Jase, knock a zero off the end of the number and that's how many mm it is fron the centre of the spindle to the position of the brake blocks, and I assume that's the maximum distance to the brake blocks at the furthest reach, although it could be the average, someone on here will correct me.
ie an MX900 is 90mm, an MX1000 is 100mm, an 890 is 89mm and a 1020 is 102mm.
Hence why a 730 caliper is so small and only works on mini frames (as I found out once when I didn't read the ebay add properly and wondered how I'd bagged a DC caliper for 99p........)
