this post was submitted on 02 Jun 2024
19 points (95.2% liked)
Motorcycles
2454 readers
26 users here now
Here we discuss everything related to riding, maintenance and gear.
founded 1 year ago
MODERATORS
you are viewing a single comment's thread
view the rest of the comments
view the rest of the comments
Same way you do anywhere else - use them properly (seriously not being snarky, there's really only one area where there's a difference, which I discuss below). Keep in mind most bike clutches are wet, so have better cooling capability than cars (though BMW likes a dry clutch).
Hills aren't really any different, and with modern vehicles brakes don't fade like they used to (especially on bikes).
Though, since a bike does (almost always) have a manual gearbox, let engine braking handle any long downhills where you need to keep speed in check, and use brakes in short, firm decelerations.
For example, there's a long downhill on I70 in Colorado, so long it has a sign saying "Truckers You Are Not Down Yet - 7 More Miles of Downhill". On such a long downhill, downshift just enough that engine braking keeps you at your target speed (say 65 mph on that hill). Then if you do start running fast, or getting too close, use the brakes firmly, not lightly, to quickly bring your speed down.
This works best because it heats the brakes intensely for a few seconds, but then gives them a relatively long time to cool off afterwards.
If you were to just lightly hold the brakes to slowly slow down, the discs would heat just as much (if not more), but you'd have less time between braking cycles, leaving less time for them to cool.
I've experienced brake fade on such downhills, it's no fun (in a truck). Passenger vehicles don't often have as advanced materials in brakes as bikes do, and this particular one had relatively cheap aftermarket pads, and I had been used to it with factory pads. Big difference.
I've watched trucks going down such hills with their brake discs glowing hot enough to see in daylight - they had to be riding the brakes a long time for that.
Essentially, any brake system could emergency stop a vehicle at speed on such a downhill one time, so best to keep them cool for as long as possible by using engine braking.
All that said, on my 35-year-old, 700lb "sport" bike, I've never experienced brake fade on downhills like that. The brakes are so oversized relative to the mass of the bike, it's just not a concern. But I still use engine braking - why take a chance.
Good comment, though I need to disagree re: quick braking based on physics principles; moto brakes are designed to handle heat load in most common environments, whether from fast hard braking or long moderate applications.
Energy cannot be created or destroyed, right? Brakes turn kinetic energy into heat, and that's a function of clamping force.
You're applying less clamping to your brakes over a long period, and rejecting that energy as heat. You're in fact generating very close to the same net heat with a sharp, fast change in velocity, as between the two options what you're really affecting is your kinetic energy.
The difference between the two options is subtle actually, quick steps allow cooling air to access the center of the brake pad between applications, long stop actions don't. But pads and fluid are now designed to conduct heat well enough to transfer the heat away faster than it can be generated, even if cooling now only affects 5 sides instead of six. That's the primary and crucial reason why brake fade is no longer common.
Fast breaking adds potential loss of control into the mix, so it shouldn't be necessary or recommended.
Which is what I said - they have a longer cooling time between braking cycles.
A longer braking cycle also occurs over a longer distance and time, meaning more time for gravity to continue contributing energy to the equation. A faster deceleration between the same two speeds is less energy dissipation overall (say 70 to 60 over 5 seconds VS 30 seconds). There's 5 seconds of additional acceleration due to gravity VS 30 seconds more.
But the biggest thing is you get a long cooling cycle instead of steadily heating the pads and rotors to simply "hold" against gravity. The rotors simply don't have the mass the absorb and dissipate that steady, continual heat input.
Thanks for your response, friend. Last point is what I disagree with, for any bike manufactured past the late 70s. I'm clarifying that although sharp braking will lead to a seemingly cooler system, it actually isn't a constraint because of how effective modern brake design is, and in fact invites danger through loss of control.
To the other points, brakes dissipate KE only, any sane designer will make brakes able to handle the heat load of a 140kg (300lb) rider on a 25% grade in ambient temps of 40c (104f) holding velocity steady at 50kph (30mph), all reasonable assumptions as I wouldn't really want to ride at the edges of those specific envelopes. We're not a truck hauling 36000kg (80000lbs), whose driver may accidentally approach the boundaries of their brake system a lot more easily.
Dot3 brake fluid is common, it's at a 205c (400°f) boiling point and (this is key) we've got airflow interacting with the brake assembly over a longer period of time, while accruing less input thermal energy vs the sharp stop per moment of time.
If we sum the energy going in over the entire time vs energy going out (via air flow, fluid flow etc), the boiling point of the dot3 isn't approached for any moto brake system designed past the late 70s, unless you're slowly decreasing speed from a very, very high initial velocity, inputting thermal energy faster than the system can discard it.
We again reach the conclusion that within reasonable limits, holding speed steady using brakes alone won't lead to brake fade on a bike manufactured past the 80s, no matter how long the descent.