John C. Kirk (johnckirk) wrote,
John C. Kirk

Bike maintenance

I went along for a health assessment last Friday, and the doctor mentioned that my feet are a bit arched. I suspect that this may be because of my cycling technique: I have a tendency to press down on the pedals with the middle of my feet, rather than the balls (front).

This in turn is partly to do with the saddle position. I'm fairly tall, so I bought a telescopic seat pillar. At first I didn't use it, so I just pulled up the main seat pillar as high as it would go, then relied on the the extra pillar (even when collapsed) to give me an extra couple of centimetres. However, I've recently been pulling the telescopic pillar up a bit as well, and that does make the ride more comfortable, i.e. I can actually straighten my legs enough to get my feet into the proper position. Unfortunately, I've found that the main seat pillar has a tendency to sink down while I'm on it; it's fairly gradual (unless I hit a pothole), but I have to stop every 10-15 minutes, then get off and pull the seat up again. I'll ask the shop about that the next time I take the bike in.

Speaking of the saddle, I've also had a problem with it tilting upwards at the front, presumably because my weight has been pushing down on the back. I couldn't push it level, but last night I dug out a hex key (left over from flatpacked furniture) and adjusted the saddle. Before and after:

Tilted seatLevel seat

Riding on it today, it was a lot more comfortable, and I hope that I'm maintaining a straighter back.

While I was on a roll, I also decided to have a look at my tyres. I've had various bikes over the years, and my standard approach has always been to try squeezing the tyres with my thumb; if it feels hard, that's fine, but if it's a bit squishy then it needs more air. However, looking at the owner's manual (and the Brompton website), they're a bit more precise about tyre pressure. I have Schwalbe Marathon tyres, so that means:
Front: 60 to 80 PSI, 100 PSI max.
Rear: 70 to 90 PSI, 100 PSI max.

I've used electric air pumps at petrol stations, which include pressure gauges, but I've heard that it's a really bad idea to use them on bicycle tyres. (Apparently they pump air at too high a pressure, so bike tyres would explode.) On the other hand, none of the pumps I've used have ever included a pressure gauge, so how do you know when you've got the right pressure?

Doing some digging on the web, the idea seems to be that hand pumps are just for emergencies, i.e. getting a puncture while you're out and about. You then keep a "track pump" at home, which includes a pressure gauge, and use that for regular maintenance. I've never been very good at fixing punctures, even with the aid of a bucket of water, so I wouldn't fancy trying it by the side of a road. Looking at the Brompton in particular, it would be much easier just to fold it up and bring it home on the bus/train. This pump business is probably old news to most people, so does anyone else have any recommendations?

In the meantime, my back tyre seemed a bit squishy, so I figured that it would be worth pumping it up. Aside from anything else, it would be useful to figure out how my Brompton pump actually works. Unfortunately, this is where it all went a bit wrong.

When the pump is clipped onto the bike frame, it looks like this (bottom right corner):
Pump on bike

Taking it off the bike (by pulling in one end):
Pump on floor

One end pulls out (as you'd expect), and the plastic cap reveals a metal thing underneath:
Pump extended

If I unscrew the metal thing, I can then move the lever in and out:
Pump with lever out
Actually, I can pull the lever out with the metal thing in place, but it's easier without it. If I screw the metal thing back on with the lever out (perpendicular to the pump), the lever automatically moves back in. So, I assume that the purpose of the metal thing is just to keep the lever in place until you want to use it.

My tyres use a Schrader valve. Quoting from the manual: "A car-type valve is used, allowing various methods of inflation. The Brompton HP pump is well suited, and can be kept on the rear frame (unless it's titanium)."

"Normal" pumps have a flexible tube on the end, so you screw that onto the valve. There's always a bit of air that escapes, but it's not too bad. This pump didn't come with any instructions, so I've been figuring it out by trial and error, and a bit of digging around the web. As I understand it, the idea is that you push the pump onto the valve, then pull out the lever to lock it in place until you've finished inflating the tyre. I've tried this, and I promptly drained all the air from the back tyre (which is now completely flat), but I can't get the pump to actually lock in place. In fact, now that the tyre is empty, if I push against the valve then it starts to go through the hole in the wheel.

I don't know whether my pump is dodgy or whether I'm just doing it wrong. Either way, it looks like I'll be taking the bus tomorrow, which is rather annoying. I'm inclined to give up on this pump as a bad job, and buy another one to replace it. Ah well, hopefully someone else can learn from my cautionary tale.
Tags: cycling

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