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Chain slipping

I have just replaced my old chain after it snapped in two while out riding. Now the new one slips when I am on the middle two cogs on the cassette when I put any pressure on the pedals. I can't see anything wrong; the only thing I can think of is that they are possibly worn? Do I need to fit a new cassette?

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22 comments

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MT63 | 9 years ago
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One of the things I like about this site. Ask a question about a chain slipping and get a physics lesson!

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matthewn5 | 9 years ago
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@Crosshouses:

Not within a normal temperature range.

If you heat the ruler from 0C to 100C it will be 0.008" longer, ie 1/128" of an inch longer.

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matthewn5 | 9 years ago
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Chains are still made in Imperial measurements (1/2") s it's more accurate to use a steel rule marked in inches and 32nds of an inch and measure over a longer distance.

Measure from one side of the link to the same side of the 12th link. 12 new links (inner & outer) of a tight new chain is exactly 12".

1/32 over? be cautious, measure again.
1/16" over? New chain.

Works for me, anyway.

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Kapelmuur replied to matthewn5 | 9 years ago
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drmatthewhardy wrote:

Chains are still made in Imperial measurements (1/2") s it's more accurate to use a steel rule marked in inches and 32nds of an inch and measure over a longer distance.

Measure from one side of the link to the same side of the 12th link. 12 new links (inner & outer) of a tight new chain is exactly 12".

1/32 over? be cautious, measure again.
1/16" over? New chain.

Works for me, anyway.

Does temperature have an effect on the accuracy of a steel rule?

If so, does a chain expand/contract proportionately to the rule?

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Jimmy Ray Will | 9 years ago
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Really interesting comments from KiwiMike about accelerated chain wear as a cassette ages.

Would that still be the case if you changed the chain at 127.4mm for example, or is it just inevitable.

I know guys that work in bike shops that simply use customer cast offs as their chain and cassettes. They'll use those worn products until they ultimately fail, then replace them with another worn set.

The downside is the slight lack in shifting crispness and loss of efficiency, but hell, its free!

There is nothing wrong with the run it into the ground approach if performance is not your goal.

Performance in competition is my goal, and a worn chain is worth anything up to a minute over an hour crit, which is not time I'd be willing to give away.

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KiwiMike replied to Jimmy Ray Will | 9 years ago
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Jimmy Ray Will wrote:

Would that still be the case if you changed the chain at 127.4mm for example, or is it just inevitable.

...

Performance in competition is my goal, and a worn chain is worth anything up to a minute over an hour crit, which is not time I'd be willing to give away.

The 127.5mm wear point has been arrived at through decades of trial, error, assessment etc etc. The wisdom of millions of cyclists and mechanics, distilled down into one easy-to-grasp measurement point. Like anything, yes you could swap it sooner at a lesser wear point, and in theory gain an advantage. Taking that logic to an extreme, you could buy a new chain every week, and maybe have your cogset/rings last 20,000km. But you'd have paid for a new chain every week.

127.5mm is the sensible tipping point, beyond which the cost of new chains is eclipsed by accelerated wear on everything.

I get your argument WRT power loss due to chain wear, but can't find any easily-spotted science to equate chain wear with power loss. I *can* find lots on cog size vs. efficiency - a larger cog is considerably more efficient - I'm guessing needs paring with a larger chainring. Get outta that 11T  1

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ajmarshal1 | 9 years ago
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I'd rather change a £30 chain four times a year than my Super Record cassette twice.

If you change your chain early enough cassettes last long enough to ride to the moon and back.

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MT63 | 9 years ago
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Oh! As ever thanks for all the info and advice.

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MT63 | 9 years ago
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To be honest I went for the run the chain and cassette and let them wear out together approach. I was told the chain was nearing replacement about a year ago and I have run it since then without any problems. It was only when it snapped recently that I thought I would replace it. However when the new 'Good bike' build is complete I think I will be keeping a much closer eye on wear of the more expensive components and going for a 'stitch in time' approach.

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crikey | 9 years ago
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I run a chain and cassette together until they die or it gets embarrassing to tell people how many years old they are. The cassette and chain on my training bike have done 3 years so far, including doing the 3 Peaks cyclocross twice. When the shifting gets a bit ropy, I change the cables and it all works again.

You can get all dedicated about chain wear or you can accept that things wear out together and it's up to you when to replace them.

As noted above, as the cassette ages, the chain wear accelerates which I would take to mean that using new chains on part worn cassettes is sub-optimal in terms of efficiency...

Financially there is no question that using a chain and cassette together is far less expensive than changing chains. In performance terms I'm sure some will insist it's worth it, but I don't think it is.

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KiwiMike replied to crikey | 9 years ago
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crikey wrote:

As noted above, as the cassette ages, the chain wear accelerates which I would take to mean that using new chains on part worn cassettes is sub-optimal in terms of efficiency...

Financially there is no question that using a chain and cassette together is far less expensive than changing chains. In performance terms I'm sure some will insist it's worth it, but I don't think it is.

If you simply run 1:1, once you get beyond 128mm for 5 links the wear will accelerate quickly, and you will strike shifting/slipping problems much sooner than had you replaced the chain at 127.5mm. At that point you have no option but to replace everything or run it into the ground as a collective, because any new chain, cogset or ring will be knackered by the rest of the drivetrain very quickly.

So you might only get 5-6000km out of a cogset (Tiagra 10spd list £25, average-spec chain £10) instead of spending just £10 on a chain and having the cogset continue to live on and shift cleanly.

Oh, and your chainrings (Tiagra £20-£27 each) will be knackered much quicker too. Another rule of thumb is to replace chainrings the same time as cogsets.

If you've gone 10,000km between cogsets, spending circa £90 on a new cogset, chainrings and chain plus another £30 on three intermediary chains means you've done 10,000 trouble-free km for £120 all-up.

Much more cost-effective than doing cogset, chain and probably rings too, twice over (~£180 - plus shifting/skipping towards end of life).

The wisdom of changing chains once beyond 127.5mm is born out of years of wisdom* and cost-effectiveness.

* not mine - Saint Sheldon Brown et al

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KiwiMike | 9 years ago
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Spend £8 on a cheap set of digital calipers.

Measure your chain over 5 full links. New it will be exactly 127mm. When it gets to 127.5mm, think about replacing soon. If you let it get to 128mm, your cogset is probably stuffed as well.

I'm now onto my 4th KMC X9.93 chain (never paid more than £10) after about 10,000KM (Tiagra cogset)

Chain wear before hitting 127.5mm, in order from new:

3,600km
3,200km
1,900km
1,300km (more than half-worn)

As you can see, as the cogset wears the chainwear accelerates. When this 4th chain reaches 127.5 I'll probably get a new cogset as well. And BB. And chainrings. and wheel bearings.

All this pretty much aligns with the rule of thumb of 3 chains to a cogset - if you catch the wear in time.

Noting that I have never had a skipped chain. Ever.

Some of the posters above seem to be erring on the side of uber-cautious, to their expense. The marginal gain of a slightly less-worn chain is probably up there with not having a beard or waxing your sunglasses for improved aerodynamics. Just keep it clean.

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Flying Scot | 9 years ago
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Tyres are indeed a good measure of chain replacement, I get about 2000 miles from a chain and if you've done tyres before a chain, have a second check.

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Jimmy Ray Will | 9 years ago
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My approach:

In season I'll change chains before any major season targets, or reaching my training peak, or at worst every two months.

Doesn't matter the mileage etc. its a time thing, so that I always have a spiffing good chain for the most important events.

This generally means I'll use five chains between March and the end of September.

This also means that I have five semi worn chains knocking about, which I will then stick on the training bike, changing them every 4 weeks or so throughout the winter.

Generally this means that the racing cassette simply doesn't wear out, or at least I'll get 2 - 3 seasons out of it, and so I just have to budget for 5x chains and a training cassette every year... ~£160.

Chains are consumables that need to be replaced more regularly than tyres in my experience.

A worn chain absorbs the same amount of power as a rubbing rear brake (~20 watts or 1/2mph in real terms) so its worth investing in.

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Shades | 9 years ago
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I've learn't how to change chains, cassettes and middle chain rings, and have adopted the 'change the chain at 0.75' approach. The other thing I do is always give my chain a clean if it gets a good soaking (normally it's the commuter bike). I have my GT85, lube and cloths near the bikes so it's a quick job after a ride. I'm getting a lot more miles out of a chain than I used to. Unless it's properly wet I've never been a fan of wet lube as it attracts the muck; I'm using juice lube dry/moist which seems to be doing well in the winter commuting conditions. Won't outlast a soaking but then I clean and re-lube anyway.

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le Bidon | 9 years ago
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I replace my chain and cassette together roughly every 4,000 miles - seems to work well for me. Though I may start changing my chain every 1,000 miles or so. Either way, definitely the cassette.

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Tinternet_tim | 9 years ago
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I'm with Aj on this one. If I change my cassette everytime I change my chain I'd be skint (exaggeration, but you get the idea).
I've got a Shimano DA rear cassette on my good bike and there is no way I'll replace that every 500-1000 miles.

I've had the same issue in the past with my commute bike after changing the chain. I ended up changing cable and cable outer and the gears worked perfectly. I'd be inclined to give that a go first as much cheaper option before shelling out on a cassette.

Out of interest, how many miles has the cassette done and when did you last change cables and outers?

Just for info, my commute bike is a little neglected in terms of replacing expensive components, but it's well maintained. I'm still on my first cassette and the shifting isn't too bad....it's currently at about 9,000 miles. I'll probably finally replace it once I get through the winter.

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Bazza155 | 9 years ago
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Cassette should always be replaced when replacing the chain.

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ajmarshal1 replied to Bazza155 | 9 years ago
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Bazza155 wrote:

Cassette should always be replaced when replacing the chain.

Disagree.

Saying you absolutely have to change both at the same time is a bike shop falsehood designed to get you to part with your cash. Inspect the cassette by all means but if there are no signs of significant wear, keep it on.

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jacknorell replied to Bazza155 | 9 years ago
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Bazza155 wrote:

Cassette should always be replaced when replacing the chain.

Not at all. Replace chain before it's critical (after 0.5 on a measuring device but before 0.75, using the Park Tools one) and it should last 3x chains. Chainrings should last even longer.

The OP's cassette is shot though, and with that sort of slippage it's probably worth looking at the chainrings too  2

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Flying Scot | 9 years ago
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Yes, new cassette required.

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Poptart242 | 9 years ago
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Almost definitely the cassette, as they wear along with the chain, especially in whatever are your favourite cogs.

Had the same issue myself in the summer. Quick swap out for a new cassette and all was good again.

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