is allowed to become very slack the only danger is that it may fall off. By contrast, a chain which is too tight wears prematurely, causes premature wear to the bottom bracket assembly (possibly to the hub too) and causes unnecessary expenditure of energy in use. It’s not a good idea therefore to adjust too often or to over adjust: better to err on the side of, “if it’s not broke, don’t fix it.”

According to Thorn, here is always a “tight spot” on all chain drive systems. When setting chain tensions there must always be some slack in the chain at this “tight spot”.  To find the tight point, measure to the mid point between the centre of the sprocket and the chainring.  Measure how far you can pull up the chain at this point and work round the chain until you find the point where you can lift the chain the smallest amount.  This will be the tight spot.

We will call the gap between the highest and lowest point the chain can reach when pulled up and down, measured at the mid-point, T1 and the gap when pulled together, T2.  See here:

Chain Diag

Do not readjust the chain tension until T1 minus T2 equals 40mm. The “crude but simple, reliable and effective” system Thorn use for locking the eccentric depends upon the points of the screws being able to bite into the alloy eccentric. If unnecessary chain adjustments are made, the holes created by the points will be too close together and the eccentric will simply slip back into its previous position.

The change should be adjusted before T1 minus T2 reaches 60 MM. Failure to do this makes it possible for the chain to become slack enough to fall off the chain ring (or sprocket).

With a new chain (and especially a whole new transmission), it may not take very long for the 40mm of slack to become 60mm of slack but this situation will improve dramatically with the passing of the miles.

Adjustment is Straightforward

To readjust the transmission chain tension on Rohloff Thorn cycles

  1. Unscrew the eccentric screws, using a 15mm spanner or large screwdriver.
  2. Rotate the eccentric to achieve the desired chain tension using the adapted spanner provided by Thorn. Depending on the model of eccentric shell fitted to your cycle you will need to use either an eccentric adjustment spanner or by inserting a metal rod. Using the spanner set simply rotate the eccentric to achieve the correct chain tension.
  3. Finally re-tighten the eccentric screws and re-check the tension of the chain.

Thorn provide these eccentric screw torque settings for Rohloff equipped cycles:

10 to 17  Newton-meter (torque)
7.38 to 12.5 for foot pound force.

Rohloff Hub Oil Change

This is an excellent video created by Thorn Cycles showing how to change the oil in the Rohloff hub in the clearest possible step by step guide.  Very reassuring for the less than technically minded like myself.

A similar video (in Dutch) can be found here:

The oil needed to be changed every 5000K or each year.  Keep records for claims reasons.  Rohloff provide a record card for this purpose. Assuming you have the Rohloff Oil change Kit (available from Thorn/SJS Cycles) the steps needed are:

  1. Clean the Hub surface.  Keep a rag to hand to catch any oil drips.
  2. Remove the drain plug (note the necessary 3mm Allan Key is not provided in the kit and you want to have a decent one as the plug is difficult to budge at the start.  Moving the plug to the 2.30pm position makes it easier to clear the bike rack if fitted)
  3. Draw 25 ml of cleaning oil into syringe and attach the drain tube. (Twisting the tube allows it to act as a ‘driver’ while you guide it with your fingers.)
  4. Push the cleaning oil into the hub and draw out 20ml of air.
  5. Replace the old drain plug (adding a blob of petroleum jelly to the end of the Allan Key will help get it into place.)
  6. Ride for at least 1K or spin the hub for 3 minutes while switching between gears 3 and 5.
  7. Refit the drain tube and leave pointing downwards for 15 minutes.
  8. Draw off the dirty oil.  Leave for a further 5 minutes to drain. (Expect to get between 35 and 50ml of oil out.)
  9. Dispose of the old oil in the container provided.
  10. Draw 25 ml of new oil into syringe and attach the drain tube. (Thorn say 15ml is enough, but I went with Rohloff’s recommendation.
  11. Push the new oil into the hub and draw out 20ml of air.
  12. Put the new drain plug into place (take care not to ‘cross-thread’ it and expect a little resistance as it comes with some sort of ‘wax’ to seal it.
I know myself to be a pretty feeble and nervous ‘mechanic’, but this procedure was very straightforward.

Rohloff Speedhubs: yes or no?

Our bikes are Thorn Raven Sports Tour models fitted with Rohloff Speedhub 500/14 hub gears.  We debated for months whether we ought to get them or something conventionally geared – and much cheaper.  After 10 months of use, what do we think?

We would answer YES to the Rohloff for these reasons:

Firstly, the pleasure of riding with them.  We currently use one of three modes when out for a run.  We (i) use gear 11 on the flat and adjust our cadence to set and maintain a speed we are happy to tour with: or, (ii) we slide up and down the gears in sequence adjusting the effort we put into our pedalling to reduce the energy needed as smoothly as we can while keeping as constant a speed as we can; or, (iii) we use gears 14, 11 and 8 to maintain the maximum speed we can in different terrains.  Each of these methods help build up our stamina and ‘time on the bikes’ towards the 50-80 mile days we would like to be able to maintain with luggage onboard.

Secondly, the pleasure and simplicity of use in the gear selector/changer.  There is something very satisfying in the smoothness and efficiency of the mechanism as you slide from gear to gear effortlessly and with absolute certainty.

Thirdly, there is the confidence that comes from knowing you will never be caught out and that if you get things wrong you can simply, ‘dial in’ the gear you need – whether on the move or standing still.

Fourthly, there is the simplicity and ease with which a wheel can be slipped in and out for cleaning and tyre changing and the associated ease of cleaning a single sprocket and chain.

Fiftly, there is the ease of adjustment and the lack of worry about external mechanisms getting  damaged in transit or otherwise.

However, some aspects do take some getting used to in use:

Firstly, there is “Mr Whirry” or gear 7 as he is more correctly known.  Our hubs are not yet fully run in, but there is no doubt we both currently try to avoid gear 7 when we can, just to avoid the ‘whirr’ that otherwise gets into your head and convinces you that you are pushing the pedals against some resistance.

Secondly, there is the nagging doubt – what on earth can I do if the sealed unit fails when I am out on the road?  Now this is a remote possibility by all accounts, but the fact remains, you carry a seed of doubt around with you at least some of the time.

Thirdly, there is the worry that comes with the cost of the hubs and hence the bikes.  Suddenly, security becomes a big thing.  We now carry two U locks and a chain between us and always lock the bikes around a lamp post or similar – even when nipping into a supermarket to buy water and grub before hitting the road. 

On balance, we have no real doubt that we took the right decision to get the Thorns with the Rohloff hubs.  As my Dad so often said – if you are buying a tool, buy the best one you can afford.