post mount or IS standard?

[baggytrousers]

Hi, I'm looking to repalce the mechanial disc caliper on my son's mountain bike - I know the rotor size is 160mm and the caliper is fixed to the front shock with two bolts 50mm apart - the brakes I'm looking at all seem to come in 74mm post mount or IS standard - is 50mm IS standard?

 

[RedBike]

IS = The bolts face left to right

Post = The bolts face front to back

There's a piccy here (a lot simpler than trying to explain it).
http://images.google.co.uk/imgres?i...133&prev=/images?q=post+mount&um=1&hl=en&sa=N

 

[baggytrousers]

They're definately left to right and probably 51mm rather than the 50mm I thought - must be IS - thanks Redbike that's a great help

 

[Steve Austin]

IS stands for international standard. which was considered to be the best way, but then nearly all the manufacturers have switched to post mount.

Which is a bit odd now as the rear of MTBs use IS and the front use post mount. Call me cynical but it now meant that you need separate fronts and rears brake mounts. Not that many systems were ever interchangeable, not many were. ignore me , i'm rambling...