A change of opening times, for a time

It’s been amazing seeing how many people rely on us to keep their bikes rolling, and the messages of support have been truly heartening – thank you.

We’re trying to keep up with demand as best we can, and we’ve made some changes to the way we work to keep everyone safe.

We’re doing lots inside the shop to disinfect bikes, our gloves and our tools and work surfaces, and you may have noticed the shop door is staying locked so that we can help everyone keep distanced. Sorry if it’s meant waiting outside the shop for a while.

The main difference from today – and we’re sorry for the inconvenience this will cause – is that on Tuesdays and Thursdays we’ll be in the workshop from only 9am to 6pm and we’ll just be servicing booked-in bikes. So we won’t be open for walk-ins and we won’t be answering the phone on those days, but we will check our answerphone messages and get back to you, so please do leave a message!

This is to make sure we have enough mechanics in the shop at busier times during the day, and to deal with the extra time needed to serve one customer at a time at the door. Basically, to make sure there are enough of us to go round! Thanks for your patience.

Why do I need to replace my chain and cassette?

(Originally published 16th October 2011)

When we service your bike, things like oils, grease and hydraulic fluid are included in the price. However, some things aren’t included and the most common extra charges are for brake pads, chains and cassettes.

The brake pads are fairly self-explanatory, and you’ll certainly notice if they’re not replaced in time. But it’s not always clear why the bike’s chain, and sometimes the cassette, need replacing.

newchain bw

As a bike chain is used, something called “chain stretch” occurs. This isn’t a great term for it, because the chain parts don’t actually stretch. At each point where the chain pivots, the constant rub of metal on metal starts to wear the parts away. Although this happens very gradually, this wear means that that pivot point starts to become a little looser. As it wears down, the distance between two consecutive chain rivets becomes very slightly further apart.

wornunwornlinks

The image above shows a very worn chain link and a brand new link. You can see the wear on the rivet, the inside of the roller and the inner edges of the inner plates.

The chain and the cassette (the set of sprockets on the rear wheel) are designed to align perfectly with each other. When both are new, this is what happens; the teeth on the sprockets all mesh equally with the links on the chain, and the force you put in when pedalling gets spread evenly to each tooth in contact with the chain.

But as the chain wears, the length of each link gets very slightly longer. Only by a tiny amount, but this can mean that the pedalling force gets transferred unequally to the sprocket on the back wheel. Because of the way the chain transfers force to the sprocket’s teeth, the teeth at the “bottom” of the sprocket will have more force on them than those at the “top” at any time in the sprocket’s rotation. In turn, this wears down those teeth very slightly. As the teeth wear down, they match the wear of the chain, the chain’s load is spread more evenly across the teeth and the wear lessens.

This isn’t a huge dramatic process (unless your components are made of very cheap metal, or you run your chain dry), but it is a gradual process that occurs steadily all the time you use the bike. In time the chain, and also the cassette, become slightly worn.

parkcc3

I use a very handy tool to measure this “chain stretch”. When new, all bicycle chains will measure exactly 1″, 25.4mm, across one link. (“one link” is the repeating unit – one inner pair of links, one roller, one outer pair of links, another roller). As the chain wears, the very slight lengthening of each link is hard to measure but because it usually happens evenly over the whole chain, one can measure the lengthening over several links.

The chain tool pictured above is inexpensive and fairly foolproof and I’ll often refer to it as the tool that determines whether the service is going to be a little more costly or not! One end hooks into the chain and the other end will fit into the chain further along if the chain has “stretched”. It has two carefully measured sides, one that will drop into the chain if it’s 0.75% longer than when new and one that drops in at 1% total elongation. Those are important measurements.

Most chain manufacturers recommend that their chains are replaced when they have elongated by 0.75%. Because the chain wears slightly faster than the cassette, this is the point where you can usually just replace the chain (and not the cassette) if both were new to start with. As an aside, if you’re fairly meticulous about swapping chains regularly, you can usually get through two or three chains for every cassette.

Once the chain wear is approaching 1% “stretch”, it’s usually time to replace the cassette as well. Because the teeth on the cassette will have worn down to more or less match the chain wear, if a new chain is fitted to a worn cassette, it won’t mesh properly and may jump or skip, especially when changing gear. Conversely, if a new cassette is used with a worn chain it will also mesh and change gear badly and the cassette will wear much faster than usual. As chains are less expensive than cassettes of equal quality, it’s much more economical to replace them before you need to replace both.

veryworncassette

The next logical question, of course, is “if my chain and cassette are worn but working well together, why do I need to replace them at all?”

There are two answers to this. One is, in turn, to reduce wear on your chainrings, the big cogs that the pedals directly drive. The teeth on these won’t usually wear as fast as the teeth on the cassette, because the pedalling forces are spread over more teeth on the chainring. A worn chain will still lead to unequal distribution of force on the teeth on the chainring and will wear the teeth down in the same way the cassette wears. But usually if the chain is kept below 1% “stretch,” most chainrings will outlast several chains and cassettes.

Back Camera

The second answer is simply that eventually the teeth on the cogs will wear out. I was asked to “have a look at” the bicycle pictured above because “the gears are slipping”. When people tell me this, it’s usually because the gears aren’t properly indexed and the chain is jumping between sprockets, but this chap’s chain had actually begun to slip straight over the cogs whenever he put any pressure on the pedals! There simply wasn’t enough material left on the cogs for the chain to grip on to, so it was jumping over the teeth. Unfortunately for this bike it needed a new chain, new cassette and a new set of chainrings, which worked out more expensive than the bike itself and he chose to scrap it.

The moral of his story? Replace your chain regularly, keep your bike running for longer…

The beauty of hand built

One important thing we do at Rat Race Cycles is hand-build wheels. In fact, we’re about to launch a specialised wheel building service – Owen Wheels – at this year’s BESPOKED – The UK Handmade Bicycle Show.

There’s no dark art to wheel building, but to consistently build strong, durable wheels requires knowledge, skill and practice. There are many reasons to choose hand-built wheels over branded wheels like Mavic, Shimano or Fulcrum. I’ll try and outline the key ones:

Changing gear at Rat Race Cycles

If you’ve been in the Nunhead area over the Christmas break, you’ll have noticed that we’ve been making a few changes to the shop. Sure, we’ve reorganised things a bit, added in some more lights and had a tidy up and given the walls a lick of paint, but none of those is the big change. The major change is that we have stopped selling bikes.

That’s right – we are now a bike shop that doesn’t sell bikes.

Sounds crazy, right? Well, yes and no.

Small Business Saturday

Think of a massive online retailer and chances are you think of a logo; a letter, a colour scheme, a design.

Think of a small shop on your high street and you probably think of a face. The owner. The person who took a deep breath, stepped out and turned their passion – their dream – into their life’s work.

Every year, more stories surface about huge multinationals exploiting yet another loophole to skip out on tax in the UK. And yet, every year, (often despite our best intentions) we throw our hard earned money at them as Christmas descends, resorting to the easiest, the cheapest, the most obvious, over-advertised option. And every year we wonder why shops are closing on the high street, why people are going out of business, why our towns and villages are becoming soulless miniature carbon copies of huge, out-of-town shopping malls.

Well, here’s a chance to shop a bit differently. This Saturday 5 December is Small Business Saturday, and a chance to get down to your local high street and support those people trying to make their dreams pay their bills.