Ducati Sporting Club UK > Model Specific - Discussion, Technical Problems and Help > 998 / 996 / 916 / 748 > Question for Weeksy.

[marksduc748]

me too!!

[Rattler]

Ah - but can material things make you happy????

---------- you bet your arse!!!

[Jasper]

Still not a yorkshireman.Ah,well,can't have it all!!

[Eamonn]

A technical question for you about wavy discs:

Brakes basically work by converting the kinetic speed of your vehicle into heat, the more efficiently they do this the better the braking performance. So in the same way that a larger contact patch of tyre on the road gives better grip wouldn't a larger contact patch of brake pad on the disc give better braking performance? Taken to its extreme, the disc should be solid with no holes, shapes etc. just like they were 25 years ago !!

I realise that there was a trade off (I think started by BMW) to put holes in the discs to dissipate water and thus improve wet weather braking - but it seems logical (to me) that cutting down on the contact area would decrease braking efficiency.

So do wavy discs really work better or is it just for show ?

[nelly]

The real key to brake performance is the swept area of the braking pads. Yes bigger pads would give a better brake, but one problem, under heavy use is the heat. This shows it's head as fade and one of the contributors to this is the gases created between the braking surfaces. These can create a sort of "aquaplaning" of the pad surface, between it and the disc face.
Drilled discs, slotted discs and Waveys, all use the holes etc. to dispel these gases. Another thing these discs do is to clean the pad faces to maintain clean friction material is always present.
Disc wear shouldn't be any worse, but you'll certainly see a reduction in pad life, mainly due to the "cleaning" effect.

The Waveys produced by Braking are about £176 each. These are the ones on Tims bike and the ones Rushjob has. Also available with Carbon centres (missed those Tim!!)
There is a new kiddie on the block in the shape of Galfer. These are really good quality to and come, initially as a kit (2 x discs and pads) for £387.

As Andy said, stay away from the cheap stuff. Brakes must never be a compromise, and with Waveys, stick with the boys that have been doing it for a while and know what they are doing.

[rockhopper]

Spot on reply Neil.

[Rattler]

I was also led to believe (but I'm easily led!!) that the waveys did disperse heat more effectively due to their larger edge surface area - if that makes any sense.

They even look good on a Suzuki!!!!



Tim

[Shazaam!]

So in the same way that a larger contact patch of tyre on the road gives better grip wouldn't a larger contact patch of brake pad on the disc give better braking performance? Taken to its extreme, the disc should be solid with no holes, shapes etc. just like they were 25 years ago !! ... it seems logical (to me) that cutting down on the contact area would decrease braking efficiency.

I know that it's counterintuitive, but the frictional force developed between two surfaces is independent of contact area. It depends only on the coefficient of friction and the force pushing the two surfaces together. The force developed between the road and a tyre is different because the soft rubber interlocks into the road surface, so a tyres grip is contact area dependent.

[psychlist]

Originally posted by Shazaam!

I know that it's counterintuitive, but the frictional force developed between two surfaces is independent of contact area. It depends only on the coefficient of friction and the force pushing the two surfaces together.........

Yes BUT.............IF the coefficient of friction and force pushing the two surfaces together was equal for two systems with different size contact patches wouldnt the one with a greater surface area develop a greater braking force?

[Shazaam!]

Yes BUT.............IF the coefficient of friction and force pushing the two surfaces together was equal for two systems with different size contact patches wouldnt the one with a greater surface area develop a greater braking forc

No. Physics 101. F=uN. Surprisingly, area doesn't enter into it.