change chainring or cassette

[panosk]

I am thinking of upgrading my crankset from 5800 to 9000.
The problem is that at the crank length i want, only 53/39 is widely available.

My current set up is 52/36 with 11-28 cassette.
With that, i can go up donna buang without much trouble and use 28 cog at the most difficult parts of the climb.

So my dilemma is:
Should i change chain ring from 39 to 36, or change the cassette to 11-32 ?

[Tim]

The 9000 range of chainrings are designed to work as matched pairs ie. 50/34, 52/36, 52/38(is this new?) and 53/39.
I tried combining a 52 and 39. It didn't work very well, the chain hung between the two rings and wouldn't change smoothly.
Apparently some other miss-matched combinations do work but I don't know which.

[BJL]

The 9000 range of chainrings are designed to work as matched pairs ie. 50/34, 52/36, 52/38(is this new?) and 53/39.
I tried combining a 52 and 39. It didn't work very well, the chain hung between the two rings and wouldn't change smoothly.
Apparently some other miss-matched combinations do work but I don't know which.

Interesting. There's only a 13 tooth gap between 52/39 but a 16 tooth gap between 50/34 & 52/36. Initially, I would have thought that the smaller difference might improve shifting.

I wonder if the angle of travel of the front derailleur is too steep for a 52/39 combo. IE - Derailleur ends up at a 'non-optimal' distance from one of the chainrings depending on position and tuning? I take it the 52/38 would be marginal but acceptable if this was the case.

[Tim]

I wonder if the angle of travel of the front derailleur is too steep for a 52/39 combo.

It's more to do with the conical profile/shape of the ramping on the large ring.
With a 52T large ring the bottom of the ramp is designed to drop the chain straight onto the top of a 36 or 38 small ring.
The 39T small ring teeth sit just too high above the bottom of the ramp causing the chain to hang in between the two rings. The side of the chain slides on the edge of the (turning) 39 ring.
Until today I'd not heard of the DA38T small rings paired with a 52T large ring. Might be worth a try one day.

[panosk]

I am aware that 53/36 is not optimal, but the 2 reviewers on wiggles 36t chainring product page, did just that, (replace 39 with 36 on a 53/39), with no problems (http://www.this link is broken.au/shimano-dura-a ... chainring/).

[Derny Driver]

You wouldnt need a 32.
36-28 is pretty close to 39-30
You could put an Ultegra 12-30. Cheapest and best option.
The ramping is different on those front rings. 36-53 will work but not real well.

[panosk]

You wouldnt need a 32.
36-28 is pretty close to 39-30
You could put an Ultegra 12-30. Cheapest and best option.
The ramping is different on those front rings. 36-53 will work but not real well.

12-30 would be ideal but i am afraid there is no 11s cassette with that ratio.
The closest i have found is 11-30 from sram and shimano 9100, at near 9000 crankset prices.

[dalai47]

What is the BCD of the 9000 crankset? Will it even take a 36?

[Tim]

What is the BCD of the 9000 crankset? Will it even take a 36?

110mm.
The new stuff fits everything from a 34 up to 55.

[dalai47]

Thanks Tim. Makes sense from a manufacturing perspective - only need to make the one crank set.

[jules21]

upgrading to a 9000 buys you a bit more cafe cred, but not if you can't get to the top of Donna! I'd stick with what you've got

[Duck!]

It's more to do with the conical profile/shape of the ramping on the large ring.
With a 52T large ring the bottom of the ramp is designed to drop the chain straight onto the top of a 36 or 38 small ring.

The 52T for pairing with 36T is a different ring to the 52T for 38T.

[Tim]

The 52T for pairing with 36T is a different ring to the 52T for 38T.

I was wondering about that.
As I couldn't get a 52/39 pairing to work I wasn't sure how a small ring only one tooth smaller was going to work any better.
So the large ring ramping is different on the 52/36 compared to the 52/38 combination?
Bugger, that means if I wanted to try out a (cheapish) 38 ring I'd have to also buy an horribly expensive different 52 big ring.
Nope.

[Duck!]

Yeah, different ramping, and also the angling of the inner face of the big ring toward the little one, which was part of the problem with your previous experiment. With a bigger small ring, the inner face of the big is more sharply angled, where the smaller small ring needs a flatter-faced big ring to guide the chain properly.