Frictions differences between Ultegra RX DI2 derailleur and Ultegra DI2 classic derailleur

Discuss light weight issues concerning road bikes & parts.
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by romanmoser

Hi !
Technical question for a change :unbelievable:

I need a DI2 Ultegra long cage derailleur
It is for my aero disc road bike, I rode in the south part of Belgium , roads are 50% bads , holes etc then 25 % okayish and 25 % good roads .
I hate cobbles and try to avoid them because of my light weight even if I did the Ronde Van Vlanderen Gran fondo twice the middle distance and the longer one .

I've read that intersting article about frictions ( and power loss thus ) in a 1X transmission .
The writter is sponsored by Sram but I guess he could use 2X ETAP or something too ...

The conclusion is that the minimal losses in power consecutives to the clutch
are compensated by the fact that the chains don't dance everywhere and stays put
It's on a 1X tough

What's your opinion about me using a ultegra rx with clutch on my 2X road bike ( 26 to 30mm measured tires ) ?
Will I loose some energy ?
I guess maybe pros sponsored by shimano would use them in others races if they was no disadvantages
But sometimes pros team don't do the best choice and if they used the rx all season they wouldn't be on dura ace :!: ... rivetrains

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by spdntrxi

I cant notice anything while riding with it on or off. I use the RX Di2 RD with a 2x system. I feel a little more resistance when turning the cranks by hand, but that pressure is nothing compared to riding leg power.

by Weenie

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by Multebear

romanmoser wrote: ↑
Mon Sep 17, 2018 8:09 pm

What's your opinion about me using a ultegra rx with clutch on my 2X road bike ( 26 to 30mm measured tires ) ?
Will I loose some energy ?
There's something wrong with these two questions.

It's not about opinion. Either you will lose some watts or you wont. It's not something one could have an opinion about. It's something, that can be tested. Pretty sure someone tested it and posted it somewhere.

I ride with Ultegra RX rear mech on a 2x system. I don't feel any loss of watts. But if there is a loss, it probably wouldn't be more than 1-2 watts. And how would I ever feel that difference.

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by IrrelevantD

I have no actual data to support this, I'm just thinking this out logically here....

I would be very surprised if you saw more than a Watt difference between different deraileurs. AFAIK, the pulleys are the same, so the only place you really should lose power would be because you have a longer chain. All of the power transfer is hapening on the top side between the chainring and the cogs. All of the extra links of chain for the longer deraileur are on the slack side as the wheelbase doesn't change. Even at that, I don't know that simply having the extra links would inherently create additional friction as the pulleys being the same size aren't going to create any additional movement. Perhaps less due to the longer cages creating more open angles.

Now, if there is more friction in the bearings/bushings in the pulleys, that obviously would make a difference, but I think you would see more of a difference in power loss between 26mm and 30mm tires than in the length of a deraileur cage.
* There is a 70% chance that what you have just read has a peppering of cynicism or sarcasm and generally should not be taken seriously.
I'll leave it up to you to figure out the other 30%. If you are in any way offended, that's on you.

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by mattr

There was some work on the difference between non-clutched and clutched MTB mechs. It's bugger all *unless* you wind the tension right up. Even then, it's only a couple.

On my MTBs, i experimented and wound the tension off until the mech stopped working (bouncing chain) then added a tiny bit of clutch. Now they work (no bouncing chain) and barely noticeable drag (even spinning by hand).

The big tell tale is the extra shifting loads when you have lots of clutch tension.......

by Weenie

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by romanmoser

@Multebear : In the first question , I don't include any word about power loss , friction : right ?
In the second I did

It may seems paradoxal
Thanks to all for yours returns anyway :)

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