V-Brakes Power Modulator

[Peter Rosenfed]

I just got a new bike with Shimano V-brakes. The front brake has a "power modulator" on it. I've
been practicing emergency braking with this new bike and I can't get the back wheel to lift off when
using the front brake. I'm unsure whether this is due to the power brake or whether I'm still
getting use to the new bike's geometry and the longer pull on the V-brakes ( I'm used to center pull
and the older-style cantilever brakes).

Pulling as hard as I can, the lever doesn't bottom out, so I assume I'm getting full braking force.

I just did some research on these things and found some of the older postings by Sheldon Brown about
what he regarded as the problem with the power modulator.

Has the problem been fixed, or do they still limit maximum braking force?

Also, what ias the worst case failure mode of the power modulators? Are they more likely to fail
than a cable without the modulator on the noodle?

Thanks

-Peter

 

[David Damerell]

Peter Rosenfed <[email protected]> wrote:
>I just did some research on these things and found some of the older postings by Sheldon Brown
>about what he regarded as the problem with the power modulator. Has the problem been fixed, or do
>they still limit maximum braking force?

That's their designed function - that bug is a feature. If you're not likely to clamp on full force
and give yourself a free flying lesson, take the stupid thing out.

>Also, what ias the worst case failure mode of the power modulators?

No brakes at all, I expect.

>Are they more likely to fail than a cable without the modulator on the noodle?

Clearly yes, to some degree - it's just extra fiddliness.
--
David Damerell <[email protected]> flcl?

 

[Sheldon Brown]

Peter Rosenfed wrote:
> I just got a new bike with Shimano V-brakes. The front brake has a "power modulator" on it. I've
> been practicing emergency braking with this new bike and I can't get the back wheel to lift off
> when using the front brake. I'm unsure whether this is due to the power brake or whether I'm still
> getting use to the new bike's geometry and the longer pull on the V-brakes ( I'm used to center
> pull and the older-style cantilever brakes).
>
> Pulling as hard as I can, the lever doesn't bottom out, so I assume I'm getting full
> braking force.
>
> I just did some research on these things and found some of the older postings by Sheldon Brown
> about what he regarded as the problem with the power modulator.
>
> Has the problem been fixed, or do they still limit maximum braking force?

It's not a problem "with" the Power Modulator, the Power Modulator itself is inherently a problem.

It is designed to limit braking power so that you _can't_ lift the rear wheel. Shimano's legal
deparment seems to think that they are at a higher risk of getting sued if somebody overbrakes and
goes over the bars, than if they can't stop in time to avoid a crash.

The fundamental concept is fallacious, and my advice is to remove the power modulator, smash it with
a big hammer and throw it in the trash where it belongs.

Sheldon "Am I Making Myself Clear?" Brown
+--------------------------------------------------------------+
| The greatest pleasure of a dog is that you may make a fool | of yourself with him, and not only
| will he not scold you, | but he will make a fool of himself too. --Samuel Butler |
+--------------------------------------------------------------+ Harris Cyclery, West Newton,
Massachusetts Phone 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts
shipped Worldwide http://captainbike.com http://sheldonbrown.com

 

[Peter Rosenfed]

Sheldon Brown <[email protected]> wrote in message
news:<[email protected]>...

> It's not a problem "with" the Power Modulator, the Power Modulator itself is inherently a problem.
>
> It is designed to limit braking power so that you _can't_ lift the rear wheel.
>

Does the modulator actually limit the maximum deceleration you can achieve, or does it simply change
the braking profile so that it is less "grabby"? In other words, does it require more pull to
achieve the same maximum braking force, or does it actually threshold the braking force?

I had thought that the mdoulator was simply an elastomer hooked to the cable that stretches when you
pull on the cable, adding a bit of non-linearity to the pull. In this is the case, if there is room
for enough pull on the lever you should still be able to reach the same force.

-Pete

 

[M Gagnon]

"Sheldon Brown" <[email protected]> a écrit dans le message de news:
[email protected]...
>
>
... The Power Modulator itself is inherently a problem.
>
> It is designed to limit braking power so that you _can't_ lift the rear wheel. Shimano's legal
> deparment seems to think that they are at a higher risk of getting sued if somebody overbrakes and
> goes over the bars, than if they can't stop in time to avoid a crash.
>

What happens in that Power Modulator? I looked at one of Shimano's instruction sheets (somewhere at
http://bike.shimano.com) and noticed there are three settings:
- H (for high or hard?)
- normal, which is the preset
- L (for Low)

They say one could change the setting, but they don't even suggest what the two other settings do.
For instance, if one sets the Power Modulator to H, does it mean the Power Modulator is more
aggressive at preventing hard braking, or does it mean that one can brake more quickly?

Also, is the Modulator limiting pulling strength in the brake cable or is it actually controlling
the speed at which the bike decellerates? The latter could be a good thing: a bit like the car's
ABS brakes.

Regards,

--
Michel Gagnon -- Montréal (Québec, Canada) mailto:[email protected]