The above reviews are true but recently the southern half of the road has been resurfaced (mostly) and this has improved the road and experience.
i done this road from muirkirk to strathaven, it was a good ride when i had my mrs on the back as i took it easy, when i went myself i went a bit harder and the road is very bumpy, i almost ended up in a field a few times after leaning the bike into the corners only to hit a bump and run wide.
overall a nice run but watch out for the bumps
"The Muirkirk Road" Starts off at the staggered junction in Strathaven onto very fast straight then a slowish left over a raised bridge.... and from there the fun doesn't stop. Fairly decent surface and open enough for cracking on.....until you pass Dungavel HMP(toot-toot) then it is'nt. From here to Muirkirk fitting a steering damper will not be far from your mind, whatever you ride .Never the less it is very entertaining.