|   Avid Discs: I know that Prestretching cables is bad but... | Carl Mega
Apr 4, 2002 10:26 PM | | what is the difference between "Honking down on the lever" when the pads are adjusted to touch the rotor during setup (immobilized arm) and doing the same when the pads are just a few mm away from the rotor? It almost sounds like you'll damage your brake doing an "Oh! sh1t" grab. I can't believe that would be the case.
Maybe it'll be obvious once I set them up but right now I don't see the difference between the two scenarios. Can anyone explain? |
| re: Avid Discs: I know that Prestretching cables is bad but... | larry
Apr 5, 2002 3:59 AM | | You sound pretty knowledgeable. *Or is it just that I am not?
Prestretching isnt bad, its necassary.*
They are going to stretch and throw off any set up you have done. They are mushy until they are thuroughly stretched, then they are still kinda mushy.
Id say, for best honking to turn the pads all the way into the rotor, then grab like hell, gradual hell.
But I dont think it'd matter unless the pads were so far away that the arm passes perpindicular to the cable while you are honking, at which point youre not getting an effective honk on the cable. Maybe that is why the manual says to do it thus.
First we were tweeter, no were |
| the difference is....... | heff®
Apr 5, 2002 5:42 AM | | .....simple.
When you have the pads locked down to the rotor, and you attempt to squeeze the lever all the way to the bar, you're putting much more pressure on the caliper piston, at a point that really isn't designed to handle it.
When the pads are backed off to the proper distance, you can pull the lever all the way, because (a) the piston is at close to full extension, where it's designed to handle the force, and (b) the piston won't move far enough to damage itself.
If you attempt to stretch the cables with the pads locked down, you'll snap the piston retaining ring in the caliper, and severely damage the brake.
I don't know who the other guy is, but he doesn't know what he's talking about. A brake cable will not stretch far enough to throw off "your whole setting". I've used several types of brake cables over the years, and four types alone with the Avid disks. None of them stretched enough to cause a problem. Now, the ferrules seating fully onto the cable? It's possible, depending on the housing. Take 'em for a test ride, you'll immediately feel if the ferrules seat further. Simply turn your barrel adjuster to compensate.
heff® |
| Heff is right on (as usual) | Spar¡cus
Apr 5, 2002 6:56 AM | | The more powerful the brake, the less force required at the lever to activate it. Avid discs aren't anything like V-brakes, where a guy can get white knuckles while trying to haul his bike down from speed. The Avids are powerful enough that a person does not need to prestretch his brake cables, and what little stretching takes place (I've never noticed any) over the course of the first week or two of break-in will easily be compensated for with a quick spin of a red knob or a minor adjustment of the barrel adjuster.
--Spary |
| re: Avid Discs: I know that Prestretching cables is bad but... | Al
Apr 5, 2002 7:18 AM | | I'm still confused. It seems that individuals are saying that if the brakes are adjusted such that the pads do not touch the rotors you can use some degree of "force" on the brake lever. How much force is still questionable to me. However,if you are in a stationary positon with the pads adjusted to the rotor you will damage your brakes. Also, there sems to be some point that when the pads are not touching and riding where you can "honk" on the lever and you will not do damage to the brake. I am having toruble with this.
I read the post regarding power of the disc brake and the suggestion that you don't need to pull with the force that would damage the caliper. Does that mean if you did yoo would damage the caliper if the lever is pulled very hard. It seems to me that in a panic situation a person is going to pull harder. When a car is in a skid people sometimes just push harder on the brake pedal. That can happen here. Lever rather than pedal and panic conditions. It does happen to some. Hoever, not me.
Can I pull my brake lever to the handlebar when riding with a properly setup brake and not damage the caliper? Will the caliper be damaged if I pull the lever as hard as I can? Thanks Al |
| as simple as I can get it............. | heff®
Apr 5, 2002 7:39 AM | | .......is this.
You can NEVER pull the lever hard enough to break the caliper when the pads are properly set. Just plain can't happen. Look at it this way, while riding, in a panic stop, you're pulling your levers about an inch inwards. Eventually, you'll hit either the bars, or the max piston extension on the brake caliper. Not to mention the fact that the pressure you're putting on the levers to "stretch" the cables is MORE than enough to put you right over the bars.
Try it sometime, when you get your Avids on, and broken in. Ride downhill, and slam the front brake on as hard as you can. You'll be chewing dirt faster than you can say "prestretch".
Conversely, if you lock the pads down, THEN pull the levers to the bars, you're simply exerting WAY too much pressure on the brake caliper. Something has to give, and in Avid's case, as well as Hayes, it's the piston ring.
Again, it's not only not necessary to "prestretch" the cables, it's damaging to the brakes. Just don't do it. I'll send you Avid's tech release on this if you want.
heff® |
| Sparty and Heff are right on (as usual)... | næstep
Apr 5, 2002 9:03 AM | | Avid's disc, compared to your standard V or canti, is all about finesse. Unlike the "stretch" of thinner derailleur cables which are held under constant tension and shifted under high load, beefier brake cables are definitely overbuilt for Avid's application and will need little or no adjustment for stretch. The mechanical advantage the disc caliper creates also means there are parts to fail if too high a load is applied at the lever, but not to worry a white knuckle squeeze of that severity would definitely send any rider over the bars under any "just riding along" secenario.
As heff is saying, don't worry about it. As your pads bed in over the first couple of rides, if you notice any slop develop in your lever due to "cable stretch", or more likely housing compression or the ferrule seating, simply give the brake lever barrel adjuster a half-twist or two and ride on.
For me, cable stretch is really only an issue with indexed gearing systems, where small changes in cable length can noticably affect shifting. For braking applications, pad wear seems to be a far bigger variable than any minute changes in cable length.
næstep |
| Sparty and Heff are right on (as usual)... | larry
Apr 5, 2002 7:49 PM | | ALrigh I see,
I was misunderstood a little tiny bit. I didnt mean that you would have to adjust everything again after the cables stretch, just turn the knobs in a little thats all. My mistake.
As well I did not know that when the pads are turned into the rotor that the caliper is in a bad position to be 'honked' on. again, my bad.
But about cable stretch. C'mon guys. Cables always stretch. When brand new, no matter if its a shift cable or brake, or oversized tandem or braided- they stretch. You may as well stretch them when you are setting up your brakes, because they will stretch. All it takes is to pull with a decent ammount of force and hold for a few seconds, thats it.
Obviously you wont be pulling hard enough to break anything. |
| No need the pre-stretch at all | shiggy
Apr 8, 2002 8:46 AM | | Why risk damaging the brake? It is much easier (IMO) to adjust the avids than any other brake. Just adjust the red knobs after a couple of stops on the test ride - as you will need to do anyway - and you are good to go.
Heck, I do not even pre-stretch the gear or brake cables on my road bike any more and have not needed to readjust.
-shiggy, NADS #69 |
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