both little rings?

joe boy

Hello everyone I'm about to buy a rear mech for the new build, just had a chat with a bloke who uses a medium cage with a regular 3 ring set.

He says that it's all good as long as you don't use both small rings at the same time, and the shorter length helps to keep it out of harms way. (Bit cheeper too).

What does everyone think and how often do you actually use both small rings at the same time?

Cheers J

stumpyjon

You shouldn't ever use both small rings at the same time as it puts a lot of lateral strain on the chain, that'll lead to premature wear and stretch (shouldn't need to as you can get the same gear ratio from other combinations of sprockets).

Depending on your budget you might wan to consider the XT shadow mech, it's new and designed to to fit more tightly under your cassette to stop it getting smacked so easily (or so the marketing spiel claims).

Personally never had a problem with long cage mech getting whacked. Shimano recommends the max capacity for a short cage shadow mech is 33 teeth on the largest front sprocket and 45 teeth for the long cage mech.

If it was me I'd put on the long cage mech (all XT mechs are the same price in Evans), I'd rather risk it getting smacked than accidentally going into small small and getting the chain stuck.

dav1

I never use both small rings, its not good for the drive train.

I use an 8 speed set-up and have 1-3 on the granny ring, 3 - 6 on the middle ring and 6-8 on the big ring. Ill vary slightly as I need to buy I wont go more then small 1-4 or big 4-8.

Keeping the chain as straight as possible means you don't put side-to-side tress on components and it prevents the chain rubbing where it shouldn't.

As i rule i hear Long cage for 3 rings, medium for 2 and short for 1. I was out with someone who has a medium cage mech and their chain was slapping their chain stay quite a lot as it was too slack in some gears.

jedi_master

stumpyjon wrote:

You shouldn't ever use both small rings at the same time as it puts a lot of lateral strain on the chain, that'll lead to premature wear and stretch (shouldn't need to as you can get the same gear ratio from other combinations of sprockets).

Never knew this my self, roughly what combination would give you the same as the 22 at front and 11 at back ? if say the front is a 32t or 34t

stumpyjon

If I've got my maths right 22 front and 11 back is a ratio of 1:2, i.e. for every rotation of your crank you get two rotations of your rear wheel, 34 & 17 or 32 and 16 would give the same ratio. On XT 16 / 17 are the fourth largest sprockets on the cassette so you can effectively get the same gear ratio with an almost straight chain line. The table below gives you the ratios fro an XT M770 crank and M770 aq cassette.

Cr ---- 44

---

32

---

22
Spr
32 ---- 1:1.4 ---- 1:1.0 ---- 1:0.7
28 ---- 1:1.6 ---- 1:1.1 ---- 1:0.8
24 ---- 1:1.8 ---- 1:1.3 ---- 1:0.9
21 ---- 1:2.1 ---- 1:1.5 ---- 1:1.0
18 ---- 1:2.4 ---- 1:1.8 ---- 1:1.2
16 ---- 1;2.8 ---- 1:2.0 ---- 1:1.4
14 ---- 1;3.1 ---- 1;2.3 ---- 1:1.6
12 ---- 1:3.7 ---- 1:2.7 ---- 1:1.8
11 ---- 1:4.0 ---- 1:2.9 ---- 1:2.0

Avoid the combinations that give the ratios in red, as you can see you can still completely cover these ratios with other combinations that don't bend the chain as much.

jedi_master

Nice one cheers.

joe boy

so the best thing to do is still go for long cage but try never to use small to small or other combos that run the chain on the piss.

Cheers guys.

Splasher

I use a medium cage mech with 3 rings. As everyone says you should not use small/small combos but you shouldn't use big/big combos as either causes premature wear of the drivetrain due to side forces on the chain.

However, with a long cage mech, if you mistakenly select one of these combos, all that happens is your wear increases for a short period of time until you realise what you've done. With a medium cage mech, you can let your chain go slack in small/small or rip it off in big/big. So why do it?

Well a shorter cage keeps your chain much tighter and less likely to bounce around on decents or to get lost from the rings. I don't want the extra weight and limited ratios of a double and chain device so that's what I do.

Hope this makes sense.