Russell's Blog

A little while ago, I was riding home on my wonderful Brompton bicycle, and the chain tensioner suddenly disengaged. That had never happened before, and I discovered that the gear on the chain tensioner had completely smashed to bits. Here's what it looked like :

After puzzling about it for a while, I think I understand what happened. I use the same chain oil on my Brompton that I use on my racing bike. The "oil" is actually a mixture of a heavy lubricant in a volatile solvent. The solvent evaporates after coating the chain, and dissolves whatever gunk has accumulated. I think the solvent damaged the plastic. I've seen this happen with some plastics when they come into contact with gasoline. The gasoline dissolves the plasticizing agents, and leaves behind an open matrix of molecules, like a very, very fine sponge. The open matrix has a huge surface area and oxidizes rapidly. Your nice flexible plastic turns into something hard and crumbly, like a stale cookie.

That's what I think happened here. The remaining bits of plastic are still relatively flexible, but the bits that broke off have turned into a powdery mess.

The guy who sold me my bike offered to let me buy an idler wheel off of one of the bikes in his stock, but I didn't want another plastic gear. Here is what I built :

I bought a standard anodized aluminum derailleur gear from a local bike shop, and attached it to the Brompton chain tensioner arm with a few pennies worth of standard hardware. The new idler wheel (gear? cog?) slides along a little stainless steel tube I picked up at the hardware store and cut to length. This gives it enough play to allow for easy shifting. The tube has just the right tolerance to allow the gear to spin very easily, but not wobble.

Here's the exploded view :

From top to bottom, the parts are :

• regular old bolt
• two washers
• stainless tube
• gear
• another washer
• lock washer
• nut

The gear is part of a Shift Biscuits pully set (though probably any pully set would work), and the steel tube is 7.94mm x 7.4mm (stock No. 7117) cut to length with a hacksaw (this took a while). The rest of the hardware is standard hardware store stuff.

I had to saw off the plastic axle tube on the chain tensioner arm because it would have prevented the idler wheel from sliding into the right position for the outer gear. I chose a bolt with a hex-head that fit snugly into the socket on the tensioner arm (similar to the bolts on the toggles for locking the frame in place). Once the nut is tightened against the lock washer, the axle is extremely rigid. The gear slips across the tube with almost zero play.

The shifting action is actually much smoother than it was with the plastic gear, and the bike seems to make a little less noise than I remember (that could be my imagination).

Yay! I've got my bike back, and without another dorky plastic gear, too. Neat!

Since I am now commuting to UCLA from Pasadena, I've spent a lot of time wondering how to cut down of the time, expense and misery of commuting. Most of that pondering happened while trapped somewhere on the Ventura freeway, or the perhaps on driving aimlessly around Westwood looking for a parking spot.

To that end, I've started using the Metro as much as possible. The Metro Gold Line is fantastic, and gets me from Lake Street in Pasadena to Union Station downtown in about 20 minutes (less if I catch an express). The Purple Line gets me as far as Koreatown, and this is where things start to suck. From Wilshire and Western, it's about seven miles to UCLA. During business hours, the 720 bus takes about an hour and 45 minutes to traverse this miserable stretch of urban leprosy. The worst part is Beverley Hills, which I would gleefully bulldoze if given the chance.

It's maddening. The first 22 miles of the trip take about 30-45 minutes, depending on intervals between trains. The last six and a half take three times that.

While I was riding a 720 bus packed with more people than I attended high school with, it occurred to me that 6.5 miles in 105 minutes is a little slower than four miles per hour. I could probably beat that walking on my hands.

So, I bought some new tires for my bicycle, and gave it a try. Sure enough, I passed five or six 720 busses as they sat like flatulent beached whales in the morning rush hour traffic. With all the traffic lights, it's a slow ride, but it takes about 50-60 minutes, so I'm averaging between 6.5-7.8 miles per hour. In West Los Angeles, velocities this high are known to cause Cerenkov radiation. I could go a lot faster if drivers would actually look at the road instead of staring blankly into space while driving their Range Rovers in the bike lane, parking in the crosswalk or on driving on the sidewalk to get around busses (yes, really). It would be certain death for a cyclist if all of this mayhem weren't happening at the speed one can push a loaded dumpster up a hill.

There is just one problem, though. When you're not riding it, a bicycle is miserable thing to carry. You may as well be traveling with an Alexander Calder sculpture.

So, I bought a folding bicycle :

This is a Brompton M6R. It folds up really, really tiny, and has little wheels on the bottom to roll it like a suitcase when it's folded up.

Surprisingly, the small wheels don't seem to make much of a difference with stability. The only difference, really, is that it takes a lot less torque to turn the front wheel, even at speed. This makes it feel "twitchy" at first, but the sensation goes away after about twenty seconds of riding. The Bromptons also have really strong breaks. You have to be careful not to pitch yourself over the handlebars.

Compared to my road bike, the Brompton is almost alarmingly responsive. This makes it ideal for crowded situations -- it's easy to avoid unexpected obstacles, squeeze through narrow spaces, and stop suddenly. When it's folded up, it's nice to be able to walk down the train platform without goring people with the pedals or stabbing them with the quick release levers.

The Brompton has two main disadvantages. First, it's a little on the heavy side. I didn't shell out for the titanium version, so it weighs in at 23 pounds. This turns out not to matter very much, except when lugging it up long flights of stairs. The second disadvantage is that I must answer a never-ending stream of questions about it.

I will write a more detailed review of the bicycle itself in a few weeks.