New Cassette

[potsy]

And as if by magic a 15% off voucher from Wiggle arrives into my inbox

 

[Garz]

Ahhaaaaaa, well in that case a £40 cassette becomes £34!

 

[MacB]

Potsy, most cranksets have removable rings, for a triple the outer two would be held together by the same chainring bolt and then the inner ring normally has seperate bolts attaching it to the spider. A lot of people have replaced an inner with a smaller ring, it's very easy to do. The limitations would be around the bottom of the front mech as the chain will be lower the smaller the ring. I think it's 2mm per tooth so replacing a 30t with a 24t would require you currently had a little over 12mm between chain and FD when in small ring. But you don't have to go as low a 24t, that's just the lower limit for a road triple(74 BCD ring).

I was just thinking of the cheapest way to give lower gearing without sacrificing a tightish spread. As an example you could use an 11-23 cassette and, with a 24t inner it would still give you a low gear of 27 inches, compared to 34 inches for a 30x23. I'm assuming that you generally ride in the middle ring and the inner only gets used for the silly stuff. Or you could go with a 26t inner and a 12-25 for a low of 27 inches again. Here's one:-

http://www.spacycles.co.uk/products.php?plid=m2b0s149p244

steel inner ring for £7, take your pick from 24-36t. Your front mech should care about gap from middle to outer, in teeth, inner to middle shouldn't matter other than the physical clearance of the chain on the bottom of the mech. Downshifts to the inner would be fine and upshifts probably a bit more agricultural.

If you don't have a crankset with replaceable rings then you'll need to replace the whole thing at some point, just make sure you get one with replaceable rings next time.

 

[Garz]

Apart from that excellent advice from MacB, I would not waste the 15% voucher on a £7 purchase though! (send it my way)

 

[potsy]

Apart from that excellent advice from MacB, I would not waste the 15% voucher on a £7 purchase though! (send it my way)

Great advice from MaccyB again, he has now confused me with the BCD measurements though, as far as I knew I had a 130mm BCD now I'm not so sure after looking at all the different options

I think looking at my crankset I can replace the rings so that might be another option instead of a new one. as you guess the middle ring is used 90% of the time so might look to replace that and get a smaller inner, I would probably go for the 26t inner combined with the 12-26 cassette, I like the sound of agricultural gear changes you've obviously seen me ride

The voucher has been spent towards a new pair of bib shorts Garz, I only have one pair which I wear whenever they are clean as they are a lot comfier than my other cycling shorts, I'd been thinking of getting them anyway so it was a timely voucher

Still waiting for a reply to my price match request, but will probably go with the 12-26 for now with a new chain.

 

[PpPete]

Shimano triples have a 130mm BCD for the outer and middle rings. The inner has it's own separate BCD of 74mm.

Shift from 26T to 38T is not too agricultural on mine !

 

[MacB]

I do wonder at the way triples are sold, you're getting a granny ring anyway, and all the stick that comes with it, so why not make the granny ring as helpful as possible? If you need it then as low as you can go makes sense, if you don't need it then the size of the ring doesn't matter a damn to you.

Let us know how you get on Potsy

 

[potsy]

I do wonder at the way triples are sold, you're getting a granny ring anyway, and all the stick that comes with it, so why not make the granny ring as helpful as possible? If you need it then as low as you can go makes sense, if you don't need it then the size of the ring doesn't matter a damn to you.

Let us know how you get on Potsy

I'm not worried about being seen in the granny ring Mac, had a good look at that site you linked to and have decided to get one probably a 28, going off Sheldons site that would take my current low gear of 32.4 down to 30.2, or if I do go for the 12-26 cassette even further down to 29.1, I'll probably get a middle ring too as I'm sure mine must be ready for changing soon as I'm hardly ever out of it in normal riding

Thanks for the help mate.

 

[HLaB]

A bit OT, I ordered a new cassette tonight (10 spd though) the 105, 12-25 which I've got is discontinued so I went with the almost identical 11-25, I was quite surprised you also get in a 11-28 good to know for the future.

 

[MacB]

looking at the comparisons, and assuming you stick to a 39t middle then you're getting(with 23mm tyres) with a 12-26:-

39t = 39.4 - 44.6 - 48.8 - 53.9 - 60.3 - 68.3 - 73.2 - 78.8 - 85.4
30t = 30.3 - 34.3 - 37.5 - 41.5 - 46.4 - 52.6 - 56.3 - 60.6 - 65.7
28t = 28.3 - 32.0 - 35.0 - 38.7 - 43.3 - 49.1 - 52.6 - 56.6 - 61.3
26t = 26.3 - 29.7 - 32.5 - 36.0 - 40.2 - 45.6 - 48.8 - 52.6 - 56.9
24t = 24.3 - 27.4 - 30.0 - 33.2 - 37.1 - 42.0 - 45.1 - 48.5 - 52.6

the ones I've highlighted are the point, on each inner ring, at which the gearing exceeds that of the bottom of the middle ring. That assumes you use all 9 gears, if you avoid the two extremes then they all chunk across one.

My understanding is that people will flick between middle and outer of a triple, or both rings on a double/compact, to maintain tempo, get the gear they want and avoid poor chainlines. But I've never heard of people doing this with middle and inner on a triple. Looking at the 30t above you've got 3 distinctly lower gears and the rest, barring maybe the 56.3, are so closely duplicated by the 39t ring as to be useless. Obviously the lower you go, inner ring wise, then the more additional distinct gears you get.

This isn't really about your choice now Potsy, it's more me just puzzling over the stock offerings on triples. The whole idea of a triple is to give more gearing options. Whether that's to get ultra low gears for touring or to give a low enough gear for general riding, while still allowing use of a close ratio cassette, is immaterial. Logic would indicate that the smallest inner ring, that works with a given setup, would be the best choice. Excepting the concept of someone flicking between inner and middle I can't think of any reason not to maximise the lower gears on offer.

 

[RecordAceFromNew]

This isn't really about your choice now Potsy, it's more me just puzzling over the stock offerings on triples. The whole idea of a triple is to give more gearing options. Whether that's to get ultra low gears for touring or to give a low enough gear for general riding, while still allowing use of a close ratio cassette, is immaterial. Logic would indicate that the smallest inner ring, that works with a given setup, would be the best choice. Excepting the concept of someone flicking between inner and middle I can't think of any reason not to maximise the lower gears on offer.

Like most things, there is a need to compromise, I think:
1) The rear mech has a wrap range limit, which has to be shared between the chainset and cassette.
2) As the difference between the small and middle chain ring becomes larger, the shift from the small to the middle becomes harder and harder (and more "agricultural") - this is the most difficult front shift in any case because the cage is the furthest away from the ring. Rear shifts are practically always quicker and sweeter than front shifts.
3) As the small chain ring gets smaller, e.g. the 24T in this case from my back of an envelope calculation - haven't checked the others, the chain will likely clash with the middle ring when it is on small front and back
4) The chain can/will drag on the front mech's tail when the front mech's range, which is usually 20T or 22T, is exceeded again on small/small.

I do appreciate one might consider 3) and 4) irrelevant because they are not "sensible" ratios, and these clashes are not as drastic as using a short chain to extend a rear mech's wrap range since large/large is also not "sensible" (and which can have disastrous consequences), but they are still clashes.

Of course, in practice what determines what one should do also includes what is worn and what isn't and cost etc.

 

[potsy]

Right, one last question in case anyone is still reading this,
Once I put the new inner ring on 28t, do I need to make any further adjustments? Or is it a straight swap?
I'm assuming the extra tooth on the cassette means I need to make my new chain 1 link longer too?

Sorry that's 3 questions

Cassette and chain have arrived, missed the postie with my new chainring so should be re-delivered Saturday

 

[HLaB]

Right, one last question in case anyone is still reading this,
Once I put the new inner ring on 28t, do I need to make any further adjustments? Or is it a straight swap?
I'm assuming the extra tooth on the cassette means I need to make my new chain 1 link longer too?

Sorry that's 3 questions

Cassette and chain have arrived, missed the postie with my new chainring so should be re-delivered Saturday

I think it should be the same. I went the other way from a 34t cassette to a 32t cassette (lost 2 teeth) and Spandex advised me to keep my chain the same length and I had no problems
If you do want to be more thorough when I changed the same bike to a 30t cassette I used bike tutors guide and that seems to have been fine.

 

[PpPete]

I'd go with biketutor method every time

 

[potsy]

Cheers lads, I'll have a look at that before I fit it all on Saturday