Right when i fitted cossie size rear discs 273mm IIRC (also had 282mm Front at the time) I found that under what could only be termed as emergengy braking in the dry and heavy braking in the wet the rear used to out brake the front just like you had pulled the handbrake up back used to slide out was a bit of a surprise the first time lol.

Now that was on a C reg xr3i not sure if i should have fitted a valve or something to reduce the rear pressure a bit im sure someone will chime in on this...

For my next car I have found brackets that will allow fitment of a 240mm disc (xr4x4 Rear) so kinda hopeing that i wont have this problem again as the front will be 278mm this time.

Not sure if anyone running the conversion on a rst has had the same problem but i sure did lol