Originally Posted by
DangerousDanR
Reading the OP's description of the new tandem it will be a disc brake bike. I am more than fine with rim brakes for a solo road bike. But when my wife was looking at a new solo bike in 2014-2015 I made sure that she got one with disc brakes. She mostly uses it for short trips to visit friends or go shopping. Disc brakes work better in the rain, and sometimes rain storms come in very fast here on the north plains.
My road bikes are all rim brakes. My MTBs are all disc brakes. Our tandem is disc. The only one that has had heat issues is the tandem, and that has been solved. For our bulk, MTB downhill brakes are, in my opinion, the best way to go. Lighter teams will probably have a different set of parameters, but even if my wife and I both got down to our ideal weight, we would be around 350 lbs. Add in the bike and gear for touring and we are in the 400 to 450 lbs. range.
Mine are Hope, SRAM, Formula, TRP, Trickstuff, and a whole lot more companies make very good downhill specific brakes. I prefer to use DoT 4 fluid because I know that I can get fluid anywhere that I am likely to travel without having to wait for it to be shipped to me. Others will prefer mineral oil fluids, used by companies such as Magura or Shimano. Drum drag brakes are mostly unavailable for new bikes. My setup as it sits today has been shown to work as both a drag brake to keep speeds below our tolerance level on descents, and as a fast stopper from high speeds.
If I am running my tires at the tire and rim manufacturer's upper limit for pressure (I do) and the PV=nRT thing pushes them up by 10 PSI I am running out of range. Probably safe, but not certified. I wouldn't want to have to stop on a steep downhill with a strong tailwind traveling 45 MPH with a rim brake bike.
From what I understand, you are nowhere near "running out of range" with a 10psi "overpressure" in road tires. I understand blowoff pressure is determined by inflating a tire on an industry-standard hook-bead rim and inflated. Blowoff pressure is divided in two to determine "max pressure" for the tire. So, a tire with a 120 max pressure rating will blow off at 240psi.* This safety margin of 100% makes sense. Bicycles do regularly heat up rims, so the tire should be able to withstand pressure increases by heat, per the PV=nRT relationship.
A friend of mine, captain of a 400 lb team regularly exceeded his road tire's max pressure by 20 to 30 pounds. He did this for years without any negative incidents or problems.
I'm pretty sure 10psi over max on a road tire isn't anything to worry about. Then again, on a tandem with rim heating a potential problem, DON'T EVER DO THIS!!!! (Thanks Lawyer Bob for requiring me to say this!)
*Unfortunately, I still have not been able to confirm this by finding legitimate sources on the subject. I had just heard this "in the bike industry." So I guess I owe it to myself and everyone else to actually track this down before stating it as fact. Something to work on. Unless someone here can confirm or deny this; I'm all ears!
EDIT: Well, that wasn't THAT hard! Shoulda consulted master Sheldon from the get-go! He says:
"The lawyers want the number kept conservatively low, in case the tire gets mounted on a defective or otherwise loose-fitting rim. They commonly shoot for half of the real blow-off pressure."
(
https://www.sheldonbrown.com/tires.html#pressure)
So there we are. From the cycling god's mouth. Don't think any more citation is necessary!