To celebrate the arrival of my new Fulcrum Red Metal Zero wheelset I also ordered a couple of Continental Race King Supersonics in 2.2 width.
There's a bit of weight variation from tyre to tyre, so if you're a real weight weenie and you're friendly with your local bike store (LBS) then you might be able to choose a particularly light copy. Of the two I bought, one weiged 455 grams and the other 467 grams. Continental list the weight of these as 460 grams so those weights are well within the ballpark of what to expect.
I mounted these tyres on a set of Fulcrum Red Metal Zero (Rim Brake) wheels using Stans NoTubes sealant (no tube). To mount these non UST versions without a tube definitely requires a good high volume compressor and ideally an extra set of hands. Removing the valve core will help to get a higher flow of air as well. If you don't have valve stems with removable valve cores then now would be a good time to get some. Also get a presta to shrader valve adapter if you don't have one of those as well.
They take a bit of patience to get inflated and sealed but the seem very secure once the bead is set. Indeed, when I later test rode them I tried an absurdly low 20psi and I could not get them to come off the bead. This is probably helped significantly by the Fulcrum's UST rims that have a very nice bead retaining goove.
One thing about light non-UST tyres - you can't rely on them to hold air, at least not without running some sort of sealant. To see what I mean have at look at this picture of the inflated tyre under water. You can see how porous the sidewalls are by looking at the small columns of air beads coming out of the tyre.
Mounted on 17mm wide Fulcrum Red Metal Zero rims, the Conti Race King Supersonic 2.2s inflated to around 35 psi give a really nice rounded profile while still retaining a slightly shallower curve on the top.
Width on the 17mm rim is around 55mm:
Height on the 17mm rim is around 54mm:
Width on Stans ZTR Crest rims (21mm inner width) is 55.8mm - this is only 0.8mm wider than when mounted on the 17mm wide Fulcrums.
These are big looking tyres. There is probably only about 6-7mm gap between the top of the tyre and the SID 2009/2010 brace arch. If they ever made these in 2.3 it would be touch and go whether they'd fit.
The single trails where I ride are hardpack with rocks and the occasional rock garden. The fire trails are hardpack clay covered with small <10mm loose rocks.
We've just had some rain so trail conditions were superb. Probably just about any tyre would have hooked up. Even so, the Race King's felt much gripier than the Mythos II's on my other wheels.
Something I have always liked about Continental tyres since I got my first pair of Vertical Pros many many years ago is that the tyres have a very rounded profile giving great predictable grip at just about any lean angle. The rounded profile also means the bike tips into the corners with amazing ease. At greater lean angles there is none of the squirminess that you get with tyres that have big side blocks.
I tried a range of pressures from 40psi all the way down to 20psi. 20psi is way too little and feels like you've got a flat tyre (which you have!) but no matter what I did the tyre would not unseat from the bead which is nice.
The tyres felt best in the 30-35psi range. 30 was probably a bit on the low side but traction was superb. After a bit more trail side mucking around I settled on a bit over 30 in the front (perhaps 32psi) and around 35 in the rear. I don't know how accurate my guage is so its best to experiment around the 30-40psi on your guage. Provided you use the same guage each time the inaccuracy should be the same so it won't matter.
Something you don't see that often any more:
A word of caution. If you run these tyres below a certain pressure and ride aggressively, then it is possible for the tyre to stretch off the side of the rim. This results in a permament stretch in the tyre casing that means it now wobbles on the rim. It seems like you've buckled the rim, but its actually the tyre wobbling.
The latest pair of Race King Supersonic 2.2s are a little heavier than previous pairs I've bought. My newest set weight 483g and 484g. If anything, there seems to be a thicker rubber coating on the sidewalls. It will be interesting to see how well they seal up once mounted tubeless style.