My front disks have developed small cracks coming off the drill holes, I would say 50% of the holes now have one or two small cracks coming off. Most cracks are probably 4-5mm but one or two are 7mm long.
These cracks are not really obvious but they are there, so is this a worry? do I need new disks?
A couple of people have said to just keep an eye on them but what should I look out for? I dont want them to crack right through.
Boothy
surfacing cracking can often happen quite quickly on a disk and that is fine. Keep an eye on the crackas and as soon as they start to open up its time to change them.
Jacobs?
common problem sadly, I even got cracks in the rear discs and my AP fronts, I now use grooved discs so it does not happen any more
My physics teacher taught me once , that, things are more brittle when cold … Heat them up proper my Son !!! Then all will be fine 
only kidding m8
I,m trying EBC turbogroove at the moment … all is fine so far …
[quote=jfk][quote=Boothy]… my physics teacher taught me once
I,m trying EBC turbogroove at the moment … all is fine so far … [/quote]
I will make sure I am not in front you when you TRY to stop mate! 
What have you got on Pete? Are you going to sign up for my trackday btw?
On my Egige I fitted the AP grooved ones. Brill as bigger diameter too!
My S2 111s has the boggy basic Lotus Sport ones, but with RS42 pads and R600+ fluid. All works fine as I dont go fast enough to give them any problem!
my rear disks are just over two years old now and the surface cracks (5-7mm on every hole) haven’t grown much beyond where they were this time last year.
the front ones had the same and didn’t grow much either but i did have to replace them as they were well scooped out about 9 months ago
i got the big AP grooved ones as well. no cracks and it really is like dropping an anchor.
I also got grooved for the rears for the same reason, a not much change for a while, then one trackday left the cracks to the edges of the discs 
Groved is the way to go. The surface cracks are there due to the rapid change in temperature when you put the brake on and the fact that the disks are to small.
Certain tracks are harder on brakes than others. Donnington for example is pretty killer on brakes, especially the old GP layout