Wednesday, 17 October 2012

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A little more gear inchery


My technical geekery knows no bounds – truly it doesn’t. 

I posted a while ago about my bikes gearing and the science of gear inch calculations.  Well it seems that I had some duff information and my calculations were wrong.

On a three speed hub gear, one gear is a direct drive and the other two are ratios of that one.  I had always assumed that, since first gear on my bike was the quiet, non-clickety one, that it was by logical deduction, the direct drive.  However, the maths behind this never stacked up.  With a 38t front sprocket and 16t at the back, a direct drive on 20 inch wheels would give 47.5 gear inches ((38/16) x 20 = 47.5).  However, I also know that the Sram iMotion 3 speed hub-gear has a total spread of 186% from lowest to highest gear.  Therefore my theoretical top gear, if the original assumption was correct should have been 88.35 gear inches (47.5 x 1.86 = 88.35).  However this is a pretty high ratio and the Dahon always felt considerably lower geared than that!

So eventually, curiosity got the better of me.  I turned the bike upside down and in each gear rotated the crank one revolution.  By counting the number of turns on the rear wheel, I got the actual drive ratios in all three gears.  With its original gearing (38/16) I found that it was actually the Dahon’s middle gear that was the direct drive, giving as it did 38/16 or 2.375 turns of the back wheel for one turn of the crank (or thereabouts).  The hub gear’s spec sheet also stated that the high and low ratios were 36% up and down from the middle one (which ought to have been a clue as to which was the direct drive, but there you go.)  And so, that yielded the following results for the Dahon’s gearing:

Gear 1 – 34.9
Gear 2 – 47.5
Gear 3 – 64.6

All of which felt much closer to the truth in practice.  I have said before that I found these gears far too low in actual use – first was rarely ever employed, second some of the time and third most of the time.  It seems that the gearings mentioned for this bike on the Dahon webste (42 – 78 gear inches IIRC) are actually for the seven speed version and not the three speed.  Anyway, I started to look at options to raise the gearing. 
The simplest and cheapest option by far was to install a smaller sprocket on the rear wheel and so I found one (14t) on eBay and, for the princely sum of about three quid, ordered it.  It arrived pretty quickly and installation was a simple matter of removing the rear wheel, taking off the spring clip which holds the sprocket and then the sprocket itself before reinstalling the new item.  Owing to the 14t sprocket’s smaller diameter it has meant that things are now very “snug” around the rear gearing.  The chain runs pretty close to the bearing cover next to the sprocket but this does not appear to be causing any damage or other problem.  The ratios since installing this modification are as follows:

Gear 1 – 39.9
Gear 2 – 54.3
Gear 3 – 73.8

Which is better but still not ideal.  From my experiments into single speed riding, I have found a gear in the mid to high 60’s to be the optimum for me.  Low 60’s is acceptable but sometimes too low for the down hills, however with the higher gear option afforded by an internal hub-gear, that would not be a problem.  Having a lower but usable first gear would also be a bonus.  So having worked things through ad nauseum, I have a couple of options.  A 48t front sprocket and 16t rear would be the best compromise all round and would require the purchase and installation of a 48t crank.  This combination would give:

Gear 1 – 44.0
Gear 2 – 60.0
Gear 3 – 81.6

However, I do have a 52t crank in the garage from my ongoing fixie project and if installed on the Dahon would give gearing of:

Gear 1 – 47.8
Gear 2 – 65.0
Gear 3 – 88.4

I do think that this would be a good combination and, as I have the necessary hardware, may give it a go first.  

I read a comment about touring on a Brompton which said that six gears are enough as long as you have the right six.  I’d go as far as to say three is enough for most people but again, it needs to be the right three.  The key to it all, as I am finding, is to have a middle gear that you can use for most of your cycling with the higher and lower gears as added options.  The middle ratio above might even be so close to my ideal that to all intents and purposes I end up riding it as a single speed.  The lower gear 1 for “knackered thighs, end of the week riding” will be really useful though as will the higher one for bombing down hills!  What I’ll actually have, on reflection will be the original gears two and three as gears one and two plus an even higher option.

It could all be tinkering over nothing but I’m an engineer and a geek so I like messing around with machinery.  There are few things that I own which I have not considered modifying in some way.  Why should the Dahon be any different?

Besides, it is great fun and through all of that spannering, you do learn an awful lot about your machine!

Tuesday, 16 October 2012

This thing is gaining momentum!

Wow, there have been some huge spikes in daily readership recently.  

I suspect that this is in no small part to a link that was posted on here.   I don’t use that forum or know anyone on it to thank them but a big “Cheers!” to whoever it was.  I started this blog as a means to amuse myself and close friends but if it’s reaching out and spreading the cycling word more widely then I’m a happy man indeed!

There’s a great comment on one of the bikeforums replies about the fact that I still, occasionally feel the pull of the car.  I have to confess that it is sometimes true and I’m glad that the option is no longer there.  It is now definitely more down to my inherent laziness than it is any inexperience now in cycle commuting though.  

The weather has taken a noticeable turn for the Autumnal now and my morning commute is often cold, dark and windy.  When I crank my eyelids open in the dark at silly-o’clock and hear the rain beating down or the wind howling, I do run a few “what options do I have than cycling” scenarios through my head.  However, I agree with what the poster on bikeforums says, in that once I’m out in it, whatever the weather, you wouldn’t get me back in a tin box for any money. 

Even if I had the money for a car of my own now, I’d spend it on another bike!

By jove, I've finally cracked it! (part 1)

I've generally been pretty happy with my Dahon bike since buying it.  However, there have been a couple of things that have niggled at me persistently throughout that time.  First among these was the need to carry my worldly goods in a rucksack with the attendant achy shoulders (on heavy days) and sweaty back that it caused.
I have always looked with envy at the front mounted luggage available to Brompton owners and wished that something similar existed for my Dahon.  There used to be a Dahon bracket listed in their website to mount bags and baskets on the front of the frame but it seems to have been discontinued (think it might still be available in the US).  I did consider modifying a Brompton one to fit the mounting holes on my bike but at over £100, the bags are a bit pricey had it not worked!  Pricey but with a super reputation for good quality, I might add.

Panners would be good too - I know plenty of cyclists who swear by them - but the standard Dahon rack sits too close to the floor and if anything sticks out beside it (as panniers would) you tend to hit your heels on every pedal stroke.  Not great.

Eventually however, and very randomly, I found an online link the Rixen and Kaul "Klickfix" range of products and was more than pleasantly surprised!  They do such a huge range of bike luggage and mounting options that it would be hard not to find a solution to most problems.  The website and downloadable catalogue is here.  They do a front mount that fits the Dahon and also a seatpost mount - all with a common interface to a range of bags and baskets.  The rucksacks that they make look great but I was concerned about the weight limit of 5kg quoted in the catalogue.  On a "heavy" day recently, with my own rucksack full of laptop, charger, change of clothes and lunch, I weighed it.  Unfortunately it came in at over 7.5kg and some of the roads I ride are a little uneven to say the least.  I had visions of snapping the bag from it's mount in the middle of a ride and, given the price of the kit, wasn't willing to fork out to try it!  Am I coming across as a cheapskate?

However, I did really like the idea of mounting luggage on the seatpost, out of the way behind me. 

Sooo, a short Google later, I found a number of seatpost-mounting luggage racks compatible with lots of standard panniers.  Even the good quality ones (with plenty of positive reviews on Amazon) were relatively cheal and so fewer than forty pounds later, I became the owner of a luggage rack and panniers.

I've had them on for a couple of weeks now and have to say that they are excellent.  It is so nice to ride unencumbered by a rucksack and although I still work up a sweat, it is nothing like before.  When heavily laden it does sway a lttle and make the bike feel odd - usually when standing up out of the saddle to pedal up hills.  It's nothing too bad though and I think would be improved if I fix a way of securing the bottoms of the panniers.  They have straps but I want something that will release more quickly to get on and off trains.

Both of the items I bought were "Avenir" products which I think are made by Raleigh:

Simple, strong and lightweight.  You can get them with removable sides
but those were wither expensive or had poor reviews.  This one is excellent.

Simple but good quality and most importantly my laptop (just) fits in.
A netbook or tablet would be no problem whatsoever.

And here's a (poor quality) picture of it all installed.  Not sure why the back tyre looks flat in the picture
as it wasn't!  Just the angle or a trick of the light I reckon.

The only slight issue I've had is that the Dahon has such a fat seatpost!  Most of the seatpost mounted luggage state that 31-32mm is the maximum diameter that they will fit.  The Dahon's is about 33.5mm.  However, although this means that the quick release link doesn't reach, by replacing it with a longer bolt and packing out any gaps (between seatpost and clamp) with rubber pads It is fitted safely and securely.  This set up has endured a couple of heavy days without any problems at all.

So the upshot of it all is that I am now a much happier bunny with a less sweaty back and less achy shoulders. 

And the second thorn in my side?  Well that'll have to wait until I have a bit of time to write it up!

Friday, 12 October 2012

2,000 miles and counting!

Well, well, well, another mileage milestone rolls beneath my wheels!

If I managed to update my blog more regularly, I could've bee closer to real-time with this post but sometime during last week, I topped 2,000 miles on the Dahon.  OK that's over several months of riding and not a few weeks touring but I never thought that my experiment in cycle commuting would go this far.

Although the nights are drawing in and the mornings are darker, I'm still enjoying it and wouldn't go back to the car out of choice.  Not that I have that choice as I don't own a personal car any longer, just the family one my wife needs.

If you'd told the overweight me a year ago (who was worrying about how best to keep his old car running againsta rising repair bill) that I'd be cycling everyday and lighter, fitter and happier as a result, I wouldn't have believed you.

I used to arrive home having battled traffic for an hour or more in a foul mood and literally buzzing from stress hormones and other such undesirables.  I can't have been too pleasant to welcome home or be around to be honest!

Nowadays, the only buzzing I do is on endorphines and so even after the toughest ride home, I feel great!

Getting rid of my car was out of necessity to be honest.  The repair bill had got to the point where it was more than the value of the car and so it had to go.  However, as I was already cycling at the time and hadn't used it for a while, it was pretty easy to let it go.  No borrowing money for a new one for me, either.

What being (sort of) car-free has done for me is reduce and almost remove entirely the crutch that a car provides.  On those cold, windy mornings or tired days when one just can't be bothered, it would have been easy to jump back in the car.  That would've gone from a day per week, to two days, to three and so on...

But I don't cycle simply because I have no other option.  I do it because I love being out in the fresh air on my bike immersed in my surroundings.  I love travelling cheaply and not harming the environment with my actions. 

I do it because I love cycling.

And so, here's to the next two thousand miles.  I hope they are as fun, inspiring and eventful as the first two thousand have been.

Mileage to date:

Week 30 - 102 miles
Week 31 - 92 miles

Total mileage so far - 2,186.5 miles

Wednesday, 3 October 2012

Another puncture

Last night, for the second time in a couple of thousand miles, I got a puncture. Now don't get me wrong, two flats in all that cycling is pretty good going and testimony to the robustness of my Michelin City tyres. I always carry a spare tube and repair kit with me and, as the Dahon doesn't have quick release wheels, a spanner for the wheel nuts. I do not fear punctures - I am prepared.

So after feeling the inevitable "thump, thump..." from the back wheel on the way to the train station, I pulled over expecting to have the inner-tube swapped over in a jiffy. I flipped the bike over, took the spanner from my tool-kit and set to work...

It is here that I should explain about the spanner.

I used to carry a good quality, six-inch adjustable spanner. However when sorting through tools at home one day I found one of those flat "multi-spanners" which you often get free with a new bike. "Wow!" thought I, "This thing is versatile and so much lighter than my original spanner! I'll pack it instead." In truth, the weight difference was probably only a handful of grams but we cyclists are a weight-obsessed crowd. The puncture last night was its first test in anger.

And it failed.


I tried to turn one wheelnut but and the spanner bent and slipped right off.  I tried the other.  No chance! Next to busy, noisy traffic I didn't fancy my chances at finding and repairing the puncture hole. Also mindful of the fact that I had a train to catch and becoming increasingly desperate, as a last resort, I pumped a load of air into the tyre and carried on. Unlike the last puncture I got, this inner tube did not have "slime" sealant in it. This is a shame as my ride to the station, even with a puncture, would have been a simpler affair. As it was I limped along stopping every quarter of a mile or so to pump the tyre up some more. Eventually even this stopped working and I ended up running and pushing the bike, making it to the train just in time. A quick emergency "Rescue me!" text to my wife and I collapsed, sweating into my train seat.

Later in the evening, I changed the inner tube in the comfort of my own garage and with a proper spanner. I found that riding the bike with the rear under-inflated had caused the tube to slip within the tyre partially tearing the valve out of the tyre.  Result - one dead inner tube but fortunately no other serious wheel damage. Writing off the tube, cheap though they are, is a shame as the puncture itself was actually pretty small.  It could have been worse though.

All of life's experiences, good and bad, serve to teach us something. So the lessons I learned were:

- Don't sacrifice quality kit to save weight
- Don't place your trust in cheap, poor quality tools
- Test out any emergency kit you plan to use before you need it
- "Slime" in your tyres is a good thing

And finally, stop to offer help to other cyclists! Three or four cyclists rode past me while I was attending to a broken bike and not one offered to help or even asked if I was OK. Maybe I looked like it was all under control but I'd have made a point of asking if the roles were reversed.

So lessons learned and bike back on the road. It ought to have been easier with better preparation and hopefully will be next time.

If all I have to fix in the next 2,000 miles is a couple of punctures, I'll be a happy man indeed!

Tuesday, 2 October 2012

Mileage to date

It was another monster day of traffic on the way through the city today.  I have no idea what the problem was that caused it all (it never seems to take much to be honest) but it didn’t slow me down one tiny bit.  Having just checked on Google maps, one of the queues was a full mile long!  I simple cruised down the outside of it, to the front of the queue and turned right at the traffic junction as usual.  No fuss and no delays – lovely!

OK, so it wasn't quite this bad but you get the picture!
As predicted, the week before last was a big week on the bike for me and certainly the longest to date since buying the Dahon.  Five full days in the office plus a bit of to-ing and fro-ing from a clients resulted in a total of 117.5 miles for the week.  Last week was much shorter though, in large part because I worked from home for a couple of days.  Not so good from the point of view of exercise but very restful and my legs thanked me for the time to recuperate!  As a result, Thursday and Friday last week were (almost) effortless blasts of cycling fun in beautiful Autumn weather. 

Mileage to date:

Week 28 – 117.5 miles
Week 29 – 48.5 miles

Grand total so far:  1,992.5 miles

So I’m only a whisker away from the 2,000 mile mark.  I think I’ll allow myself a small moment of self-congratulation and a celebratory cup of tea!