10 speed cassette swap out

[Ootini]

Hi,

My bike is currently running a 50-34 chain set and a 12-25 rear cassette and I'm finding I really struggle on hills. Would swapping to a 12-30 cassette help? And is it easy enough to do yourself?

Ta

 

[Ootini]

Or would the cassette swap out make very little difference? Should I be looking at swapping the chainset for a triple?

 

[Cubist]

Yes. You'll need a chainwhip and lockring tool (assuming with those ratios it's a 9 or 10 speed). You'll also need to adjust the B tension on the rear mech to allow for the bigger cassette. You may need a new chain, but that's no bad idea if you're putting a new cassette on.

 

[Cubist]

A 30T cassette is pretty good. You can fit an 11-32 if you have a med cage rear mech. It's cheaper than fitting a triple chainset, as you'd need to change front mech and possibly shifter to do that.

 

[Dogtrousers]

Yes it's easy to do, but requires a couple of tools (cassette tool and chain whip)
Will it make a difference? Your current bottom gear is 34/25 which is (by my calc) 36". 34/30 would be 30", so YES, it would make a difference (IMO)
The only outstanding question is whether your rear mech could cope. 50/34 with 12-30 needs a mech with a capacity of at least 34 teeth (difference between big-big and little-little) and a largest sprocket of 30. If you have a short cage mech, it might struggle to meet these criteria. Have a search to see what the spec is.

 

[Cubist]

A gear calculator shows you which will give you a better lower gear (I'm ignoring the big gaps in an 11-32 to concentrate on bottom gears. )

Your current bottom gear is 34/25... 35.8 inches
A 30T cassette will give you 34/30 ... 29.7 inches
A 32 t cassette will give you 34/32 or 27.9 inches

The bottom gear on your average triple will be 30t
So a 30t/25 bottom gear will be 31.6 inches. The advantage of a triple will be closer ratios and a lower gear than you have now, but if you're struggling on hills a 30t cassette on your compact will be lower bottom gear still , AND much cheaper.

 

[Nigelnaturist]

I will put my two pence in, with a triple you can keep tour current cassette which is a closely group set of ratios, if you get a chainset with a 74BCD inner you can fit a 26/38/50 for a range of 27-109" on a 12-25, with a compact double to get the same range you will need to have bigger gaps between the rear gears.
A couple of charts showing the difference in gear inch's and on 700x23c tyres

The other draw back many seem to forget out compact doubles is that most people will be spinning on the extremes of the cassette 12-15 on the 34 or 16-21(ok not extreme) on the 50, on the 38 ring I have I spin with a pretty straight chain 38x15-17 (I think this is why I seem to get more miles on my chain then many seem to), also there is much less of a gap when you change on the front.
Its true the cheapest option short term is just to change the cassette, however if you want choice a triple is the answer as you have so many options, I use a square bracket chainset from Spa cycles £20, rings £20,15,10 for outer to inner, in a range of sizes, you may need to change the BB though £10-20, then a shifter.

 

[Ootini]

With regards to the rear mech, would I expect to see a size or model number printed on the mech itself? I'm not sure how I'd be able to figure out if it's a large or small.

 

[Cubist]

Depends on the make. On MTB groupsets Shimano use GS for a medium and SGS for a long cage. HOWEVER, just to confuse matters, this depends on use. On a road bike a GS is called a long, and SGS extra long

The only safe way really is to measure it, as the cage length isn't stamped on the mech because only the cages differ.

I'm going to guess that your current mech is a standard or short mech, and that if you want to exceed 28 t you're going to need a GS. It may well be possible to run a 30 with a short mech, but you'll have to be very very wary of cross chaining, especially in big-big.

 

[RecordAceFromNew]

With regards to the rear mech, would I expect to see a size or model number printed on the mech itself? I'm not sure how I'd be able to figure out if it's a large or small.

I assume you have a Shimano system.

Shimano offers cage length in 3 categories, SS, GS and SGS, with progressively longer cage and maximum sprocket size and range capacity. There is no such thing as a SGS road mech, but MTB mechs do come in all 3 categories. All current road mechs except DuraAce whether SS or GS can handle no less than a 30T large sprocket and a range of 34T, officially.

In practice whether a mech can handle more and how much more is also dependent, amongst other things, on the length of the mech hanger, which varies according to the bike frame's make and model etc. This is a good guide on how to push the mech's boundary. You can use a chain length calculator to work out how long the new chain needs to be.

However it is impossible to tell whether your mech is a current model until you find out. You can look it up with a torch and good eyesight, the model info (RD-xxxx) and sometimes category are stamped on where it is shown in the middle of the photo below. A photo of the cage in relation to the mech body might also help to confirm cage length if the cage category is not shown.

 

[Cubist]

My 10 speed 105 road mech is a GS and handles a 32 OK. My new 11 Speed will have an Ultegra GS and a 32 cassette, both on compacts. Perfectly possible to put a 10 speed MTB mech on a 10 speed road cassette, but I seem to remember you need a 9 speed shifter, or it could be the other way round, ie 9 speed long cage SGS mech and 10 speed shifter. Could be wrong of course.....

 

[Nigelnaturist]

Depends on the make. On MTB groupsets Shimano use GS for a medium and SGS for a long cage. HOWEVER, just to confuse matters, this depends on use. On a road bike a GS is called a long, and SGS extra long

The only safe way really is to measure it, as the cage length isn't stamped on the mech because only the cages differ.

I'm going to guess that your current mech is a standard or short mech, and that if you want to exceed 28 t you're going to need a GS. It may well be possible to run a 30 with a short mech, but you'll have to be very very wary of cross chaining, especially in big-big.

A GS on a road bike is a medium.