Having recently purchased my second set of SIP rims, (the 1st set were to wide and my exhaust rubbed the tyre sidewall,) I've just had air instantly escape on my rear tyre. Luckily I had just set off from a set of traffic lights going slowly and felt instantly something wasn't right and pulled over. Even more luckily I was only half a mile from home, (with no spare,) and so pushed it home. I removed the rim to investigate and could see nothing obvious, so took it to a local garage to try and reinflate it, but the valve wouldn't accept air from the machine. Took it to another garage - same again. I then tried to remove the valve with a valve removal tool, and the whole valve just folded in on me and broke. Totally p*ssed off.
I know it's each to their own, but my experiences of these rims leave me thinking that their not all there cracked up to be. Firstly tyre fitting. I know SIP have done a tutorial on how to fit tyres to a sip rim, but the tyre they used must have had a soft sidewall. I tried fitting some heidenhau k61 59p rated tyres to 2.10 x 10 rims myself - no chance. Took them down to the local proffessionals, and it took two of them half an hour to fit two tyres to their respective rims. The machine they were using simply didn't have enough torque to mount the tyre. In the end, and with the use of the circular tyre fitter, two large crowbars, copious amounts of lube and WD40 and massive amounts of elbow grease the tyre went on. ( This is the third set of tyre fittters I've settled on after one said they couldn't fit them, giving up half way through, another damaging a tyre whilst fitting it, and finally this lot who do manage to fit the tyre, but you can see they've got their doubts.)
So finally tyre fitted, but after 30 miles or so the tyre rapidly deflates, and the valve is knackered. I think I'll be contacting SIP to let them know, and am seriously considering going back to split rims and tubes which I've never had a problem with.