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  1. #1
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    Rotor size, heat and pad wear.

    I used to run hope e4 brakes, 205 up front and 185 rear. Pads lasted over a year and brakes were great.

    I'm currently using v2 brakes with 203 up front and 183 rear. The front brakes is great, the rear is also great but sets through pads 5 times quicker than the front.

    I don't drag the back brake, the pads aren't rubbing, pistols aren't sticking. I'm riding the same bike in the same weather, in the same places, in the same way as before. The only thing that has changed is the brakes, even though pad compound and rotor size are the same.

    So, why am I killing rear pads?

    One theory is that because the brake is more powerful, it's used less and therefore doesn't get up to temperature. This in turn means as the top layer of pad material which is bedded in, wears away, there's not enough heat to cure the layer underneath and hence a higher wear rate.

    Interested to know what people think to this theory and should a smaller rotor be the answer?

    I know there's people on here who love the geeky science side of this stuff so let rip guys and gals!

  2. #2
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    That's kind of an interesting question. Let me ask you this - do the pads on the rear wear equally on the inside and outside pad? What about wear from top to bottom or front to back on each pad? I'm not sure that heat is the answer to the question, and here's why:

    Assuming you weigh the same amount now as you did before, and you're riding just as fast as you were before, in order to control your momentum to the same extent you were before you are changing the same amount of energy (speed) into heat with the brakes to slow down, no matter whether you're doing it in 5 seconds or two seconds. Technically, with the slightly smaller rotors, I'm assuming less mass in those rotors, they should heat up FASTER than the old ones.

    Anyhow, maybe myself or someone else can get to the bottom of this.

  3. #3
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    Hi Cotharyus, thanks for the reply. Nothing has changed regarding weight, speed, location, riding/braking style and ground conditions. That's why I'm so puzzled by this. All that has changed is the brake. From a Hope E4 to a Hope V2. You make a good point though, the amount of kinetic energy is the same and still needs to be changed to heat energy. I guess the new brake is more efficient at getting rid of this heat (phenolic pistons, deeper braking track, larger pads) and perhaps doesn't reach the same peak temperature.

    It would be interesting to see any figures people might have on the optimum temperature for brake pads and whether different rotor sizes can go above or below these optimums.

  4. #4
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    That's not information anyone but manufacturers are likely to know, and odds are they aren't telling. Maybe Magura might know? He seems to do an awful lot of research.

  5. #5
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    A that small difference in diameter sure isn't the cause of your trouble. I'd lean towards some kind of misalignment or faulty rotor.

    Oh, and the rear brake is much more subject to sand, dirt and other particles that are definitely present when you ride. They are sure to cause abrasion.

  6. #6
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    Hi Saul, thanks for joining in the debate. I'm interested to hear other theories as to what's causing this phenomenon. I agree that trail conditions play a big part but this is one of the constants between these brakes and the last. Plus the wet/dry issue should have averaged out over the year I've been running them.

    I did consider a faulty rotor so gave it the good news with some wet and dry. Then bedded some new pads into the smooth clean disc. It then munched through those in about 15 miles. It was a gritty ride but not out of the ordinary. I've put some sintered pads in now and the first new ones on the front. I'll see how that goes.

    Still tempted to think running hotter might be the answer.

  7. #7
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    Now that I re-read the OP, looks like I read sloppily.

    You ride in the same places as before -> dirt and stuff would have been an issue before.
    Disc size is essentially the same -> which you said as well, but the difference is that the new brakes are more powerful.

    So the pads could be pressed harder against the disc and you get the desired effect more quickly and they don't have time to heat up, that's the hypothesis?

    In that case I suggest that you are using the brake levers with the same force as before and your braking outcome is more aggressive than before. Since the brakes are more powerful, you could squeeze the levers more lightly to brake in the same fashion as before. But if you want the kind of braking power you didn't have before, then shorter pad life could be the price you have to pay for it.

    What puzzles me is that it's your rear brake. I have no braking power issues with my rear brakes and actually switched to a 160 mm disc to be able to modulate the power more easily. With 185 mm rotors I was locking out too easily even with my weight back.

  8. #8
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    I had the same thought as Saul, if you have the parts trying swapping to a 160mm on the rear and see if thats changes the wear. 183/5mm in the rear is a massive amount of stopping power.

    Pop the rotor off and lay it out flat, maybe you have a tiny warp in it causing uneven contact. I had this with a rotor on rear and it caused me to chewed through a fresh break pad in 4months..
    2012 Giant Reign 1

  9. #9
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    Hi guys, thanks for your thoughts on this. I'm not really noticing a difference in deceleration compared with the other brakes as both systems caused the tyres to be the limiting factor.

    My theory was that the more powerful brakes was converting the same kinetic energy to heat energy over the same time but doing it more efficiently (ie, better cooling) and therefore not causing the pads or rotor to get as hot. This in turn wasn't setting up a fresh transfer layer and curing the top surface of the pad. This then leads to friction braking and high wear rather than relying on cohesive braking and less wear.

    Like I say, it's just a theory.

    The rotor is perfectly true but I am starting to wonder if it might be the rotor that's the problem.

    Now here's a fresh theory. When I bedded this rotor in, there was snow on the ground and the air temp was about -10 degrees C. Maybe I just didn't get enough heat into that rotor the first time and it's been too rough ever since, running through pads like a belt sander.

  10. #10
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    Look for something stupid. Really. You have reached for some unlikely theories to explain the increased wear. Look for a simpler solution, even if you have dismissed these previously. Look twice.

  11. #11
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    oh i know, check to make sure all your nuts are tight on your rear rotor, if one or two are a little lose that could cause extra flex/wobble increasing ware.
    2012 Giant Reign 1

  12. #12
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    I have given the heat dissipation hypothesis some thought and I have a problem with it.

    If the surface of the pad and rotor must reach a certain temperature to set up a layer that prevents accelerated wear, the temperature of the surface is all that matters. I don't believe the heat dissipation characteristics of the brake caliper has much to do with that. They are more effective in dissipating heat during prolonged braking, but have little to zero effect on the sudden change in surface temperature when you start braking and the pad and rotor gets hot.

  13. #13
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    You might well be right. I had a chat with Hope last night and the chap there said he really couldn't see the temperature for difference rotor sizes varying that much. Maybe there's something fishy about my rear rotor then.

  14. #14
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    There is a veeery small difference in temperature between 180/203 and almost similar pads wear, from my experience

  15. #15
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    What does your new rotor look like? By that I mean the style of vents/ cutouts in the rotors braking surface, if there are slots rather than holes, there may be more of a 'cheese grater' effect on the the pads. That, coupled with the rear being used disproportionately to the front for turning/front end washout reasons may indicate something. But just a random shot in the dark on my part.

  16. #16
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    The vent pattern is the standard V2 rotor and matches the front and isn't a massive departure from the vents in the old rotors.

    I know a couple of guys with the same set up actually, they've worn pads fairly evenly as it happens. I think there must be something quirky about the surface of my rear rotor.

  17. #17
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    I wonder if the cutting process for the rear rotor has lest a raised edge for all of the vent slots, which are acting like razors for your pads?

    Regardless of whether rotors are punched or CNC cut, a crappy tool bit would leave microscopic burrs on all of the cut edges, and would become the equivalent of sandpaper for the pads.

    Vent pattern should not matter, as the overall surface should be level...vents are just that, vents, and help clear grit away from the pad surface and dissipate heat..

  18. #18
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    That's a sound theory. I did give the rotor the good news with some wet and dry then cleaning it and bedded some new sintered pads into it. It's only been out a couple of rides so it's a bit early to tell. With a bit of luck, that might have cured it. if not, I'll buy a new rotor and see how that goes.

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