Thursday, 11 September 2014

Gears (again)

I hope you find this interesting, especially if you're of a technical mind.  I make no apology for sleep-induced, keyboard-prints-on-the-forehead if you're not.  Caveat emptor and read on...
One of the first things I noticed about riding my 3 speed Dahon Vitesse was that the standard gearing was WAY too low for normal riding.  I’ve blogged about gear inchery a couple of times (technophobes look away now) here and here.

A little over 18 months ago, after much deliberation I pimped my ride a bit, splashing out on a new  front crank, 46t chainring, chain (as the original one was completely shot) and 16t rear sprocket.  This resulted in a pretty useable set of gears and has been the configuration in which I’ve ridden the subsequent 5,000(!) miles.  The crank, being a proper one, rather than the cheap thing fitted by Dahon, also offered the benefit of enabling me change the chainring on its own in future.

Inevitably though:

  1. Drive components wear out
  2. Being an engineer, the urge to fiddle with gear ratios once again becomes too much to bear

The former circumstance probably reached the point where new parts were required quite some time ago.  My chain is now stretched so severely that getting it to a consistent tension is impossible and as a result, both the chainring (to a lesser degree) and rear sprocket (to an almost comedy degree) are now hooked.  I’ll post up some pictures in due course and you’ll see what I mean. 
SheldonBrown’s outstanding website has a far more detailed explanation of why this happens than I’m going to offer here.  Suffice to say that it’s a combination of lengthy metal on metal wear (which is governed by miles ridden and the laws of physics) and half-arsed maintenance (which is governed by my inherent idleness).

And so I’ve had to part with some hard-ebayed cash in order to buy a new chain and sprockets. 

The straight swap choice of a 16t rear was pretty simple but I’ve elected (after an amount of consideration that marks me out as a deeply sad individual) to up the chainring size to 48t.  The main reason for this is that I tend to spend quite a lot of time in second gear and it now has a tendency to feel slightly too low.  The new gearing will raise second from 57.5 to 60 gear inches.

Inevitably, with only 3 gears on tap, gear choice is a bit of a compromise.  However, 60 inches is also the gearing which I had my single speed MTB for a good while and I always found it to be a nice, multi-purpose ratio.  I know there will be times (tired hills and headwinds) when I’ll be fondly remembering the slightly lower gear two, but it’ll be just that bit better as a gear to spin along in most other times.  Furthermore, first gear has always been way too low – used only for severely steep or tired climbing.  Hopefully, rather than a two-speed bike with a bail out gear (which, effectively, is what I have now) I’ll have three usable gear ratios.

I told you I was sad.

Best of all though, I’m having some shiny new bike parts and that means a couple of hours spent in grimy-fingered, cycle maintenance heaven!  The Royal Mail is (I hope) bringing the components with haste to my letterbox and so I’ll post up a load of pictures when they all arrive and I swap everything over. 

No comments:

Post a Comment