Barrettscv 

I have two bikes that are used on gravel that might get new derailleurs this year. Both are disc brake bikes with 142 thru axles and mechanical shifting systems. One is a 2x11 46/33 with a 11-36 cassette, the other is a 2x11 48/31 with an 11-32. Both bikes run perfectly with a 5800 105 series GS rear derailleur. I’m not using a wolf link on either bike.

Shimano now has the RD-RX800 and the RD-RX810 rear derailleur. Both of these have a clutch that can be switched off. It turns out that using the clutch increases mechanical friction slightly, and switching the clutch off is recommended when primary on smooth pavement. The new derailleurs are also heavier and more expensive than the r7000 or r8000 series rear derailleurs.

It it would be nice to cut down on chain slap, but I’m thinking: Don’t fix what’s not broken. Has anyone replaced their road derailleur with the new gravel models?

frankm1

How about the Ultegra RD-RX805-GS?

Barrettscv 

You tell me.

mstateglfr 

I switched from a 5800rd to the Ultegra RD-RX805-GS. There is less chain slap when the clutch is engaged, obviously, but I think there is less slap when it isnt engaged too. That second part may be wrong and just gut feeling, no idea.

I wrap a strip of old inner tube around the DS chainstay still, mostly out of habit/ritual. Redundant for sure.

Anyways, the Ultegra RD-RX805-GS works fine and I dont notice increased resistance when using the clutch. I am already on gravel and bouncing off small rocks a bunch- it's pretty difficult to determine what watts are lost from the clutch versus what watts are lost from the road surface.


I was very much in the camp of 'dont fix what isnt broken', but had the chance to use my 105 RD on a different frame build I'm going to do soon, so that made for a good excuse to buy the Ultegra RD-RX805-GS.

If building new, I would absolutely have gone for the Ultegra RD-RX805-GS or a new gravel model without a doubt. Seems like a good upgrade if you are looking for something to change and have a hundred bucks burning a hole.

Barrettscv 

Thanks, great info. The 5700 derailleurs are 3 years old with lots of dusty miles. I’d also like to match the crank & FD.

Cyclist0108

I haven't replaced mine on my main ride, but we now have a few bikes with clutches.

For 1X mountain bikes, I think it is an asset, but is one more maintenance item.

For my 2X drop-bar off-road touring bike, I turn the clutch off. I found it introduced a large amount of resistance when used with my larger chainring. If you want to get rid of the extra weight, you just have to take it out.

On my kid's 1X 12-speed mountain bike, we are on clutch #3 . They have been a bit problematic. Fortunately, they are cheap to replace. More on that experience on my mtbr thread.

csrpenfab

I have the Ultegra RX800 on my Niner, and I run the clutch engaged 100% of the time. I see no difference in shift quality with the clutch on;off, and I get zero chain slap.

katsup

I'm running the Ultegra RX800 GS and keep the clutch enabled. It's a little stiffer to shift when in the large chain ring and small cogs, but it works fine. I don't notice any difference with the pedalling.

rosefarts

I use an SLX rear derailleur with a clutch on 1x.

With proper chain length on a 1x, there isn't hardly any slap anyway. It causes a lot of drag, not noticable when pedaling but I bet it actually costs quite a few watts. I keep it switched off unless I'm doing something pretty heinous.

I hear some systems, maybe higher end Shimano or the Sram setup that doesn't have a switch, don't cause measurable drag.

dwmckee

It is for more than reducing chain slap. It is helpful for reducing chain drops as well... Thise can cost you time in a race, or can cause frame damage in some cases... If you ride mostly road, maybe no need to change, but if you ride regularly on gravel they are pretty useful.

mstateglfr 

Sure, clutch is beneficial for 1x. I didnt mention since the op has 2x.
I've ridden all my gravel on 3x and 2x- haven't dropped a chain. Hasn't ever been an issue. I dont constantly check the drivetrains and only do maintenance when shifting gets worky, but no chain jumped off the rings due to lack of clutch. Obviously this is a test group of 1 so it's limited.

You are the shop owner- do you hear a lot from rider with 2x and properly adjusted drivetrains losing their chain due to a lack of clutch?

unterhausen

I have been using a SRAM clutched rear derailleur on my road bike for a couple of years and am pretty happy with the way it shifts. I have a Shimano Ultegra GS on my travel bike, and I can't really tell the difference between the two. 10 speed on both bikes, if that makes a difference.

My gravel bike has a RD with a heavy spring, it was the last generation before clutches came out. Clutches are definitely better

csrpenfab

I’ll have to disagree with your comment that a clutched rear mech costs watts. Chain is still going around same pulleys, all the clutch is doing is holding the rear cage tight to prevent chain slap, That’s not increasing friction in any way.

redlude97

A clutched RD generally has a higher tension spring in addition which is where most of the extra friction loss comes from. You also lose watts when shifting with the clutch on. As for clutches and 2x preventing drops I would say it does, at least while racing and in really sloppy conditions. I raced cx my first 1.5 seasons without a clutch on 2x followed by attempting 1x without a clutch on a 5800 rd with increased pulley tension. Still didnt help and still got drops. Since then ive gone clutched for both my 1x race bike and my 2x gravel bike and havent experienced a drop since then knock on wood.

Cpn_Dunsel

Interesting info in here:

https://www.ihpva.org/HParchive/PDF/hp50-2000.pdf

From the work: "Experimental results indicated that
the efficiency of the chain drive varied
as a function of chain tension. It was
found that the efficiency varied linearly
with the reciprocal of the average
chain tension with the highest efficiencies
occurring at high chain tensions
and lowest at low chain tensions. For
example, the highest efficiency measured
in the study, 98.6%, was measured
at a chain tension of 305 N and
the lowest, 80.9%, at 76.2 N."

Looks like a clutch increases efficiency, according to that study.

redlude97

I believe that is referring to chain tension along the upper run of chain between the cog and chainring, whereas pulley cage tension affects the lower run of chain which includes the two small radius bends around the pulley which does not contribute to forward propulsion

Barrettscv 

Both are a factor. Friction is the result of the contact between the pin and the bushing and at the contact area between the side plates. This friction is most critical when the chain starts to wrap around the cog or chainring, it’s equally critical as the chain unwraps or becomes linear. The load on the chain increases the amount of friction from negligent to significant. I’ve supplied Industrial chain to people like Caterpillar, so this is an application I’ve studied.

redlude97

Under load, what is the relative contribution of the upper wrap/unwrapping compared to the bottom wrap/unwrap? My understanding is the tension along the top is orders of magnitude higher

Barrettscv 

Certainty the upper run, connecting the torque at the chainring to the cog at the wheel is going to be greatest source of friction, especially under acceleration or when climbing. However, the lower run must wrap around the derailleur sprockets and this is a significant source of friction, especially if the derailleur uses a spring and clutch to limit slap. Shimano would have to provide data on the clutch tension to determine the loss in efficiency.

Koyote

So the question is: will you be slowed down more by losing a few watts, or by a dropped chain? Seems like the answer would depend on the ride or race, and hence a clutch that can be disengaged (a la Shimano) is best.

shoota 

I'm running the the new RX Ultegra rd 1X with clutch engaged and dropped my chain for the third time today since I've installed it. Maybe I'm the unlucky one but I haven't dropped the chain one single time between my other two bikes that are running non-clutched RDs 1X.

Bryan C. 

I'm not sure how many other people run a wide range 40t+ cassette but I had a problem with abruptly stopping pedalling at a high cadence rate. The momentum of the cassette causes it to continue spinning for another half rotation or so. This creates slack in the chain momentarily and is sometimes enough to cause a chain drop if you pedal forward during this event. My bikes with clutched derailleurs do not have this issue.

I had this condition sporadically on my road bike with a Ultegra R8000 GS derailleur and an 11-32 cassette. My hybrid/touring bike with a Tiagra 4700 and an 11-40 cassette has this issue too. A shorter cage(SS) DA derailleur helped the road bike but I suspect only a clutched derailleur will fix my touring bike with very long chainstays.

rosefarts

I believe it's possible to keep a clutch and have low enough friction that it doesn't matter.

On the workstand, there is a huge difference in the force required to pedal. Correcting this was actually one of my projects for sick leave.

I was only pointing it out because if you search for friction and clutched derailleur, it quickly becomes obvious that I'm not the only one who has experienced this.

redlude97

I've had the momentum issue with 11-36 and 11-40 cassettes. My understanding is that the chain derails off the top of the chainring when it loses tension and that is what causes the chain to drop when you resume pedalling. A clutch doesn't necessarily stop that, at least that was the case with aqua blue and trek segafredo
https://road.cc/content/tech-news/24...-talking-about
https://www.cyclingnews.com/news/mec...wqxSLzfq6QCZtk

redlude97

Under what conditions is the chain dropping, can you tell if its off the top or bottom of the chainring and to the inside or outside?