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Old 10-16-09, 03:25 PM   #1
freebooter
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Advice needed on fitting Tektro cr720 brake

I have bought a cr720 to replace the Oryx on the front wheel in the hope that it will improve braking and get rid of shudder. I am reasonably familiar with setting up cantis but their are a few points about the 720s I am not sure of.

Firstly, the instructions don't give any guidance on the height or angle of the straddle wire other than having enough clearance above it to the cable housing. I know that the angle of the straddle wire makes a large difference to ordinary cantis. What should I aim at with these? 90 degrees?

Secondly, a couple of minor queries on the yoke. I suspect this will be obvious when I actually fix it but I am not sure about the main brake cable fixing bolt. Normally in this type of fixing there is one fixed piece of metal (brake, straddle yoke etc) with a bolt, nut and washer. The cable goes through a hole in the bolt and the nut is tightened to trap the cable between the washer and fixed metal part. In the 720 yoke the metal bit is two sides of one molded metal part. Using the normal method to clamp the cable will involve squashing it between the two sides by bending them together. Is this right? I am just a bit concerned about the stress on the yoke.

The other strange aspect of the yoke is the grub screws that hold the straddle cable. One simply pushes against the other side of the yoke. On the other one there is another hole opposite that has a screw in it. I don't understand the point of that screw. Why aren't both sides the same?

Another question is about the pads. I wasn't expecting them to be the best but I have seen a couple of references on line saying that they wear the rims badly. They do seem quite hard, almost plastiky. Are they really that bad?

thanks
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Old 10-16-09, 04:41 PM   #2
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I'll do what I can.

First, in regard to straddle cable height and all that, read this.
It should answer all your questions.

I haven't actually dealt with that cable hanger, but I've used similar, and it seems like you have the general idea. The bolt at the top of the hanger should (somehow) attach to the brake cable, while the straddle cable goes through the bottom. The grub screw is a set screw, allowing you to make sure the straddle cable stays centred on the hanger. There is only one because you only need one, having a second would be redundant (although symmetrical).

As far as the pads, well Tektro makes good brakes...pads not so much. They will probably stop you fine, but this may be one of the few times when its ok to upgrade before you've worn out the part.
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Old 10-16-09, 05:07 PM   #3
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When I made the same switch, I kept my stock straddle hanger because ever since the late 80s with Ringle's "Mojo" series, I've hated fixed-position hangers.

Don't bother with Tektros pads. Toss 'em out and buy some KS Salmons.
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Old 10-16-09, 05:30 PM   #4
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I have been using CR720 on two bikes for over a year and once set up properly, they have been quiet and free of brake chatter. I also tossed out the Tektro stock pads and installed Koolstop (reds, not salmon because I like in a mostly arid climate). The result is the best rim brake that I have ever used on a road bike.

I used the Tektro straddle wire and straddle wire carrier (yoke) that came with the CR720. On the front, the yoke is set up near the top of the lower headset bearing, and the yoke angle is just under 90 degrees. When the brakes contact the rim, the yoke angle is almost exactly 90 degrees, which is what provides such good leverage. I did not use the screw on the back of the yoke. That is supposed to be somewhere to park the loose end of the straddle wire. I leave the straddle wire uncut and park the end of it on one of the canti brake springs.
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Old 10-16-09, 09:25 PM   #5
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Originally Posted by CliftonGK1 View Post
When I made the same switch, I kept my stock straddle hanger because ever since the late 80s with Ringle's "Mojo" series, I've hated fixed-position hangers.

Don't bother with Tektros pads. Toss 'em out and buy some KS Salmons.
CR720's come with a hanger that is adjustable and lockable. Either you didn't get the original parts for that brake or you weren't installing 720's.
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Old 10-16-09, 09:27 PM   #6
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I leave the straddle wire uncut and park the end of it on one of the canti brake springs.
This is major fail, do not do this.
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Old 10-17-09, 03:49 AM   #7
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Because the arms on a wide profile cantilever stick out horizontally from the brake pivots, the arms are not drawn together much as the cable pulls. So straddle height matters much less than it does on low profile cantilevers. Sheldon's article misses this point. When he claims, "The mechanical advantage is strictly determined by the yoke angle," it is incorrect.
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Old 10-17-09, 10:15 AM   #8
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Because the arms on a wide profile cantilever stick out horizontally from the brake pivots, the arms are not drawn together much as the cable pulls.
Aren't they drawn together more than traditional canti's? In fact, isn't that why cross racers like them, you can set them further from the rim and increase your mud clearance?
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Old 10-17-09, 03:38 PM   #9
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I mean if the anchor points are set horizontally out from the pivot points, then the distance between the anchor points doesn't change much through the stroke. The anchor points basically move vertically the same distance that the cable pulls, no matter the yoke angle.

On narrow profile brakes the mechanical advantage decreases as the cable pulls because the anchor points move closer together as the arms rotate (which brings the yoke angle into play). So if you want to have good mechanical advantage for braking, you have to run the pads real close.

Traditionalist cross setups go the opposite way from low-profiles and set the anchor points way below the pivots -- causing the MA to increase with the stroke, buying you even more pad clearance.
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Old 10-17-09, 04:59 PM   #10
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I mean if the anchor points are set horizontally out from the pivot points, then the distance between the anchor points doesn't change much through the stroke. The anchor points basically move vertically the same distance that the cable pulls, no matter the yoke angle.

On narrow profile brakes the mechanical advantage decreases as the cable pulls because the anchor points move closer together as the arms rotate (which brings the yoke angle into play). So if you want to have good mechanical advantage for braking, you have to run the pads real close.

Traditionalist cross setups go the opposite way from low-profiles and set the anchor points way below the pivots -- causing the MA to increase with the stroke, buying you even more pad clearance.
Ahh, sorry, just misinterpreted you there.
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