More Brakes

On 13/12/15 18:08, wrote:

snip

How do I post a picture?

Is good enough for this.

http://picpaste.com/Boat-DGqctqz9.jpg

In the pictures you can see that the angle is a little long
un-actuated. But the closer to full-on the closer to 90 degrees the
angles get. So the change in angles isn't the problem since the
harder you pull the better the leverage gets.

Since the pads are stock I think that I'll try your advice and try a
softer higher traction brake pad.

On Sunday, December 13, 2015 at 12:08:35 PM UTC-5, wrote:
On Sunday, December 13, 2015 at 8:46:10 AM UTC-8, Frank Krygowski wrote:
On 12/13/2015 10:54 AM, Sir Ridesalot wrote:
On Sunday, December 13, 2015 at 10:41:23 AM UTC-5, wrote:
On Friday, December 11, 2015 at 3:44:55 PM UTC-8, Frank Krygowski wrote:
On 12/11/2015 5:18 PM, wrote:

To get to the point - are linear pull brakes superior?

If it really requires super hand strength to operate your brakes, I'd
think something else is wrong. Maybe you could give us more details: Is
the bike new? What model? What brake levers? Are the cantilevers the
classic L-shape, or the newer "low profile" shape?

Regarding potential problems: Do the brake shoes need to be replaced?
(Try Kool-Stop Salmon.) Do the cables need to be lubricated or replaced?
Are the cables well aligned, or is there a chance the inner wire is
scraping around some sharp corner? Is there any interference of moving
parts?

Sorry about the delay, lots of home improvements to get through.

The bike is a Ridley XBow. The brakes are Shimano BR-R550's. The levers are Shimano 6800 105 with the internal cables.

I'm using the "F" spreaders that come with the brakes.

I've tried all of these things before but since recovering from my concussion after two and a half years I can't remember these things.

Now I'm sure I could improve the brakes marginally with softer pads I don't know if it would be significant enough to bother with.

Also it appears to me that the "racing" cantilevers are mainly designed to do nothing more than reduce weight. The levers are more perpendicular to the cable but the "Y" in the cable is longer. Does this balance out or actually lighten the brake loads?

I'm not kidding about how much muscle strength it requires to operate. So much that it makes steep downhills dangerous on the bike.

A link to a closeup image of your brakes front and rear would be a big help in diagnosing the problem.

Remember that if you do go to linear pull brakers aka V-brakes you'll need an adapter like a Travel Agent in order to use your 105 brake levers.

I'll second that request for a photo.

How do I post a picture? In the pictures you can see that the angle is a little long un-actuated. But the closer to full-on the closer to 90 degrees the angles get. So the change in angles isn't the problem since the harder you pull the better the leverage gets.

Since the pads are stock I think that I'll try your advice and try a softer higher traction brake pad.

You have to upload the image to an image sharing site like FLICKR or PHOTOBUCKET and hen post the limk to the image here.

Cheers

On 12/13/2015 11:45 AM, wrote:
On Friday, December 11, 2015 at 5:45:24 PM UTC-8, Frank Krygowski wrote:


I suppose we could get into a technical discussion about what affects
the performance of cantilever brakes. I'd say a prerequisite would be
to read and understand Sheldon's article. Then be prepared for some
equilibrium calculations - you know, free body diagrams, summing forces,
summing moments, all that.

Frank, in Sheldon's discussion of the U-brake it sort of hit a spot. As you apply the Cantilevers the angle between the actuation cable and the brake reduces thereby causing successively lower mechanical advantage. And that is what my problem felt like.

V-brakes do not have this change in leverage.

OK, if you have low profile cantilevers (those with arms that are nearly
vertical), you'll see a change in mechanical advantage as the cable yoke
pulls upward on the transverse cable. But almost all that motion
happens when the brakes are merely moving the shoes through open air,
essentially taking up slack; and that change in mechanical advantage
doesn't matter much. One the brake shoes contact the rim, there's a lot
less motion, and a lot less change in mechanical advantage.

I suppose the change in cable angles that occurs between light brake
shoe force to heavy brake shoe force (due to flexing of the rubber brake
blocks, spreading of the cantilever bosses, bending in the cables, etc.)
does decrease the mechanical advantage. And I guess this decrease in MA
tends to make the brakes less linear in their action. IOW, if you
applied your brakes, then wanted a 20% increase in braking force, you
might have to apply 25% (a wild guess) more hand force. But I haven't
found that to be a problem.

I'll note that the classic wide profile cantilevers (here's a modern
verson: http://www.ecovelo.info/images/neo-retro-1-485.jpg) had hardly
any of that change the relevant angles. The distance the cable yoke
moves up almost exactly matches the distance the end of the cantilever
arm moves up. The shape of the straddle cable barely changes.

Those wide profile brakes do have other disadvantages, though. The big
one, in my book, is the clearance problem. For example, they tend to
interfere with my rear panniers. Because of that, I use low profile
cantis even on our tandem. Set up with a fairly short transverse cable,
they are very powerful.

--
- Frank Krygowski