Changing to Compact chainring

Mr Velo

Following my disastrous attempt at climbing Castle Hill on last Saturday's Tour De Burren, i'm seriously contemplating switching to a Compact Chainset.

Currently have a Felt F5 (2010) which has a Shimano 105 (53/39T; 11-25T cassette)

I've been looking on Wiggle, CRC etc - and my question is, is it possible to just change the chainrings at the front, (i.e. buy a 50T and a 34T for the front) and replace the current setup?

If so - do i need to change the cassette also?

I know you can replace the whole chainring set which includes the crank arm etc, but i'm hoping to cheap out on having to do that.

Lumen

No, you need a new crankset.

Maybe just get a 28T cassette.

Mr Velo

Thanks Lumen.
Can I ask a stupid question and ask why it's not possible to just change the rings and fit to the existing crank?

I never thought of changing to a 28T cassette... looks to be a number of options... 11-28; or 12-27

http://www.wiggle.co.uk/shimano-105-5700-10-speed-cassette/

Lumen

Mr Velo wrote: »

Thanks Lumen.
Can I ask a stupid question and ask why it's not possible to just change the rings and fit to the existing crank?

The bolt pattern is different. 130BCD for 53/39, 110BCD for 50/34.

You can buy 53/39 rings for a compact 110BCD crankset (I have some), but not vice versa because the chainring teeth and the bolt holes would be in the same place.

07Lapierre

Lumen wrote: »

No, you need a new crankset.

Maybe just get a 28T cassette.

New chain too

death1234567

Just for future reference is there much work/cost in changing a rear casette? Like if I wanted to go from 26T to 24T or something like that?

Briando

Would going to a bigger cassette on the back help you much?

Like a 12-28? Or does that make very little difference?

Lumen

Briando wrote: »

Would going to a bigger cassette on the back help you much?

Like a 12-28? Or does that make very little difference?

Going from 25 to 28 gives you 12% more cadence for a given speed.

http://www.sheldonbrown.com/gears/

com1

death1234567 wrote: »

Just for future reference is there much work/cost in changing a rear casette? Like if I wanted to go from 26T to 24T or something like that?

A cassette about €50 - €100, cassette lockring tool €5-€10, a chain whip €5 - €20 an adjustable spanner and about 5 minutes should get the job done.

Of course a good lbs will probably do it for free if you buy the cassette from them, as long as you dont have to re-index the gears

Mr Velo

07Lapierre wrote: »

New chain too

So if I go for an 11/28 cassette, I'd need a new chain too??

TheBlaaMan

Mr Velo wrote: »

So if I go for an 11/28 cassette, I'd need a new chain too??

Not necessarily.

Changing cassette such that you now have a larger maximum sprocket (28t instead of 25t) means that the chain has to stretch a bit more and if it was already tight there may not be enough slack. You'll just have to make a judgement when you do the job

BTW, changing from 53/39 double to 50/34 compact means:

• changing complete crankset
• moving front derailleur down the seat tube c2cm (as the 50 chainring has a smaller diameter than the 53)
• probably removing a link or two from the chain

A few hours work, but no real drama if you are reasonably confident

Mr Velo

TheBlaaMan wrote: »

Not necessarily.

Changing cassette such that you now have a larger maximum sprocket (28t instead of 25t) means that the chain has to stretch a bit more and if it was already tight there may not be enough slack. You'll just have to make a judgement when you do the job

BTW, changing from 53/39 double to 50/34 compact means:

• changing complete crankset
• moving front derailleur down the seat tube c2cm (as the 50 chainring has a smaller diameter than the 53)
• probably removing a link or two from the chain

A few hours work, but no real drama if you are reasonably confident

Thanks for that info. Really appreciate it.
Will probably go for it, make the hills a little easier.

doozerie

You should check whether your rear derailleur can handle a 28T too. A rear derailleur is spec'ed to handle a defined range of gears, or cog sizes, and anything outside of that range will be problematic. A 28T isn't massive so you'd probably be okay with it but it's worth a quick check of the derailleur specs if you can find them online.

07Lapierre

Mr Velo wrote: »

So if I go for an 11/28 cassette, I'd need a new chain too??

If your existing Chain and cassette are worn, your existing chain will not work correctly on the new cassette. The gears will skip/jump when you put pressure on the pedals.

Its good practice to change both at the same time. You could just replace the cassette and see how you get on. If it works, great, but if the gears start skipping/jumping, buy a new chain.

Mr Velo

So assuming I change the entire crankset, this one: http://www.chainreactioncycles.com/Models.aspx?ModelID=50444

which is a Shimano 105 5750 Compact - will fit fine with my existing setup which i believe is Shimano 105 5600?

My front derailleur is a brazed on version, so i assume there should be enough adjustment room to move it down after putting in the new crank.

skauldy1

Sorry to hijack op but just a quick question. If you change the crank to a compact, would it be possible to have a 34t inner ring with a 53t outer ring.

07Lapierre

Nope. Max difference is 16 teeth. So a 34 inner ring and a 50 outer ring is the Max.

Lumen

07Lapierre wrote: »

Nope. Max difference is 16 teeth. So a 34 inner ring and a 50 outer ring is the Max.

What is the limitation here? With a triple you have a much larger difference in front teeth. Might need a medium cage derailleur and shifting wouldn't be great.

Not much point though tbh. If you're fast enough to need the 3 extra teeth at the front you don't need a compact.

C3PO

Worth mentioning that a Compact is much less "satisfying" to use (IMHO)! I have one on my training bike and while I appreciate the lower ratios, on my usual haunts in Wicklow, I find myself constantly having to match a front ring change with a change at the back! Although I suspect that the larger gaps in a 12-28 cassette might give similar issues?

Mr Velo

I normally cycle in the big ring on front (53), and feel comfortable about 3/4 down at the back (21-19).

Once i go any further down the cassette it's just not comfortable and i'm not getting the cadence up.

Do you think that by changing the cassette to a 12-27 i might make things easier for myself and negate the need for actually changing to a compact crank?

Current cassette is 11-25 (11-12-13-14-15-17-19-21-23-25)
The 12-27 cassette: (12-13-14-15-16-17-19-21-24-27)

clog

You wouldn't really want to be running the big ring with a 25-27 tooth rear. you would be putting a lot of side strain on the chain especially.
It seems to me that the gears you're looking for are already on your bike just drop down to the little ring and search for them

skauldy1

07Lapierre wrote: »

Nope. Max difference is 16 teeth. So a 34 inner ring and a 50 outer ring is the Max.

May just get bigger legs so. Thanks for the reply.

Mr Velo

Lumen wrote: »

No, you need a new crankset.

Maybe just get a 28T cassette.

Seeing as I have the 105 5600, according to shimano tech docs the biggest small ring I can have is 27

If I put on a 12-27, and stayed at 53/39 at the front, do you think that would be as good as putting on a 50/34 and waiting with 11-25T at the back?

Lumen

Mr Velo wrote: »

Seeing as I have the 105 5600, according to shimano tech docs the biggest small ring I can have is 27

If I put on a 12-27, and stayed at 53/39 at the front, do you think that would be as good as putting on a 50/34 and waiting with 11-25T at the back?

Honestly, no.

I am a fan of compact gearing. I'm an even bigger fan of triples (just ordered a 50-40-30 for a new build). A wide range of narrowly spaced gears is pleasant to ride.

C3PO

Gear ratios as follows:
34/25 = 1.36
39/27 = 1.44
39/28 = 1.39

I'm pretty sure there have been posts here where people have used a 28 cassette without issue despite Shimano's advice?

Mr Velo

Lumen wrote: »

Honestly, no.

I am a fan of compact gearing. I'm an even bigger fan of triples (just ordered a 50-40-30 for a new build). A wide range of narrowly spaced gears is pleasant to ride.

So your advice, go 50/34 and stay 11-25t cassette?

Lumen

Mr Velo wrote: »

So your advice, go 50/34 and stay 11-25t cassette?

Cost aside, yes. You can then stick a 28 on for really steep hills.

TheBlaaMan

C3PO wrote: »

Gear ratios as follows:
34/25 = 1.36
39/27 = 1.44
39/28 = 1.39

I'm pretty sure there have been posts here where people have used a 28 cassette without issue despite Shimano's advice?

I ride on a 105 5700 Compact 50/34 and cassette is 11/28. No probs

colm_gti

TheBlaaMan wrote: »

I ride on a 105 5700 Compact 50/34 and cassette is 11/28. No probs

As did I until changing to an 11/25, seems 50/34 and 11/28 is the standard offering on most off the shelf bikes, which would make shimanos advice pretty contradictory!

Mr Velo

Yeah, but you guys probably have the full 5700 set up? My bike is all 5600 currently. Shimanos tech sheets state the 11-28 only works with 5700 derailleur/shifters. Would love to be proved wrong on this though.

http://techdocs.shimano.com/media/techdocs/content/cycle/EV/bikecomponents/CS/EV-CS-5600-2455C_v1_m56577569830608751.pdf

http://techdocs.shimano.com/media/techdocs/content/cycle/EV/bikecomponents/CS/EV-CS-5700-3016_v1_m56577569830703168.pdf

camaghead

A 50/34 & a 11/25 gives a range of 2.85m - 9.53m (assumiing a 700x23c) that is in 1st gear for each pedal rev you travel 2.85m and in 20th you would travel 9.53m.

A 53/39 & a 11/28 will give you a 2.92m - 10.10m range. Realistically you would be unlikely to notice the difference except on a fast downhill. Changing to an 11/27 with the 53/39 would go up to 3.03m which you would notice unless you are skinny.

I don't know about the 5600 RD compatibiity - put you could change the rear derailleur as well as the cassette (to 11/28) instead of the Crank. A 5700 RD should work with 5600 stis.

Mr Velo

camaghead wrote: »

A 50/34 & a 11/25 gives a range of 2.85m - 9.53m (assumiing a 700x23c) that is in 1st gear for each pedal rev you travel 2.85m and in 20th you would travel 9.53m.

A 53/39 & a 11/28 will give you a 2.92m - 10.10m range. Realistically you would be unlikely to notice the difference except on a fast downhill. Changing to an 11/27 with the 53/39 would go up to 3.03m which you would notice unless you are skinny.

I don't know about the 5600 RD compatibiity - put you could change the rear derailleur as well as the cassette (to 11/28) instead of the Crank. A 5700 RD should work with 5600 stis.

Thanks Camaghead. Can u explain the 3.03m I'd notice (cos I ain't skinny)

camaghead

Mr Velo wrote: »

Thanks Camaghead. Can u explain the 3.03m I'd notice (cos I ain't skinny)

The difference between 2.85m and 2.92m is 7cm per rev (not to much of a difference), a further 11cm (to 3.03m) may be a bridge to far on a steep incline.

Mr Velo

camaghead wrote: »

The difference between 2.85m and 2.92m is 7cm per rev (not to much of a difference), a further 11cm (to 3.03m) may be a bridge to far on a steep incline.

So you'd be another one to recommend 50/34 and 11-25?

camaghead

Mr Velo wrote: »

camaghead wrote: »

The difference between 2.85m and 2.92m is 7cm per rev (not to much of a difference), a further 11cm (to 3.03m) may be a bridge to far on a steep incline.

So you'd be another one to recommend 50/34 and 11-25?

No you have options.

They are;
1. 50/34 with a 11/25. Here you need to change you crankset.
2. 53/39 with a 11/28. Here you need to change your cassette + maybe your rear derailleur.

Both will give you equivalent gearing.

You could also do 11/27 with option 2, however that would be more challenging but at least you could keep your existing rear dérailleur.

Mr Velo

colm_gti wrote: »

As did I until changing to an 11/25, seems 50/34 and 11/28 is the standard offering on most off the shelf bikes, which would make shimanos advice pretty contradictory!

So I take it running the compact with an 11-28 or an 11-25 is just a personal choice thing? Does the 11-28 add any other benefit apart from the obvious help with climbing?

Dubba

A 11-26 with a compact or double is better that a gappy 11-28 in my opinion.
Same ratio as a 11-25 but with one easier gear for the steep stuff.

11-25 (11-12-13-14-15-17-19-21-23-25)
11-26 (11-12-13-14-15-17-19-21-23-26)
11-28 (11-12-13-14-15-17-19-22-25-28)

Mr Velo

Dubba wrote: »

A 11-26 with a compact or double is better that a gappy 11-28 in my opinion.
Same ratio as a 11-25 but with one easier gear for the steep stuff.

11-25 (11-12-13-14-15-17-19-21-23-25)
11-26 (11-12-13-14-15-17-19-21-23-26)
11-28 (11-12-13-14-15-17-19-22-25-28)

I don't think Shimano do an 11-26 cassette though do they?

Dubba

No, but sram and Shimano are compatible as far as I know.