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I have recently purchased a Raleigh folding bike second hand. I had to take it back for servicing (within warranty) when there were problems with the gears and derailleur. The dealers have replaced the chain and the cassette, but when I tested it hard up a gentle hill in top gear, the chain was still prone to slipping. The dealers were happy to take it back and look at it further, but also suggested that I had tested it too hard (e.g. standing up).

Are my expectations unrealistic - should I accept that a folding bike is less suited to high intensity riding than other bikes? Or am I sensible to test it so vigorously before accepting it?

  • Are you sure the chain is really slipping? With new cassette, chain and chainrings and a derailleur keeping proper chain tension I can’t imagine how this could happen. Even if the frame flexes the derailleur should keep the chain under tension. I could imagine the chain falling off the chainring if you manage to twist the frame far enough. – Michael Nov 1 '18 at 22:19
  • Do you mean that hard riding can actually bend the frame? It may be that the derailleur was not set exactly correct. We had a bit of difficulty calibrating the gear shift cable. – CJB Nov 1 '18 at 22:32
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    How worn is the front chainring? You said it was a second-hand bike. – Criggie Nov 2 '18 at 2:24
  • Also clean and inspect the frame for any cracks or flexing welds. – Criggie Nov 2 '18 at 2:24
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Its largely comes down to quality of the bike, which comes down to price, and your size and strength. A well build bike with quality gear set should not do this. A cheap bike, especially a folder, with entry level gears its not entirely unexpected. If you big or strong (or both) the problem is worse

The problem comes from frame flex. The gear spacing on the rear cluster is about 5mm, and the chain is around 8mm wide, the amount of movement needed to initiate a gear change onto the next cog can be as small as a millimeter. When a rider cranks hard on a flexible frame, its easy to get enough flex to cause a gear shift to initiate.

This is flexing not normally considered a big problem - high cadence (pedal revolutions) with lower force is much better riding style than 'mushing' at low cadence. Flexing is not desirable for a number of reasons, so experienced cyclists tend to ride bikes with stiffer frames.

Folding bikes are always going to be compromise as its hard to make a folder stiff. It may be that a folder is not for you and you would be better with a non folding bike, or you may decide to change your riding style to suit the limits of the bike.

Ultimately any modern derailleur type bike is a finely tuned, precision machine. While they are reliable and can last a very long time, they are far from being indestructible. When poorly ridden they are almost certainly going to fall apart.

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    “When a rider cranks hard on a flexible frame, its easy to get enough flex to cause a gear shift to initiate.” But the position of the rear derailleur relative to the cassette doesn’t change because of flex. Folding bikes also have continuous cable housing so the length change between cable stops shouldn’t be an issue. – Michael Nov 2 '18 at 7:20
  • I see your point, @Michael, but mattnz's comment does fit with my experience. When I pressed hard, sometimes the bike changed down a gear. – CJB Nov 2 '18 at 14:25
  • I’d check that the cable housing is really continuous and loosely enough attached to the frame so that flex in the frame won’t stretch the housing. – Michael Nov 2 '18 at 14:58
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In relation to the chain transmission directly, a folder should not be more or less likely to slip than a non folding bike. The rear chainstay of a folder is still a rigid structure whether it be discreet chain and seat stays, or one big main beam that performs both functions.

Ie, folders don't fold the chain.

HOWEVER absolutely folders will make the chain slip and run poorly compared to a physically larger bike. The reason for this is the small wheels and the short chainstays.

If your bike is equipped with an 8 speed (or more) cassette, it will be the widest cassette possible. This makes the chain angle more extreme as it enters/leaves the chainring and cassette, with the worse possible case being big/big.

My folder was upgraded from 1x6 to 3x8 and now suffers from some annoying chain drops due to chain angle.

The best technical fix is to fit an Internally Geared Hub to your folder, and do away with the derailleur. This would also permit use of a drive belt for cleanliness, and that would require a single chainring for weight and simplicity. But its not a cheap solution.

  • Internally geared hubs have relatively tight torque limits. If OP is a strong rider and really grinding those gears uphill it might break. Though the large chainring on a folding bike (due to small wheels) could help to reduce torque. – Michael Nov 2 '18 at 7:26

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