Shimano Power Modulators

[hatler]

I've got a Shimano Power Modulator (in a bag of odds and ends from SJS).

What's its point ?

I don't think I'm ever going to use it.

Does anyone want it for the cost of postage ?

SM-PM70 (SM-PM70:For V-BRAKE (trekking use))

https://bike.shimano.com/en-EU/technologies/component/details/power-modulator-unit.html refers.

[Jakob W]

I think some of their roller-brakes have them as well; AIUI they do something clever with the MA as the cable pull increases, so that if you grab a fistful of lever you're less likely to send yourself over the bars.

[Brucey]

they just have a spring inside them with a controlled stiffness, so that the brake has some movement modulation rather than practically none (which can happen with a rigid frame/fork in which the bosses don't move, with a short cable run). This supposedly makes the brakes feel more like other bicycle brakes, and more like other brakes in general.

An effect of this is that if you want the maximum possible force from the brake, you have to really mean it; eventually the spring will go coilbound and any further pulling of the lever will quickly ramp up the force as if the spring wasn't there. 

Presumably shimano were worried about folk chucking themselves over the handlebars when they grabbed a handful. I think they were right to worry; with a powerful, unfamiliar brake, it can and does happen.  Once you are used to the brake, probably it  isn't needed so much but in a panic one tends to 'revert to type' so you never know....

cheers

[hatler]

they just have a spring inside them with a controlled stiffness, so that the brake has some movement modulation rather than practically none (which can happen with a rigid frame/fork in which the bosses don't move, with a short cable run). This supposedly makes the brakes feel more like other bicycle brakes, and more like other brakes in general.

An effect of this is that if you want the maximum possible force from the brake, you have to really mean it; eventually the spring will go coilbound and any further pulling of the lever will quickly ramp up the force as if the spring wasn't there. 

Presumably shimano were worried about folk chucking themselves over the handlebars when they grabbed a handful. I think they were right to worry; with a powerful, unfamiliar brake, it can and does happen.  Once you are used to the brake, probably it  isn't needed so much but in a panic one tends to 'revert to type' so you never know....

cheers

Aha !  The emboldened bit explains the yellow and dark grey traces on the graph on that link.

Thank you for the explanation.

Given that virtually every bike I have ever ridden has a different response to pressure on the brake lever, I wonder how we've ever managed without these things. (Clue: Do we perhaps adapt our actions in response to what happens?)

From my perspective, it's a solution to a non-existent problem.

[Kim]

I've seen people who were perfectly competent cyclists go over the bars due to forgetting that their bike had been in for a service earlier in the week.

It's never happened to me, possibly demonstrating a fringe benefit of doing your own maintenance.  But I can see why a risk-averse manufacturer (or, say, hire bike provider) might think it was a good idea.

[hubner]

If you squeeze really hard, like in an emergency, will you definitely go over the bars?

[Kim]

If you squeeze really hard, like in an emergency, will you definitely go over the bars?

Depends on the bike.

[rogerzilla]

If you shift your bum right back off the saddle, you can skid the front wheel instead.  I have form for locking up both wheels but I've never gone over the bars, except that time when I was five and experimentally rode straight into a kerb to see how much it would hurt.