Ultegra chain rings options

murr_walker

Hello all,

I have an ultegra crank set with mid compact chain rings, 52/36,

I think i would like to change the lower chain ring for a 34, has anyone any experience of this?

Dont want to do it if the jump is to large from 34 - 52 when shifting and this would cause any issues....

any advice much apprciated!

P.s think this will have much noticeable effect on the lowest gearing?

Thanks

apreading

I am not sure that you can get a 34 ring on you current cranks - I think they are 130mm BCD and a 34T wont fit on that.

Heatwave48

I've been wondering about running this as well for doing long steep climbs. I think the 4 arm shimano chainsets are all 110mm BCD so every combination should fit but I'm also worried about the shifting. I think shifting down should be okay especially with a chain catcher but up could be an issue as the ramps are designed specifically for the 53/39, 52/36 and 50/34? I think it'll probably work but not just not as smoothly.

dgunthor

34 will be fine, in effect you'll gain one extra easier gear. it's more normal to see a 50-34 combination though.

unless you are running a 28T or 30T sprocket at the rear cassette already, you'd get the same benefit by fitting a different cassette.

52-36 is a new combo, I'd personally stick with that and change the cassette - cheaper this way too

apreading

My mistake - not familiar with these new fangled 11 speed things! Seems like a good move as I always wondered why they didnt use 110BCD for all chainrings in the past...

ben@31

I'm running a 50-34 compact and 11-28 cassette. Looks like I can't go any bigger with the cassette using my current Ultegra Di2 rear derailleur. Can I get lower gearing the other way around by fitting an even smaller chainring? Would a 33 chainring make much difference?

murr_walker

ben is correct, you need a long cage deraliier to go to a 32 t casette,

i think i will give the 34t chain ring a go, there only 20 quid!

trailflow

Would a 33 chainring make much difference?

I recently changed from 34 to 33. Its not massive but its definitely noticeable. I didnt think 1 tooth would make much of a difference on the small ring but it did. i can feel it spin easier and i can hold a higher cadence overall. One of those upgrades i wish i'd made sooner. Well worth it i think. It was much cheaper than buying a new RD and cassette.

ben@31

trailflow wrote:

I recently changed from 34 to 33. Its not massive but its definitely noticeable. I didnt think 1 tooth would make much of a difference on the small ring but it did. i can feel it spin easier and i can hold a higher cadence overall. One of those upgrades i wish i'd made sooner. Well worth it i think. It was much cheaper than buying a new RD and cassette.

Which chainring did you buy?

ben@31

With a Ultegra ss rear derailleur what is the maximum chainring difference? I mean how small a chainring can you go on the front while getting bigger on the back? Could you have 30T on the back with a 33T on the front, or is this too much of a difference?

This is what the Shimano website said, but I'm not familiar with the terms used.

ULTEGRA SS Rear Derailleur

Model Number : RD-6800
Series : ULTEGRA
Cassette Compatibility : CS-6800
Maximum Sprocket : 28T/12T
Minimum Sprocket : 23T/11T
Maximum Front Difference : 16T
Total Capacity : 33T

Ashbeck

Another, cheaper solution, is to buy a mechanical Ultegra or 105 medium cage derailleur for £23-38 and simply take the cage off and stick it on your current Di2 rear derailleur. Then you can run a 11-32 cassette.

Its a lot cheaper than buying a medium cage Di2 derailleur and a new cassette.

ai_1

ben@31 wrote:

With a Ultegra ss rear derailleur what is the maximum chainring difference? I mean how small a chainring can you go on the front while getting bigger on the back? Could you have 30T on the back with a 33T on the front, or is this too much of a difference?

This is what the Shimano website said, but I'm not familiar with the terms used.

ULTEGRA SS Rear Derailleur

Model Number : RD-6800
Series : ULTEGRA
Cassette Compatibility : CS-6800
Maximum Sprocket : 28T/12T
Minimum Sprocket : 23T/11T
Maximum Front Difference : 16T
Total Capacity : 33T

I have no particular expertise with this but it would seem self explanatory that the above means the following:
Maximum Sprocket : 28T/12T
Largest big sprocket is 28 teeth and biggest small sprocket is 12 teeth

Minimum Sprocket : 23T/11T
Smallest big sprocket is 23 teeth and smallest small sprocket is 11 teeth

Maximum Front Difference : 16T
Simply the maximum tooth difference between the two chainrings. i.e. 50-34=16, 52-36=16, 52-34=18 so your proposed 52/34 chainring combo is not consistent with Shimano's recommendations.

Total Capacity : 33T
I assume this is the tooth difference between small-small and big-big. And working this out for a 52-36 chainset with 11-28 cassette just so happens to give 33.
i.e. (52+28)-(36+11)=33
However your proposed 52/34 chainring combo combined with the same 11-28 cassette is again not consistent with Shimano's recommendations: (52+28)-(34+11)=35

So unless Shimano have played made allowances for the fact that many people will use these components beyond the specificed ranges, you're likley to have issues with the SS rear derailleur not clearing a bigger sprocket than 28 teeth and not taking up sufficient slack for a 35 tooth difference. The later is unlikley to be a problem if you ensure you don't cross chain (don't use big/big and small/small)

janwal

Ben@31 you can run a 12-30 cassette on Ultegra Di2.Had one on mine for a year with no problems.Just make sure you have the rear screws adjusted so the 30 clears the jockey wheels.It does run close but does not cause me any probs at all.I use the Tiagra 12-30,only £12.49 at CRC.Slightly heavier by a few grams but changes perfectly.

trailflow

Which chainring did you buy?

Stronglight CT2 from Acycles

DKay

janwal wrote:

Ben@31 you can run a 12-30 cassette on Ultegra Di2.Had one on mine for a year with no problems.

You can't get a 12-30t 11speed cassette and I think the OP is running 6870.