John, my experience (see my first comment above, June 9 2015) is that the cornering can get squirrelly with pressure below 55 psi rear and 45 psi front. This is with Barlow Pass 700×38 tires mounted on Velocity Synergy rims with 19mm internal width, me at 190 lbs and the bike at 24 lbs. I did some hard sharp turns at low speed to watch what happens – the sidewalls partially collapse and wrinkle up when you feel the tire wash out. At high speed it would be dangerous. By increasing the pressure from 50/40 psi or a bit less (my preference for ride quality) to 55/45 psi, the tire becomes rigid enough under cornering loads to prevent washing out. Obviously, the pressures needed will vary depending on rider+bike+cargo load and cornering style. I needed to carefully sneak up on the best compromise.

I just changed out my wheels to some really wide ones I’ve built: H+Son Todestrieb (really a 29er mountain bike rim) laced to road hubs. These are about 25mm internal width and 32mm external width. The wider rim pretty much eliminates the “light bulb” cross section of these wide tires. The cross section is now similar to a 25mm tire mounted on a standard road rim, just scaled up. The wider rim definitely improves stability in turns. I’ve done a couple rides this week (one in pouring rain), with the pressure dropped to my preferred 50 psi rear/40 psi front, and it is just as stable as it was at 55/45 psi mounted on the narrower rims. The down side of course is that the wider rims weigh quite a bit more – the Todestriebs are listed at 600g each online, but this is optimistic for even the 26″ (559mm) size. My 29″ (700c / 622mm) rims actually weighed in at 740g each, so these are comparable to other large heavy duty rims. Yet the bike rides so nice with the wider rims, I don’t think I mind the heavier wheels.