Converting FC-R8000 "53-39" to "50-39" DI2

[scale29]

50/39 doesn't work well on the new Shimano rings. The chain misses the pick up ramps on the big ring and gets jammed between the inner and outer rings. I tried to make it work for a good while, but was too unreliable to stay.

[alcatraz]

If you feel adventurous then by all means try. It'd be cool to find out how much better it can get.

Although I just want to say: be aware that you're already on a top level front shifting setup. Shimano has great front shifting and a standard crank helps to improve this a lot by going 14t difference instead of 16t. 53/39 = 14, 52/36+50/34=16t

Shimano has likely taken extreme care to design those rings as they are common in pro cycling.

Sure you'll get benefits from a smaller tooth difference but what you won't get is chainrings designed to work together. What could happen is that the teeth don't line up optimally at the ramps so you don't get a perfect transition.

I think for an amateur it'll still work great so if you want it go ahead. Personally I wouldn't though if my goal were to achieve amazing front shifting.

[hythamf]

Thanks Russells , philbar72 , bigfloor , scale29 , alcatraz for your usefull inputs , that what i was afraid of , different height of big ring and ramps place to cause any problem "although i'm maintainning <16T difference and even going to a smaller difference"
The thing is i really liked the 39T over the 36T which was useless on flats where i live ,
Moving from 53T to 52T may not be significant i assume (i'm now running 12-25 cassette as i like close cogs .)
So i really can't find a satisfying solution .. however , giving the facts we have here , i will buy a used compact or semi-compact small and big ring together in case mixing standard and semi/compact mix didn't work , in that case i will either use 52,36 rings and sacrifice 39T "Try to spend more time on 52T" , or use 50,34 and stick to the big ring more often ,
In all cases i will use the E-tube app to try to change how syncro shift works to get similar gear ratio (may be go up one cog only instead of two when FD move from small to big ring"
@ scale29 , you tried on R8000/R8050 , correct ?

[ms6073]

52-36 u mean ?

Nope, replaced the DA 53/39 rings on my Shimano Powermeter with Absolute Black 52/38 rings, although I have recently started to consider going down to AB's 36t ring for when we head out to the hill country.

[rainerhq]

50/39 doesn't work well on the new Shimano rings. The chain misses the pick up ramps on the big ring and gets jammed between the inner and outer rings. I tried to make it work for a good while, but was too unreliable to stay.

That what I experienced too. R8000

[scale29]

Yes, on 8000, and 6800. I tired twice as I have the same problem as you, I no longer race so a 50/39 would be the perfect combo for me.

The shifting was fine, no issues at all and super smooth, just sometimes the chain would slide right between the two rings and need the chainring bolts slackening to retrieve it, eventually it bent the inner ring as it did so, so I abandoned the project.

[hythamf]

Yes, on 8000, and 6800. I tired twice as I have the same problem as you, I no longer race so a 50/39 would be the perfect combo for me.

The shifting was fine, no issues at all and super smooth, just sometimes the chain would slide right between the two rings and need the chainring bolts slackening to retrieve it, eventually it bent the inner ring as it did so, so I abandoned the project.

I see , thanks for the reply .. so what you think is better , get a 50,34 rings , or 52,36
If 52,36 : i will try the 52/39 combo , if it give a problem i would change the inner ring to have 52,36 as normal ..
If 50,34 : i will swap both rings right away to 50:34 and change syncro shift of Di2 to shift at earlier sprockets to big ring ,,

[alcatraz]

How about 1x and a wide range cassette like an 11-36. Might do the trick.

What cassette are you using today?

/a

[hythamf]

How about 1x and a wide range cassette like an 11-36. Might do the trick.

What cassette are you using today?

/a

CS-R8000 12-25 .. i like small cogs jumps .. i live mostly in flat terrain so 25T is fine for small climbs .

[alcatraz]

Check some cassettes out, even with big cassettes some still have small high speed jumps.

Shimano cassettes are not the best for preserving low jumps while providing a significant low gear. It's because they don't want the cassette to have a deep valley in it to improve shifting.

An 11-32t cassette and 50t chainring is enough to cover the same low gear you have now. With 12-32t you save one jump.

Sram is better at preserving 1t jumps for high speed gears.

[alcatraz]

If you go 11-28t cassette a ~45t chainring also covers the same gear ratios as 50/39t + 12-25t. 28t 11s sram cassettes have 1t jumps all the way to the 17t cog, which is generous.

[hythamf]

I made a gear ratio comparison for my 12-25 cassette , along with my current 53-39 and 52-36 .
Anyone tried the 52-39 combination ??

[scale29]

52/39 should work reasonably well I’d have thought

[SilentDrone]

This doesn’t directly answer your question, but I’ll throw it out there for those who are interested...

I’m running dura ace 7800 with a 50/39 up front and an 11/28 out back. In the 7800 this was a Shimano designed combo. I absolutely LOVE the 50/39 up front. It’s a great combo. Front shifting is effortless and smooth, and I like that there’s not a huge gap. Makes a very useable combo on rolling terrain and flats.


Sent from my iPhone using Tapatalk

[hythamf]

@ scale 29 , thanks , probably i that is what i will try and update the result here .
@ SilentDrone , thanks for your input , yes i think it's indeed a great combo in flats , short climbs and rolling terrains .