Concerning ratios

TLDR: One drawback of owning a bicycle that is out-of-the-ordinary is that you can’t just walk in a bicycle shop and get parts off the shelf. Getting a front changer to work with the cranksets I use has become one of those struggles that put you off further tuning once you’ve managed to get it all working.

 

I went round Scandinavia using a Stronglight 99 triple (42-36-28) with 170mm crank lengths driving a Suntour 14 – 32, giving me a lowest gear ration of 0.875. I used a Shimano 600 rear changer, and a Suntour  front changer. It took me a long time to get the front changer to select all three chainrings. Part of the problem was that there was no downtube for the front changer to be clamped around. Individual Bicycles got around this by a bolt-on attachment to the twin seat tubes which had a small stub of suitable tube around which a front changer could be clamped.

 

I didn’t meet any hills worthy of the name until I entered Denmark, but up until then I had spent almost all of the time on the lowest chainring and largest two rear cogs because of the continual gale-force headwinds.  Even when I came into Denmark I still wasn’t able to ride on anything higher than the middle chainring and middle back cogs, and so I could overlook the tricky shifting I was experiencing between the middle and top chainrings. I concentrated on getting an easy shift between the inner and middle chainrings because of my requirements for a very low ratio. It wasn’t until my return as I came from Norway into the relative flatlands of Denmark that I got a chance to use the outer chainring, and by that time I had just about managed to get a reliable shift from middle to outer, and my legs were now strong enough to hardly need the inner chainring now that I had left the mountains behind.

Back in England I had taken off the 28-tooth ring and substituted a 32-tooth one, which now allowed me to be able to shift through all three of the rings, at the expense of having a lowest ratio of 1:1. Having a larger inner chainring meant I could raise the front changer on the stub bracket, which seemed to improve selecting the largest ring. After six years I moved to where I am now, stopped smoking, put on weight, and struggled up the hills.

 

When I resurrected the Pedersen in 2007 I found the Stronglight crank arms reluctant to release the pedals, which required at minimum a strip-down and probably replacement. Reluctant is perhaps too mild a word, the crank arms refused to let go of the pedal threads. Readers of the blog will know I experimented with a Biopace triple I scrounged from a dumped bike, but I was forced to abandon this because of persistent problems with the bottom bracket working loose. I realised after the last episode that the oscillating forces produced by the elliptical chainrings were slowly working the bottom bracket cups loose. I managed to get a new bottom bracket set loctited in place, but now found that the Stronglight was too far out from the frame for the front changer to get the outer chainring, and was reluctant to put the Biopace set back on. But as the intermittent sticky pedal on the Stronglight had almost caused an accident twice, I had to do something.

I switched to a Suntour 42-34-24 from that well-know auction site, and after a lot of experimenting with different front changers managed to get all three chainrings reliably. I had already changed from 27″ to 700c rims by now, and with the change had also gone back to a standard Shimano 28-14 rear block. My lowest ratio was now 0.857, and with it I was able to climb a nearby hill that had always defeated the Stronglight setup. I did though have to take off the original Shimano rear changer and put on a more modern version that seemed designed to allow for more variation in chain length that occurred when having a wider range of gears.

So far, so good. There were, however, other hills nearby even steeper than the one I was now able to surmount, and I found myself scheming how to get even lower ratios. I saw another Suntour triple set, this time 42-32-22 with 175mm cranks, and got it. This time, though, things did not go so smoothly with the front changer, in fact, they didn’t go at all. I could get the inner and middle chainrings easily, but there was no way I could make the front changer stretch out enough to get the outer chainwheel. Even with the limit screw removed, the changer just didn’t move across enough for the chain to even start to brush against the outer chainring.

However, there was another benefit which made me decide to live with this issue and ride around on a 12-speed: the increased crank length. 5mm doesn’t sound much, but I found I had to lower the saddle so that I could still keep a foot firmly pressed against the pedal at the bottom of the stroke, and that small reduction in saddle-height made quite a difference to mounting and dismounting. The biggest drawback to the hammock-saddle arrangement on the Pedesen is that you can’t slip forward off the saddle and perch on the crossbar when waiting at a road-junction, because the strap continues to rise from the nose of the saddle. So, I lived with the lack of a top chainring and enjoyed myself wobbling up some ridiculous hills with my new 0.785 lowest ratio.

Two years later, having accidentally retired and begun to cycle a lot more, I began to feel the lack of the top chainring, and switched back to the Suntour, raising the saddle once more and doing a ballet-dancer-en-point impression each time I had to stop at road junctions to wait for a gap in the traffic. I managed.

Four years later (now), I had started to notice issues with the chain jumping when I applied sudden load, such as coming off the points of my toes and trying to get across the road in a suitable gap in traffic. My first thoughts were the chain had worn, so I went in search of a new one, finding I had actually already got one several years back. It improved the jumping problem but didn’t fully eliminate it. I didn’t have a new rear block, but inspection didn’t reveal any worn teeth, at least, none visibly worn. So I decided to try the original rear changer in case the jumping was due to weak springs in the changer I had been using. The changer worked, giving me all six rear cogs, but I could no longer select all three front chainrings.

I spent an evening trimming bits of metal off parts of the front changer mounting where it was bottoming against the stub bracket, and off the stub bracket where the changer arm was contacting it when going into the inner chainring position, with no improvement. So I switched back to the rear changer that had worked, up until my rash experimenting, only to find it wouldn’t get the inner chainring any more. One puzzle was that with the Pedersen up on the centre stand I could change between all three gears, but not when I was actually on the bike and pushing on the pedals. I went to bed feeling moody, with dark memories of how long it had previously taken me to get the setup right.

Next morning, I decided to once again try the Suntour crankset with the 175mm cranks, because my diary recorded I had been able to get the inner and middle chainrings with ease, and after changing them all over (note to self, stop using spray grease to lubricate the chain and pedals, the mess is awful), I was able to go out and ride up and down some of the local mountains on the inner and middle chainring, and have an easier time getting on and off the Pedersen.

So I’m back where I was in 2014, able to go out tomorrow and ride fifteen miles to video a steam train as I hoped, but wondering just how long can I put up with riding a 12-speed around with a very low top gear?

And as I said at the very start of this post, I can’t really go into a local bike-shop and ask for a combination of changers to solve the problem, because I have

1. an unusual bicycle for which there aren’t any parts lookup-tables
2. a bottom bracket which is possibly shifted too far towards the chainring side but daren’t be altered (last time I tried to shift it the loctite said ‘eff-off’)
3. not enough money from my pension to just say to a bike-shop “sort this”
4. a determination to do things my way.

What I am doing is going back to 2014 and taking a different course, back then I decided to alter the setup so I could use the bike instead of spending time trying to get around a problem. My task now is to see what needs to be done to get all three chainrings selectable. It might mean dismantling the Suntour and spacing all three rings further away from the crank, it might mean softening the Loctite and shifting the crank axle an eighth of an inch towards the other side, it might mean making up a new stub bracket to allow the front changer to be offset outwards by an eighth  of an inch, who knows? Damned if I do.