vqdriver
02-10-2015, 11:54 AM
this post will be mostly informational.
this is very specifically regarding this particular pairing, not any other disc caliper. completely different from bb7, cx75, spyre, etc.... they have nothing to do with this. cable only disc calipers are fundamentally different than the mixed mech/hydro nature of the hy/rd calipers.
so basically, campy levers don't pull enough cable for this caliper. with stock levers and by-the-book installation, the levers will pull nearly to the handlebars before the pads make contact. from there the lever feel is good but too close to the bars for comfort. it doesn't bottom out, but really it's just too close. with a thick bar tape or non ergo bend bar it probably would touch.
there are a couple homegrown remedies for this online, neither of which are ideal.
first is to introduce some more hydraulic fluid into the system. with the pistons only slightly extended (and pads removed), add a few drops to the reservoir, just enough so that when you close it back up a small amount will seep out. that ensures it's full up. this will effectively push the pads closer and reduce the lever pull but you sacrifice some pad clearance. this may not be an issue if the rotors can still spin freely, but tolerances come way down and even a slightly warped rotor will rub.
alternatively, you can mount the cable on the inside of the mounting bolt, as opposed to the outside position the caliper is designed for. this shortens the lever arm, shortening the required cable pull. this does not affect pad clearance but does require you to file off a bit of aluminum that blocks the cable path. (easier to understand if you're looking at the caliper as you read this. but if you have them, you'll know immediately what i'm saying here). downside is, of course, that you're taking a file to your brakes.
i've read online that someone simply screwed the bolt in from the bottom up instead of top down and routing the cable the same way on the inside of the bolt. this works as well, but didn't seem as secure to me seeing as how it's a smooth finish down there with nothing to really "grip" the cable.
a call to trp (tektro) was educational. yes, they are certainly aware of this. their response:
the new shimano levers pull more cable than 'traditional' road levers that we're accustomed to. sram levers pull more as well. not quite as much as shimano, but close. campy has increased their cable pull too, but not as much as sram, a fair bit behind shimano.
what is interesting is that the pull curve for campy is non-linear. meaning the first bit of lever pull pulls a lot of cable, and then it tapers off as the lever pull progresses. ostensibly, this is to give more pad clearance with traditional calipers. when you pull the brake lever it will quickly bring the pads in to the rim then the tapering off of the pull ratio allows improved modulation. great in theory, not so great with these brakes.
the hy/rd calipers were designed with lots of cable pull, pulled in a linear fashion. a la new shimano.
new sram pulls a bit less cable, pulled in a linear fashion.
new campy pulls even less cable, pulled in a non-linear fashion.
so there it is. all the design specs and number crunching aside, this is the reality with parts in hand on a real life frame. anyone considering this combo can decide for themselves what's acceptable. to be clear, this combo does work insofar as to say that campy levers will stop the bike. but you have to pull the levers awfully far to do so.
this is very specifically regarding this particular pairing, not any other disc caliper. completely different from bb7, cx75, spyre, etc.... they have nothing to do with this. cable only disc calipers are fundamentally different than the mixed mech/hydro nature of the hy/rd calipers.
so basically, campy levers don't pull enough cable for this caliper. with stock levers and by-the-book installation, the levers will pull nearly to the handlebars before the pads make contact. from there the lever feel is good but too close to the bars for comfort. it doesn't bottom out, but really it's just too close. with a thick bar tape or non ergo bend bar it probably would touch.
there are a couple homegrown remedies for this online, neither of which are ideal.
first is to introduce some more hydraulic fluid into the system. with the pistons only slightly extended (and pads removed), add a few drops to the reservoir, just enough so that when you close it back up a small amount will seep out. that ensures it's full up. this will effectively push the pads closer and reduce the lever pull but you sacrifice some pad clearance. this may not be an issue if the rotors can still spin freely, but tolerances come way down and even a slightly warped rotor will rub.
alternatively, you can mount the cable on the inside of the mounting bolt, as opposed to the outside position the caliper is designed for. this shortens the lever arm, shortening the required cable pull. this does not affect pad clearance but does require you to file off a bit of aluminum that blocks the cable path. (easier to understand if you're looking at the caliper as you read this. but if you have them, you'll know immediately what i'm saying here). downside is, of course, that you're taking a file to your brakes.
i've read online that someone simply screwed the bolt in from the bottom up instead of top down and routing the cable the same way on the inside of the bolt. this works as well, but didn't seem as secure to me seeing as how it's a smooth finish down there with nothing to really "grip" the cable.
a call to trp (tektro) was educational. yes, they are certainly aware of this. their response:
the new shimano levers pull more cable than 'traditional' road levers that we're accustomed to. sram levers pull more as well. not quite as much as shimano, but close. campy has increased their cable pull too, but not as much as sram, a fair bit behind shimano.
what is interesting is that the pull curve for campy is non-linear. meaning the first bit of lever pull pulls a lot of cable, and then it tapers off as the lever pull progresses. ostensibly, this is to give more pad clearance with traditional calipers. when you pull the brake lever it will quickly bring the pads in to the rim then the tapering off of the pull ratio allows improved modulation. great in theory, not so great with these brakes.
the hy/rd calipers were designed with lots of cable pull, pulled in a linear fashion. a la new shimano.
new sram pulls a bit less cable, pulled in a linear fashion.
new campy pulls even less cable, pulled in a non-linear fashion.
so there it is. all the design specs and number crunching aside, this is the reality with parts in hand on a real life frame. anyone considering this combo can decide for themselves what's acceptable. to be clear, this combo does work insofar as to say that campy levers will stop the bike. but you have to pull the levers awfully far to do so.