Fixing the most common mechanical problem with bikes in London

I’m trying to turn right. I’m waiting for a gap in the traffic. Suddenly, I spot it. I push my foot down on the pedal expecting a smooth forward motion. Instead, I hear a horrible grinding sound. My foot slides further than I expected and the bike cowardly inches forward. I spot the gap in traffic narrowing and rushed I try to pedal again.

I must be one of thousands of London cyclists who’ve experienced this. How do I know it? Because I hear the grinding sound all the time. At traffic lights especially.

But why? Why is your beautiful bike causing you so much hassle at this moment of need and potentially putting you in a dangerous situation?

The answer probably lies in the cassette.

The beautiful old cassette that needs replacing

The cassette is a true thing of beauty. A complex marvel representing the progress of bicycles. But when it is worn out it’s a true pain the %*$£”!

When you apply pressure to the pedals the chain tries to grip the teeth. If the teeth are too worn then the chain will simply slide forward.

Before definitely pointing the finger of blame on the cassette it is worth noting that there are other potential culprits. One is the chain. Two is the rear derailleur indexing.

With some Poirot style investigating you should be able to find whodunit. The first thing to do is to check if the chain is worn.

If the chain seems worn then maybe it is a good time to replace it. It is also worth checking the teeth on the cassette. The one in the picture above is worn out where as the below is a new cassette. You can see a new cassette has more clearly defined teeth.

Newly replaced cassette

Replacing the cassette

If this is your culprit then replacement is fairly easy. For the bike shop route you’ll be looking at £25 for labour plus the cost of parts. For a Shimano cassette the cost can be as little as £23.99. But the prices go up from there.

You could also choose to do it yourself. The only bad news about this is that you do need some bike specific tools. Namely a chain whip and a lockring tool. This will set you back £10 – £20. You’ll also need a spanner or a wrench.

Doing it yourself will work out cheaper even with purchasing the tools.

I put together this below video while I was doing the cassette replacement on my bike. Note that it is common practise to replace the chain at the same time as installing a new cassette (unless the chain is only a few weeks old anyway).

Also in the overhauling your bike series:

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As seen on The Guardian, BBC and The Independent.

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31 Responses to Fixing the most common mechanical problem with bikes in London

  1. Craig 08/02/2011 at 5:14 pm #

    You could of course just buy a complete tool set for about £30 and have most of the standard tools at your finger tips. Not great quality, but sufficient for most basic needs.

    Nice to see someone not doing bike maintance with a full workstand and wearing an apron.

    • Andreas 08/02/2011 at 5:18 pm #

      Appealing to the everyday cyclist 😉 If you’re planning on getting into bike maintenance then a full kit can definitely help vs getting everything together bit by bit..

  2. John 08/02/2011 at 5:19 pm #

    Was the green screen on the video caused by dropping your camera into the jar of swarfega!

    • Andreas 08/02/2011 at 6:05 pm #

      I have no idea. I bought this Sony Vaio laptop with the view that the new Core i3 processor would be able to handle video editing piece of cake. Wasn’t to be!

  3. Dave Escandell 08/02/2011 at 5:20 pm #

    Great addition to the collection of DIY posts.

    I do hope you also changed that tyre – it’s got ‘soon to puncture’ written all over it… :o)

    • Andreas 08/02/2011 at 6:03 pm #

      Haha – I replaced the front tyre – which, believe it or not, was worse than that tyre! This is what happens when you ignore bike maintenance for 12 months..

  4. chris 08/02/2011 at 5:46 pm #

    Or you could save yourself from ever having to do this again by investing in a hub.

    I ride a bike with a Rohloff 500/14 and only have to do a small oil clean/change every year or 3000km. Never have to worry about it not performing because its caked in mud and I don’t require any specialist tools. On top of that, the service life is 50,000km but people are still riding some having done +150,000km!

    • Andreas 08/02/2011 at 6:04 pm #

      Agreed Chris – those hubs are a great call – Although to switch my bike over to a hub I’d have to probably buy a new back wheel which wouldn’t be ideal.

      • Marc 11/02/2011 at 10:56 am #

        I bought a Dahon folder with a five speed Shimano hub three years ago and am abivalent about it at best. Anything that requires removal of the back wheel (eg replace tyre, new brake blocks, change inner tube) becomes major hassle.

        When I eventually get enough money to replace the bike, I’ll be going for a traditional derailuer set up: it may be exposed to the air and crud, but it is much, much easier to maintain the bike as a whole.

  5. whitey 09/02/2011 at 9:20 am #

    Hi. Cheapest option: buy cassette removal tool, and chain tool (also you must have adj. wrench), buy cassette and new chain plus two bottles of beer. From old chain make chain whip (you’ll need a piece of steel/aluminum pipe) tools all together with postage about 15quid.

    • Andreas 09/02/2011 at 10:10 am #

      Yep – I’ve seen a few home made chain whips. Applaud the good DIY effort!

      • whitey 09/02/2011 at 3:47 pm #

        I know that DIY is not a good solution for all, but for me the feeling afterward is just priceless. Not because of saved money (which is ok), but because of physical activity and work (I work in rather “virtual reality” normally) and being not just a standard consumer (

  6. Andrea 09/02/2011 at 10:44 am #

    Gears in London?? Not necessary in my view. Get yourself a singlespeed kit for a tenner and maybe a tensioner (if needed) for another tenner and you’ll never look back :-))

    • thereverent 09/02/2011 at 12:45 pm #

      I have a single speed for my commute bike. It’s ok as I have a fairly flat (although long) ride in.
      I’m not sure I would want to go over Dog Kennel Hill every day on a singlespeed though.

  7. JonF 09/02/2011 at 11:09 am #

    Here are a couple of lessons from my recent experience with trying to rectify the chain slipping on my girlfriend’s bike. Hope these add to the collective understanding.

    The problem appeared to be that when pressure was put on the pedals the chain slipped – which was disconcerning obviously, and could have resulted in loss of control. The chain looked knackered and the cassette was looking worn so I replaced both. Actually the cogs were on a screw-on freewheel, so after I’d hunted down one of those- Evans looked puzzled, (it was a Shimano Mega-range btw), I fitted it (I already had the extractor) and the chain, however the standard length KMC chain was TOO SHORT because the Mega-range requires 2 EXTRA links added to a standard chain. First of all I made the mistake of adding a couple of links from the old chain. That didn’t work satisfactorily because you could feel the old links go round the freewheel. I went back to Waldens of Kingston and the guy there happily found some extra links (which he takes off for fitting to most bikes) for me to use with the new chain.

    But the slipping problem persisted. Grrr. I decided that the problem must now lay with the jockey wheels on the derailleur which on inspection also looked smoothed-off, but these tend to get ignored because they’re small and covered in oil. Rather than replace just the jockeys I thought I’d replace the whole unit with an ‘upgrade’ which was only £13 anyway ordered on the internet (Shimano TX71 Tourney). This worked beautifully I thought at first, except that when the lowest gear was engaged the outer cable for the derailleur got hooked under the wheel axle bolt and trapped it, stopping subsequent change to a higher gear. Went back to Waldens, got a bit of longer gear cable outer that would route the cable over the axle bolt and a new gear cable; home to fit them. Now works perfectly.

    Costs: £20 Freewheel, £10 chain, £13 derailleur, cable £3: Total = £46.

    So the lessons are:
    (1) think about replacing the jockey wheels or else the whole derailleur at the same time as the cassette/ freewheel
    (2) look carefully at how everything works together and…..
    (3) pay attention to detail if you buy non-direct replacements – you may need to alter something to make it work properly.
    (4) Never give up!

    • Andreas 11/02/2011 at 9:49 am #

      JonF – was very interesting to read this. Good on you for managing to sort out the slipping chain and also pleased to see it didn’t break the bank too much.

    • Marc 11/02/2011 at 10:59 am #

      That’s the modern Evan’s in a nutshell: they’ve expanded so fast, they have lost a lot of the expertise I used to expect from them when it was just two shops in Waterloo.

      They’re the Starbucks of the London cycling scene (that’s not a compliment).

  8. thereverent 09/02/2011 at 12:42 pm #

    Regualr replacement of the chain is not too expensive and will reduce wear on more expensive compoments.

    With derailleur indexing it’s worth noting that gear cables will streach over time so you will need to adjust them every so often. But doing thsi also reduces wear on the chain and cassette.

    A little bit of tinkering with cables and a clean of the drive chain system can leave a bike feeling like new (also a good time to adjust the brake cables if they are getting loose).

    Don’t leave it too long to replace a cassette. I tried to replace one on my old commute bike and it would not be seperated from the wheel (it had been on there for many years). I ended up getting a new back wheel as even the bike shop couldn’t free it.

    • whitey 09/02/2011 at 2:36 pm #

      The other technique (which I’ve never used) is to have 3 same chains and replace them every ~1.5-2kkm or so. When everything is worn completely you’ll need to replace whole drivetrain: chainrings, chain cassette and probably jockey wheels.
      Don’t throw old stuff if you have enough space to keep them, you never know how usable might be worn old jockey wheel (, old spokes/nipples (, some cogs, some springs etc…

  9. David Cohen 11/02/2011 at 12:40 pm #

    Andreas… keep up the good work. I would certainly like to see you tackle adjustments to rear derailleur, and front mech. It’s which screw, which way to tighten / slack etc.

    • Andreas 24/02/2011 at 10:41 am #

      All been covered in the Bike Doctor app for Android and iPhone but I’ll consider doing a little piece on London Cyclist too..

  10. Nick 12/02/2011 at 3:59 pm #


    How often would you expect to change a cassette? (or how many miles). At my last service the bike shop recommended a new cassette but I declined to save on costs. I have only had the bike for a year (approx 1500 miles mostly commuting in London) and thought it should last longer than that.



  11. Jon Fray 15/02/2011 at 12:46 pm #

    Nick, 1500 does seem low mileage for a cassette to me. I’d be expecting 3-4 times that, but it depends on conditions. Have you had any problems with the chain slipping? Have you been lubricating your chain? Maybe the shop is having you on. Did you get a new chain anyway? Sounds to me a bit like they recommend changing the chain and cassette together, but I believe in general that you can change the chain and get more life out of your cassette – if it isn’t too far gone.

    Take a look at the teeth. Modern designs have teeth that vary in shape to assist with indexing, so looking for odd looking teeth may be difficult. Thing is once you change the cassette you are probably advised to have a new chain…..and then you have to wonder if the chain rings will mesh with the new chain?… and so it goes. If you’re not having problems then I’d leave it alone, just clean everything and lubricate it. TBH I don’t see a great deal of wear in the cassette Andreas has used to illustrate wear.

  12. bob 04/03/2011 at 3:00 pm #

    I bought the Lidl cycle toolkit a couple of years ago for 25 quid. The only addition I have made is a parktool chain wear tool.

    I take off the chain, cassette, jockey wheels and chainrings twice a year to give them a proper degrease and clean ie before winter and in spring.

    For me the lidl toolkit, while not top top quality, is more than sufficient to keep my bike running smoothly. Highliy recommended, unless you want to spend a lot more on a quality toolkit.

    P.S replacement jockey wheels, while availble are quite pricy so give them a clean andd re-lube before replacing

  13. Mr Colostomy 08/03/2011 at 11:56 am #

    The internal hub gears made by Sturmey Archer are easily as straightforward to remove as a dérailleur set-up when you need to take a wheel off. It is baffling how dérailleur gears became standard on even utilitarian bicycles. They are great for sport cycling but I wouldn’t want to depend on them for everyday use.

  14. Clinton 13/03/2011 at 3:24 pm #

    Another thing to bear in mind is the freehub body on some bikes. Over time these can become gummed up with dirt and grime and the effect is a bit of slippage in the drivetrain when moving off from a stop, as the pawls in the freehub are slow to engage. WD40 sprayed liberally around the hub is a temporary fix, but the problem will get worse and worse with the end result being pedals, chain and cassette all spinning round with the back wheel motionless.

    The easiest thing to do is buy a new freehub body for about £12. Hopefully you will do this before replacing all the other components of the drivetrain like I did!

  15. Matt Bee 24/03/2011 at 10:47 am #

    I really enjoy doing all my own maintenance on my bike and changing the chain and cassette is a nice regular bit of maintenance. I find youtube is a great source for how to videos, in addition to this blog or course.

    I usually find that getting the gear adjustments perfect is harder than changing the components, which I totally understand, but I tell people to persevere, as they say practice makes perfect and it is a joy to be able to keep your bike running perfectly with little cost and lots of fun!

    I actually think I change my components much more than I need to – but if I enjoy messing with my bike, there’s no harm in that, just means I have plenty of spares should I need them!

  16. Goonz 18/04/2011 at 2:36 pm #

    This is a great read thanks!

    It is comforting to know the slipping of chain does not only happen to me as it can be rather disconcerting when I am trying to speed up to overtake and suddenly I nearly lose the bike because of the chain slipping.

    The only worrying thing from what I have read above is that my bike is only a couple of months old and only had a months max worth of hard commuting. Why would the chain be slipping already?

    I will give my bike a nice clean next this bank holiday weekend and the comments above have given me more confidence in attempting my own bike DIY. The main reason for steering clear from it was to ensure I didn’t do more damage and then have to leave my prize at home and use good ol public transport again! *Shivers*

    I hope they still stock that bike kit in LIDL’s. Sounds like a great piece of kit.

    • Andreas 27/04/2011 at 5:55 pm #

      You are very welcome!
      It is a little odd that the chain is slipping already after only 2 months – I’d suggest if it is a new bike then it’s worth talking to the bike shop about that and perhaps they supplied you with a particularly weak chain. However, the likelihood of the components already being worn is very slim therefore in your scenario it is possible that gear adjustment may be to blame instead.

  17. Goonz 18/04/2011 at 3:34 pm #

    I also echo the sentiments about Evans Cycles. I took my bike for its free service after a month and the bike felt worse than before! Not what I expected from supposedly the leading brand in cycles shops in England.

    Needless to say I will be doing most of the DIY myself from now on unless I really have to take it to a bike shop.

  18. phil 17/12/2012 at 10:21 pm #

    Just to say thanks for the video, i have been putting off changing my cassette for ages but a broken change finally forced me to do so. First website i thought of for instructions was here and i was able to do the change out in 15 minutes once i figured out which way to pullt he tools.


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