Discussion
George29 said:
bass gt3 said:
Prof Prolapse said:
Lincsblokey said:
In race terms, they disperse the heat faster and its less MG of unsprung weight.
I get the second point about weight... But how do they disperse heat faster?You've reduced the total metal in disc. You've also probably reduced the total contact area with the pads as well, and the overall surface area to metal ratio is actually reduced, if anything they should run hotter?
Am I missing something bloody obvious again?
Or not
Either which way, I think they look cool (no pun intended)
bass gt3 said:
But as brakes need friction to function, less area equals less braking, no??
Yes I'm fairly sure it would give less braking if you compared like for like materials, one wavy, one cross drilled. If I get bored one day at work I might even do some quick FEA on it to see. I suspect that Galfer discs are made out of a different material to OEM hence people reporting on the different feel.
Edited by George29 on Thursday 4th December 11:47
bass gt3 said:
George29 said:
bass gt3 said:
Prof Prolapse said:
Lincsblokey said:
In race terms, they disperse the heat faster and its less MG of unsprung weight.
I get the second point about weight... But how do they disperse heat faster?You've reduced the total metal in disc. You've also probably reduced the total contact area with the pads as well, and the overall surface area to metal ratio is actually reduced, if anything they should run hotter?
Am I missing something bloody obvious again?
Perhaps (just perhaps) the wavy outer edge profile being longer than a simple circular circumference, as well as the slashes and such allow the core of the disc to cool faster rather than just the surface. Maybe. So the entire mass of the disc is cooled rather than just the two external surfaces.
Or not
Or maybe the slight loss of surface area is mitigated by the better thermal dynamics and looking really awesomely cool.
Brembo T drives are designed to conduct more heat away from the friction face and into the rotor hub for better cooling.
Weren't wavy discs first put on MX bikes as they aren't as prone to getting covered in dirt?
I once read somewhere that the "wave" pattern helped distribute air better as compared to conventional ones. I thought that was s
t, but I haven't heard anyone actually explaining the claim that they cool quicker.
I once read somewhere that the "wave" pattern helped distribute air better as compared to conventional ones. I thought that was s
t, but I haven't heard anyone actually explaining the claim that they cool quicker.ccr32 said:
If it wasn't generating as much heat in the first place, wouldn't that mean that braking performance would be reduced, as in (kinetic) energy cannot be created or destroyed, only conserved or transferred (to heat energy, in the case of a brake)?
Either which way, I think they look cool (no pun intended)
That's my point. Less area, no real increase in ability to lose heat and the same materials. So any claims of better braking are difficult for me to understand.Either which way, I think they look cool (no pun intended)
Unless your original discs were made of monkey mental, which I actually suspect is part of the reason for so many motorcycling peasants saying they were better.
Prof Prolapse said:
bass gt3 said:
George29 said:
bass gt3 said:
Prof Prolapse said:
Lincsblokey said:
In race terms, they disperse the heat faster and its less MG of unsprung weight.
I get the second point about weight... But how do they disperse heat faster?You've reduced the total metal in disc. You've also probably reduced the total contact area with the pads as well, and the overall surface area to metal ratio is actually reduced, if anything they should run hotter?
Am I missing something bloody obvious again?
Perhaps (just perhaps) the wavy outer edge profile being longer than a simple circular circumference, as well as the slashes and such allow the core of the disc to cool faster rather than just the surface. Maybe. So the entire mass of the disc is cooled rather than just the two external surfaces.
Or not
Or maybe the slight loss of surface area is mitigated by the better thermal dynamics and looking really awesomely cool.
Brembo T drives are designed to conduct more heat away from the friction face and into the rotor hub for better cooling.
If you consider a disc, it has it's friction surface area and it's non friction surface area. The circumference of a round disc is set, whereas the longer circumference of a wavy disc presents a greater circumference therefore a greater surface area to the oncoming air for cooling. Now add in the numerous cuts and slashes in the disc and they, like cross drilling, present more surface area for cooling.
By example, a 10mm hole costs the disc 78.55 x 2(each side) = 157mm sq mm of surface area from the disc. However, the area inside the cylinder made by this hole is the circumference x the depth equalling 157mm based on a 5mm thick disc.
So in effect, holes lessen mass, provide equitable surface area for cooling lost by the holes and allows the core of the disc to cool rather than just the surface. Add this to the much greater outer edge surface area and it could be considered that Wavy discs offer greater surface area for cooling by convection.
bass gt3 said:
But as above, a reduction in the creation of heat from the act of braking, or converting kinetic energy, equates to a reduction in braking performance. So Wavy discs would be less effective if that were the case.
If you consider a disc, it has it's friction surface area and it's non friction surface area. The circumference of a round disc is set, whereas the longer circumference of a wavy disc presents a greater circumference therefore a greater surface area to the oncoming air for cooling. Now add in the numerous cuts and slashes in the disc and they, like cross drilling, present more surface area for cooling.
By example, a 10mm hole costs the disc 78.55 x 2(each side) = 157mm sq mm of surface area from the disc. However, the area inside the cylinder made by this hole is the circumference x the depth equalling 157mm based on a 5mm thick disc.
So in effect, holes lessen mass, provide equitable surface area for cooling lost by the holes and allows the core of the disc to cool rather than just the surface. Add this to the much greater outer edge surface area and it could be considered that Wavy discs offer greater surface area for cooling by convection.
Well that's exactly my point, I struggle to see how they could possible be more efficient at braking. If you consider a disc, it has it's friction surface area and it's non friction surface area. The circumference of a round disc is set, whereas the longer circumference of a wavy disc presents a greater circumference therefore a greater surface area to the oncoming air for cooling. Now add in the numerous cuts and slashes in the disc and they, like cross drilling, present more surface area for cooling.
By example, a 10mm hole costs the disc 78.55 x 2(each side) = 157mm sq mm of surface area from the disc. However, the area inside the cylinder made by this hole is the circumference x the depth equalling 157mm based on a 5mm thick disc.
So in effect, holes lessen mass, provide equitable surface area for cooling lost by the holes and allows the core of the disc to cool rather than just the surface. Add this to the much greater outer edge surface area and it could be considered that Wavy discs offer greater surface area for cooling by convection.
I'm not convinced by your maths on the SA mate. I take your point but drilling is a much more effective way at increasing the SA than taking chunks out of the sides. To say the increase in overall circumference increases the heat lost is to ignore any cooling that the face of the disc has been robbed of, which itself is probably going to lose, what 8cm^2 every single notch? That's large amount of SA to lose, and I'm not obviously not convinced the increase circumference would override it.
I guess the only way to settle would be to know exactly what the actual difference is between designs.
According to Galfer there are a range of reasons but the main one is reduced heat build up:
Lots of good theory in there though. Potentially the best of which being that they're good at getting rid of dirt.
Galfer Website said:
On a normal round rotor, the leading edge (think toe-in) of the brake pad is in contact with the entire height of the blade as the pressure is applied. Because the contact covers the entire height of the blade heat buildup takes much less time to occur and you end up with heat related problems like brake fade, thermal lockup, and inconsistent braking performance.
What the Wave® pattern does is take that leading edge of contact between the blade and pad and constantly move it up and down, thus minimizing heat build up and its inherent problems. Cool air is also introduced in greater amounts. In addition, through centrifugal force, any foreign matter is thrown clear of the outer rim of the blade and doesn’t get lodged in the pad material.
It's also interesting to note that Moto GP bikes don't have any holes in their discs. Again according to Galfer:What the Wave® pattern does is take that leading edge of contact between the blade and pad and constantly move it up and down, thus minimizing heat build up and its inherent problems. Cool air is also introduced in greater amounts. In addition, through centrifugal force, any foreign matter is thrown clear of the outer rim of the blade and doesn’t get lodged in the pad material.
Galfer Website said:
Holes in the “blade” of a disc (the part that the brake pad sweeps over as it is in motion) will save a bit of weight but contrary to public opinion, they do not help to cool a braking system. Notice on Moto GP motorcycles and most race cars, there are no holes on the rotors. There are actually situations where holes can be detrimental to your braking.
In muddy conditions, dirt gets trapped in these holes and proceeds to chew up pads that, in turn will chew up rotors because of the constant uneven abrasion between the pads (which have the dirt imbedded in their surface) and the rotors, which get gouged to heck by that dirt. If you’ll notice, if there are holes in a Galfer rotor, they are never round. They are usually oval, teardrop or cylindrical in shape so that foreign debris is directed away from the rotor via centrifugal force.
It's interesting how little there is out there (after a brief internet search) about how much more efficient these things are. You'd think that people would be making comparisons and highlighting why their brake discs are X% more efficient but I can't find anything like that.In muddy conditions, dirt gets trapped in these holes and proceeds to chew up pads that, in turn will chew up rotors because of the constant uneven abrasion between the pads (which have the dirt imbedded in their surface) and the rotors, which get gouged to heck by that dirt. If you’ll notice, if there are holes in a Galfer rotor, they are never round. They are usually oval, teardrop or cylindrical in shape so that foreign debris is directed away from the rotor via centrifugal force.
Lots of good theory in there though. Potentially the best of which being that they're good at getting rid of dirt.
Prof Prolapse said:
Well that's exactly my point, I struggle to see how they could possible be more efficient at braking.
I'm not convinced by your maths on the SA mate. I take your point but drilling is a much more effective way at increasing the SA than taking chunks out of the sides. To say the increase in overall circumference increases the heat lost is to ignore any cooling that the face of the disc has been robbed of, which itself is probably going to lose, what 8cm^2 every single notch? That's large amount of SA to lose, and I'm not obviously not convinced the increase circumference would override it.
I guess the only way to settle would be to know exactly what the actual difference is between designs.
Well the face won't loose surface area, as a 10mm hole in a 5mm thick disc provides the same interior surface area of the resulting cylinder as was lost in the drilling. So now gain but no loss. As for the outer circumference, consider the disc in 3D. A standard 320mm disc has a circumference edge of circa 1000mm. Now @ 5mm thick thats 5000mmsq. Now if you increase the circumference by adding the waves, you increase the edge surface area by the same amount. I'm not convinced by your maths on the SA mate. I take your point but drilling is a much more effective way at increasing the SA than taking chunks out of the sides. To say the increase in overall circumference increases the heat lost is to ignore any cooling that the face of the disc has been robbed of, which itself is probably going to lose, what 8cm^2 every single notch? That's large amount of SA to lose, and I'm not obviously not convinced the increase circumference would override it.
I guess the only way to settle would be to know exactly what the actual difference is between designs.
I would have to take pics but the high point or wave crest on the waves are higher than the outside diameter of a normal disc, whereas the low points or troughs of the waves still sit beyond the pad so are probably equal to the normal disc. So there's a small increase in outer diameter as well, which obviously increases the overall SA
And if the internal SA of the holes when considered as a cylinder are the same as the SA of the hole that's drilled, theres no loss.
Simple Pi..........
10mm hole has a SA of Pi* Rsq
So 3.142* 25 (5x5) equals 78.55.
Now we have lost SA on each side so that's 2x 78.55= 157.1Sqmm lost in SA from the disc sides
Now the SA of the cylinder wall created from that same hole is-
Pi*D gives the circumference of the hole
So 3.142*10 = 31.42mm
Now 31.42x 5 depth/thickness(5mm nominal) = 31.42 x 5 = 157.1
So for a 10mm hole, there is equality between the cost in rotor face SA vs the gain in hole wall SA
Obviously this is based on a 10mm hole, but if the hole is smaller such as 8mm, there is actually a gain on the internal SA vs the loss of the rotor face SA to a value of circa 25%
8mm hole has a SA of Pi* Rsq
So 3.142* 16 ( 4x4) equals 50.27
Now we have lost SA on each side so that's 2x 50.27= 100.54 sqmm
Now the SA of the cylinder f that same hole is
Pi*D
So 3.142*8 = 25.14mm x the 5mm depth/thickness(5mm nominal) = 25.14 x 5 = 125.68 sq mm
So we can see for a loss of 100mmsq we gain 125mmsq.
Obviously this is the same for a wavy or round disc, until we consider.......
the additional edge SA of the outer perimeter of the rotor, which may be 30 or 40% greater than a normal round disc and you can see a much greater OVERALL SA on a wavy disc vs a normal when considering all the inside edges of the holes etc
I think the important point is that the top of the wave is higher or greater diameter than a standard disc of the same nominal size rather than a situation of equilibrium where what is lost in the trough is gained in the crest. The crests are all extra as well as adding to the edge SA. This makes wavy discs quite tight in the calipers
Finally, there might also be effects on the air movement over the surface of the disc caused by the waves. A wavy disc would disturb the air more, potentially aiding the convection of heat from the disc, although i suspect an aerodynamicist would confirm or deny.
Finally, i doubt a company such as Galfer would subscribe to a fashion fad rather than using sound engineering principles considering it's more time consuming to machine a wavy disc compared to a round one. Hong Fong
o discs maybe. By comparison, Brembo now use T drive which improves the thermal conductivity from rotor to hub so aiding heat dissipation through convection rather than the wavy approach. It would be interesting to weigh my 198 Wavy discs and a standard one and compare, as well as overall dimensions.
I appreciate your valient attempt at doing the maths Bass (Steve is it? I'm having difficulties with the continued use of your username) but you've misunderstood my point I think.
Look I know the SA isreduced increased, but its offset by this. So I'm curious, by how much as it's difficult to see how it would produce a positive
Also I know Pi for fks sake.
Edit: To reduce stupidity.
- I understand drilled discs advantages. That's not under dispute.
- I understand the difference between the parts of the discs and the pads. There's no dispute there either.
- I understand the perimeter of the disc has increased by a large amount. However....
Look I know the SA is
Also I know Pi for f
ks sake. Edit: To reduce stupidity.
Edited by Prof Prolapse on Thursday 4th December 14:58
Prof Prolapse said:
I appreciate your valient attempt at doing the maths Bass (Steve is it? I'm having difficulties with the continued use of your username) but you've misunderstood my point I think.
Look I know the SA is reduced, but its offset by this. So I'm curious, by how much as it's difficult to see how it would produce a positive
Also I know Pi for fks sake.
I don't thinkthereisa point, rather offering possible explanations why some believe Wave discs are better than round etc. I don't actually care TBH, but the science of it kind of interests me. - I understand drilled discs advantages. That's not under dispute.
- I understand the difference between the parts of the discs and the pads. There's no dispute there either.
- I understand the perimeter of the disc has increased by a large amount. However....
Look I know the SA is reduced, but its offset by this. So I'm curious, by how much as it's difficult to see how it would produce a positive
Also I know Pi for f
ks sake. And since Steeler's informative post, the matter is resolved I think,
And yes, i don't you know Pi, but you commented that the loss of SA on the surface was not compensated for. So just a simple demonstration was all.
Anyway, onto new subjects, I hear there's a skirmish in the tyre thread.
And yes, it's Steve. Feel free to call me Steve Mr Prolapse
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