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NJ Gator
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Hey all!

I am old school- so I was taught to never-ever--E--V--E--R shift to a lower gear when under load. Meaning when I am climbing I would never shift to an easier gear in order to avoid damaging/bending parts.

Flash forward to now- I am riding my first really modern drivetrain. SLX 12 Speed stuff.

I thought I read it was now okay to downshift under load on these newer drivetrains.

Is this legit or did I make it up?

I ask because I find without a gear indicator window the shifter I find I am in the wrong gear in g-outs and I have been shifting under load more and more.

Is this a bad habit I am developing?
 

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since 4/10/2009
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the old rule you were following was overly simplistic. increasingly modern drivetrains have become slightly more forgiving than older ones in regard to shifting under load. It's still best practice to give a little soft pedal if you're trying to shift under load, and it's still best practice to anticipate shifts before you absolutely have to. these techniques have always worked for conventional drivetrains (gearboxes and internal gear hubs work differently so different rules apply) and they will always work as long as conventional drivetrains exist.

It's not a "you could never do it before and you can now completely abuse your drivetrain" black/white scenario. it's never been that.
 

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since 4/10/2009
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Shimano says go for it and that it actually shifts better under load. Some of our rentals have it and it doesn't seem to be a problem.
I've been riding on it for a couple years now. it shifts under load a little (but noticeably) better than 11spd, which was a little (but noticeably) better than 10spd (and so on). I've absolutely found limits to its ability to shift under load. I actually searched for those limits because I was curious about shimano's claims, and I definitely was able to make it jam, and I can replicate that. I also teach clinics for beginners and I demonstrate to them what a bad shift sounds like.
 

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I've been riding on it for a couple years now. it shifts under load a little (but noticeably) better than 11spd, which was a little (but noticeably) better than 10spd (and so on). I've absolutely found limits to its ability to shift under load. I actually searched for those limits because I was curious about shimano's claims, and I definitely was able to make it jam, and I can replicate that. I also teach clinics for beginners and I demonstrate to them what a bad shift sounds like.
Yeah I ride it a lot too, nearly every day and haven't discovered it's limits yet.

I'm just saying that for all practical purposes it's no problem and nothing to worry about.
 

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the old rule you were following was overly simplistic. increasingly modern drivetrains have become slightly more forgiving than older ones in regard to shifting under load. It's still best practice to give a little soft pedal if you're trying to shift under load, and it's still best practice to anticipate shifts before you absolutely have to. these techniques have always worked for conventional drivetrains (gearboxes and internal gear hubs work differently so different rules apply) and they will always work as long as conventional drivetrains exist.

It's not a "you could never do it before and you can now completely abuse your drivetrain" black/white scenario. it's never been that.
^^^THIS^^
 

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I've posted this before, but for as long as I can remember there've been people telling me you can shift under load, and for the same period of time, I've bent cassettes every time I've tried to do it. I don't think I have superhuman legs or anything so I guess I just live in a different universe than those people.

Granted I've never run 12speed so I'm not sure about that. It sort of stands to reason that with the cogs closer together, maybe it would be better because the angle is not pulling sideways as much when you shift.
 

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XTR cassettes are too expensive for me to experiment on. But as I RARELY feel the need to slam down several gears at once, I just use my usual method. I click, feel it shift, then click again if I need another one. With a modern cassette you are looking at shift ever pedal stroke, maybe two shifts? I do tend to lighten the load on the cranks for that instant too, but it feels like on the modern drivetrains that unloading is pretty damn minimal.
 

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Modern 12-speed (as embodied in the SLX M7100) is much more tolerant of shifting under power than transmissions of yore, but the same physical limits remain when you derail a chain from one cog to another: for at least some part of the process, the tension that is being transmitted to the cassette becomes supported by a decreasing number of teeth until the shift is complete. In extreme cases, you can damage the load-bearing teeth/tooth under peak loads at the wrong time. In not-extreme cases, you're still putting all that work into a very small contact area, which will accelerate its wear.

So more fault-tolerant, but still benefits from mechanical sympathy.
 

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Modern 12-speed (as embodied in the SLX M7100) is much more tolerant of shifting under power than transmissions of yore, but the same physical limits remain when you derail a chain from one cog to another: for at least some part of the process, the tension that is being transmitted to the cassette becomes supported by a decreasing number of teeth until the shift is complete. In extreme cases, you can damage the load-bearing teeth/tooth under peak loads at the wrong time. In not-extreme cases, you're still putting all that work into a very small contact area, which will accelerate its wear.

So more fault-tolerant, but still benefits from mechanical sympathy.
Independently of any claims, the chain would gradually have load distributed over less and less teeth of the smaller gear, then that awkward angled larger gear engagement comes turning until it "snaps" and then load is supported by many teeth again, no?

I don't know how better that transition has been made, but if you want to break or bend a chain sideways, that's the best method - multiple shift and maximum power.

Unless they figured a way where there are perfect 2 chain displacements every so often between adjacent gear teeths, and some magical grooves and bumps only call the chain at those points.

Myself, 2x10 is still working, likely OK next 20 years...
 

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Hey all!

I am old school- so I was taught to never-ever--E--V--E--R shift to a lower gear when under load. Meaning when I am climbing I would never shift to an easier gear in order to avoid damaging/bending parts.

Flash forward to now- I am riding my first really modern drivetrain. SLX 12 Speed stuff.

I thought I read it was now okay to downshift under load on these newer drivetrains.

Is this legit or did I make it up?

I ask because I find without a gear indicator window the shifter I find I am in the wrong gear in g-outs and I have been shifting under load more and more.

Is this a bad habit I am developing?
Just keep on keeping on, it won't hurt the drivetrain if you do shift under load when you need to
 

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I have this issue. But then I am running sram xx1 chain and cassette with xtr shifter and derailleur.

Torn the chain twice under heavy torque changing from second lowest to lowest gear. When I say torn, it is not the chain rivet popping out and the chain breaks, but literally shear in tension the inner chain link in 2 pieces, on both sides.

This is happening at steep, about 25% grade and I am hammering away trying to avoid the lowest cog. Usually it gets unbearable and I needed to shift to the largest cog.

So it happens. But perhaps mixing drivetrain had something to do with it.
 
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