The Dark Secret of Pottiehill

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All right, I can see you’re not convinced: how can a place called Pottiehill have a dark secret? Yet it does; I have seen it. I have pictures (though some of them are a little odd – an unfamiliar camera).

But first, the curious case of Benjamin Button. (you see what I am doing here? Suspense! The craft of fiction)

Some time ago I pondered the need for an improved gear set-up on my Dream Roadster. In a flurry of energy I actually obtained the necessary 14T cog,
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– which is a good deal smaller than the 18T it replaces –
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I fitted it (with the usual pantomime of levering off spring clips with screwdrivers and wondering where they will fly to – but at least I had the good sense to wear eye protection)

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and set out, only to find, to my chagrin, that somewhere in the few hundred yards I had travelled from the house I had lost the changer button on one side of my Schlumpf Mountain Drive.

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I retraced my steps several times, back and forth, but to no avail; so there was nothing for it but to ring Ben Cooper at Kinetics – a splendid shop in Glasgow where I got the Mountain Drive originally, many years ago now – to see if he could supply a replacement. He could, but of course that meant a further delay.

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The button comes with its own delicate Allen key, used to secure the tiny grub screw in the centre against the end of the changing rod, where it acts (as far as I can see) rather like a lock-nut.

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Though I tightened it vigorously as advised, I am still nervous of losing it again – I wonder if a set of natty leather gaiters (perhaps in matching red) designed to fit the top end of the crank would bring peace of mind? Something to ponder, perhaps even make, in the long winter nights.

In the meantime I obtained another replacement, for my Lucas Mileometer (or Odometer, if you will) which disappeared in the course of my last major excursion – the same one that convinced me my gear set-up needed changing.
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But to our tale: it being a fine class of Autumn day for the first of November – All Saints’ Day – I resolved to make an excursion. Not only did I rig the mileometer, I also transferred my ferociusly powerful Smart BL201 headlights (powered by a rechargeable lead-acid battery) from the 1923 Royal Sunbeam. Here we see them blazing futilely against the light of day, ‘crying like a fire in the sun’ as Bob Dylan might say:

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Why the lights? Well, if you are off delving into dark secrets, it is wise to have some; I also took a torch, being unsure that I would be able to take my bicycle where I was going. You may notice that I have repositioned my trusty Lidl handlebar bag behind the bars to accommodate the lights, but this proved impractical, as my knees hit against it, so after a short distance on the road I transferred it to the saddlebag position.

I set off over the hill by the Edinburgh Road and down into Strathearn. There had been a heavy shower of rain while I was working on the bike, but the weather was clearing steadily, with sunlight on the distant hills.

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In Bridge of Earn I paused to take some pictures, first of a signpost, then of a curious agricultural implement on display near by.

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Then off I went along the Wicks o’ Baiglie Road, which once upon a time was the smart route to take if you were driving to Edinburgh and there was a lot of slow-moving traffic ahead:  you knew you would never pass it in the tortuous passage of Glenfarg, but if you belted over the Wicks o’ Baiglie you might well beat it to the other side. These days are gone now, since the M90 motorway now bypasses Glenfarg altogether. But how was my new gear set-up, I hear you cry, plaintively. Very good, I am happy to say, though I did lose my chain very early on ascending the Edinburgh Road; the Mountain Drive in low gear under stress seems susceptible to any variation in chainline. Happily there was no repetition, and I found that I was glad of even my lowest gear ascending the Wicks o’ Baiglie Road, seen here looking back – a long steady mercilessly straight climb:

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Earlier, on the flat, I had tried out my Lord-of-Creation one-hundred-and-fifty-inch top gear and found it every bit as delightful as I hoped:  you bowl along at tremendous speed, yet pedalling in a slow and stately manner.  However, I was a little wary of the quantities of wet leaves – a notoriously tricky surface.  At another point there was a constant crepitation as I cycled through beech-mast:  the sounds of Autumn.

The first sign of my destination was the remains of what had been a railway over-bridge looming ahead:

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On the other side of it I found a gate which was locked, so I lifted the bike over but was content to duck myself through a large gap in the wire fence, as befitted my years and diminished athleticism.

And there I was, on what was once the North British Railway line from Mawcarse Junction to Bridge of Earn via Glenfarg.  A distant tree caught the sun and blazed out bright gold, which I took to be a happy augury;  there was also a rainbow, and a splendid buzzard which flew up from right to left, which the Romans would doubtless have deemed auspicious.

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The line was closed in January 1970, having evaded the Beeching axe, probably because of the proposed route of the M90, mentioned above. It must have been a pleasant one to travel, fairly high up one side of a broad valley at this point, with fine views across to the confluence of Strathearn and Strathtay.

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I cycled on through pleasant Autumn woodland, past a great stack of felled timber

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And then up ahead, there it was, the dark secret of Pottiehill:

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This is the northernmost of two tunnels, each about 500 metres in length, which took the line from Glen Farg across into Strathearn.
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I like tunnels. My first serious experience of them was not on the railway (though I have been through many, I am sure, but in a train it is just a darkness) but on the more ancient transport route of the English canals, where there are some splendid and very lengthy tunnels. Transiting a tunnel in a narrowboat is an eerie experience: you are surrounded by dark, with only a narrow horsehoe of light some sixty feet ahead, thrown out by the small bow light, which is not so much for illumination as to let others know you are coming.  The first few times I did it I suffered the consistent hallucination that I was actually in a much vaster space, and not the narrow confines of a tunnel just wide enough to let two boats pass one another and just high enough to give them clear passage.  (My canal tunnel experiences found their way into my writing – in my third published book, City of Desolation, my young hero Jake finds himself on a Dantesque journey through Hell, which has evolved somewhat since Dante’s day, having acquired (among other things) an underground canal system – see here)

The Pottiehill tunnel is a fine feat of engineering and the interior for the most part is dry and entirely sound; the ground is a little uneven, but is not difficult to cycle, though I was glad of my powerful lights, as the tunnel has a considerable bend so that you cannot see the far end and the near one at the same time.

I had heard tales that these tunnels had been used to store old steam locomotives as a precaution against nuclear war (the reasoning being that a steam engine would be easier to fuel than a diesel in the disruption that followed) but I think that is just wishful thinking on the part of old steam men and romantic civil servants.  In this case it would not be terribly practical, since the line has been taken up, and as far as I know, the tunnels (unlike some others) have never actually been closed off.

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I emerged from the North tunnel onto a pleasant stretch of overgrown trackbed running between autumn woods, but it was very muddy underwheel and for some distance was in fact the bed of a stream;  but this is the kind of thing that imperial roadsters take in their stride.  I would not attempt it on a narrow-tyred mount.  After some distance I came on a conundrum: the main path rose steeply to the right, with a more overgrown fork descending to the left.
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I dismounted and tried the upward path, but had not gone far before reason told me it was much too steep for any railway line. So I turned back, left the bike, and made my way ahead on foot.

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The path was not cyclable: it was criss-crossed with fallen trees, and in places was very boggy.

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But I persevered and was rewarded with a sight of the North portal of the South tunnel, though it did not look exactly like this:

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I went through with the aid of my torch, and again found the surface dry and sound.

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There is the rusted shell of a car at the Southern end; I was expecting it, as it is mentioned on various websites; but I still wondered how it got there.

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A little way beyond the tunnel, a fine viaduct crosses Glenfarg, and down the side you can glimpse (a good way below) the river Farg and the road running beside it.

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I crossed the viaduct and went as far as the gate that bars it; the line runs on invitingly,

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while looking back you have a fine view of the South Portal across the viaduct

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but for me it was time to turn back. At the South Portal, I came on a strange fellow hanging around:

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The South tunnel is straight enough to see both ends from the middle, though you need to stand to one side, so it clearly has a bend in it. I went back through without using the torch, just for the fun of it. It is surprising, once your eyes get used to the dark, just how much you can see, and one thing you notice is how any surface that faces the tunnel mouth behind you catches the light. In honour of my brother Brendan, who instituted a tradition of tunnel-singing on the canals, I tested the acoustic with a verse of the Tantum Ergo. Fortunately there was no-one else to hear.

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Emerged on the other side and reunited with my bike (I had chained it to a tree – doubtless an unnecessary precaution, but peace of mind is a great thing)

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I made my way back through mud, stream and tunnel,

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pausing to snap a harrow sheltering in the North portal, like the remains of some giant insect or alien creature

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I think that my attempts to take pictures in the tunnel must have confused the automatic settings, because the shots I took after I emerged had an odd sort of old-fashioned-postcard quality to them,  like this  vista of Strathearn meeting Strathtay.

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I saw that there was an alternative route off to the left and hoping to avoid the gate I took it, only to find I had miscalculated somewhat – to my surprise, instead of rejoining the road a little further up the hill than I left it, I found myself swinging right and passing under a substantial bridge that I had not realised was there;  yet I must in fact have crossed it. The reason for it was clearly the stream that I was now cycling alongside, with the road I wanted  on the farther side. However, I was not too perturbed, reasoning that a well-made track must lead somewhere, and it was heading in the right general direction.  A little way on I came on some substantial but derelict farm buildings, which had the haunting quality all such buildings have, enhanced in the picture by the weird colour setting, which nonetheless captures the atmosphere surprisingly well

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Carrying on for some way I emerged at last onto a side road; a sign at the point where the track debouched informed me that it was a private road with no vehicular access, so had I come on it at that end, I probably would not have gone up.  As a matter of fact, the way I went is more direct and easier, apart from negotiating the gate, but this was a very pleasant return route.

The light was failing rapidly, not so much from the onset of night as the weather, but as I had neglected to rig a rear light with my headlights, not thinking I would be out so late, I made one more stop for pictures then headed home.
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All in all, a most satisfactory excursion and a sovereign specific for driving away melancholy. The route can be seen here.

Gearing dreams and reality (another one for epicyclists)

Sometimes, you do not fully appreciate why something is the way it is till you try to do it differently (as a writer and a lover of books, I hope that may be the lasting effect of e-readers such as the Kindle:  they will make people appreciate just what a clever piece of technology a book is – but that is by the way). My Dream Roadster, as its name suggests, is an attempt to realise an ideal form of the Imperial Roadster bicycle by retaining its desirable features while overcoming its shortcomings, principally in gears and brakes.

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In practice, I have found that the Dream Roadster has served mainly to deepen my appreciation of the production Imperial Roadster, in particular the two versions of it that I own, a pair of Royal Sunbeams. The matter of braking systems I will consider another day (the Dream Roadster has drum brakes, where the standard Imperial has rod-operated rim brakes) – but my excursion earlier this week ,  which involved the strenuous ascent of Necessity Brae on my 1934 Sunbeam,

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revived a question I had asked before, how many gears does a man need?.  The Sunbeam’s low gear is around 54”. I had managed to climb the hill in that, though it took a deal of effort and determination – at several points I had thought about stopping, but had willed myself on.  Evidently, then, a lower gear would make things easier, but how much lower should it be? That was the question I set out to answer the next day, when I repeated the same route using the Dream Roadster.

The Dream Roadster has a five-speed rear hub (SRAM/Sachs P5) coupled to a two-speed bottom bracket gear, a Schlumpf Mountain Drive. On the present set-up, this gives nine distinct gears (two are duplicates) – a normal range of (approximately) 47”, 58”, 75”, 96” and 118” with a lower range of 19” 23” 30” 38” and 47”.  My guess, from previous experience, was that the lowest useful gear would be the 30” one so I resolved to put that to the test. Before setting out I made a couple of trial ascents of hills near by, Glenlyon Rd

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and Quarry Rd

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which confirmed my suspicions: the 19” is effectively useless – though it offers virtually no resistance, the speed at which it must be turned to make even the slightest headway requires a far greater effort than walking, for less return. The next gear up – 23” – is only marginally useful as it still requires to be spun at a higher rate than I find comfortable to achieve a forward progress less than walking pace.

So I set out to repeat the trip of the day before (map 4 here) with a minor variation at the start – a new secret way such as Craigie (the district of Perth where I live) abounds in

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My aim was to use 30’’ (the mid-gear of my lower five) as my lowest gear. The ascent of Necessity Brae was still strenuous,

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but less so than the day before, and at one point where the slope lessens I actually changed up to the 38” gear for a time. Though I already knew I could ascend the hill in a substantially higher gear, my aim was to find the most practical lowest gear for the Dream Roadster, and the answer to that appeared to be around 30”.

This was borne out by the fact that I continued without dismounting, save to record the occasional rarity –

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and some wild flowers here and there:

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(it’s nice, with the hedgerows so dominated by red, to find a touch blue and purple)

I even managed the sharp ascent to Craigend which had undone me the day before, though this time I was expecting it. I returned as I had previously, with occasional stops for blackberries and to record the onset of Autumn,

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(a sight that recalled a line from Eliot:  ‘the communication of the dead is tongued with fire beyond the language of the living’)

and so home via another secret way:

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The one casualty of the trip was my mileometer, which I must have shed somewhere along the way (I did have to stop at one point to adjust the front wheel, which had slipped, so I think it was some time after that – I retraced my route on foot next day, but to no avail).

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before setting out…

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…after returning home

So, the conclusion to be drawn (besides the obvious one of checking the tightness of all fixtures before setting out) is that around 30″ is as low a gear as I need. However, once I fell to my calculations, I found a familiar problem. An earlier version of the Dream Roadster had coupled the Mountain Drive to a 7-speed SRAM/Sachs hub, giving 14 gears with a spectacularly wide range of 763%. This setup was arrived at before I ever built the bike and sprang from a couple of simple-minded comparisons – the fabled (and fabulously expensive) Rohloff Speedhub had 14 speeds but a range of ‘only’ 526%, so an arrangement that was cheaper but offered the same number of gears over a wider range had to be better, surely?

In practice, I soon encountered the difficulty I describe above – the lower end of the gear range was something like 17, 20 and 24 inches – of which only the last was even marginally useful. This led me to conclude that the SRAM/Sachs 7 speed hub offered an adequate range in itself, so I swapped it for the SRAM/Sachs 5 speed I had installed in my daughter’s bike, giving us both (I hoped) a more useful range of gears.

However, setting 30” as a bottom gear with the P5/Mountain Drive combination and a 28” wheel implies a direct drive  of some 119”, not only ridiculously high in itself and giving an unfeasibly huge 188″ top gear, but requiring a gear ratio (front to back) of 4.25:1, meaning that a 48T chainwheel would need an 11T sprocket (impossible to obtain for a hub gear – 13T is the smallest I have come across). With 13T at the back a 55T chainwheel would be required to maintain the same ratio.

The upshot is that I have ordered a 14T sprocket which, with the present 48T chainwheel, would give a gear ratio of 3.4:1, meaning a direct drive of c95” and a lowest gear of c24” – still barely useful. The full range would be (approximately)

lower: 24, 30, 38, 49, 60        upper: 60, 75, 95, 122, 150

I look forward to testing that – the long-striding twelve-and-half foot top gear should be fun* but I have to admit that I am already toying with the notion that for my purposes six gears might be enough – using the same 14/48 set up with a typical 3 speed would give me approximately

lower: 28, 38.5, 52        upper: 70, 96, 131.

That gives a bottom gear much closer to my tested useful minimum and makes an interesting comparison with the fabled six-speed Sunbeam of 1908, which offered 49, 66, 72, 88, 96, 129:

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(photo by kind permission of Leon Wise)

Some might object to the increasingly wide gaps in my upper range but I think that is a matter of taste and cycling style. The justly-celebrated Rohloff offers 14 evenly-spaced gears (at 13.6% intervals) but for me that is an epicyclic hub brilliantly conceived to do the same job as a derailleur, only better – it’s all about maintaining cadence, keeping the same input and varying the gear to suit.

Riding a roadster bicycle is about varying input to suit the conditions: you are prepared to labour up a hill, or even dismount and walk, knowing that eventually you will reach the top and be able to freewheel down the other side; and on the flat, there is no more lordly feeling than to sweep along at great speed by turning a tall gear at a dignified, leisurely pace. Large steps between high gears are not a problem as you only use them when you are already travelling at speed; it is in the low gears that you want to avoid the jarring shock of too wide a gap.

Around 70 inches was the common single-speed gear for the Edwardians, who liked to calculate at 10 gear inches for each inch of crank, and regarded 7” cranks as the standard. I reckon that a future 6-speed Dream Roadster with the set-up above would give me in one bike the equivalent of two three-speeds, one well-suited to the hill country, the other formidable on the flat.

I have to say I’m sorely tempted…

* 13 yards on the road for a single turn of the pedals, or better than 26mph at a modest 60 rpm – though I expect wind-resistance would be a factor.