Changing rear cassette

[steveindenmark]

I have a Specialized Roubaix with Tiagra groupset. The current cassette is an 10 speed 11-36. I would like to change it for a 11- 42, using a wolftooth.

I am trying to lower the gears to make it easier to get up mountains. would changing the chainring have the same effect. It is a 50 - 34 at the moment. What would I change it to.

I am unsure about bike mechanics but am happy to give it a go.

For those in the know. Any hints or suggestions would be gratefully listened to.

 

[Yellow Saddle]

I doubt that would be a solution to anything.
What is the problem you're trying to solve?

 

[MichaelW2]

You will need a new chain or two.
These massive sprockets seem to be for 1x10 (or higher) systems.

 

[neil_merseyside]

I've got a Spa Elan with 50/34 and 11-42 and it shifts perfectly, and gives a nice low gear similar to my old 105 triple, you'll need 116 links as a minimum (depending on chainstay length) and most 11sp are 114!. I was supplied with the chain using two quick links and a half link (inner) and that worked, but looked messy, I've now got a new chain setup with effectively two half length chains - so two places to split that are more than an inch apart...

 

[gbb]

I've got a Spa Elan with 50/34 and 11-42 and it shifts perfectly, and gives a nice low gear similar to my old 105 triple, you'll need 116 links as a minimum (depending on chainstay length) and most 11sp are 114!. I was supplied with the chain using two quick links and a half link (inner) and that worked, but looked messy, I've now got a new chain setup with effectively two half length chains - so two places to split that are more than an inch apart...

Did you need to do anything with the rear mech out of Interest ?

 

[steveindenmark]

Did you need to do anything with the rear mech out of Interest ?

You will need to add a wolftooth.

 

[Ajax Bay]

Tiagra groupset . . . cassette is a 10 speed 11-36. I would like to change it for a 11- 42, using a wolftooth.
I am trying to lower the gears to make it easier to get up mountains. Would changing the chainring have the same effect? It is a 50 - 34

Steve - swapping to an 11-42 would make significant demands on the RD. You can address one aspect by using a 'wolftooth' but not the other which is the RD's wrapping capacity which at 47 (16+31) would be way over its spec. It works for @Neil but he doesn't say what RD he has fitted.
The drop in gear from 36t sprocket to 42t is 17% (0.94 to 0.81). To get the same drop by reducing the inner ring you'd need a 29t chainring - let's call it a 30t. But your crankset has a BCD of 130mm (guessing a CS-4600) which means you can't drop the inner ring at all, so getting a lower gear that way would involve a new chainset (with a 110 BCD) and given you do not need the 50-11 top gear (I suspect), a 46-30 chainset (with current 11-32 cassette and the current chain with a 1" link less) would do the business and keep the RD efficient.
HTH (?Danish mountains?)

 

[Ajax Bay]

you'll need 116 links as a minimum (depending on chainstay length) and most 11sp are 114! . . . . I was supplied with the chain using two quick links and a half link (inner)

If your chain has 116 links, @Neil , how long is the half-link? Maybe your chain has 58 links.

 

[MontyVeda]

...
I am trying to lower the gears to make it easier to get up mountains. would changing the chainring have the same effect. It is a 50 - 34 at the moment. What would I change it to.

I am unsure about bike mechanics but am happy to give it a go.

For those in the know. Any hints or suggestions would be gratefully listened to.

have a play on this gear calculator

 

[steveindenmark]

Steve - swapping to an 11-42 would make significant demands on the RD. You can address one aspect by using a 'wolftooth' but not the other which is the RD's wrapping capacity which at 47 (16+31) would be way over its spec. It works for @Neil but he doesn't say what RD he has fitted.
The drop in gear from 36t sprocket to 42t is 17% (0.94 to 0.81). To get the same drop by reducing the inner ring you'd need a 29t chainring - let's call it a 30t. But your crankset has a BCD of 130mm (guessing a CS-4600) which means you can't drop the inner ring at all, so getting a lower gear that way would involve a new chainset (with a 110 BCD) and given you do not need the 50-11 top gear (I suspect), a 46-30 chainset (with current 11-32 cassette and the current chain with a 1" link less) would do the business and keep the RD efficient.
HTH (?Danish mountains?)

Thanks for that. It sounds easier to change the chainset. I rarely use the top gears. I am thinking of riding the Trans Pyrenees Race next September.

 

[gbb]

You will need to add a wolftooth.

Aha, not conversant with the system so did wonder

 

[neil_merseyside]

A pic of my mech you can see the drop link (wolftooth) it's Shimano 105, presumably medium or long cage, measures around 85mm pivot to pivot. The chain I bought was labelled 114 links as I said - the ins and outs (ers) of labeling doesn't really matter does it?

 

[steveindenmark]

If I change the chainset. Does it matter if it is a 10 or 11 speed?

 

[Ajax Bay]

Not really, but I'd expect an '11 speed' to be more expensive and offer no mechanical advantage.
I don't know what BB you have but if threaded, a(n e-)visit to Spa Cycles would give you an idea of the choices.

 

[steveindenmark]

Shimano Tiagra 4700 threaded bottom bracket.