Saturday, 4 October 2014

Testing – a new chain wheel and the Akatarawa Road


The Folding Goldies’ suggestion of cycling the Akatarawa Road for our next ride, and my misgivings about the hill climbs, got John thinking of how he could modify the gearing on my bike so that it would make it easier for me to bike uphill.

So he had a chat to Francis at Johnsonville Cycles and got the necessary bits. Then he spent a fair few hours in the garage tinkering. In essence, he has replaced the 52-tooth chain wheel with a 39-tooth one, which gives me greater leverage in the lowest gear, i.e. more oomph to get up the hill! But I’ll let John describe the details of what he did at the end of this post (or you can look at his website. You’ll have to scroll down to the last three paragraphs of the Technical Details section).

I had the first try of the modification on the steep dead-end road round the corner from where we live. It seemed reasonably OK to get to the top of the hill, but the bike was making some noises. John doesn’t like it when mechanical things make noises they shouldn’t, so more time was spent in the garage to remedy that. So far, so good.

The next thing to check out was the gradient and condition of the Akatarawa Road.  Since it was fine last Tuesday, we drove to Upper Hutt, and headed up the Akatarawa Road (in the car, not on the bike!). Much of it is very tortuous, with lots of twists and turns, and lots of “blind corners”. On the whole the inclines do not seem too bad, as they are short-ish, and interspersed with dips or flat stretches. And the surface is good. But the road is quite narrow. There is only just enough room for two cars to pass each other, and there is no shoulder for a cyclist to get out of the way in a hurry. I must admit that this aspect of the road worries me. What would be the chances of getting hit by a car coming up behind you around a blind bend? Then again, there is very little traffic. We met only three cars during the whole trip.

But there were dozens of cars at Staglands that got there before us. This is the first week of the school holidays – as we found out when we got to Staglands. We pulled into the carpark and had trouble finding a spot. There were two big buses – one of the drivers informed us that the passengers had been children on a school holiday programme. The valley was ringing with excited children’s voices and the calls of birds of various descriptions (peacocks, geese, tui, chickens). I hoped the kids and their minders would not all be in the café where we were planning to have lunch.

It was after 1pm, so it was relatively quiet in the café. We sat out on the deck, near a tree that was labelled “Native Bird Feeding Station”, and lots of little wax-eyes and a tui or two came to feed from a container that contained a milky-looking liquid.

Waiting for lunch on the deck at Staglands (photo by John)
Wax-eyes at the “Native Bird Feeding Station” (photo by John)

Staglands is about 16 km from Upper Hutt, then it is another 4 km to the highest point – probably the most testing uphill bit. The downhill stretch to Reikorangi is quite steep, and there is a drop on the left side of the road – you can’t afford to lose concentration, lest you tip over the edge. It will require a firm grip on the brakes too, I think, as I’m not game to go hurtling down at full speed.

Once out of the forest cover, the view opens up over a beautiful valley (photo by John)

When we got to Waikanae, we decided to try the bike out some more by cycling the Waikanae River track loop. We parked near the estuary, and headed up the north bank. We had gone only a couple of kilometres, when the chain of my bike fell off. John restored it, but it fell off again after the first couple of pedal strokes. This happened several times, much to John’s frustration. He tried taking off the new chain wheel and turning it around (outside-in), hoping to improve the chain line. That did not solve the problem. In the end he discovered what was going on: one of the chain plates was splayed, which caused the chain to keep falling off.

Trackside bike repairs

Out came the full toolkit, but what he needed – a pair of pliers – was not in it. What to do? Squeezing it by hand did not work, banging it didn’t either, but in the end, with the help of a rock and a spanner, he managed to coerce it into the correct shape, and hooray! the chain stayed put, and we were able to continue on our way.

There were quite a few people on the track, and families having picnics on the little beaches. We saw a trio of cyclists – two by the water’s edge taking their shoes off, and one emerging from the bushes – so I reckoned that they’d gone for “a pedal, a piddle, and a paddle”.

A great school holiday activity – a picnic by the river
Approaching the SH1 bridge, you go though a nice wooded area (photo by John)

We crossed the SH1 bridge, and made our way down the southern bank of the river. We stopped to take off a layer, as it was getting quite warm. In the photo below, you can see the difference in the size of the chain wheels on our bikes (click on the photo to enlarge it).

Compare the size of the chainwheels on our bikes (photo by John)

A bit further along we saw some ostriches in a paddock. I wanted to take a picture of them, and here I discovered what was wrong with my camera (it had misbehaved during our last ride). It was the zoom that didn’t work. The camera must have been knocked inadvertently, as there were a couple of small dents in the lens surround. Darn!

Four ostriches in a paddock, eating cabbage leaves (photo by John)
The estuary, with Kapiti Island in the background (photo by John)

Apart from the problem with the chain falling off, it was a very pleasant 12 km ride. But John spent more time in the garage that evening to deal to the errant chain. And today (Friday), he removed a link from it. So we had to go and give the bike another try.

We drove out to Plimmerton, from where we biked up the hill to Pukerua – the hill that had defeated me a few weeks ago. That day there had been a slight southerly, which probably helped me up the hill to nearly, but not quite, the top. Today though, there was a near-galeforce northerly, i.e. a fierce headwind as you go uphill. It would be as good a test as any.

I made it to the top without having to step off! Yay! I won’t say it was easy – but it was easier than before. The new chain wheel had definitely made a difference.


I made it! (photo by John)

The downhill, of course, was a blast! Not only did I not have to pedal at all, but we were being pushed along by the tailwind. I did find it a bit disconcerting that once at the bottom of a downhill, and starting to pedal again, in top gear, I had nothing to “push against”. John said that this was the trade-off for having the different gearing. Well, so be it. I think that with this change, I will probably do OK on the Akatarawa Road ride in a few weeks’ time.

* * * * * * * * * * * *

I asked John to write about the technical details of the changes he made to my bike.

Technical details – by John Patterson

In cycling most people have a comfortable gear which they use often. Ideally, this should be in the middle of the available range. With our bikes, that range is limited to a factor of two, when three would be ideal.

With difficulties in hill climbing the simplest way to help is to reduce the size of the chain wheel. The chain needs to be shortened to compensate. The number of inches to remove from the chain should be approximately:

(old chain wheel teeth – new chain wheel teeth)/4

Another inch may be required if smooth running is not obtained.

I replaced the 52-tooth chain wheel on Désirée's bike with a 39-tooth chain wheel. Therefore I needed to remove (52–39)/4 or 3.25 inches from the chain. In order for the chain to join up, only whole inches can be removed. I started with three inches, or six half-inch links.

My old chain tool was not very good as it was hard to get the pin and plate set right when joining up. This caused the chain to come off later, when running in the highest gear. A new Park multi-tool fixed that.

In the lowest gear, the top derailleur wheel also conflicted with the largest cog, which made a rumbling noise. As the chain is shortened, this top wheel moves in an arc upwards and then downwards. Adding an inch to the chain made it too loose in high gear. The final solution was to remove four inches of chain.

Longer term, a 44-tooth chain wheel would be ideal. In that case, two inches of chain would need to be removed.

The gear range is now from 27.2 to 54.5 gear inches, or 2.17 to 4.35 metres development, or a 2.03 to 4.07 gain ratio. The lowest gear is the same as that on my Jamis Allegro road bike. The highest gear is now similar to the set-up found on some single-speed commuter/shopping bikes. (An explanation about gear ratios can be found here.)

I also added a recycled BMX chain guard as shown below. These chain guards don't have the "right look" for BMX cyclists, so they are often removed from new bikes before sale. Enough room was left to allow a larger chain wheel to be fitted.

The new chain wheel and chain guard (photo by John)




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