lower gearing & shorter cranks-help.

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patmac
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lower gearing & shorter cranks-help.

Postby patmac » 17 Apr 2011, 4:54pm

Hoping someone with the know-how can advise with this. Due to illness hardly used my bike-GB compact audax-last year.
Just been out for a first run this year and I don't think my little legs are up to Surrey's short sharp hills anymore! Therefore I'm thinking about lowering the gearing to get me up those hills, and shortening the cranks at the same time to clear a bit of toe overlap which has always been in my mind as a potential problem, but which has only caught me out once, years ago, when the bike was new to me.
At the moment I've got Sora triple on the front,52/42/30, and 13-26 on the back.That big ring certainly gets the speed up, but I'm not so interested in speed now that I'm an old man, and though 30-26 gets me up the hills, just, I'm puffing and blowing a bit when I get there! My idea is to come down to 48/38/26 on the front, and replace the cassette with 11-32. If I get a Stronglight or Sugino chainset I can come down from 170 cranks to 165,Impact touring,or 160, Sugino, and relieve the toe overlap and make the ride that bit safer, and I believe more efficient, being only a shortarse, as I am! Would I then have to fit new chain and rear changer?
All help most wecome.

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gaz
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Re: lower gearing & shorter cranks-help.

Postby gaz » 17 Apr 2011, 5:19pm

If your rear mech is a Sora or from any other road group it's specification will not cope with a 32T cassette (in practice it might but it's not likely) and you'll need a MTB rear mech.

It would be wise to get a new chain, even if you can get away without it being any longer, as an old chain will wear the new cassette and chainrings faster than a new one.

You may face problems with the front indexing, reducing the chainring sizes takes the mech outside it's optimum range but you may well get away with it.

Leaving toe-overlap aside, ideal crank length should be in proportion to inside leg length rather than overall height, someone else will provide further details of the formula. Personally I prefer to ride 165 but I'm not uncomfortable on 170 or 175 for that matter.
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cycleruk
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Re: lower gearing & shorter cranks-help.

Postby cycleruk » 17 Apr 2011, 7:08pm

I went down from 170 to 165 cranks.
The bike "seemed" harder to ride. :?
The idea was that I would "spin" more with the shorter cranks, to help with the knees.
The cranks are now hanging up in the shed and the rings have been used as replacements on my 170's.

I altered my 13-26 cassette by swapping the two largest sprockets for a 24 & 28T which dropped the gearing from approximately 31" to 29".
The Sora (long cage) just copes with 28T but it has helped.
My next mod will be to try swapping the 30 for a 28T chainring which would give me a gearing of 27".
A gain of 13%.
Fitting a 32T cassette would give 25" - (19% gain.) but will need a new rear mech'.

If that helps. ( and my maths is right. :roll: )
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rualexander
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Re: lower gearing & shorter cranks-help.

Postby rualexander » 17 Apr 2011, 7:26pm

Bear in mind that going to shorter cranks effectively increases your gearing (due to the effect of shorter levers), so you need to think about that in your calculations of what chainrings/casstte you are changing to.
Although having said that, I didn't find it very noticeable when I dropped from 175mm cranks to 165mm when recovering from a knee injury.
I actually prefer the 165mm cranks now and have stuck with them.

reohn2
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Re: lower gearing & shorter cranks-help.

Postby reohn2 » 17 Apr 2011, 7:30pm

patmac
You don't say how short you are,as has been said above crank length is in proportion to leg length.
Whatever crank length you choose, initially I'd say go with 48-36-26 as there'll be less duplicated gears in the different chainrings with the existing cassette, this will give you a bottom gear of 26inch which is quite a bit lower than you're present 30x26=30inch.If you find your gearing is still too high then you could change the cassette,bearing in mind that anything over 28tooth biggest sprocket and you'll need an MTB rear mech to cope as road rear mechs can only handle upto 28 teeth usually.
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velorog
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Re: lower gearing & shorter cranks-help.

Postby velorog » 18 Apr 2011, 9:06pm

I am currently running a Sora rear mech with a 11-30t cassette. The centre to centre distance on the gear hanger is 35mm. If you have a similar hanger you should be able to get away with a 30t sprocket.

zoxed
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Re: lower gearing & shorter cranks-help.

Postby zoxed » 19 Apr 2011, 12:24pm

Firstly note that there are many theories about crank length, and I am not sure that any have been proven/disproven:
- 170mm is OK for everyone
- crank length should be proportional to leg length
- shorter cranks are better for your knees
- shorter cranks are more efficient, whatever your thigh length.

Last year I went from 170mm to 140mm and I am very happy so far, although I still have to get the gearing right. So far it looks like Sheldons "Gain Ratio" is correct: you have to gear down when you shorten your cranks. So if you want shorter cranks AND lower gears you will have to step down twice (if that makes sense !!).

After the switch my average cadence immediately went up 10, and is slowly climbing as I get more used to the new cranks.

Note that typically when you fit shorter cranks you would change the seat height at the same time, so that your leg is still straight-ish at the bottom (e.g. 170 to 140 would raise the seat 3cm). Unless you ride a recumbent this can mean it is harder to touch the ground when stationary, unless you have a custom frame made to compensate !

Synapse
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Re: lower gearing & shorter cranks-help.

Postby Synapse » 19 Apr 2011, 1:15pm

I was thinking the doing the same, lowering my gearing, to climb those steep hills. I have a double crankset Ultegra. One option that has been suggested was I use the new SRAM Apex cassette 12-32 and rear mech., to replace my 12-27, would that be compatible with the Shimano STI shifters? Another would be the Velo Orange 50.4bcd crankset with 46 & 30 chainrings.

andrew_s
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Re: lower gearing & shorter cranks-help.

Postby andrew_s » 19 Apr 2011, 2:05pm

reohn2 wrote:initially I'd say go with 48-36-26

recent Shimano triple front mechs have very deep inner plates, and require a 12T gap between middle and outer (unless you just have the outer plate further above the outer chainring).
You could also go for a 24T chainring. If you are going to use a granny ring, make it a proper one - you are only going to use it when riding up steep hills anyway.

willem jongman
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Re: lower gearing & shorter cranks-help.

Postby willem jongman » 19 Apr 2011, 8:43pm

The Sora triple crankset looks like it is for an older FD, given the 10t difference between middle and outer. If that is so you can fit smaller chainrings, down to 48-38-26 or even 48-38-24 (probably). Lower your FD accordingly. If you also want to fit shorter cranks because your current cranks are too long for you, you should go for 110 bcd cranks like the Sugino XD, as these will allow you to go down even lower: 46-36-24 is a common combination. So either way, a 24 t granny gear is feasible, and makes for quite a difference. The next step depends a bit on the cassette wear. If it is worn, I would replace it with a 28t largest cog (with a new chain). Chances are this will be enough, and it saves you buying a nee rear derailleur. If it is almost new, I would keep it, and only fit a new chain.
I hope this helps,
Willem

JEJV
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Re: lower gearing & shorter cranks-help.

Postby JEJV » 20 Apr 2011, 9:24pm

willem jongman wrote:The next step depends a bit on the cassette wear. If it is worn, I would replace it with a 28t largest cog (with a new chain).
Willem

If it isn't worn (or even if it is), you can get a 13-28 (13-14-15-17-19-21-24-28) from a 13-26 and a 11-32 cassette (11-13-15-18-21-24-28-32),
by taking the rivets out of a £10 Shimano (not SRAM) 11-32 cassette, and using the cogs that you want. Drilling the heads off the small-cog end of the rivets is easiest way to remove them.
Use the 21-24-28 from the MTB cassette.

You can then also make 13-32, if you prefer that: (13-15-17-19-21-24-28-32), but you'll need to leave the chain 3 half-links longer, and need an MTB rear derailleur (Acera:£15, Alivio £20).

If you don't use the top few cogs on the 13-26 much, you might as well have more lower gears.
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BigG
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Re: lower gearing & shorter cranks-help.

Postby BigG » 20 Apr 2011, 11:05pm

You cannot leave the chain 3 half links longer. It surely has to be 2 or 4, doesn't it?

snibgo
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Re: lower gearing & shorter cranks-help.

Postby snibgo » 20 Apr 2011, 11:07pm

You can get half-links for chains.

JEJV
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Re: lower gearing & shorter cranks-help.

Postby JEJV » 21 Apr 2011, 1:09pm

I just meant leave that much extra slack in the chain, rather than using half-links - normally I'd make the chain at least 1" (two half-links) longer than it needs to go round big front and big rear - but if I want to use a bigger cassette later, for every two extra teeth on the bigger cassette, I want to make sure I have an extra half-link of slack before I trim the chain. The rear mech will cope with an extra inch or two of chain - in this case we're probably talking about an MTB mech, and it's not being used near its capacity. Even with a (medium cage) road mech, it's only likely to be near slack in small/small.
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simon1
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Re: lower gearing & shorter cranks-help.

Postby simon1 » 21 Apr 2011, 7:58pm

Am trying to source cottered cranks for my short wife's town bike, a vintage Balmoral c. late 1960s. Currently 44 tooth chainring and 6 1/2" cranks. I fitted a contemporary SA 3 speed hub a couple of years ago, which was much appreciated, but I think she would like to lose the top gear and gain a new bottom gear! Her 'proper' bike is an Isla Luath 26 with a bodged-on 22t granny ring. She likes to cycle slowly and spin.