Author Topic: Front and Rear Derailleur Recommendations  (Read 562 times)

Front and Rear Derailleur Recommendations
« on: November 23, 2019, 05:50:25 pm »
I am planning a gear revamp, with a compact double 48-34, paired with a 12-36 rear cassette.

The previous set-up was a front triple 52-42-30, paired with a 12-27 cassette.

The old capacity was: front 22 + rear 15 = 37T.

The new capacity is: front 14 + rear 24 = 38T.

So overall capacity nearly the same, but made up VERY differently!

Will my old front and rear mechs work with the new set-up?

The biggest differences are front chainwheel dropping from 52T to 48T, and rear largest sprocket rising from 27T to 36T.

If you don't reckon they'll work, what would your recommendations be?


LittleWheelsandBig

  • Whimsy Rider
Re: Front and Rear Derailleur Recommendations
« Reply #1 on: November 23, 2019, 06:19:52 pm »
You don't say what your current derailleurs are. Some rear mechs can stretch to 36t cogs without modification, some need a Wolf Tooth or similar to cope with a 36t, some just have to be replaced with something else.
Wheel meet again, don't know where, don't know when...

Re: Front and Rear Derailleur Recommendations
« Reply #2 on: November 23, 2019, 06:20:44 pm »
I'll have a closer look when I get back to the bike (bits).

Re: Front and Rear Derailleur Recommendations
« Reply #3 on: November 23, 2019, 06:38:09 pm »
the old ratios sound like 3x10  campag. If so, the answer is most probably  'no'.  For many years long-arm campag mechs have had a large total capacity but have only a limited capacity for the largest sprocket, typically in the range 27-29.

You can try a hanger extender but the likely result is shifting that will be a bit below par on the smaller sprockets.

cheers

Re: Front and Rear Derailleur Recommendations
« Reply #4 on: November 27, 2019, 05:35:05 pm »
the old ratios sound like 3x10  campag. If so, the answer is most probably  'no'.  For many years long-arm campag mechs have had a large total capacity but have only a limited capacity for the largest sprocket, typically in the range 27-29.

You can try a hanger extender but the likely result is shifting that will be a bit below par on the smaller sprockets.

Yes, apart from very recent generations of Campagnolo 10-speed (which I think can go up to 30T), max officially supported sprocket size on the back was 29T with their 10-speed rear mechs - I can believe this is likely true in practice too, I have a medium cage 10-speed Chorus rear mech on my Mercian and there's really not a lot of clearance even with a 27T sprocket on the back (I'm running 12-27 and 50/34, but this is on a non-load carrying relatively lightweight road bike).

Either way, you'll certainly need a new front mech to be able shift a 48/34 nicely, if you've been running a front mech for a triple - the later 10-speed Campagnolo double mechs support both "standard" and "compact" chainring setups, though, and the Veloce ones can be had cheaply.

BTW which era of Campagnolo shifters are you using? The earlier ones (pre-2009-ish) aren't fully compatible with the more recent 10-speed rear mechs, due to weaker spring tension on the latter, but IMHO are still preferable to the newer nerfed "Powershift" shifters.
Old enough to know better, but young enough to do it anyway

Re: Front and Rear Derailleur Recommendations
« Reply #5 on: November 27, 2019, 05:43:11 pm »
You don't say what your current derailleurs are. Some rear mechs can stretch to 36t cogs without modification, some need a Wolf Tooth or similar to cope with a 36t, some just have to be replaced with something else.

Having located them in the parts box (the bike is currently stripped down for a minor repair, and for Argos to machine the BB faces), they are standard Shimano 105 mechs from the previous set-up of 52-42-30 front and 12-27 rear.  [edit] and dating from around 2002.

Re: Front and Rear Derailleur Recommendations
« Reply #6 on: November 27, 2019, 05:52:58 pm »
You don't say what your current derailleurs are. Some rear mechs can stretch to 36t cogs without modification, some need a Wolf Tooth or similar to cope with a 36t, some just have to be replaced with something else.

Having located them in the parts box (the bike is currently stripped down for a minor repair, and for Argos to machine the BB faces), they are standard Shimano 105 mechs from the previous set-up of 52-42-30 front and 12-27 rear.  [edit] and dating from around 2002.

In that case feel free to ignore wot I wrote, although still think you're likely to need a new front mech, at least, to run a compact chainring setup
Old enough to know better, but young enough to do it anyway

Torslanda

  • Professional Gobshite
  • Just a tart for retro kit . . .
    • John's Bikes
Re: Front and Rear Derailleur Recommendations
« Reply #7 on: December 03, 2019, 10:04:32 pm »
The 105 mech will not run 36 unless you can extend the hanger but an XT Shadow M772 will work with 9 or 10 speed and Tiagra 10 -> 4600/105 -> 5700/Ultegra -> 6700 shifters will match the cable pull. The front mech will need to be a double for clean shifting but can be operated with a triple shifter without too much trouble.

Let me know which shifters you will be using for a more detailed explanation.
VELOMANCER

Well that's the more blunt way of putting it but as usual he's dead right.

Re: Front and Rear Derailleur Recommendations
« Reply #8 on: December 04, 2019, 01:42:04 am »
105 mechs from around 2002?  Sounds like a 3x9 setup.  Are you thinking of 2x9 or wanting to use more sprockets at the back?

cheers

Re: Front and Rear Derailleur Recommendations
« Reply #9 on: December 04, 2019, 08:30:03 am »
Thanks for all the help so far.

Yes, it was originally a 3x9 set-up, and I'm not looking to increase the number of sprockets on the back.

Re: Front and Rear Derailleur Recommendations
« Reply #10 on: December 04, 2019, 08:30:58 am »
The 105 mech will not run 36 unless you can extend the hanger but an XT Shadow M772 will work with 9 or 10 speed and Tiagra 10 -> 4600/105 -> 5700/Ultegra -> 6700 shifters will match the cable pull. The front mech will need to be a double for clean shifting but can be operated with a triple shifter without too much trouble.

Let me know which shifters you will be using for a more detailed explanation.

Thanks, Mr T - I'll have a look at those.

Re: Front and Rear Derailleur Recommendations
« Reply #11 on: December 04, 2019, 11:01:28 am »
Thanks for all the help so far.

Yes, it was originally a 3x9 set-up, and I'm not looking to increase the number of sprockets on the back.

are you going to be happy with the larger gear ratio intervals that you will get with a 2x9 setup?

cheers

Re: Front and Rear Derailleur Recommendations
« Reply #12 on: December 04, 2019, 11:12:27 am »
Yes, I do a lot of my riding on fixed, so used to a wider cadence range, I suppose.  I would be using the set-up as two distinct ranges, rather than trying to achieve a seamless progression from 108 to 29 gear inches.

Torslanda

  • Professional Gobshite
  • Just a tart for retro kit . . .
    • John's Bikes
Re: Front and Rear Derailleur Recommendations
« Reply #13 on: December 04, 2019, 06:32:43 pm »
A Deore M591 rear mech would also work very well with your proposed setup.
VELOMANCER

Well that's the more blunt way of putting it but as usual he's dead right.

Re: Front and Rear Derailleur Recommendations
« Reply #14 on: December 04, 2019, 08:14:55 pm »
your old and new proposed gear ratios are compared here

http://ritzelrechner.de/?GR=DERS&KB=30,42,52&RZ=12,13,14,15,17,19,21,24,27&UF=2185&TF=90&SL=2.6&UN=MPH&DV=gearInches&GR2=DERS&KB2=34,48&RZ2=12,14,16,18,21,24,28,32,36&UF2=2185

I am surprised to see that there is very little duplication between the chainrings with the proposed new setup, but (for my tastes anyway) I'd far sooner that there was a ~67" gear that wasn't 34/14. I'd dislike using that gear (because it runs cross chained and uses small sprockets, so is doubly inefficient) and I'd find myself constantly swapping between 48/18 and 48/21 instead.

IIRC with that kind of cassette a 32-46 chainset works well for me.

cheers