Friday, February 29, 2008

Q&A: Brakes and Tyres

Q: Hi Jim,
Thanks for your FAQ - most interesting. I have a couple of questions.
1) I had to replace the inner tube on my bike last night as it was
punctured. I took the old one off and it was 26" but the wheel itself is a
24" wheel. The tyre was 26". What is the correct size tube? I stuck a 24"
one on which I happened to have - will this be a problem?
2) My brakes are not effective. There seems to be plenty of rubber on the
blocks and I have adjusted them so that they are as close to the rim as I
can get without actually touching and I hardly need to touch the brake lever
to apply them but even if I really squeeze both levers, I cannot stop
rapidly. There seems to be no friction between the brake blocks and the rim.
What should I attribute this to?

Kind regards and many thanks in advance,

A: Thanks for the email, Will. I bet someone didn't have the right size tube
so they put that 24-incher in there. That will work in a pinch because tubes
are made of stretchy butyl rubber, and also because the difference in size
between 24- and 26-inch wheels isn't that great, however, the right size
usually makes it easier to install the tube. So, you might want to replace
the 24 with a 26 at some point. Functionally, once the tube is inside the
tire it'll work fine.

On your brakes, what might have happened is that the brake pads might have
gotten old and hardened, or maybe they're filled with debris (small bits of
gravel from the road and metal bits from rim)? It's a good idea on most
bicycles to replace the pads about yearly depending on how much you ride
just to ensure that you have good, sticky rubber on there. If you don't have
replacement pads available you can sometimes get old pads to grip better by
checking them and removing any embedded debris in them with an awl or pick
or pocket knife, and then sanding them gently with sandpaper to expose a new
surface of rubber. Obviously, this won't work on worn-out pads. You'll need
to replace these. Ultimately, for safety, it's always best to go with new
pads, but if you were stuck without you could try cleaning and sanding the
old ones like this and it might get you by until you can get the news ones.
Keep in mind that most bike shops have a good selection of replacement pads
and replace them for you while you wait in most cases and not charge you too
much, either.

The other possibility is that the rim has some lube on it or even simple
dirt and grime from the road. As the braking surface the rim needs to be
kept nice and clean. For this you can use something like rubbing alcohol
that will cut through any grime and oil and evaporate quickly, too.

Just to be clear, you should check both the brake pads and clean the rim,
not just one or the other. The brakes are a system and all components should
be checked. Along that line I would also take a close look at the cable and
make sure that there's no extra friction in the cables and housings when you
operate the lever and also that the brake springs are nice and tight and
cause the brake to open smoothly when the levers are released.

As I said, most shops would have any parts you need and be happy to check
your brakes out and set you up with what you need to tune them up yourself,
or do the job for you for not too much money. Any time brakes are involved,
it's worth it to be safe and if you're not sure about proper adjustment you
might want to leave it to the pros. Sometimes they'll even show you what
they're doing or walk you through what you need to do so you can learn, too.

Have fun fixing up your bike!

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