Wrong,

You can not tell the diffrence simply by measuring the disc's as both calipers used the same 278mm ones. The easies way is to look at the disc and if it has a ring of rust in the very centre then it has the samller caliper and pads whereas the larger ones use the whole of the disc surface and hence no rust ring.

The ST170 is a good upgarde but not a sgood as the ASBO upgrade that I have on mine!!!!