wheel bolts length !? :(

[Gaz]

*Sigh*

Was going to fit the borbet A's today and have noticed another problem.

Looks like my wheel bolts aren't going to be long enough?

After placing a bolt in the wheel I first thought i was going to still have enough length, but then noticed that some of that thread is going to be lost by the thickness of the brake disc.

So, my two questions are, Exactly how much thread do i need protruding from the wheel for it to be 'safe' ?

And from where can i get longer wheel bolts?

cheers.
Gaz.