Drilled disks - why do they crack?

[MarkCup]

Out of idle curiosity...

I've had bikes over the years with drilled disks, and I know a lot of bikers also, and I've never heard of a drilled disk on a bike cracking.

Yet everyone advises against drilled discs on cars as they crack.

Is it because they're fully floating?

Didn't BMW stick floating discs on an M3 once? Do they still do so?

 

[Englebert]

It is simply the heat variation that causes small cracks which grow. The bad reputation is down to poorly made discs.

 

[Fred@BTM]

also the holes get full up with dust

porsche's discs always start cracking if you abuse them AFD, my mates GT3 gets through them

 

[Ali]

Ditto about the dust. We used to go through pads like no tomorrow with drilled disks.

The only way we got away with not breakin disks was with floating disks.

 

[MarkCup]

So it's because the disks on modern cars don't float as a rule?

Why don't more manufacturers fit floating disks then?

Cost/complexity?

Probably lack of demand?

 

[Fred@BTM]

So it's because the disks on modern cars don't float as a rule?

Why don't more manufacturers fit floating disks then?

Cost/complexity?

Probably lack of demand?

COST!!!!

 

[Turkish]

the E36 M3 had "floating" discs, Porsche's do not. Some of the models do have a seperate bell and rotor as opposed to a one piece casting but they're bolted together solidly.

 

[Neil G]

Agree on the dust....also a problem with grooved discs

 

[fizzy_drink]

I've seen drilled discs crack on a car (and they weren't cheap ones at that).

I've never cracked a disc on any of my bikes (and they've all been drilled).

 

[disco]

Probably just to do with the weight difference between a car and a bike!