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Wave rotors -Petal rotors - are they really better?

7K views 27 replies 17 participants last post by  bwringer 
#1 ·
Some of the newer model bikes coming out have these petal type rotors or Wave rotors.
Even the dirt bikes have them too.

What benefits do these offer over standard rotors ?

Is this something that might show up in the Vstroms Future ? :wink2:
 
#3 ·
They help keep things clean, the crud gets hit by the cut-outs and is thrown clear.
 
#5 ·
You can buy wave rotors from eBay now m- I've installed them on two 650's. The big advantage of the more mellow ones was offroad where they cleared grit off the pads a lot better, they do work better than OEM pads all round though, particularly in wet conditions.

Downside, not recommended with sintered pads as they wear quickly. Off road with organic pads though they are noticeably better.
 
#6 ·
Gotta think

Usually more rotor mass is better, especially for sporty street bikes where the brakes are likely to be used hard. On dirt bikes, I can see that they might self-clean better than solid rotors.

Moslyl I think they are for visual appeal rather than performance.
 
#8 · (Edited)
+1 on the above.

We sell a lot of brake lines. It is an upgrade that results in tangible improvement. The upgrade does what is claimed.

The reps occasionally call me in an effort to market their brake discs. My response is always that i have owned over 40 motorcycles in my lifetime and never once needed to replace a brake disc.

That isn't to say that people don't experience warped discs, but with modern floating discs it is truly rare.

Wave rotors make a difference for guys riding true dirt bikes in muddy conditions. In the same conditions on a V-Strom you would not need brakes since that kind of mud would have already locked up the front wheel between the tire and fender.

I strongly suspect the greatest improvement a person can make to their V-Strom (unwarped) disc is to de-glaze it and the pads. I think it is overlooked because we are programmed from the moment we start watching TV that to get an improvement we need to buy something.

This video shows the deglazing the disc, but the pads can need deglazing as well.

 
#9 ·
I agree that wave rotors score more points for styling than for the fractional physics gains. I have never put them on any of my bikes.

The only time I gave them any serious consideration was on that BMW K1200rs I had for a few years. It didn't suffer from a lack of power so the rotational inertia penalty didn't matter. That bike was genetically over weight and had the telelever suspension so saving 4 pounds of rotor weight, while tempting, was still no sale.

What made me think about getting wave rotors was brake fade when riding in the Sierra mountains. After 30 - 40 minutes of carving my way down a mountain the brakes would heat up enough that I'd have to alter my pace. At one point, I replaced the front pads with some boy-racer units which helped but they were really (yikes) bad when operating at more normal riding conditions. I even bought another 2 OEM pads and tried a combo of both street and race pads on the front end. Yes it proved to be a compromise _ at best. I could not find any definitive specs saying how much cooler wave rotors would run. I did not want to join that lottery so I sold the bike.
 
#10 ·
The angled outside edges of the wave rotors create a continuous cleaning edge - helps clear the disc of dirt. Which is why they're so prevalent in the dirt world. As seen on street bikes, there's no real benefit other than that they look cool. Sometimes looking cool is reason enough.
 
#11 ·
Among things that affect braking is "swept area". ie the actual area of disc that is swept by the pad. If the diameter was kept the same, the swept area would be less, leading to less braking efficiency. If the diameter is increased to compensate for that, then you have a change in rotational forces which has its own set of effects on handling and braking. Yes, modern rotors have grooves and holes but their positive (better cooling) more than offsets their negative. I would bet a beer that the main reason, on a road bike, is fashion/style/fad. Ask yourself this......how many motogp bikes have wave rotors? I would think that if they provided even a modicum of increased braking efficiency, they would all be running them, carbon ceramic or not.
 
#13 ·
Sinterred pads stop you better, but wear faster/don't last as long and wear disks faster. That doesn't mean they are not worth it for some, especially those carrying a lot of weight on the bike (e.g., passenger and full luggage compliment or larger rider, or pulling a trailer (see my avatar)), but it's not a free lunch.

Galfer has sinterred pads as well.
 
#14 ·
Question about wave rotors. I've not seen these on a bike so I have not been able to answer this question. Does the brake pad see metal, then the 'wave cutout' as the wheel turns? In other words, the swept area of the disc by the pad includes the 'valleys' of the wave?

Logically, the answer to my q is a yes, or what's the point. But if the wave form only sweeps the outside 1/5 of the pad, you are only going to be cleaning the pad of dirt and mud on that area. The wave has no effect on the unswept major portion of the pad. The wave cannot sweep the whole pad's area or the pads would collapse inward.

It's possible that the sweeping action of a fraction of the disk's area makes a difference, but I confess to being skeptical until I hear from a pro (who is not being paid by the mfr of rotors) that the improvement in braking is real.
 
#16 ·
I have, and I've put them on two DL650's so far. And yes the swept area includes the valleys because the slots in the disc get what the petals miss.

And strangely it works better than OEM even with Chinese made rotors off eBay. You also drop the rotating mass by some margin which allows the bike to turn faster.

Frankly the two sets I've put on have been better made and assembled than OEM and both performed significantly better through their life than OEM as well. I wouldn't change them just for that, though the second set did get done earlier than the first because I had no reservations about using the eBay rotors the second time but in terms of replacing worn rotors they'd be my go to now and not just on cost.

I certainly notice the lack of squeal from the brakes and the more consistent brakes. They certainly work better on dirt and on wet seal, can't pick a difference on dry sealed roads.
 
#15 ·
The disc spins inside the calliper so fast there is very little chance for the crud to penetrate then the discs have holes or slots to remove the rest.


When I had drum braked dirt bikes I could not stop the mud & crud getting in so I cut slots in my brake shoes, they were cat at such a angle that as the brake hub spun it pushed the mud out.

This was especially helpful with my son"s bikes as the smaller wheels collected more mud.
 
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#18 ·
First bike, stock rotors lasted ~80,000k's and REALLY needed replacing. i.e. if the gouges on the rotor faces had been opposite one another the rotor would have parted. I sold that bike @120,000 and I think it made it to ~140,000 without the eBay rotors being replaced. (Cooling system failure supposedly killed it).

Next bike stock rotors lasted ~60,000's and would have been below the official service limit but were missing the deep gouges. I now have 130,000k's on that bike and the eBay replacements are starting to show signs of wear and I'd probably replace them now but the bike is just doing the commute. Yes I still need brakes on the commute but there's no hard braking from speed and near no wear.

One thing I have noticed, with the OEM rotors and a week of commuting I'd need several hard stops to get the brakes up to full function again (just build up of oily crap on the rotors I think), with the eBay rotors, one hard stop and they are back up to good again.
 
#21 ·
From the above link from the inventor...One of Sunstar Engineering’s bestsellers is SK2, a wave floating brake disc. Its non-round design enables a better radial expansion of the rotor under extreme heat conditions. Other advantages are a better handling, stable power in all conditions and an outstanding reactiveness thanks to more braking grip.
 
#22 ·
I'm going to throw some gasoline on the fire. As I said in an earlier post, I am skeptical of the claims made for wave rotors. It was my suspicion, based on schooling many years ago, that the reduction in weight for a wave rotor when compared to a standard disc shaped rotor is negligible when you look at the entire front wheel/tire/caliper/lower fork assembly. And that means that any reduction in rotational inertia and/or unsprung weight will have a very very small change in handling. And, based on my observations of other riders in the 3 mc clubs I hang out with, few if any of them would or could notice any difference changing the rotor. Cleaning efficacy? I don't ride in mud and gnarly off road conditions, however, over thousands of miles, I have never seen an oily film on my rotors unless either the forks or calipers were leaking. Asphalt and gravel roads around here are, at worst, dusty or wet w/ rain water, and that dirt seems to get cleaned off by the normal operation of the caliper. Plus, I clean my calipers and slide pins whenever I service the brake pads/brake fluid. (Been doing that on my cars and bikes for over 35 years).

Anyway, I asked a friend who is an engineering prof at a university for his thoughts on this. He is a bike rider and has been for ages. The 'Q's' are my questions, the 'A's' are his answers:

I have very limited knowledge of these wave rotors but here is my take in Q&A format:

Q: Am I correct that the drop in rotating mass of a petal brake rotor compared to a traditional rotor is negligible?

A: My guess is that the difference in weight - and therefore rotating moment of inertia which affects the resistance to changing direction - is negligible and I doubt that a street rider could tell the difference. A racer might, but I’m sure that I couldn’t.

Q: If slots clean out the dirt in rotors on off road bikes, why bother with the wave pattern? Why not simply use slots?

A: it could be that some types of debris / water etc. are more effectively cleared off with the wave shape - but I don’t know for sure.

Q: Would not slots have the same effect at reducing mass (if this were an issue) and allow better braking? Obviously, no metal seen by the pad (valley of wave or slot) means no braking by the pad, but we are talking off road bikes where you don't want aggressive brakes.

A: There are two aspects to mass reduction:

the amount of material removed or eliminated by the modified geometry of the wave / slotted rotor and,
the distance from the centre of rotation of the remaining parts of the rotor.

The further away from the centreline of the rotor, the bigger the effect of changing the mass on the moment of inertia (the resistance to changing orientation (such as in turning). However, if you only consider the unsprung mass of the rotor from the standpoint of the front fork suspension, then the geometry of modifying the weight of the rotors doesn’t matter at all.

As for the difference between slots and the wave shape - I doubt there is a big difference from the standpoint of mass reduction.

For the vast majority of street riders, these rotors are largely a styling exercise IMO. We don’t use anything like the capability built into modern street bikes, but they sure look cool!
 
#24 · (Edited)
I'm going to throw some gasoline on the fire. As I said in an earlier post, I am skeptical of the claims made for wave rotors.....snipped by STC

You missed the real question I have touched on twice now and the inventor once.

From another engineer:nerd: me

Q - will a wave rotor distort less than a round one when heated up.
A - yes.

Q - is there an advantage to less distortion.
A - yes, if you heat the brake disc up enough.

A fluted disc has the similar effect as mounting a disk with floating rivets. Even round disks on decent bikes are mounted with floating rivets. These provide a braking torque connection to the wheel hub that will allow expansion of the disc with less warpage. That is why many disks do not have mounting holes drilled through a solid piece of steel, they have a two part (hub/disk) design now.

I agree with your professor on rotational mass. But reducing unsprung weight is important for a suspension. However, disks with petals do not weigh much less anyway, some maybe weigh more. His other answers were correct also. But, the correct question was not posed to him.

Most of the stuff stated as advantages is marketing hype, some of it is not.
 
#25 ·
The reason for the petals on the outside is that you can't get away with full depth notches with an open end without making the disk radius larger (Reason you don't want that more mass is bad and as below). So to get a full sweep there are notches which alternate with the slots.

Rotational inertia is proportional to 1/2mr^2 and the weight reduction is at the outside of the disk. It wasn't much but it's where it makes the most difference.

The main point for me was "No downsides".
 
#28 ·
On a somewhat related note, anyone got anything bad to say about the fleaBay rotors? The rotors on my Vee are pretty well roached at about 115,000 miles.

I've seen lots of good reviews on the Chinese rotors and don't recall seeing anything negative about them at all. (Or at least nothing negative about their actual function.) I don't care at all how they look, but yeah, they do look kinda neat.

I do notice that some come with Chinese no-name brake pads which I do not want. I've had some first-hand experiences with cheap brake pads and I won't be repeating that mistake again.
 
#27 ·
You would think the wave would cool and keep things cool better.
 
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