Originally posted by rljones
cmh,
I'm not an engineer,
I am!
and maybe someone more knowledgeable than I can comment, but I would not go too high with the tire pressure. The bead of the tire is forced out onto the lip of the rim with the pressure exerted from either type of clincher proportional to their pressure. Also, the tube inside the TUFO is still in contact with the central part of the rim as the tube is expanded; it is not 'floating' off the rim and somehow isolated. All of this pressure is still exerted on the rim.
The Mavic KSYRIUM SSL SL (also Mavic Open Pros and Elites) with a 23mm tire are rated for 138 psi.
True, and correct me if I'm wrong, but we're talking about Tufo's tubular clinchers, not an ordinary clincher.
Try this: Take a normal clincher, put a tube in it. Don't mount it to a rim. Inflate the tube to 100psi. What happens? The tube expands without bound until it pops, well below the 100psi. That's because the rim works with the tire to contain the tube (and the air inside of it).
Now try the same with a tubular tire, or a tubular clincher, which is a tubular with the little rubber mounting wings on it. You can inflate the tire to full pressure off of the rim, because the tire fully contains the tube. (in the case of the Tufos, there's no separate tube, but the idea is the same)
So what this means is that a tubular clincher at 130psi is not putting nearly as much stress on the rim walls as a conventional clincher at the same pressure because the rim is not being used to enclose the tube and resist the air pressure. Therefore, we can inflate the tire to a higher pressure.
Visual aids:
A conventional clincher tire
A tubular clincher
Also notice how Tufo lists the same psi range for both the tubular and tubular clincher tire, and this particular one ranges up to 220psi!
Tufo info on Elite Road
We read about aluminum frames having a fatigue factor after which they can precipitously fail (unlike steel that is gradual). Why should the failure of aluminum rims be any different? Personally, I don't want to test it. I had my son only put up to 120 psi into the TUFO despite their greater rating. (Also, as the meter on the pump is not calibrated, if you go to 138 psi on the above rims, you could easily be putting 150 into your tire. I would allow some margin for error.)
Aluminum is different from steel in that it does not have a fatigue limit. That means that any time there is any stress in the material, it gets closer to failure. Steel has a fatigure limit, where if the stress does not exceed this limit, the material will have, for all intents and purposes, an infinite lifespan.
What this means in terms of rims is that ANY stress on the rim gets it closer to failure. Even inflating a tire to 20psi will do this, although it'll take a whole bunch of cycles (probably millions) of inflating and deflating to get there.
Increasing the stress will decrease the number of cycles to failure, naturally, and the 138psi limit you see is Mavic balancing a reasonable, safe fatigue life against a rim weight and strength. These are the same considerations taken into effect by the folks who design aluminum bike frames, airplanes, and lawn chairs.
Conclusion?
Since the rim isn't holding the tire pressure the same way that it does with a conventional clincher, I don't see any risk in inflating the tubular clincher to Tufo's numbers.