Techniques for braking on steep descents

[Vorpal]

I have ridden a loaded tandem + trailer down long Norwegian descents with only rim brakes.

What I do is
-alternate between front and rear braking and do it periodically instead of constantly or 'feathering' (so my speed can vary somewhat)
-never letting speed get too high
-I try to be aware of how the brakes feel & stop for a cool down if there is any change in the braking performance
-become a slow descender

Some people just stop periodically & feel the rims (or discs). You obviously have to be careful with this, as you can burn your fingers. Discs both get hotter and can withstand more heat

[plancashire]

Any other tips?

There are two circumstances when the brakes generate no heat at all:

1) When they're not applied
2) When the bike's not moving

Sometimes you can get close enough to the former, but you can always get close enough to the latter.

More physics: if you move slowly the descent takes longer and heat has more time to dissipate. The total amount of heat generated is related to the potential energy lost (descent). Therefore the pads will be cooler. I suspect this effect will far outweigh anything related to braking technology - all brakes convert the motion into heat. The technology is relevant when you want to stop very quickly or in the wet, or you need something that doesn't fade at high temperature (but see above).

The only other way you can dump the potential energy is in heating the air by wind resistance, so sit upright. The effect is small at low speed.

[531colin]

The physics is unforgiving….all the time you are braking you are building up heat; when you are not braking the heat can dissipate. The hotter you get the brakes, the faster the heat will dissipate because the differential between pad and ambient is greater.
Don’t drag the brakes whatever you do; you have to find a way to let them cool by braking alternately front and rear, or scrubbing a lot of speed off before a bend then letting it run.
It doesn’t help that the stuff is made for light riders and graded Alpine descents, I guess you need the biggest discs you can fit in, or the biggest the mountings are OK for .
Am I right to be cynical about finned pads? The fins are on the metal backing, but it’s the friction surface which gets hot?
Interesting, the post above has the opposite advice!!

[Vorpal]

Am I right to be cynical about finned pads? The fins are on the metal backing, but it’s the friction surface which gets hot?
Interesting, the post above has the opposite advice!!

Fins increase the surface area for heat dissipation. The heat spreads through the metal first, so that's a good place to dissipate heat. Obviously, it would be better to do it on the braking surface, but that's the part that's generating the heat.

Fins on the metal backing will do the most good during braking. When not braking, the the pads themselves will be cooled by the air.

edited to add: that said, fins need to be designed properly to be worth the extra weight. the principle works well in other areas; I do not have direct experience with finned pads on disk brakes

[mattheus]

It's easy to kill disc pads in the Peak District, rim blocks last better!

:O Shots fired!

[mattheus]

Any other tips?

There are two circumstances when the brakes generate no heat at all:

1) When they're not applied
2) When the bike's not moving

Sometimes you can get close enough to the former, but you can always get close enough to the latter.

... to which I'd add:
- they cool fastest when the bike's moving - preferably fast - and they're not applied.

[drossall]

More physics: if you move slowly the descent takes longer and heat has more time to dissipate.

Interesting, because I once read an argument that over-caution, leading to over-braking and hence additional heat, can be more dangerous. I suspect there's some truth in both, but your argument makes perfect sense.

Good news for me because, the older I get, the more cautious.

[mattheus]

More physics: if you move slowly the descent takes longer and heat has more time to dissipate. The total amount of heat generated is related to the potential energy lost (descent). Therefore the pads will be cooler.
< snip stuff about technology...>

The only other way you can dump the potential energy is in heating the air by wind resistance, so sit upright. The effect is small at low speed.

Hence higher speed will dump more energy into the air.

On a VERY steep descent, you might get cooler brakes by really crawling down the hill (I susoect this si the kind of speed where it starts getting harder to balance).

On very gentle descents, you will get cooler brakes with intermittent big stops (hairpin bends are a good time to do this, if you're on that kind of road .

Someone else can do the maths to work out the values of very steep and very gentle [but I have a gut feel for the real world values]

[Pebble]

Is there a type of pad that handles long, heavy descents better? Should I be intermittently braking to allow the discs to cool? Any other tips?

Do you get your discs to glow red ? and are you getting brake fade (it feels like they go spongy and don't work as well)

as already suggested up thread, bigger discs to dissipate the heat or just desend a lot slower to give more time for them to cool.


I used to drive wagons back in the 80s, worrying about how hot your brakes might be getting was a big part of the job back then - brake fade when fully freighted downhill was a scary thing.

[JohnR]

In addition to the basic Shimano Ice Tech rotors there are also the Ice Tech Freeza rotors that are designed to dump extra heat https://www.amazon.co.uk/SHIMANO-SM-MT9 ... 07H2VY698/.

I'll be going over some alpine passes in the summer and wonder what measures I need to avoid any braking issues. There's only 65kg of rider on the bike and minimal baggage. At the moment I have some finned pads in my box. The next step would be the basic Ice Tech rotors. I've considered putting a 180mm rotor on the front but it's unknown if the forks would like the extra braking torque that could be applied.

[rareposter]

In addition to the basic Shimano Ice Tech rotors there are also the Ice Tech Freeza rotors that are designed to dump extra heat https://www.amazon.co.uk/SHIMANO-SM-MT9 ... 07H2VY698/.

I'll be going over some alpine passes in the summer and wonder what measures I need to avoid any braking issues. There's only 65kg of rider on the bike and minimal baggage. At the moment I have some finned pads in my box. The next step would be the basic Ice Tech rotors. I've considered putting a 180mm rotor on the front but it's unknown if the forks would like the extra braking torque that could be applied.

I wouldn't worry about it at all. I've ridden numerous descents around there (including Mont Ventoux) on 160mm and never had any issues at all. You only really get problems on disc brakes if you drag them for very long periods and you simply don't need to do that on Alpine passes - plenty of opportunity to let them off, use the airspeed on the descent to cool them (even just for a few seconds) and then reapply.

Plus discs do actually need at least some heat in order to work properly.

[Pebble]

Don’t drag the brakes whatever you do; you have to find a way to let them cool by braking alternately front and rear, or scrubbing a lot of speed off before a bend then letting it run.

why would periodic braking help ?
On a long steady slope
a) holding brakes at constant pressure so as speed remains at a constant 20mph
b) repeatedly letting it go up to 25 then braking down to 15
c) alternate harder braking from front to rear brakes but keep speed at constant 20

It is the same amount of kinetic energy being transferred into heat.

I'm not saying you are wrong, I certainly use periodic braking myself, esp in the wet as it helps get rid of that horrible grinding noise (rim brakes) but why would constant pressure braking not be a good technique.

Plus discs do actually need at least some heat in order to work properly.

Do they ? ceramic ones on F1 cars may be, but cast iron ones why would they need to be warm, or is it some sort of pads work best in a certain temperature range

[mattheus]

Don’t drag the brakes whatever you do; you have to find a way to let them cool by braking alternately front and rear, or scrubbing a lot of speed off before a bend then letting it run.

why would periodic braking help ?
On a long steady slope
a) holding brakes at constant pressure so as speed remains at a constant 20mph
b) repeatedly letting it go up to 25 then braking down to 15
c) alternate harder braking from front to rear brakes but keep speed at constant 20

It is the same amount of kinetic energy being transferred into heat.

I'm not saying you are wrong, I certainly use periodic braking myself, esp in the wet as it helps get rid of that horrible grinding noise (rim brakes) but why would constant pressure braking not be a good technique.

It's all about how air resistsnace goes up with square of speed. So with option (B), you will dump more energy into the air* than with option (a) EVEN IF your average speed down the hill is the same.

win-win

*yes, as heat - but noone will every notice how much you warm the air up by

[geocycle]

How often do people check disk brake pads and is there a rule of thumb for when to replace them? I get that wear will depend on riding style and conditions but do folk remove the pad and check every few months, before a big trip or when you get strange noises from the disks?

[JohnR]

I wouldn't worry about it at all. I've ridden numerous descents around there (including Mont Ventoux) on 160mm and never had any issues at all.

Thanks. In addition, as my handlebars are relatively high, I naturally have some useful (in this situation) aerodynamic drag (highlighted to me recently while going down a shallow hill and someone with low drop bars shot past me). I did the descent from the Oberalp pass last summer and alternately dragged the front and rear brakes to keep speed under control - one doesn't want to enter one of those hairpin bends too quickly - but more confidence in the brakes means I can descend a bit faster knowing that I can shed speed as a bend approaches.

How often do people check disk brake pads and is there a rule of thumb for when to replace them? I get that wear will depend on riding style and conditions but do folk remove the pad and check every few months, before a big trip or when you get strange noises from the disks?

With many calipers it's possible to see how much the pads are worn without needing to remove the pads so I take a look whenever I'm doing any bike cleaning or maintenance. However, now that winter is almost over I'm thinking of removing the pads for cleaning. I fit new pads before embarking on trips and take some spares.