Originally Posted by
old's'cool
The general case is, there is a fixed amount of potential energy that needs to be dissipated somehow, during a descent. The higher the allowable maximum speed, the more of this energy can be dissipated via aerodynamic friction, not to mention tire friction and bearing friction. Let's hope bearing friction is inconsequential. Tire friction is probably a minor factor, otherwise we'd be overheating and blowing tires simply due to road friction (i.e. at high descent speeds).
If you can descend at terminal velocity safely, great, that means no energy absorption by the braking system.
To the extent that the safe speed is lower than the terminal velocity, the braking system must take up the slack. So called "stab braking" can take advantage of this, by allowing the actual velocity to exceed the terminal velocity momentarily, and reap the marginal benefit of the non-linear effect of aerodynamic drag during these moments. Furthermore, a braking system that is intentionally or accidentally optimized for stab braking, can take advantage of momentarily higher braking surface temperatures to dissipate marginally more heat to the environment, on average, compared with a system that has assymptotic surface temperature rise (i.e. due to steady braking to a defined terminal velocity). If any, the downsides to stab braking, especially if the system is not designed as such, are excessive peak temperatures (a likely concern), and excessive peak torques & other loads (a less likely concern). Keep in mind, the advantages are marginal, not fundamental.
That was a highly intellectual response, but in a nutshell from what I've learned off the internet (due to this subject here) and from 40 years experience riding mostly in mountains is that stab braking works. By hitting the brakes for 5 seconds then releasing for 5 seconds and repeat it allows time for the aluminium rims to cool down enough to prevent overheating the tires. I knew tandem riders who use this method all the time coming down mountains and didn't have a rear drag drum brake due to weight concerns for a racing bike. Of course this braking technique has to be used with some ahead thinking so that you hit the brakes at the right time when approaching a turn.
Another technique for braking we did was to use the front brake only for hard braking then for less braking to scrub off some speed use the rear, this allowed more time for the front to cool.
Both methods work because it allows the airflow to cool the rims, these methods do NOT work for carbon fiber rims because it takes much long for the CF rim to get rid of heat compared to aluminum rims.