Big cassette for extra gear in mountains? Help please.

slowbutkeenMag

I'm entering the Marmotte this year. I did it last year for the first time, and did the Etape the year before. In both previous years, I used a compact chainset (34/50) and a 12-27 cassette. I completed last year's Marmotte in just inside silver time.

The problem this year is that my training hasn't gone according to plan. If I was looking for a scapegoat, I would blame it on the puppy that I have brought into my world (and who has turned it upside down). I've not transitioned seamlessly into mornings that are no longer completely my own.

Enough excuses. :oops: My question is - I'm thinking of getting a new cassette: 12-30. I figure that will give me an extra bottom gear. I also read from Sheldon Brown that a 30 on a 9-speed should still be okay with a short rear derailleur.

My regular cycling buddy thinks that a 30 is a step too far. On the other hand, he's used a triple for the last two years (same events), and has only just moved to a compact, so he's not tried a compact in the mountains yet.

So - should I move to a 12-30 (and then move back next year when I'm fitter...)?

All help gratefully received.

Toptube531

I use a Shimano 11-32 9sp with a 34-48 double.
It's not often I use the 32 sprocket but it's good to have it there just in case.

Mettan

Similar to Toptube, get a 32 - not just as a facility for steep climbing, but also "recovery" when your tired and still going up ~ 5 %........

dennisn

Not sure that a 30 will work with any of todays "short" rear D's. I'm running DA and it doesn't work. Now, thats on a newer bike with vertical dropouts. On my older bike
with (somewhat) horizontal dropouts I was able to move the rear cog far enough away from the rear D to allow a 30 tooth with the same DA rear D. It's all about the distance
between the axle center and the hanger center. If you get my meaning. This dimension is fixed on vertical dropout bikes, but due to the "slot" in horizontal dropouts you can move
the rear D further from the hanger center. Whew, did that make sense?

Toptube531

dennisn wrote:

Not sure that a 30 will work with any of todays "short" rear D's. I'm running DA and it doesn't work. Now, thats on a newer bike with vertical dropouts. On my older bike
with (somewhat) horizontal dropouts I was able to move the rear cog far enough away from the rear D to allow a 30 tooth with the same DA rear D. It's all about the distance
between the axle center and the hanger center. If you get my meaning. This dimension is fixed on vertical dropout bikes, but due to the "slot" in horizontal dropouts you can move
the rear D further from the hanger center. Whew, did that make sense?

I use my 32t with a Campagnolo Veloce medium cage rear mech.It works perfectly even though it's capacity is 29t.

andrew_s

It's not cage length that's the main problem - it's that the parallelogram of road mechs is at too shallow an angle to allow the top jockey to clear sprockets bigger than 30T (the official limit is 27T). Fiddling with the B-screw and chain length may be required to make 30T work, but it should be possible.
32T or bigger will require an MTB rear mech.

Just to add to the possibilities, Shimano have recently announced a new HG61 12-36 cassette for 29er mountain bikes. 34-36 should be low enough for most things.

andrew_s

It's not cage length that's the main problem - it's that the parallelogram of road mechs is at too shallow an angle to allow the top jockey to clear sprockets bigger than 30T (the official limit is 27T). Fiddling with the B-screw and chain length may be required to make 30T work, but it should be possible.
32T or bigger will require an MTB rear mech.

Just to add to the possibilities, Shimano have recently announced a new HG61 12-36 cassette for 29er mountain bikes. 34-36 should be low enough for most things.

maddog 2

just whack on a 11-32 and a mtb mech for the Marmotte. Wife did the Fred Whitton the other Sunday and I did the same to her bike, to get her up HardKnott.

as said, 27t is the official max, although the latest DA 7900 mechs are 28t rated. In practice 30t is sometimes possible with b-screw tweaking but 32t is pushing it.

Toptube531

andrew_s wrote:

32T will require an MTB rear mech.

WRONG!

dennisn

Toptube531 wrote:

dennisn wrote:

Not sure that a 30 will work with any of todays "short" rear D's. I'm running DA and it doesn't work. Now, thats on a newer bike with vertical dropouts. On my older bike
with (somewhat) horizontal dropouts I was able to move the rear cog far enough away from the rear D to allow a 30 tooth with the same DA rear D. It's all about the distance
between the axle center and the hanger center. If you get my meaning. This dimension is fixed on vertical dropout bikes, but due to the "slot" in horizontal dropouts you can move
the rear D further from the hanger center. Whew, did that make sense?

I use my 32t with a Campagnolo Veloce medium cage rear mech.It works perfectly even though it's capacity is 29t.

Somtimes it works and sometimes it doesn't. I'm pretty sure I could get 28(if one was made) on the back of my vertical dropout bike with DA. Maybe 29. Definately not 30.
It's rated at 27 teeth.

maddog 2

Toptube531 wrote:

WRONG!

you wouldn't be a troll by any chance.....

Steve928

Every time that this topic comes up (frequently) there are a series of conflicting opinions on what sprockets various rear mechs can handle: Yes it'll work, no it won't, it DOES work, no it DOESN'T etc..

I reckon that there is another variable at work in the equation here: the bike.

There is no standard for placement of the rear mech attachment in relation to the centre of the rear axle, or at least if there is then the frame manufacturers choose to ignore it. Just take a look at bikes hanging in your shed, or the rear mech hangers in your spares box: the rear mech placement moves up and down and fore and aft by more than a few mm. For example I've one bike where it is so close that the skewer needs removing to get the rear wheel in or out.

So I'll suggest that on some bikes a combination of mech and sprockets will work just fine, while on another bike it won't, and evryone is right