Rear mech question?

[PJ79LIZARD]

I'm currently running a 50/34 front and 11/28 rear, the rear mech I've got is medium or long cage I'm not sure, anyways I'm after a new rear mech could I put on a short cage rear mech, or would that not cope with the 28 tooth rear sprocket?

 

[Granville Kuosonsavath]

what make is it , shimano sram or campag?

 

[accountantpete]

According to Sheldon - no.

To get a general idea then simply subtract the lowest rear sprocket from the highest (28-11) =17

Then do the same for the chainrings (50-34) =16

If the combined totals (17 & 16 ) come to 28 or less you are ok.

 

[PJ79LIZARD]

Right then it's a medium/long cage then. The other problem is I'm running an 8 speed system, I want an ultegra rear mech but lots of mechs I've looked at they just say 9 or 10 speed. I've seen the ultegra RD-6600 which is 8,9,10 speed compatible, I don't understand this as I thought the spacing between the rear sprockets were different between 8,9 and 10 rear cassettes. And as a result needed an 8,9,10 specific rear mech?

 

[PJ79LIZARD]

what make is it , shimano sram or campag?

It's shimano

 

[Fattman]

Right then it's a medium/long cage then. The other problem is I'm running an 8 speed system, I want an ultegra rear mech but lots of mechs I've looked at they just say 9 or 10 speed. I've seen the ultegra RD-6600 which is 8,9,10 speed compatible, I don't understand this as I thought the spacing between the rear sprockets were different between 8,9 and 10 rear cassettes. And as a result needed an 8,9,10 specific rear mech?

The mech itself does not do the indexing - the shifter does that. The mech moves continuously and the shifter will pull the appropriate amount of cable for each gear change, hence a mech being compatible with different numbers of sprockets.

So I don't think there are any problems with a fancy new mech on your 8-speed.

Also, though Sheldon does indeed do the maths re. tooth difference, the Shimano short cage mech will in fact run with a 34F 28B combo, but your chain needs to be exactly the correct length and you may need to go for a 12-28. The fact that you are getting towards the edge of the design envelope means you can get in a terrible pickle (I did!). In all probably best to stick with the medium cage (I now have that and have no problems at all with 50/34 and 11-28).

 

[PJ79LIZARD]

Ok so when it says the rear mech is 9 or 10 speed, I could in fact use that on am 8 speed system? I know the teeth size are smaller on 9 and 10 speed chain sets and the chains are thinner, so 10 speed components are going to be too small for an 8 speed chain, and the 9 speed components should be ok?

 

[Fattman]

Ok so when it says the rear mech is 9 or 10 speed, I could in fact use that on am 8 speed system? I know the teeth size are smaller on 9 and 10 speed chain sets and the chains are thinner, so 10 speed components are going to be too small for an 8 speed chain, and the 9 speed components should be ok?

I don't think the teeth sizes vary because of the 'speed' - the chain has the same number of links per foot no matter what speed it is, it has been standard for years so the teeth will have the same spacing. There has been some tinkering for years over how much they stick up but again that is not, I believe, a speed thing.

The chain is narrower on 10 speed but this does not translate to a material issue of narrower jockey wheels.


A 10 speed rear derailleur should work happily with an 8 speed chain/cassette, so long as you have the 8 speed shifter.

Check out this from Sheldon as a full summary.

A quick perusal of reviews and I reckon you might as well go with, say, Ultegra 6600/SL - it's deffo as good as the new Ultegra 6700 (if a tiny weeny bit heavier) and you can be confident it will work with 8 speed.

 

[PJ79LIZARD]

I've gone for the ultegra SL 6600, See what it's like when I stick it on!

 

[e-rider]

not a chance with a short cage

39x27 or 34x25 is as much as a short cage can handle (with a 50T or bigger chainring)

 

[PpPete]

The GS (medium cage) version will certainly handle your required range. Mine copes with a whopping 24T range at front and 18T range at the back (total of 42 - way more than Shimano's spec of 37 max)

You have a total range of 28T.... Shimano says 27T max for the SS (short cage). I've never used a short cage, but I'd be surprised if it didnt work only just outside the spec for total range. You may have to be careful on getting the chain length and B-screw adjustment exactly right.

 

[RecordAceFromNew]

I think we are all reasonably happy that while it is a possibility, maximum rear cog size limit is unlikely to be an impediment for the OP since he is exceeding the spec limit of 27T for Ultegra road mechs (of whatever cage length - max cog size is largely determined by the parallelogram geometry rather than cage length) by only 1T.

Regarding the other limit, Shimano's wrap range spec for 6600 series Ultegra short cage (i.e. SS) mech is 29T, while the OP requires 33T (50-34+28-11). There is still a chance that it will work if set up with care, as Harris Cyclery have found at the bottom of this rather good article, their short cage Ultegra was only at its limit wrapping a total of 36T.

 

[heretic]

Three things.
1) Indexing has 3 variables, ie cog spacing, cable pull per click and amount of sideways movement of the mech for a given cable pull. Until very recently all Shimano mechs were the same except some ancient Dura Ace. I believe some new series MTB 10 speed mechs are different.

2) The max cog size is independant of the chain wrap figure. For a Shimano road mech it's quoted as 27 teeth, for mtb 34, Campag it's 29. There is a bit of leeway, it depends on the amount of drop between the rear hub and the mech hanger. For road mechs if the centre to centre is over 24mm add a tooth for every 2mm.

3) Chain wrap as stated above is (large sprocket minus small sprocket) + (large chainring minus small chainring).

 

[PJ79LIZARD]

I put the mech on this weekend, it works fine no problems!

 

[Fattman]

I put the mech on this weekend, it works fine no problems!

Good news, thanks for the update!