What RD for a 36 10-speed cassette?

[jamesofyorkshire]

I know this is the best place on-line for tech info having been on here for quite a few years....so here goes....

I want lower gearing on my flat-barred road bike. At the moment I have a Shimano road 10-speed Tiagra drive train , 34/50 compact, 30 cassette.

So anyway, I doubt I can go 34 or 36 with this RD....but I want to replace my present cassette with a 34 or 36. I don't think I can go down this road with Shimano as their 10-speed road/MTB stuff is NOT compatible, so I'm thinking to go with Sram.

Can I replace my current (30 Tiagra) cassette with a 34 or 36 Sram cassette? and if so, what Sram RD should I fit? AND will all this work OK with my Tiagra flat bar shifters? I don't understand the 'pull' on the shifters with Shimano but I understand that Sram is the same with road & MTB?

I don't like the idea of wider ratio cassette, I'd prefer a 30/46 chainset but these are not common, and expensive.....so I'll go with the cassette.

Just to put what kind of rider I am into perspective....I've been down in the Pyrenees for the last couple of months and been climbing every big 'Col' down here that's open (including Col de La Pierre St. Martin 5 times - the one that C. Froome gained time on - stage 10 in 2015 TdF). So I like climbing, and do a lot of it. I have been fortunate(?) enough to get a place on the Fred Whitton this year. I just want lower gears! I'd happily swap my 6 highest gears for an extra 6 lower gears....as would most aging MAMILS I guess. How often do we use the 11/12/13/14/15 - 50 ??????

Thanks for any help/info/suggestions.

[531colin]

46/30 chainset £60 at Spa, in the new CTC mag....http://forum.ctc.org.uk/viewtopic.php?f=5&t=103107&hilit=chainset&start=15

[Brucey]

if you go with the cassette, you want a 9s MTB mech (they come in 34T and 36T flavours, check the spec first). Plug and play with your 10s system.

NB a 10s shimano MTB mech will not do.

BTW you can make a custom cassette if you want to, so 13-36 or something like that; just takes a bit of fiddling around. Some canny blighters have been known to build these using two cassettes that contain duplicates of the most used sprockets, thus getting two cassettes' worth of wear out of them even though not all the sprockets are used, if you see what I mean.

cheers

[jamesofyorkshire]

I was expecting a reply from you Brucey...you've helped me before......

I'm not sure I follow you....is your advice referring to a Shimano RD? Or a Shimano 9-speed cassette?

[Brucey]

a 9s MTB mech is what I meant; it has the same shift ratio as a 10s road mech, so will work with a 10s cassette and 10s shifters. Lots of touring bikes run this setup.

From memory the older 9s mechs (eg RD-M591) go to 34T and the later 'shadow' ones go to 36T, but do check before you splash out.

cheers

[jamesofyorkshire]

OK. Thanks for clarifying that part......as for the cassette, does it matter is it's a Shimano or Sram?

.....AND....I don't get how a 9-speed indexed mech (RD) works with a 10-speed drive train?

[Brucey]

SRAM and shimano 10s cassettes are effectively interchangeable in terms of their fitment and spacing etc.

Its the sifter that does the indexing; rear mechs move an amount sideways when the cable is pulled a certain amount by the shifter. The ratio of the cable pull to the sideways movement is called 'the shift ratio' and is the same for 9s shimano (all) as shimano 10s road, so rear mechs are interchangeable, and the respective shifters pull different amounts of cable in proportion to the spacing of the sprockets in the cassette.

If you read CJ's excellent 'shimergo' (beat the system) article all should become clear.

cheers

[cycleruk]

My 105 rear mech' (10 speed GS) works with a 34T cassette. This did surprise me but a lot will depend on the dérailleur hanger length. So I would say just try the Tiagra.

[markjohnobrien]

I'm using a 9speed XT shadow rear mech on a 36t cassette - M772 - and it works fine

[jamesofyorkshire]

[quote="531colin"]46/30 chainset £60 at Spa, in the new CTC mag....[url]http://forum.ctc.org.uk/viewtopic.php?f=5&t=103107&hilit=chainset&start=15[/url][/quote]

I find that link confusing. It goes off all over the place.

Are you saying Spa (My LBS) has a 30/46 chainset that works with 10-speed?

My current chainset/BB is BB30 press fit....will this Spa thing fit my frame?

[keyboardmonkey]

I'm using a 9speed XT shadow rear mech on a 36t cassette - M772 - and it works fine

+1 for the M772 with my 10sp triple setup. I have a 34T largest sprocket on an XT cassette, but there is clearly greater capacity.

[531colin]

46/30 chainset £60 at Spa, in the new CTC mag....http://forum.ctc.org.uk/viewtopic.php?f=5&t=103107&hilit=chainset&start=15

I find that link confusing. It goes off all over the place.

Are you saying Spa (My LBS) has a 30/46 chainset that works with 10-speed?

My current chainset/BB is BB30 press fit....will this Spa thing fit my frame?

You'll need an adapter to fit a square taper BB unit to a BB30 frame, but other than that, yes....provided you can drop the F. mech. down

[jamesofyorkshire]

Thanks to all the above replies. I found them all useful. Now I know what my choices are. I think I'll go with a different rear derailleur and a 36 cassette temporarily (for the Fred Whitton), and long term will go down the smaller chainset route when I've looked into it a bit more. How often do I use 11/12/13/14 and the big (50) ring? Maybe once a month. I don't need those high gears.

The only thing I'm not clear about is when setting up the rear derailleur if I put a 9-speed mech onto a 10-speed cassette............
Assuming I lined-up the RD under the smallest cog and 'indexed'....won't I run out of RD movement when I get to the second largest cog (2nd gear) if using a 9-speed RD? Or does it handle more than 9 increments???

[531colin]

9 sp. RD has more than enough "throw" to cover 10 sprockets....you will still need to set the limit screws for top and bottom gear.....9 & 10 cassettes are comparable in width....so are 8, come to that
Its the shifter that does the accurate indexing stuff, the derailer just does as its told

[jamesofyorkshire]

OK. I get it now. The RD moves across the cassette width smoothly...not in increments - it's the shifter that has the increments. That was the bit I couldn't get my head around.

One last question....assuming I have a 34/50 up front, and a 36 (no bigger) at the back, which model of M772 do I need at the back....a long cage (GS) or a super long cage (SGS) ?