Wave rotors. Waste or wonders?

[WALRUS]

I've always liked the look of wave rotors and am occasionally tempted to purchase.
Devil is whispering in my ear again, but...

Proponents say the wave reduces brake heat. I always wonder if they reduce feel and increase distance, since it seems counter-intuitive that less metal rubbing against brake pads results in shorter stops.
For this reason - and advice from my race guru - I've never tried them on the street or track.
But they sure are purty.
Your two cents?

[Ray]

Your two cents?

FWIW (maybe less than 2 cents), I've overheated my Galfer Wave floating rotors on my mountain bike just as often as the more traditional designs with lots of cutouts. That said, I've noticed less warping, so there might be something to their claims. Not sure where the claim for more surface area comes from, as surface area is determined by the area of the pads, and with all the cutouts on the rotor, one gets the impression, if anything, of less surface area on the rotor. 

I guess, if you're wearing or warping rotors, they are probably worth a try.  That said, in spite of the fact I spend a lot of time braking (in order to go fast), have yet to wear out a rotor on the R1200. So..., might not have much feedback to this question on this forum.

[Grumpy Goat]

Not sure where the claim for more surface area comes from, as surface area is determined by the area of the pads, and with all the cutouts on the rotor, one gets the impression, if anything, of less surface area on the rotor.

I think that they are referring to more edge surface area for cooling. If the inner and outer diameters are constant the swept area in way of the pads would be the same, but the edge surface area is greater for cooling, even if the total surface area is smaller. I would think that this increase in edge surface area makes the edge cooler and probably helps resist warpage.

As for the efficacy of the petal rotors vs normal ... when I see them on race bike is when I may spend extra money to get them, and even then ... probably not. Now if one likes the look, I say go for it ... it's your bike.

[Ray]

Not sure where the claim for more surface area comes from, as surface area is determined by the area of the pads, and with all the cutouts on the rotor, one gets the impression, if anything, of less surface area on the rotor.

I think that they are referring to more edge surface area for cooling. If the inner and outer diameters are constant the swept area in way of the pads would be the same, but the edge surface area is greater for cooling, even if the total surface area is smaller. I would think that this increase in edge surface area makes the edge cooler and probably helps resist warpage.

As for the efficacy of the petal rotors vs normal ... when I see them on race bike is when I may spend extra money to get them, and even then ... probably not. Now if one likes the look, I say go for it ... it's your bike. 

Thanks GG. 
Got it. (Mind was on work..., as it should be, and I thought they meant surface area used for braking....  )

So are those edges and perhaps as important, edges of holes, catching the air more important to cooling than surface area of disk? Or is the increase in edges on a thick rotor, simply a way of increasing surface area of the disk (without a marked increase in mass)?

(All I know is, Ari Henning has promoted them, which is usually good enough for me.)

[Grumpy Goat]

Got it. (Mind was on work..., as it should be, and I thought they meant surface area used for braking....  )

So are those edges and perhaps as important, edges of holes, catching the air more important to cooling than surface area of disk? Or is the increase in edges on a thick rotor, simply a way of increasing surface area of the disk (without a marked increase in mass)?

(All I know is, Ari Henning has promoted them, which is usually good enough for me.)

I hold Ari in much the same regard.

I'm no brake rotor expert of course, but area is area (if I remember my thermodynamics sufficiently well) and the size of the swept area should radiate more heat than the smaller edges. That is why I think that the pedal contour is more for resistance against warping as the rotor heat cycles. AFAIK, the holes are mostly for venting gases generated during braking, and the increase in thickness would just be for increasing wear-out life, since it runs counter to cooling efficiency, although it helps regarding warping. This illustrates well an engineering problem, which usually has many variables, often working against each other. I have had many hours of fun chasing design rabbits down holes playing with finite element models.

Engineers know that our design challenges are typically exercises in compromise. People who like to fiddle and buy aftermarket parts often fall prey to marketing BS which may tout one quality even at the expense of another. Then there is the question of cost, also a very (perhaps the most) important variable.

[Chris216]

Another aspect to look at is the weight of the rotors, being rotating/unsprung mass. I know when I replaced the stock rear rotor on my VTR with a Galfer "petal" rotor it weighed only 2/3 of stock. Probably not noticeable most of the time, but since I went thru the trouble (expense  ) of putting Dymags on the VTR...
Chris

[DRC]

I'd wager there is little more advantage than aesthetics with wave rotors. My cage runs 365 mm wave rotors as standard on the front (and a fair bit of marketing guff about the wave rotors). The next years model runs 375 mm drilled non wave rotors (regular round).