As nina says the ST4 can take 140mm and is warranted to do so:

http://www.orangebikes.co.uk/support/warranty.php

It does raise the BB a bit so its not quite as snappy as when run with 120mm but is still a serious amount of fun!

seeeeeeeee!

by raises the bb what stu means is that it no longer scrapes the ground…

interesting… the website says max. 130mm in the blurb on the bike
I guess I could just run more sag on the forks if conversion is not possible (they're Rev dual airs)

you a man or a mouse? get. it. done

The last thing I'd do to an ST4 is anything that raises the BB height. The low slung centre of gravity is it's greatest asset IMO!

It's the closest thing to a Star Wars speeder bike you can get… 😀

Indeed Gary, starwar speeder bike is a good analogy – usually run the forks at 120 but find it useful to wind them out for steep downhills, always with a fair amount of sag though!

could someone please translate the last two posts? unfortunately i don't speak geek

forks are what you eat with, usually paired with a knife
downhill is the opposite of uphill
sag is what old people get

could someone please translate the last two posts? unfortunately i don't speak geek

This:

and this:

Ride about the same.

pffft, hardly, the top one aint got wheels

Sag aloo is spinach and potato. Forks are for tuning.