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PostPosted: Thu Aug 02, 2012 1:12 pm 
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Pondering front mech designs (sad but true) can anyone help me debunk the following truisms?

1) Bottom swing is the original design of front mech, and pretty much all road bikes still have them, even those with triple chainsets

2) Top swing was originally developed to help with the band placement on full suss bikes, and also found favour on bikes with short seat tubes especially if one wishes to avoid the bottle cage bosses getting in the way of the mech's band around seat tube

3) Bottom swing is more robust and shifts better

4) Bottom swing mechs look nicer, and are easier to clean!

5) Bottom swing mechs allow the cage to sit further inward than a top swing, by as much as 8-10mm


Finally an actual question... which swing type (presuming I have two mechs that both suit my MTB frame ie correct clamp size and pull type) would work better on a wide ratio chainset - 22/36/48 - and be less likely to cause any rub while in the granny ring? Based on truism # 5) I'm thinking a bottom swing... do front mechs have capacity ratings like rear mechs? :?


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PostPosted: Thu Aug 02, 2012 1:44 pm 
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I have a bottom swing on my modern and top swings on everything that's more than 5 years old. From my experience, there's no reason to prefer one over the other, except for the position of bottle cage bosses an/or the rear end design of a full suspension bike.

22/36/48? That's a 26 teeth difference :shock: .
Keep in mind that modern long-cage rear mechs usually have a 43 teeth capacity, so with that difference at the front you can only have a 17 teeth difference on the rear end. (11-28, 13-30 etc). You'd better be building a roadgoing MTB that has the granny on there for emergencies, because that front gearing basically limits you to a road cassette.

Sure, you can put a modern MTB cassette on there, but in that case you'll have to think about almost every shift to avoid accidentally getting it wrong and wrecking the mech, chain and lord knows what else.


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PostPosted: Thu Aug 02, 2012 3:38 pm 
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Raging_Bulls wrote:
I have a bottom swing on my modern and top swings on everything that's more than 5 years old. From my experience, there's no reason to prefer one over the other, except for the position of bottle cage bosses an/or the rear end design of a full suspension bike.

22/36/48? That's a 26 teeth difference :shock: .
Keep in mind that modern long-cage rear mechs usually have a 43 teeth capacity, so with that difference at the front you can only have a 17 teeth difference on the rear end. (11-28, 13-30 etc). You'd better be building a roadgoing MTB that has the granny on there for emergencies, because that front gearing basically limits you to a road cassette.

Sure, you can put a modern MTB cassette on there, but in that case you'll have to think about almost every shift to avoid accidentally getting it wrong and wrecking the mech, chain and lord knows what else.


Don't worry, the granny is only there for emergencies!

I take your point - nonsense IMO :wink: but I do observe correct shifting methods (ie only biggest rears on the granny and smallest rears on the outer) and my outer is 'only' 4-6 teeth bigger than stock, also using the chainring set-up in conjunction with a modern-ish M580 LX rear mech that has a slightly longer cage than my old M750 :wink:

RM capacities are somewhat conservative for obvious reasons, ie you'd be surprised what a mech can do so long as you don't run big to big (why would you!?), such as a short cage M750 XT will run 38 capacity IME

Anyway, the bike runs really well believe it or not - 48/36/22 and 11-34! reason I'm pondering is that I may go back to flats from drops so considering which FM to choose. FWIW, the bike is a rigid 29er, about as versatile as you can get hence the super wide gears.


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PostPosted: Fri Aug 03, 2012 7:37 am 
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number 1) is true, as for the other questions, I have no idea... Top swing mechs are fugly, in my opinion!

edit: I said top pull, I meant top swing!


Last edited by foz on Fri Aug 03, 2012 8:12 am, edited 1 time in total.

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PostPosted: Fri Aug 03, 2012 8:08 am 
South East Deputy AEC
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got any pics up rats?


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PostPosted: Fri Aug 03, 2012 10:29 am 
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BobCatMax wrote:
got any pics up rats?


of the bike in question?


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PostPosted: Fri Aug 03, 2012 10:43 am 
South East Deputy AEC
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Si, si Baroné


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PostPosted: Fri Aug 03, 2012 10:54 am 
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BobCatMax wrote:
Si, si Baroné


this is before I swapped out the rear mech to the m580 with it's super long cage, front mech is an Ultegra triple via a DMR Mech Verter

Image


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