Changing chain ring ok?

[MrWill]

I've just bought an 105 5800 chainset with 50/34.

I want to change it to a 50/39, which I would prefer over the 53/39 because I have an 11 tooth cog on my cassette.

So if I put a 39t ring from the matching groupset, will it work flawlessly like it does now, or are they designed to work as 50/34, 53/39, 52/36 as they come?

 

[Hacienda71]

Should be fine, just make sure you buy a chainring with the right bcd/compatability.

 

[gbb]

As Hacienda says, if the BCD is correct, it will work fine.
if you have a dogfang fitted to prevent the chain offing onto the BB, just raise it level with the new chainring.
You might find with generic chainrings such as Stronglite, the shifting MAY not be as crisp, the ramping on more expensive chainrings is better, but its not really a big deal, you may find no noticeable difference.
I always ran a 40t instead of a 34. Worked flawlessly.

 

[byegad]

Ramping helps you change up to a ring, changing down requires no ramps for a smooth change and the larger ring will be ramped anyway.

 

[cyberknight]

As Hacienda says, if the BCD is correct, it will work fine.
if you have a dogfang fitted to prevent the chain offing onto the BB, just raise it level with the new chainring.
You might find with generic chainrings such as Stronglite, the shifting MAY not be as crisp, the ramping on more expensive chainrings is better, but its not really a big deal, you may find no noticeable difference.
I always ran a 40t instead of a 34. Worked flawlessly.

Can you get 40 inner rings in a compact BCD ?, i always thought that 38 was the maximum which would be close to the OP`s requirement .I currently run a 50 /36 which to me is just right as you get the same tooth drop from 50/36 as 53/39 .

 

[gbb]

Yep, I ran Dural 40t on mine, ordered in by my LBS. 36, 38, 39, 40...I think 40 is the max you can get.
My terrain is mostly flat, slightly hilly in places. I spent most of my time on a 40, with a 11-25, i found it just right.
Different terrain, different riders will of course have different combos, we all find what suits. The good thing is, an inner doesnt cost too much and you can afford to experiment without breaking the bank.

 

[youngoldbloke]

110 bcd chainrings from Spa from £10, large selection.

 

[Hacienda71]

I suspect 105 5800 may only take a four bolt ring, so the op needs to double check compatability as well as bcd.

 

[youngoldbloke]

I suspect 105 5800 may only take a four bolt ring, so the op needs to double check compatability as well as bcd.

Didn't spot that - think it will have to be a 5800 chainring then, but aren't the new Shimano 11 speed chainsets designed to take any size chainring - no difference in bcd whether compact or 'standard' double
edit: Spa sell Ultegra 6800 chainrings, haven't seen 5800 available anywhere yet - could give them a call maybe?

 

[MrWill]

Yep this 5800 is 4 bolt. And it appears exactly the same and the Ultegra 6800 stuff it's bizarre. It'll be a few weeks before the specific 105 rings are out, but the Ultegra ones are the same it appears.

I just hope it shifts the same, because it's quite remarkable how well it shifts at the moment and it's a 16 tooth difference. I suspect it may because the design of the inner side of the 50t chain ring is a sort of parallel fin arrangement then the usual pins and ramps start towards the teeth. Hopefully the 39 ring does not skip the fin arrangement, this seems to be where the magic comes from.