Julius Czar Posted December 30, 2010 Report Share Posted December 30, 2010 Depending on your budget you could get either, if set up properly they will both work amazingly, the only difference is that you get more adjustment with the pads on a bb7, but as said previously, it's something there to break that otherwise wouldn't on the bb5. Quote Link to comment Share on other sites More sharing options...
rupintart Posted December 30, 2010 Report Share Posted December 30, 2010 bb7 every day bigger pad does mean better brakeing if the same force is applied to it No, it doesn't. It's a common fallacy that a larger pad = better braking. Larger pads are only better for dissipating heat. There is no surface area in the friction equation: Fr = μN Fr is the resistive force of friction μ is the coefficient of friction for the two surfaces (Greek letter "mu") N is the normal or perpendicular force pushing the two objects together μN is μ times N Fr and N are measured in units of force, which are pounds or newtons. μ is a number between 0 (zero) and ∞ (infinity). In other words, it is just as difficult to move a 1 square-cm object as a 1 square-meter object if they both are pressed to the surface with the same amount of force. The difference in braking power you're noticing is from the friction coefficient from pad compound, not the surface area. Incase that mathematical approach doesn't suffice for you, here's a cut/paste from the Willwood brake website: ---------- Q: Will larger brake pads improve my stopping distances? A: Not necessarily, a larger pad of the same compound in the same location as a smaller pad will not yield shorter stopping distances. The amount of pressure applied, the pad friction coefficient, and the diameter of the rotor at which that pressure is applied, determine the torque reaction, or stopping force. A larger pad does not apply more pressure, only the same pressure over a bigger area. The size of the pad does matter in terms of heat capacity and wear rate. A larger pad will absorb more initial heat, hence less thermal shock, and have better wear characteristics resulting in longer pad life. ------------- So no, a larger pad doesn't help you stop faster in a trials brake application (no nominal generation of heat). 1 Quote Link to comment Share on other sites More sharing options...
monty221ti Posted January 1, 2011 Report Share Posted January 1, 2011 why does rotors havi holes in then? just for cooling or? Quote Link to comment Share on other sites More sharing options...
Miles Mallinson Posted January 1, 2011 Report Share Posted January 1, 2011 Yeh for cooling and weight, if they didn't have holes they would just start to smoke after a downhill run or something. Quote Link to comment Share on other sites More sharing options...
monty221ti Posted January 1, 2011 Report Share Posted January 1, 2011 Yeh for cooling and weight, if they didn't have holes they would just start to smoke after a downhill run or something. okay, but isnt's they also there so it brakes better or? Quote Link to comment Share on other sites More sharing options...
Miles Mallinson Posted January 1, 2011 Report Share Posted January 1, 2011 Yeh well there going to perform better when they aren't above boiling point Quote Link to comment Share on other sites More sharing options...
JD™ Posted January 1, 2011 Report Share Posted January 1, 2011 The holes are actually mainly there for something for the pad to bite into, otherwise all trials riders would run solid discs because we don't run the risk of boiling brakes. Quote Link to comment Share on other sites More sharing options...
dann2707 Posted January 2, 2011 Report Share Posted January 2, 2011 The holes channel water away and prevent a film of water between the pad and the rotor. Cools the disk down too. Also uses less material. Haven't heard anything about it being for saomething to bite into though. Quote Link to comment Share on other sites More sharing options...
RossMcd Posted January 2, 2011 Author Report Share Posted January 2, 2011 Well i got the bb5. Was definitely a good choice! Powerful as anything like! Holds and bites like no other front disc i have ever had! And its really light at the lever too All in all. Good buy Quote Link to comment Share on other sites More sharing options...
Gibbon on an Orange 2 Posted January 2, 2011 Report Share Posted January 2, 2011 The holes channel water away and prevent a film of water between the pad and the rotor. Cools the disk down too. Also uses less material. Haven't heard anything about it being for saomething to bite into though. Groves on motorsport discs are there to help de-glaze hot pads, but it also improves bite. As the pads are put under pressure and the pads leading edge reaches a grove, it deforms smightly into the grove. This amount of material is then skimmed off the pad (its only slight, but this is what keeps the surface of the pad deglazed). The material's resistance to the skimming increases the bite of the brake. Quote Link to comment Share on other sites More sharing options...
SamKidney Posted January 2, 2011 Report Share Posted January 2, 2011 Im running some random Shimano cable disc caliper at the moment with an old Avid 185m rotor and its Immense. Good modulation but lock on everything I throw at it. Miles better than the previous BB7 I'd tried with a 180 rotor but havent triad the BB5. Il get the Model number of the caliper later for you all to have a look at Quote Link to comment Share on other sites More sharing options...
cai Posted January 2, 2011 Report Share Posted January 2, 2011 In my experience of owning 2 BB7's and 2 BB5's both new and old styles I'd say they are all great brakes, and I would happily run any of them again. I find the newer style BB5's and BB7's flex a tad more than the older versions when the brake is pulled hard - which annoys me slightly as I like a stiff brake. I also find it much easier setting up a BB7 when compared to the BB5 as you can adjust both pads inwards and outwards. Because of this I'd say the older style BB7 is slightly better than the rest.. I don't know why people are saying that the BB7 is more powerful, and others are saying that the BB5 is more powerful though. Because I've never felt a difference in power between any of my Avids. Q: Will larger brake pads improve my stopping distances? A: Not necessarily, a larger pad of the same compound in the same location as a smaller pad will not yield shorter stopping distances. The amount of pressure applied, the pad friction coefficient, and the diameter of the rotor at which that pressure is applied, determine the torque reaction, or stopping force. A larger pad does not apply more pressure, only the same pressure over a bigger area. The size of the pad does matter in terms of heat capacity and wear rate. A larger pad will absorb more initial heat, hence less thermal shock, and have better wear characteristics resulting in longer pad life. If this is true then why arn't pads made as small as possible? According to what you've said you could have a pad the same size as a 5p coin, or a pad thats a couple of inches long and they'll have an idendical preformance Surely the friction from the bigger surface area plays a part in all of this? Quote Link to comment Share on other sites More sharing options...
rupintart Posted January 2, 2011 Report Share Posted January 2, 2011 (edited) In my experience of owning 2 BB7's and 2 BB5's both new and old styles I'd say they are all great brakes, and I would happily run any of them again. I find the newer style BB5's and BB7's flex a tad more than the older versions when the brake is pulled hard - which annoys me slightly as I like a stiff brake. I also find it much easier setting up a BB7 when compared to the BB5 as you can adjust both pads inwards and outwards. Because of this I'd say the older style BB7 is slightly better than the rest.. I don't know why people are saying that the BB7 is more powerful, and others are saying that the BB5 is more powerful though. Because I've never felt a difference in power between any of my Avids. If this is true then why arn't pads made as small as possible? According to what you've said you could have a pad the same size as a 5p coin, or a pad thats a couple of inches long and they'll have an idendical preformance Surely the friction from the bigger surface area plays a part in all of this? Heat is why. A larger pad disappates the heat, therefore, less pad glaze and brake fade. Goto ANY of the braking websites and they always have to put it in the faq that a larger pad doesn't equate to shorter stopping distances because people feel that a bigger pad increases the friction coefficient, and it doesn't. A bigger disc and caliper exerting more force is how you shorten distances. The only way to stop faster with the same size rotor is a different pad compound or a rotor that exerts more force. That's why a 185 hope trials can lock better than another 185 brake, it has a larger piston in the caliper exerting more force on the pad. Edited January 2, 2011 by rupintart Quote Link to comment Share on other sites More sharing options...
Scoox Posted February 6, 2013 Report Share Posted February 6, 2013 (edited) If this is true then why arn't pads made as small as possible? According to what you've said you could have a pad the same size as a 5p coin, or a pad thats a couple of inches long and they'll have an idendical preformance Surely the friction from the bigger surface area plays a part in all of this? Pad size is a trade-off between weight and practicality. Performance wise pad size does not make any difference, as rupintart explained. System with small brake pads (BB5): Pros: Lighter, because pads are smaller and rotor braking area can be reduced to match the smaller pads. Cons: Pads get hotter becasue the same amount of energy needs to be absorbed by a smaller pad; pads wear faster becasue there is less material in them; narrower rotor may be easier to bend/damage. Will require more frequent adjustments. System with large brake pads (BB7): Pros: Run cooler, don't wear as fast and rotors may be stiffer due to larger braking area. Good for a low-maintainance brake, durable brake. Cons: Heavier. In addition the BB7 is easier to adjust. If you are looking for something light then get the BB5, if you want convenience get the BB7. A mate runs BB5s front and rear on his 24" trials bike and they are sharp as hell, makes me hate my HS33s which constantly require tweaking and tedious maintainance. My next bike will defo run Avids throughout. Edited February 6, 2013 by Scoox 1 Quote Link to comment Share on other sites More sharing options...
dann2707 Posted February 6, 2013 Report Share Posted February 6, 2013 Christ it's a good job you replied only 25 months later! I hate the thought of keeping him waiting. 2 Quote Link to comment Share on other sites More sharing options...
ghostrider88 Posted February 6, 2013 Report Share Posted February 6, 2013 Lol,this guy is master of bumps. Quote Link to comment Share on other sites More sharing options...
Ash-Kennard Posted February 6, 2013 Report Share Posted February 6, 2013 lol someone put this spanner back in the toolbox Quote Link to comment Share on other sites More sharing options...
dann2707 Posted February 6, 2013 Report Share Posted February 6, 2013 Spanners are useful. I'd say he was more of a vaselined door handle. Quote Link to comment Share on other sites More sharing options...
Maxx Posted February 6, 2013 Report Share Posted February 6, 2013 I don't see why bigger pads apply the same pressure. For me bigger pads = more surface, but less pressure Smaller pads = less surface, but more pressure But the total amount of force is the same. F = P.S If force behind pad is the same, in one case surface is bigger (bigger pads) so to have the same F pressure need to be lower And in the other case the surface is smaller (smaller pads) so S is smaller so P is higher. Quote Link to comment Share on other sites More sharing options...
cai Posted February 6, 2013 Report Share Posted February 6, 2013 stuff I've been patiently waiting for a response to my comment for over 2 years, thanks for finally getting back to me x Quote Link to comment Share on other sites More sharing options...
N.Wood Posted February 6, 2013 Report Share Posted February 6, 2013 Spanners are useful. I'd say he was more of a vaselined door handle. This guy isn't as pleasureable as a vaselined door handle. 1 Quote Link to comment Share on other sites More sharing options...
Scoox Posted April 29, 2013 Report Share Posted April 29, 2013 (edited) My comment will be as valid 20 years later as it is today, just as Newton's F=ma is. So perhaps you gentlemen should be out riding your bikes instead of searching the forum for thread bumps to point out. Just saying... Edited April 29, 2013 by Scoox Quote Link to comment Share on other sites More sharing options...
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