Triple chain set advice please

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COYB
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Joined: 22 Jun 2019, 11:41pm

Triple chain set advice please

Postby COYB » 26 Feb 2020, 8:53pm

Advice needed please. I have a 24 speed Specialized Tricross and have decided to give it an overhaul. I've had the bike since new ( 2010 ) so its well overdue for some serious maintenance. I'm changing the 8 speed 13-26 cassette for the same spec and fitting a new chain. I'd also like to change the triple chain set chain set which is 52-42-30 and looks well worn. My question is: Would a 48-38-28 touring chain set make a huge difference to the bikes performance. Advice would be greatly appreciated.

Jamesh
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Joined: 2 Jan 2017, 5:56pm

Re: Triple chain set advice please

Postby Jamesh » 26 Feb 2020, 9:25pm

Not a lot in my opinion.

Your only dropping two teeth.

Better would be a larger cassette on the back say a 11-32? But then you will have bigger jumps between gears.

Cheers James

seph
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Re: Triple chain set advice please

Postby seph » 26 Feb 2020, 10:04pm

Yes, it will be fine. You may have to move the front derailleur down a smidge.

I’d stick with the 12/13 to 26 cassette. The smaller jumps between gears help to maintain a smooth cadence.

Look at the SRAM PG850 cassettes, 12-26. They’re about 100g lighter than the Shimano ones.

whoof
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Joined: 29 Apr 2014, 2:13pm

Re: Triple chain set advice please

Postby whoof » 26 Feb 2020, 10:26pm

The change in gearing is not very much.
Are all three chain rings worn? If it's a Shimano (inner 74 mm BCD middle/outer 130 mm BCD) one then you can get a 28 tooth replacement inner from Spa Cycles for £6

https://www.spacycles.co.uk/m2b0s185p0/ ... -Clearance

and a middle from 38 to 44 tooth for £14
https://www.spacycles.co.uk/m2b0s149p29 ... -44T-inner

Cheaper than a new chainset

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The utility cyclist
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Location: The first garden city

Re: Triple chain set advice please

Postby The utility cyclist » 26 Feb 2020, 10:50pm

If you're after one a have a new square taper Truvativ 48/38/28 for not very much.
But in answer to your question, it will no difference to the performance, just slightly change the upper and lower gearing.

Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Triple chain set advice please

Postby Brucey » 27 Feb 2020, 12:38am

not a big difference in the gearing

http://ritzelrechner.de/?GR=DERS&KB=28,38,48&RZ=13,14,15,17,19,21,23,26&UF=2170&TF=90&SL=2.6&UN=MPH&DV=gearInches&GR2=DERS&KB2=30,42,52&RZ2=13,14,15,17,19,21,23,26&UF2=2170

but you may find that a 'favourite gear ratio' is missing or different.

FWIW most standard cassettes have a 1T interval between the two smallest sprockets. Folk have different priorities of course but IMHO this is often 'a waste of a sprocket'. In any event cassettes about this ratio have 2T intervals between the middling sprockets.

If you do a lot of riding in one or two 'cruising' gears, then it is a good idea to take reasonable steps to ensure that

a) the chainring and sprocket are as large as possible to achieve those favoured ratios (so for example 52/19 is almost the same ratio as 48/17, but the former is inherently more efficient)
b) that the chainline in the favoured ratios is good (I.e.you are not running cross-chained) and
c) that you don't have to doubleshift or put up with an extreme chainline to be able to use the neighbouring ratios.

cheers
Last edited by Brucey on 27 Feb 2020, 2:01am, edited 2 times in total.
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Tigerbiten
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Re: Triple chain set advice please

Postby Tigerbiten » 27 Feb 2020, 1:40am

Going 52 -> 48 is a 10% drop so you'll lose your top gear, how useful is it to you ??
But 52/13 is 4:1 and 48/12 is also 4:1 so in theory if you shrink every sprocket by one tooth to a 12-25 cassette you would have the same gear ratios over the whole range with the new chainset.
Therein lies the problem, the 12-25 cassette looks likes it only shrinks the first two sprockets and the last one.
This will give you a nasty big jump 2-3 and a very small step 7-8.
If you want to keep the close ratios then 12-23 with the 23 replaced by a 24 will work better.

Luck .......... :D

De Sisti
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Joined: 17 Jun 2007, 6:03pm

Re: Triple chain set advice please

Postby De Sisti » 28 Feb 2020, 6:58am

Brucey wrote:not a big difference in the gearing
52/19 is almost the same ratio as 48/17, but the former is inherently more efficient)
cheers

Why do you think that is the case?

Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Triple chain set advice please

Postby Brucey » 28 Feb 2020, 9:30am

De Sisti wrote:
Brucey wrote:not a big difference in the gearing
52/19 is almost the same ratio as 48/17, but the former is inherently more efficient)
cheers

Why do you think that is the case?


It is because of chordal losses. Every good test that has ever been done on real transmissions has confirmed this. in this case there won't be a big difference but every mickle makes a muckle and all that; of course it can be a much bigger effect.

FWIW the effect is sufficiently powerful that it often overwhelms the extra losses through cross-chaining. This means that if (on a 2x11 transmission, say) you have a choice of cross-chaining on a large-large combination or a straighter chain run onto a small-small combination, often the former will be more efficient.

Friction facts published test results which showed that you only started to 'lose' with this strategy when using the very largest sprocket of all (and the worst possible cross chaining) on the 2x11 setup they tested.

Of course the optimal efficiency is when you have large chainring/sprocket and a perfect chainline too. Clever choice of chainrings and sprockets to suit a given rider will make this the case more of the time.

Larger chainrings/sprockets run smoother and last longer too. Arguably the only downsides to them are that

a) you need more capacity in the RD for any given %age rage of gearing and
b) they are a bit heavier

Regarding the weight increase, even a 0.5% increase in efficiency is enough to 'pay for' a lb or two weight increase, even on quite steep hills.

cheers
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COYB
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Joined: 22 Jun 2019, 11:41pm

Re: Triple chain set advice please

Postby COYB » 28 Feb 2020, 12:24pm

Many thanks for all the advice. The other reason, apart from worn parts, is my age. I'm 70 this year and cycling is very much a leisure cyclist now. I usually do short rides 10 or 20 miles, usually 3 times a week but hope to increase this to 100 miles a week. The route I usually cycle has a couple of long strength sapping hills and with the 8 speed I sometimes find myself wishing I had just one more lower rear. If ever it comes down to NO bike or an E Bike then it will have to be E Bike but hopefully not yet.

David9694
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Re: Triple chain set advice please

Postby David9694 » 28 Feb 2020, 6:16pm

You’re way off an E bike!! You wouldn’t be human if you didn’t sometimes wish you could be carried up the hill by some other means.

But that last post clinches it - I run a Stronglight chainset with the sort of rings you mention and I don’t miss “top gear” one little bit.

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531colin
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Re: Triple chain set advice please

Postby 531colin » 28 Feb 2020, 6:36pm

Your first post didn't come over as somebody who was actually looking for lower gears.
You can get lower gears using a chainset with smaller bolt circle diameter (BCD) . 110/74 BCD gets you 34T smallest middle ring and 24T smallest small ring; big ring chosen to suit your front mech.
24T instead of 30T is a noticeable difference , about 20% or 2 gears lower with a sort-of average gear spacing.

Brucey
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Re: Triple chain set advice please

Postby Brucey » 29 Feb 2020, 9:44am

COYB wrote:Many thanks for all the advice. The other reason, apart from worn parts, is my age. I'm 70 this year ……. The route I usually cycle has a couple of long strength sapping hills and with the 8 speed I sometimes find myself wishing I had just one more lower gear. ....


Upthread I noted that having 13-14-15 close-spaced ratios as in your present cassette is arguably 'a waste of a sprocket'. In the link below I compare the ratios you have at present with a notional 13-15-17-19-21-23-26-30 cassette. This is identical to the one you have at present except that the 14T is gone and a 30T is added.

http://ritzelrechner.de/?GR=DERS&KB=30,42,52&RZ=13,30,15,17,19,21,23,26&UF=2170&TF=90&SL=2.6&UN=MPH&DV=gearInches&GR2=DERS&KB2=30,42,52&RZ2=13,14,15,17,19,21,23,26&UF2=2170

provided the rear derailleur will cope with a 30T sprocket this (or similar) might be the easiest way to get lower gearing.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

slowster
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Joined: 7 Jul 2017, 10:37am

Re: Triple chain set advice please

Postby slowster » 29 Feb 2020, 11:54am

When cruising on the flat(ish) mid-ride, what gear are you in? More specifically, which chainring and roughly where on the cassette (bigger sprockets, middle sprockets or smaller sprockets)? The answer to that question should give you a good indication of whether 52/42 and your current cassette is optimal for you.

For example, if you are very comfortable riding in 42 x 17 or 19, then you probably either want to keep that combination on your bike or ensure that whatever chainset and cassette you replaced them with gave a similar gear with the chain somewhere in the middle of the cassette.

Conversely, if you routinely find yourself cross chaining on the flat - e.g. 42 x 23, 52 x 23 or 42 x 14/13 - then you should be considering what alternative chainring and/or cassette options will again give a similar gear with the chain somewhere in the middle of the cassette.

You can use the Ritzelrechner website to which Brucey has provide a link above to experiment with different chainring and/or cassette options and compare your current gearing with alternative options, in order to determine for yourself what combination is most likely to suit your needs and preferences.

The question of how best to get that extra bottom gear (or two) will depend somewhat on what you decide about what chainring(s) you decide you want for riding on the flat/shallow gradients. If you decide on a smaller outer/middle ring combination, then that will probably allow you to have a correspondingly smaller (or even more so) inner ring (with the front derailleur capacity likely to be the constraining factor, but possibly also the capacity of the rear derailleur). This is a somewhat iterative decision process: if you wanted to keep 52/42 chainrings, that would likely limit the reduction in size of the inner ring, and so you would need to consider alternative cassettes to get the extra lower gear(s).

As it happens, I have the same 13-26 cassette fitted to an old frame. I didn't want a wider cassette because I liked the small intervals between 17, 19, 21 and 23. I fitted a Spa RD2 triple with 48/38/26 rings. I would have preferred the TD2 triple with 46/36/24, but the frame required a braze on front mech and I doubted it would lower sufficiently for a 46 outer.

Currently your lowest two gears are 31" and 36". With a 26t inner they would be 27" and 31", and with 24t they would be 25" and 28". I can't see any reason to choose a 28t: fit the smallest you possibly can within the constraints of your derailleurs.

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The utility cyclist
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Re: Triple chain set advice please

Postby The utility cyclist » 29 Feb 2020, 12:59pm

Brucey wrote:
COYB wrote:Many thanks for all the advice. The other reason, apart from worn parts, is my age. I'm 70 this year ……. The route I usually cycle has a couple of long strength sapping hills and with the 8 speed I sometimes find myself wishing I had just one more lower gear. ....


Upthread I noted that having 13-14-15 close-spaced ratios as in your present cassette is arguably 'a waste of a sprocket'. In the link below I compare the ratios you have at present with a notional 13-15-17-19-21-23-26-30 cassette. This is identical to the one you have at present except that the 14T is gone and a 30T is added.

http://ritzelrechner.de/?GR=DERS&KB=30,42,52&RZ=13,30,15,17,19,21,23,26&UF=2170&TF=90&SL=2.6&UN=MPH&DV=gearInches&GR2=DERS&KB2=30,42,52&RZ2=13,14,15,17,19,21,23,26&UF2=2170

provided the rear derailleur will cope with a 30T sprocket this (or similar) might be the easiest way to get lower gearing.

cheers

From at least the 10 speed Shimano era onward the short cage rear derailleur's have been able to handle 30T, from personal use the 11 speed Ultegra and Dura Ace handle a 32T large sprocket without issue and large/large with an actual working capacity of 38T.

Campagnolo short cage users have said that a 3OT sprocket is fine (Campag have a 29T max anyway) and possibly even 32T on the older models, there's a topic on weight weenies that discussed this some while back that I ventured onto when mixing a Shimano cassette with campag spacers so i could continue using my 1990 Gitane Team replica with Campag and have a lower gear option.