Non-retro gear drivetrain advice please

Agency_Scum":2lsaqy9s said:
Ah, thick twit alert, I thought he was doing it with the itsy-bitsy short-arse road mech. :roll:

"2007 Trek SL1000 cheapo road bike, double front chain rings 39 & 53T - 8 speed SRAM cassette 12-23T - Tiagra short cage rear mech. "

There's nothing to misunderstand there Agency Scum.

I think it's One-eyed Jim read it wrong. Not you.
 
one-eyed_jim":2arndbru said:
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?

Errr. no.

Tiagra short-cage is a road mech. Not to be used with more than 27T.
 
dbmtb":2xjriu4h said:
one-eyed_jim":2xjriu4h said:
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?
Errr. no.

Tiagra short-cage is a road mech. Not to be used with more than 27T.
I know that Tiagra is a road group, as is clear from my earlier replies.

REKI says he has a Tiagra short cage and wants to run a 32t sprocket. I replied that it might work (as a 105 5500 - a short cage road mech - has worked for me with a 32 in the past) but he may need to use an mtb rear mech and a longer chain, or a smaller biggest sprocket than 32t.

Agency Scum says:

You'll have a shagging awful time of it with all the extra chain and new mech
Note, the *new* mech. Then:

old short one won't work
So the context of his remark seemed to me to be that he didn't think an mtb mech (because you wouldn't change one short cage road mech for another) would work well. I wasn't sure that was what he meant, hence my check.

In any case, increased wear isn't an issue: either the mech clears the sprocket or it doesn't. That depends on the axle-hanger dimension.
 
one-eyed_jim":1xthinrt said:
REKI says he has a Tiagra short cage and wants to run a 32t sprocket. I replied that it might work (as a 105 5500 - a short cage road mech - has worked for me with a 32 in the past) but he may need to use an mtb rear mech and a longer chain, or a smaller biggest sprocket than 32t.

In any case, increased wear isn't an issue: either the mech clears the sprocket or it doesn't. That depends on the axle-hanger dimension.

On these points we agree.

At the end of the day - if the guy wants to be sure that his kit is covered by warranty and product liablility - then the only sure way, is to follow manufacturer's recommendations.

"Someone on an internet forum told me it might work" is unfortunately not going to cut any ice with the warranty department, and any injury claims compensation if it all goes pear shaped.
 
dbmtb":1lvjug7y said:
At the end of the day - if the guy wants to be sure that his kit is covered by warranty and product liablility - then the only sure way, is to follow manufacturer's recommendations.
... and buy from an authorized dealer and have the components fitted by a Shimano certified mechanic?

I understand why Shimano publishes the specs it does, and I understand why they're conservative. If product manager A orders 1000 of derailleur B he wants to know they're going to bolt right on and work with cassette C - no fussing with chain length or b-tension. Shimano have to guarantee that. That's not REKI's case - he wants to put together a special system for a special ride, and wants to know what he might get away with.

"Someone on an internet forum told me it might work" is unfortunately not going to cut any ice with the warranty department, and any injury claims compensation if it all goes pear shaped.
That's true. But anyone who wants to know the official, straight-down-the-line Shimano spec can go to the Shimano website and read it off a chart. Anyone asking questions on an internet forum gets internet forum answers - things that work that aren't supposed to, a mix of bad advice and good, experience and hearsay.

If we'd all followed Shimano spec, we'd never have found the hidden click in our XT thumbshifters or put Ultegra freehub bodies on our XT hubs. Surely that's all part of what a forum like this is about.

Anyway, it's late. Let's join Agency Scum for an Ovaltine.
 
yawn.... tired after my shift so wont go into it too much....

heres my then 8spd commuter with very short cage mech (XT/ 105 Hybrid), 53 front, 32 rear, long chain and a GING tensioner - works a treat.... does 9spd as well
 

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