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PostPosted: Wed Jun 11, 2008 6:57 am 
Anglian Deputy AEC
Anglian Deputy AEC
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Location: Livin' in a dust bowl
I have a 2007 Trek SL1000 cheapo road bike, double front chain rings 39 & 53T - 8 speed SRAM cassette 12-23T - Tiagra short cage rear mech.

I am doing the London to Brighton ride on Sunday and want to ride up Ditchling Beacon without stopping. Could I fit an 8 speed XT 11-32T cassette without too much hassle or am I facing the fact of getting off and walking when my knees finally crumble halfway up the final climb?


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PostPosted: Wed Jun 11, 2008 12:21 pm 
Old School Grand Master
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The Tiagra mech may struggle with the 32. Try it, but you might need to use an mtb mech, or limit yourself to a 28-30t top sprocket.

You'll probably need a longer chain too, of course.


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PostPosted: Wed Jun 11, 2008 5:22 pm 
Gold Trader
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The Tiagra mech will die if you try to run a 32T on it.

Unless it's long cage don't put more than 28 on.

Shimano tech support is my 9-5 job.


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PostPosted: Wed Jun 11, 2008 6:11 pm 
Old School Grand Master
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dbmtb wrote:
The Tiagra mech will die if you try to run a 32T on it.

Unless it's long cage don't put more than 28 on.

I've had a short cage 105 (5500) clear a 32t - it took a bit of playing with chain length and b-tension, but there's enough variation in axle-to-hanger position that it's impossible to say definitively what the biggest possible sprocket is without trying. If there isn't clearance, it'll be obvious in the workstand. No mechs need die.

That said, the simplest solution is probably to fit an mtb mech along with the cassette.

Quote:
Shimano tech support is my 9-5 job.

Shimano mech tech specs are often conservative, and making things work together that shouldn't is my hobby.


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PostPosted: Wed Jun 11, 2008 7:00 pm 
rider | rBoTM Winner
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I used to run a short cage Shimano mech with a 32 on my 'cross bike and it worked - but with some 'fiddling' with chain length etc. Didn't work with the big ring though :lol:

I think it was 14-32 x 48/34. Get up virtually anything on a 'cross course with that - when I was fit!


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PostPosted: Wed Jun 11, 2008 7:35 pm 
retrobike rider
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You'll have a shagging awful time of it with all the extra chain and new mech ( old short one won't work* ). Get a 12-28 block and chain and go as far as you can.


* As I learnt recently as team race mechanic; please feel free to ignore my advice but call me when you explode so I may turn up with a flask of tea and gloat. :lol:


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PostPosted: Thu Jun 12, 2008 7:00 am 
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Agency_Scum wrote:
You'll have a shagging awful time of it with all the extra chain and new mech.

Why?


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PostPosted: Thu Jun 12, 2008 9:18 am 
retrobike rider
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The system will work ( just ), but the wear-rate will be ferocious; you could measure it in days instead of months with your standard pattern of gear changing. Shimano love slick changes and longevity so design their systems to within tight tolerances inside certain matches of mech to cassette.
Hey, don't believe me. It's more fun finding out! :lol:


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PostPosted: Thu Jun 12, 2008 9:29 am 
Old School Grand Master
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Agency_Scum wrote:
The system will work ( just ), but the wear-rate will be ferocious;

Can you explain why there should be more wear? Just to be sure we're on the same page, we're talking about a road double up front with an mtb mech and cassette at the rear, right?

Quote:
Hey, don't believe me. It's more fun finding out! :lol:

The thing is that I don't believe you, because I've run mixed systems like that for thousands upon thousands of miles without any problems at all. And I can't figure out why someone who claims to have done the same would have had the problems you claim to have had.


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PostPosted: Thu Jun 12, 2008 9:38 am 
retrobike rider
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Ah, thick twit alert, I thought he was doing it with the itsy-bitsy short-arse road mech. :roll:
Like that it'll be fine.
I'm off for a cuppa and a scone.


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