Just wondering if discs that are worn past minimun thickness actually perform worse (cant dissapate as much heat, perhaps?) as thicker discs? Mine are almost down to min but will probably last a few more miles yet. And at £120 a pop id like to get as many miles out of them as poss! Any thoughts?

Probably more prone to warping as well

I guess the thing you really don't want to happen is that they get thin enough that they can't take the brake force and come apart when you try to pull a panic stop. That would really ruin your whole day.

Put it this way, is your life worth so little?

Worn discs are more prone to warping, splitting, over-heating. All things that reduce braking performance.

I have a picture somewhere of a write off bike I picked up a while ago where the owner had run on discs only 2.5mm thick. He didn't manage to stop when the dustbin wagon pulled out - the discs shattered as soon as he pulled the anchors on (according to eye witnesses).

As above but would there be a possibility that if you had thin discs and thin pads would they not generate enough clamping force?
Just an idea but I have always changed out braking equipment as a priority

It is a higher risk of failure.. not something you want on a bike is it?

oh god, i'm not suggesting using them past min thickness, they're a little way off that yet.

I just want to know if the braking effect is reduced the thinner/closer to min thickness that they get or does the braking efficiency not directly correlate to the efficiency?

I guess if you put too much thought into it, you could say that thinner discs mean they'll get hotter quicker, and be more prone to fade, but then if you're pushing a road bike hard enough to make the brakes go soft then perhaps you might want to find a racetrack!

it is the small cracks in them that worry me.

Have a proper good look at them - you get cracks in old rotors from hole to hole.....

And it wont pass its next mot..............