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I have a specialized allez, probably 10 years old. A combination of 8 speed Claris and Sora kit. The Claris cranks say octalink on them. I have been given a friends old tiagra 4700 group (a triple). So...how do I work out which bottom bracket to use on the tiagra cranks?

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StraelGuy [1517 posts] 3 months ago
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Does the chainring side crank have a 24 mm diameter steel tube sticking out it? If it does, you want a Hollowtech II bottom bracket.

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gfcv [1 post] 3 months ago
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Simple answer to that would be “not sure, do I?”  Hopefully the picture shows it, but looks wider than 24mm to me

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huntswheelers [135 posts] 3 months ago
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4700 Tiagra has Hollowtech.... best BB is BBR60, it'll never give you any bother.....

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StraelGuy [1517 posts] 3 months ago
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Sorry for the confusion, I does meant the donor Tiagra crank have a 24 mm tube bonded into it? The picture looks like it could well be Octalink.

I have the BBR60 on two bikes and have never had a moment of bother with either of them, cheap as chips as well.

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John Stevenson [368 posts] 3 months ago
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Your Octalink cranks come in — essentially — three pieces: the two crank arms and an entirely separate bottom bracket unit that comprises the axle and bearings.

The equivalent parts of a Tiagra 4700 set are a right-hand crank with the axle permanently attached to it, a left-hand crank and two separate bearings.

If you haven't got the bearings, then you'll need some. The BBR60 105/Ultegra bearings everyone recommends are 16 quid from CRC.

You'll need a crank puller to get your Claris cranks off, plus an Octalink adapter