Increasing range of SRAM 9 cassette

[beatlejuice]

I own a Specialized Sirrus Elite 2008 (not the 2009 I thought I had) and I am looking at replacing the chain and cassette. It comes with Shimano Tiagra long cage rear changer. The cassette is a SRAM PG-950, 9-speed 11-28. Could I can fit say a 11 - 32 cassette with the existing rear changer? Reason: steep hills + old fat rider = unhappiness!

Whilst trying to make sense of this I have just found out why my LBS sold me this bike cheap last July, it was a 2008 model they had left over and they didn't tell me. I am not impressed!

 

[PpPete]

Tiagra is either a medium cage (GS model) or short cage (SS model)
Not long cage. I guess you have a medium cage.
Shimano say 27 teeth max. (increasing to 28T on 2010 models?)

My experience (another old fatttie) with Shimano medium cage mechs is that a 30 tooth will work OK with some care. Others have said 32 works for them.

If you want an 11-32 cassette I suggest you try it. Be prepared if it don't work to spend an extra £20 on a Deore long cage which is designed for the job, and will work just fine with the Tiagra shifters.

BTW I doubt a 2009 model would have an MTB cassette (or the mechs for it)

 

[RecordAceFromNew]

To add to porkypete's comment, whether a 32 tooth cassette will work uneventfully with your Tiagra depends on:

1) your frame/dropout dimension and B screw adjustment as to whether the 32 tooth sprocket can be made not to clash with the top jockey wheel. At a stretch some make it work by swapping the rear mech's top jockey wheel with a smaller one (e.g. from a spare mech).

You can perhaps check by observation if there is going to be enough clearance, given that a 32 tooth sprocket's radius is 0.32 inches larger than that of a 28 tooth one.

2) You might need a mountain rear mech if your combined front and back tooth difference exceeds your Tiagra's capacity to take up chain slack (assuming you use all front/back gear combinations). The official capacity provided by Shimano is 37 teeth, but the actual allowable is likely higher.

 

[beatlejuice]

Thanks RecordAceFromNew and porkypete for your replies. One more question please. Wouldn't it be easier to replace the smallest front chain ring to say 28 teeth instead of 30? Then I would only get problems of too much chain when using that ring and I wouldn't have such a large gap between the lowest ratio and the next one up.

 

[RecordAceFromNew]

As long as you are aware that the gearing with a 28 tooth chainring (from 30) would only be equivalent to changing the rear cassette from 28 to a 30 (i.e. not 32 per your original post). Also if your front mech is a FD 453 then its official max range capacity is 20 teeth, although it may be able to handle more.

You can explore the effect of different options by using the calculator here.