Third chainring advice

[jorgemartin]

Hello,

The following is my current setup:
- Double crank-set (53T and 46T)
- 9 speed short cage derailleur (SRAM x9)
- 11-34 cassette
- SRAM dualdrive 3xspeed gear hub.

I'm finding it extremely difficult to climb hills with this kind of arrangement and I'm considering adding a third chainring to the front. Something like 38T. Would that work? Or could I go with something a bit smaller? Will I have problems with chain tension? Thanks!

 

[Angelfishsolo]

Hello,

The following is my current setup:
- Double crank-set (53T and 46T)
- 9 speed short cage derailleur (SRAM x9)
- 11-34 cassette
- SRAM dualdrive 3xspeed gear hub.

I'm finding it extremely difficult to climb hills with this kind of arrangement and I'm considering adding a third chainring to the front. Something like 38T. Would that work? Or could I go with something a bit smaller? Will I have problems with chain tension? Thanks!

I am not supprised you are struggling with a 46-34. I am almost certain you could drop to a 39T with your current front mech.

 

[PpPete]

With a short cage mech you might be limited in the range of chainrings you can use. Certainly I would say a triple is likely to be out of the question without changing to a medium or long cage mech.

 

[Angelfishsolo]

With a short cage mech you might be limited in the range of chainrings you can use. Certainly I would say a triple is likely to be out of the question without changing to a medium or long cage mech.

Sh*t I misread teh post. I was thinking about swapping the 46t for a 39t!

 

[jorgemartin]

Why is triple crankset out of the question? Also, I'd consider swapping 46t for a 39t.

 

[Angelfishsolo]

Why is triple crankset out of the question? Also, I'd consider swapping 46t for a 39t.

The distance that it is designed to travel will almost certainly be designed to handle a double not a triple. Also if it is an indexed front mech your shifter will only have two clicks and not three so that will need changing as well. Score one for friction shifters

 

[PpPete]

A short cage mech just won't be able to take up the difference between three chainrings and a big cassette like that. Whether short cage will cope with a 53-39 is another question. Have a look at the limits in SRAM's technical docs.

 

[jorgemartin]

Out of curiosity... what would happen if I used a triple crankset?
I have a three speed shifter for the front mech.
I think I'd be happy swapping the 46t for the 39t if this is a possibility. The only reason I used 46 is because I had an old one lying around.

 

[Angelfishsolo]

Out of curiosity... what would happen if I used a triple crankset?
I have a three speed shifter for the front mech.
I think I'd be happy swapping the 46t for the 39t if this is a possibility. The only reason I used 46 is because I had an old one lying around.

See PpPetes last reply.

 

[ASC1951]

I am not supprised you are struggling with a 46-34.

What about his three speed hub gear as well, though? Surely that drops the final ratio?

 

[Angelfishsolo]

What about his three speed hub gear as well, though? Surely that drops the final ratio?

TBH I didn't notice that and I am not even sure what it is

 

[PpPete]

Out of curiosity... what would happen if I used a triple crankset?
I have a three speed shifter for the front mech.
I think I'd be happy swapping the 46t for the 39t if this is a possibility. The only reason I used 46 is because I had an old one lying around.

What will happen is that your mech will fold up on itself before it has taken the slack out of the chain.
It might sort of work on the three biggest sprockets of the cassette, but beyond that your drive train will come to a grinding halt..

Put a 39 on there first. Wind the "B" screw right in. See whether it all works on the workstand. Wind the B screw out again so the chain wraps as much of the cassette as possible of the cassette when you are in 39/11.

If it doesnt work, you have a choice of trying an intermediate size ring, or buying a longer cage mech, which will work with a triple should you decide to go down that route in the future .

 

[RecordAceFromNew]

AFAIK there is no such thing as a sram x-9 short cage rear mech, since it is a mtb mech - there is a medium, and a long (see page 23 of this).

The shorter one has a wrap range of 37T. Since your cassette has taken up 23T of that, as a minimum you should have 14T range capacity available for the chainset, so a 53/39 double should work just fine mechanically.

The outstanding issue of course is whether it will deliver low enough gears for you.

Obviously it depends on what size wheel you use and what load you pull. The existing 46T up front with the 34T at the cassette and low of the 3 speed hub should deliver a 27" gear for 700x28c tyres, while a 39T will deliver 23". If you do have 700c wheels, I bet you never use the the 53T with the 11T of the cassette and high at the 3 speed hub - according to Sheldon's gear calculator (which has the facility to incorporate your gear hub's ratios) it is a 175 inch gear!!

Obviously it depends on the wheel size, but according to page 19 here the recommended setup for a Sram dual drive 3 speed hub is to couple a 38/33T chainset with a 11-34 cassette.

 

[jorgemartin]

I bought the Sram x-9 as a short cage derailleur but I've just checked both the website and the manuals and as RecordAceFromNew rightly points out, there's no such a thing as a short cage version of this for the 9 speed one (but there's one for the 10 speed one)... I think that 53/39 coupled with the Dualdrive, should be enough... although I'm afraid I can not know this until I try it... Is the difference between 46t and 39t substantial enough to justify getting a new chainring? Could I push it to 36t? I'm using 20 inch wheels (recumbent). What I had before was a single 46t front chainring and I found that this was a 'okay for most normal things' solution, but didn't allow me to go really fast and was also not great for steep hills (although I could almost swear that it was easier to go uphill when I had the 46t front chainring and the 11-32 cassette set up, could this be?... but maybe I'm just one year older).

 

[PpPete]

Being 'bent changes things - maybe. Are there other chain tensioning devices that will "take up the slack" ?

On a DF I would say a change from 46 to 39 would definitely be worthwhile, I had a "half-step + granny" on the tandem until we wore out the chainrings, and the half-step (from 46 to 42 IIRC) was quite noticeable.