can anyone explain avid's Speed Dial?

The speed dial feature is a on the fly adjustment, used to adjust the feel of the lever.

It does change the leverage, which in turn should change how touchy it is. I haven't used those levers, but on my XT v-brake levers changing the leverage makes a substantial different in brake feel.

after using it on long rides with low and high leverage, i've found the difference., it's hard to explain, but i just put it in the middle.

The speed dial moves the little cam that the cable attaches to, thereby moving the point of leaverage. When the cam moves to the top of the leaverage point (ie, away from the handlebars) the brakes are stronger but less precise. As you dial the thing down towards the bars the you get more control over your braking but less force.

You get the choice. You want the maximum power but least modulation, or least power and maximum modulation, or anywhere in between.

I have these levers and they work great. I've got them connected to SD7 calipers and started off with the cam set for least power, dialing them upward as I got used to the awesome stopping power of these great v-brakes.

I'm afraid you've got things totally the wrong way around Jim. Shortening the pivot increases the mechanical advantage of the brake and thus gives you more power, though with less modulation.

Sam

Jim is correct, and you have things backwards Allo, because you're not just shortening the pivot with the speed dial.

Dial the speed dial all the way down towards the handlebar, and you get maximum modulation and the least power. Dial it all the way out and you get instant on-off, maximum power, but virtually no modulation.

The speed dial changes how much cable is pulled, not just the mechanical leverage. Watch as you dial it in; you pull less cable when dialed in and considerably more when dialed out. Test it yourself.

The speed dial controls leverage and the amount of cable pulled.

So much for just lurking on these forums...

Thanks fonseca, for the defense.

Think of a large metal bar about two metres long. Tie a rope to the top and pull it toward you. The effort required to pull on that rope will be greatest and the distance moved the most.

Now tie a rope somewhere near the bottom. Moving the metal bar the same distance will move the rope only a short distance. The effort required will be much less than previously.

Speed Dial levers work in much the same way. As the cam moves toward the centre of the pivot (ie toward the handlebars) the effort decreases and so does the mechanical effect on the brakes.

Good analogy, much clearer explanation than my above post.

The speed dial is a pretty neat feature. I even use it while riding on occasion, dialing it out when I do a trail that is fast or has long downhills. But it generally stays all the way in since a lot of the stuff I ride has slow technical sections. I wouldn't want to use avid discs without it. 😎

I'm afraid you guys are full of ****. Your analogy about the bar is perfect though Jim - if the rope is near the bottom you have much greater leverage (mechanical advantage) and a better chance of moving whatever that rope is attached to. If you want to learn more go here http://www.sheldonbrown.com/cantilever-geometry.html

Sam

I forgot to add one thing, Fonsecas, leverage IS the amount of cable pulled.

I think we're confusing ourselves by discussing physics rather than brakes.

This we know for sure:

With the cam dialled out any given movement of the brake lever will result in a greater amount of cable pulled than with the cam dialled in. (Think back to the bar analogy.) There will be greater force required by the braking hand, but in effect the rider probably won't notice this. What they will notice is the brakes come on sharper and harder. There is less modulation but more immediate braking.

With the cam dialled in we will see less cable pulled through for any given movement of the brake lever. We do have an actual mechanical advantage here, being able to apply greater pressure to the brakes with less force at the lever, but in effect the rider will notice that the brakes feel 'softer' or 'spongier'. The rider has to move the lever further to gain the same braking force on the wheel. There is less sensitivity to movement of the brake lever, corresponding to greater modulation, or the ability to control the braking input.

I think in essense we're all arguing the same thing, except from different angles. In short:

Cam dialled out, brake are hard and sharp
Cam dialled in, brakes are softer and control is greater.

The speed dial effect is more pronouced if you use cable disc brakes, like the Avid. I changed my levers to the speed dials and immediately noticed the ability to change brake feel front to back. Maybe the V brake configuration is not as sensitive to this adjustment.

Hence the purpose for my short blunt answer.

OK Jim, so we're getting closer. I think we agree that less cable pull = more leverage = stronger braking. We now just have a problem with the definition of modulation.

You say this:
"The rider has to move the lever further to gain the same braking force on the wheel. There is less sensitivity to movement of the brake lever, corresponding to greater modulation, or the ability to control the braking input."

However, the greater the mechanical advantage and the higher the braking power the LESS modulation the brakes have. I think if you carefully read the Sheldon Brown article you'll see this is the case. This is why newcomers to v-brakes should always start off on the highest cable pull setting, because the high power and low modulation of the low cable pull setting results in too abrupt a braking action.

Sam

One thing I did remember about speed dials that might have caused some confusion, is that moving a dial in an anti-clockwise direction (which might fell like winding "out"😉 actually moves the pivot closer to the bars, reducing cable pull, increasing power, and reducing modulation.

Quoted post said:

Originally posted by Allo
One thing I did remember about speed dials that might have caused some confusion, is that moving a dial in an anti-clockwise direction (which might fell like winding "out"😉 actually moves the pivot closer to the bars, reducing cable pull, increasing power, and reducing modulation.

Regardless of physics or sheldon brown, if you turn the dial counter-clockwise, moving the pivot closer to the bars, you get maximum modulation and the least power.

That's a fact, so you are still incorrect.

Perhaps if you completely readjust your pad engagement point and the cable at the brake itself, you can change that, but everyone who uses speed dials knows that when you turn the dial counter-clockwise while riding, moving the pivot closer in, you get more modulation, less power, and the lever engages closer to the bars.

Allo, I have to confess that I didn't read the article by Sheldon Brown. It looked lengthy and immoderately technical.

I still say that if you require more movement of the lever for any given movement of the brakes (ie -- the thingy dialled in) then you have an increase in modulation. Try setting your mouse to maximum sensitivity then tell me whether you think you have more modulation or less. When the pointer zips all round the screen at your slightest touch you'll have to agree that you have less modulation. Set the mouse for least sensitivity and you'll have to agree you have the greatest modulation. You can put that sucker anywhere (should you have the patience) but you have to move the mouse a great deal. You have sacrificed control for speed.

This is the same as you would do with the speed dial adjustment. The only difference is that a mouse requires the same force to move, regardless of the settings within Windows. With speed dial controlled brake levers you have a choice of moving the lever further, for any given braking force, increasing modulation, or you can move the lever a shorter distance, decreasing modulation.

You point out that screwing the speed dial in increases your mechanical advantage, and that is true, but user won't notice this. He might, at the end of a long downhill, notice less arm-pump, but the immediate effect of this change will be that the brakes feel softer or more spongy than in the top-most setting. I think you're halfway there, wrong only in believing modulation does not grow with mechanical advantage.

James.