can anyone explain avid's Speed Dial?

rudeboymcc

hi. i bought a pair of v-brake levers made by Avid. they are "Speed dial 5" and have a red knob on them.

when i turn it, it moves the position of the bracket that holds the brake cable so the cable is pulled with a different leverage. or at least that's what i think it does. from completely screwed in and completely screwdd out, i hardly notice a difference. the levers still have to be pulled the same distance and the brakes don't move at all when turning the knob. can anyone tell me what this thing is for?

i've tried searching Google but it comes up with hydraulic ones.

Hunter

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

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srf

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.

rudeboymcc

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.

Jim

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.

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Allo

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

fonseca

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...

Jim

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.

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fonseca

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.

Allo

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

Allo

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

Jim

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.

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Cessna

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.

Hunter

Hence the purpose for my short blunt answer.

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