Why do some brake discs have teeth? What's the advantage?

I was just wondering why some brake discs are perfectly circular and smooth while others have ‘teeth’. My bike has teeth but judging by catalogue photos, stock was smooth. Any idea why the previous owner would swap them?

when you say teeth? do you mean ‘wavy’? 

As in something like this?

Without being able to answer technically, the common argument I’ve heard is they offer better braking. How, why or which ones do it better than the round ones, I cannot answer you. 

I always thought it was just for cooling purposes to avoid brake fade.

They’re to act as a saw to cut up small woodland creatures into slices instead of them getting all caught up in the calipers.

Yeah - that sort…

The pattern is to save weight. For racing purposes.

Honda website states “…heat dissipating brake discs”

in any case, I would most often consider it an improvement, unless the wavy discs are of unknown origin

I’ve thought the main reason was, similar to the different patterns in tyre tread, to look cool.

The pattern is to save weight. For racing purposes. silveR6
Except racers don't use them?

I’ve heard that it’s for cooling, weight saving or to deglaze brake pads - I suspect the real answer is aesthetics

motogp bikes have carbon disks, as shown in that photo. they need to stay warm to for optimum braking. 

wavy steel disks are for increased air turbulence to dissipate heat better.

OK, bad example but look at the WSB bikes or Isle of man TT - they all seem to be regular round discs too

As above, their main purpose in life is heat dissipation, this is achieved because the cuts and waves increase the surface area proportionately to the available contact area of the disc. Overall weight is not such an important factor as where that weight is. Wavy discs carry more of their weight towards the centre which means that less effort is required to spin them up or and slow them down. The downside of some disc patterns is there is less contact area between the pads and discs, this is normally compensated for by having larger pads and/or larger callipers with more pistons. Of course, lets not forget that larger multi piston calipers require larger master cylinders. Its all about the hydraulic ratio, that’s the surface area of the master cylinder piston compared to the combined surface area of all those calliper pistons.

The bottom line is that the entire braking system needs to be balanced and each part of the system (discs, pads, callipers and master cylinder) needs to work in harmony with each other part, don’t mess with one part without the others.

OK, bad example but look at the WSB bikes or Isle of man TT - they all seem to be regular round discs too
Might be part of the rules in having to use standard parts.

Heat dissipation and weight saving (unsprung mass). Cars like Audi RS6 have wavy rotors (unsprung mass). On RS6 they save couple of kilos on big heavy rotors across all 4 corners. Although as NT mentioned it’s important where on the wheel that weight is.


If all the brochure pseudo science re heat dissipation etc. is correct, then why do none of the 2017 litre class sports bikes have wavey discs anymore?

Thinking about it, have Brembo actually ever made wavey discs?

Bottom line is: for everyday use, and MotoGP, standard rounds are fine. For aesthetics and racing that isn’t MotoGP, patterns and shapes are real cool and light and save you something or other.

As above, its all in the science. Less contact area between pad and disc requires bigger pads and bigger callipers and bigger master cylinder to maintain sufficient hydraulic ratio and grab.

Once the whole braking system has been balanced there is no weight saving. So the real question is do they add to braking efficiency allowing later braking into corners without locking up the wheels or any undesirable effects to the suspension or frame geometry?