Customising a Shimano HG50 Tiagra/Deore cassette

I’ve never been able to push a really big gear; anything much over 100″ is not much use to me. There must be plenty of people who can as, for instance, most off-the-peg ‘sportive’ bikes – a growing market these days – come with 12T or even 11T as the smallest rear sprocket. But paired with a large chainring of 50T or more this gives a top gear which, for me, is redundant.

Shimano CS-HG50 Deore and Tiagra cassettes with HG53 chain. At the time of writing available for less than £50 online including delivery.

My latest bike wasn’t quite off-the-peg: most of the components were swapped on to a 51cm Kinesis Racelight T2 2010 frame from a 54cm Ridgeback Horizon for delivery on Chrismas Eve. I am not going to blame anyone else for my newest bike having a few compromises. And I should have pressed the bike shop for a woman’s saddle (the Ridgeback-branded components were replaced with a range of others) so that Mrs Bailey might use the bike in the summer. By which time I would have broken in the Brooks B17 standard saddle she bought me for Christmas, and put it on the Ridgeback Panorama I hoped to get in the summer. Well, plans change and I’m unlikely to get another bike this year. Instead I’ve slightly adapted this ‘winter training bike’ Kinesis in to a light tourer/Audax bike. I’ve added a pannier rack for a rack bag and a week ago I fastened on the fittings for a handlebar bag. But the most significant change has been to the rear cassette. I don’t think compromise is the right word here. No, customise is the right word. This is an account of the simple steps required to swap a Shimano Tiagra 11-25 HG50 cassette for a Shimano Deore/Tiagra custom 13-34 cassette.

My original Tiagra cassette went like this: 11/12/13/15/17/19/21/23/25. The two biggest gears were bigger than anything I was able to push with the 50T chainring even on long descents. And at the other end the 30T inner ring on my Sora triple chainset gave me a gear that let me manage the biggest hills locally, but I didn’t feel I would comfortably cope with on longer, steeper hills, say, during day rides in the Yorkshire Dales carrying the gear I like to take with me. My Sora triple is a standard 50/39/30.

After a few calculations on the Tiagra and Deore HG50 cassettes available for me to buy online I settled on these two:

Tiagra 13/14/15/16/17/19/21/23/25
Deore 11/13/15/17/20/23/26/30/34

Broken up they would become 13/15/17/19/21/23/26/30/34

Apart from at the very top end – which I don’t use much anyway – there are no big jumps. And now when I’m using the big chainring I can make use of the 21T sprocket (giving me my preferred option of an inch gear in the mid-sixties) that wasn’t previously available to me from the large chainring.

The six largest sprockets on a Shimano HG cassette are held together by retaining pins. They will need to be removed.

After drilling out or grinding off the heads of the retaining pins they will come out easily. I used an automatic centre punch, but be careful that there are no burrs left on the edges of the rivet head or you may break the plastic spacers. [Edit: an alternative method is to tap out the pins from the small sprocket side with a hammer and centre punch]

Taking off the existing cassette requires a chain whip and a locknut tool.

Slot the new sprockets and spacers on to the freehub. HG sprockets will only fit in one position because of the splines on the freehub body. If you break up two cassettes to customise your gearing some of the functionality of the HyperGlide system will be lost (the ramped edges that aid with downshifts will no longer be in synch). In practice I haven’t found this to be a concern.

Reuse the retaining pins if you wish. However, they are mainly for convenience during initial assembly, and your locknut is there to keep the cassette in place. Ideally, you should use a torque wrench to tighten the locknut.

If you use a large rear sprocket as big as my 34T, you may need to change the rear derailleur. I had a spare Deore mech, which can be picked up online for about £25. With 50/39/30 chainrings and 13-34 cassette I have a range of gears from about 104” to 24”.

My Kinesis Racelight T2 2010. I had, briefly, considered replacing the chainset with a MTB version. However, there are compatibility issues with STI levers and mountain bike chainsets and front derailleurs.

I’ve had to shrug off comments from sixty-something blokes in my local group; two about being able to get up brick walls and another about dinner plates. I’m not bothered. At the moment I’m neither fit enough nor light enough to cope with really steep hills without the option of a couple of gears below 30”.

My original cassette gave me a top gear of approximately 124″ and a bottom gear of 32″, a difference of 92″. My custom cassette has a top gear of 104″ and a bottom gear of 24″, a difference of 80″. So not only do I have narrower ratios between gears, I can now make use of them all.