Bicycle braking technique on long descends

Bicycle braking technique on long descends

Updated: 08/11/2018.

One of the nicer parts of cycling, at least for the author of this text, is riding down hills – the longer and faster, the better, whether on paved roads, or through forests. 🙂  This post will explain good bicycle braking on long descends techniques, that allow for safe and fun cycling down long, steep descends. Fist the technique will be explained. Then, an explanation why it is the best and safest way, in author’s opinion and experience.

When talking about descending, many readers might find the following two posts useful: Bicycle braking technique and Fast bicycle cornering.

 

1. Braking technique on long descends

Technique is very simple to explain and apply, there are only three rules:

  • Let the bicycle go as fast as possible, up to speeds you feel safe and comfortable at. The speed depends on cyclist’s skill level, each will choose it for themselves.
  • Brake as hard as possible, so that the bicycle slows down as much as possible, within the shortest time (and distance) possible – also within the limits you feel safe and in control.
  • If a descend is too steep and fast, stay more upright, increasing air drag as much as possible.

It must be stressed again – it is not recommended to cross the line where one feels safe and in control. Faster speeds and harder braking will come slowly, gradually, with practice. Going over the “comfort limit” results in fear, adrenaline (survival reactions), and is not likely to make one faster, or better at braking, quite the contrary. Riding near that limit, with practice and concentration allows for that limit to be pushed further and further. Also, it is very important to pay attention to road conditions, visibility and traffic.

Many people wrongly believe (and advise others) that it is better to keep “dragging” the brakes throughout the descend, so that the bike keeps going at a lower speed all the way down. Why this is not good and can even be dangerous will be explained in the following chapters. For now it should just be mentioned that the main problem is overheating (of brakes and tyres).

 

2. A bit of elementary physics

To understand why it is counterproductive to keep dragging the brakes when riding down a hill, a few elementary things from physics need to be kept in mind. Let’s start:

  • Brakes work by using friction to transfer kinetic energy into heat – so when braking, brake pads and rims (or discs with disc brakes) get hotter. Consequences of overheating are explained in chapter 4.
  • Kynetic energy rises with the square of the speed. So a cyclist going 20 km/h, trying to slow down to 0, needs to transform 4 times as much kinetic energy into heat, than they would if they were slowing down from 10 km/h speed.
  • Gravity force that accelerates a cyclist on a down-hill is constant, regardless of the speed at which a cyclist travels.
  • Air drag, that slows a bicycle down, increases with a square of speed – exponentially!
  • Power needed to overcome air drag and accelerate further, raises by the power of 3 with the speed increase. In plain words, in order to go at a speed of 20 km/h, it takes 8 times more power than it does for going at 10 km/h!
  • The greater the profile of the rider and the bicycle, the less aerodynamic it is, the more air drag is produced.
  • Speed of cooling is directly proportional to the rim/disc/pad temperature – the hotter they get, the quicker they cool down. For example, if the air temperature is about 20 ℃, the time it takes for a rim to cool down from 50 ℃ to 30 ℃ is about the same as the time it takes to cool down from 30 ℃ to the atmospheric 20 ℃. 
  • Speed of cooling is also proportional to wind speed – the faster one goes, the better the air cools them down.
  • Finally, this is important for rim brakes, at greater speeds, rim gives more heat to the air, than it does to the tyre, since the rubber is a better heat insulator.

 

3. What does this mean in practice?

In plain English:

  • The faster one goes, the more braking is done by the air, protecting brakes from heating up, wearing and working hard.
  • If the fastest speed one feels comfortable at is say 30 km/h, it is better to let the bike speed up to that, then brake hard to some 10 km/h, then let it speed up again. Dragging the brakes all the way down, to keep a steady 30 km/h speed can lead to brake (and/or rim) overheating.

Let the bicycle go as fast as comfortable, especially on straight parts of the downhill. That way brakes will cool down better, while the air will do the most of the braking – instead of the brakes. Just make sure not to underestimate an oncoming turn, so that all the needed braking and slowing down can be done in time, without stress.

 

4. Consequences of brake pad, disc, rim and tyre overheating

  • On really long descends, if using rim brakes, check tyre pressure from time to time. As rims and tyres heat up, pressure will rise, eventually causing a tyre to blow off a rim. So, if one notices the pressure rising, it is good to stop and release some pressure from the tyres (inflating them back when the tyres cool down some time after the descend). Narrower tyres get a faster pressure increase from the heat!
  • For those riding with tubular tyres, tubular glue will melt from excess heat, so tyres will start sliding on the rim, bulging a bit at the valve stem (which is fixed), and, if one doesn’t stop to mount the tyres properly and let them cool down, they will finally lift off the rim near the valve.

Disc brakes can “get hurt” from overheating in two ways:

  • Brake fluid overheating – with hydraulic brakes, if brake fluid reaches it’s boiling point, it will start boiling (or absorbed water turns into vapour, for DOT brake fluids), creating bubbles and loosing all the stopping power. Brake lever will “drop” all the way to the handlebars, without practically any braking force applied.
  • Brake pad overheating, that leads to pads “melting” and, when they cool down a bit to “brake pad glazing” – formation of a layer that is a bit harder, with a lot less friction. Feel on the brake lever is normal, firm (unlike with brake fluid overheat), but there is very little stopping power.

All these are the reasons why it should be allowed for the air to do as much braking as possible and be careful not to overheat the brakes, or the tyres.

 

5. Common misconceptions

When talking about braking (controlling bicycle speed) on long, fast descends, there are a lot of bad information and misconceptions. Some of the most common will be “debunked” in the remainder of this text.

  • One should be braking all the time, how do cars and lorries brake using their engines?
    Yes, cars and lorries (and motorcycles) often brake with their engines when coasting down hills. This is in fact so they don’t overheat the brakes! Bicycles, except for fixed gear ones, don’t have the option of engine braking (and even with fixies legs would tire rather quickly).
  • Brakes are to heavily loaded when bicycle gains much speed.
    Brakes are more heavily loaded when braking harder, at higher speeds. Still, that is what they are designed and made for! What they are not made for is overheating.
  • I’m too heavy, once I get to a high speed, there’s no stopping.
    If one doubts the ability of their brakes to stop the weight of the bicycle, cargo and the rider, then it’s not about braking technique, but about the brake quality. In that case, such brakes should be considered malfunctioning (bad). Better tuning, better choice of brake pads, or replacement for good quality brakes is what’s needed. Bicycle brakes should be such that one brake is enough to stop the bicycle (in case the other brake stops working for any reason).
  • Skilful riders only use brakes to control the speed on descends, not for real braking, so they don’t need strong brakes.
    When approaching a sharp corner during a fast descend, speed is often shed from some 70 km/h to 10-20 km/h, in a very short time (and distance). Even though this is not doing a full stop, it is harder on the brakes, than doing a full stop from 50 km/h on a flat (which is about as fast as one gets on the flats), since higher speed carries more kinetic energy, plus, on a descend, gravity is working against the brakes all the time!
  • Only mad men ride fast down hills!
    With variations: “She/he speeds like a madman!”
    It is crazy to ride beyond one’s skill level and ability to react. Experienced cyclists often ride in a way that seems too fast, too dangerous, but it is within their skill level and ability to react in time, for whatever comes behind the next corner.
  • I know this road.
    Famous last words. Even if riding a well known road for a thousandth time, one never knows if a broken down/turned over trailer is stopped right behind the corner. Always ride as fast as visibility allows. In other words: never ride faster than you can see!

 

Author of this text hopes it will help cyclists to enjoy the ride even more, especially when it all goes down hill. 🙂  Keep practising, make sure not to overstep your safety limit, and enjoy cycling.

Relja “Thunderbolt” Novović

Related post – Bicycle braking technique:

Proper cycling braking technique explained
Proper bicycle braking technique explained
Share this article...

Leave a comment

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.