How to brake without falling during wet weather?

Question

A couple of days ago I fell off my bike. I was on a wet, steep downhill, asphalted road with a lot of curves. I didn't expect neither the weather, nor the 15+ km downhill route. I was always reducing my speed to 9-10 kph before taking a turn. However, just after a taking a turn and before another curve, when I pressed the rear brake lever, the wheel stopped turning immediately, despite the slight pressure, and started to slide. Worse, the bike didn't stop, it started to accelerate. I pressed the front brake lever, slowly initially, but since the bike was still accelerating, I pressed more was thrown off. Never mind the damage; I got off with minor injuries, the bike as well. This could have been due to my being careful to begin with, but not enough, apparently, so my question is how can I be better prepared in the future? And what might have caused the tyre to slide? The road was wet and with minor holes and bumps, sure, but I had gone through similar terrain seconds ago and I could brake just fine. And I'm sure I didn't press the lever way too hard than perceived. Also, there wasn't any wet sand. None that I could see anyway.

In hindsight, there are a few things that came to my mind. I'm not entirely sure about any of them, however, since I have just recently started to cycle since my childhood/high school years and I just discovered that there was stuff I was missing out on back then (such as bike fitting and geometry).

1. The saddle could've been lowered. I normally ride so that my knees bend at a 25-30 degrees at the pedals' lowest position. I assume lowering the saddle would've necessitated much more effort from the front brake to throw me.

2. My bike is suited for XC racing. Would picking a downhill bike, with the appropriate frame geometry, have made a difference, provided we're talking about an asphalted road?

3. Should I have kept the rear or both brakes engaged constantly? At the time, I didn't want to do this out of fear that they, being disc brakes, would overheat and the rotor would be destroyed. The route I was on was at least 28 km long, mostly steep downhill, save for the last 10 km or so, which were a rather pleasant, slight descent.

Answer 1

when I pressed the rear brake lever, the wheel stopped turning immediately, despite the slight pressure

if it locked up with only slight pressure, either your brakes lack modulation, or it had really poor traction.

The first (modulation) is generally adjustable.

The second depends on your tyres, the road surface, possibly oil/petrol/diesel spills, loose material etc. etc.

Since you don't think there was loose material, and say the traction was fine previously, an oil spill is certainly possible - look out for those rainbows on the road surface.

Worse, the bike didn't stop, it started to accelerate

If the back wheel is locked, skidding it should still have some braking effect, so I'm inclined to view this as evidence for poor traction.

I assume lowering the saddle would've necessitated much more effort from the front brake to throw me

Did you go over the handlebars, or just lose grip with the front wheel and crash?

If the former, which I think is what you're suggesting - lower saddle might help on steep downhills, but generally you need to brace yourself down & backwards with your arms. The goal is to stop yourself sliding forward relative to the bike as it slows down, and also to reduce the angular moment about the front axle by keeping your weight low.

Interestingly, this does suggest there was no traction problem with your front wheel, so something happened to impair traction at the back only.

My bike is suited for XC racing

Does that mean it has knobbly tyres? More contact area is generally better on asphalt, so slick or textured tyres will have better traction (and, as a bonus, generally lower rolling resistance).

Should I have kept the rear or both brakes engaged constantly

I'd usually drag the back brake to control speed on descents - to avoid overheating, don't do this continuously, but pump it and ease off to let it cool. Alternating with the front will also give the back brake a chance to cool - but note the front brake affects steering more, so definitely keep braking to the straights as much as possible.

Answer 2

A lower saddle will compromise your riding comfort at all other times. Instead you should have unweighted the saddle and put your backside further backwards to weight the rear wheel.

Also, were you braking on the straight only? Or were you braking into the turn? In the dry we can get away with a lot of bad behaviours like braking while turning, that cause problems in the wet.

Technique - I'd alternate between a good squeeze on the front and then release, and then the back, then release. If its steep you can alternate so one brake is always on, and if its getting away from you then use both together, but only on the straight

If you're cornering and only realised your speed is too high, then you have failed to read the road right. At best its going to be a scary turn, at worst you're trying to mitigate the upcoming slide/fall.

Tyres may help - Slick ones are generally better at contact with a smooth road, but if there was gravel or ice or leaves or even a painted line then smooth tyres lose their advantages. Big knobbly tyres are generally poor on the road, both on cornering and general power transfer.

28km is quite a long descent too - its easy to get blasé about each corner and get a bit faster on each one. An unexpected camber or kick on a corner could be all it takes to throw you.

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Obligatory "I've been there" - this particular corner has a kick, and is known for catching out both cyclists and motorcycles.

Answer 3

And what might have caused the tyre to slide?

When braking, push your weight as far back as possible.

When emergency-braking, standing on the pedals (easier with bike shoes attached to the pedals), you might even stick your bum behind (off the back of) the saddle. That maximizes your weight over the back wheel. It also puts your weight low and away from the front (not high and near the front), and your arms pointing forward instead of pointing down, so you're less likely to flip over the front.

Slow down. After falling you may be more careful in future. I slipped (and fell) recently on a little mud in an otherwise dry path, which reminded me that mud is much more slippery than a dry surface.

Brake with both brakes (front and back) at the same time. Weight is pushed onto the front wheel (by deceleration), and friction is proportional to weight (no weight implies no friction): so if you brake equally on both wheels, your first warning that you're braking too hard is that your unweighted back wheel starts to skid (at which point you start to fish-tail, but might not fall off ... I think the point of no return is if the front wheel starts to skid). This (the back wheel skidding) is early warning that you're braking too much and are near to skidding the front, at which point you ease off slightly on both brakes.

disc brakes, would overheat and the rotor would be destroyed

I don't know whether that's possible? I've heard of people bursting their tires by overheating with rim brakes.

I don't know about the rotor but maybe it is possible to glaze the brake pads by overheating: and maybe that depends on what the pads are made of (e.g. whether they're "organic" or "sintered").

Answer 4

It sounds like you have your weight far too far forwards when braking.

My reasoning comes from 3 things:

1. Your rear wheel skidded as soon as you applied a small amount of rear braking
2. You flipped over the front as soon as you applied a small amount of front braking
3. You were going downhill.

You should shift your weight further back on your bike and brace against your handlebars when braking (especially when downhill).

Now here is the science bit.

Friction is limited by

• Normal Contact Force (Weight)
• Coefficient of Friction (Grip)

Normally when going downhill, your weight is further forward than it is normally.

• More weight on your front wheel
• Less weight on your back wheel

Also, it was raining. Water, reduces grip.

When you tried to brake with your rear brake, you had no weight on your back wheel, AND you had very little grip. THEREFORE, there was no friction (slippage).

When you tried to brake with you front brake, you had ALL your weight on your front wheel, and very little grip. THEREFORE, MUCH MUCH MORE friction. Your BIKE (not you) slowed down.

However, since your weight was already far forward on your bike. Your bike slowing down, causes you to be FURTHER forward on your bike. At some point, your bike stops, and you ... don't...

By shifting your weight further back, you give yourself more time to react to your bike slowing down. You weight down your rear brake (giving it more friction/braking power). Put yourself in a better position to brace against your bike.

Answer 5

I have a very steep portion of my ride which has a sharp corner at the end which I need to slow down for. During the rainy season the only way I can do this is to use both brakes carefully AND put a foot down. I put my foot down with my calf against the pedal and apply pressure downwards.

My old bike had very dodgy brakes so I started doing this. But even my new one which has excellent brakes needs this technique during the rainy season when the road is very slick.

Answer 6

However, just after a taking a turn and before another curve, when I pressed the rear brake lever, the wheel stopped turning immediately, despite the slight pressure, and started to slide. Worse, the bike didn't stop, it started to accelerate. I pressed the front brake lever, slowly initially, but since the bike was still accelerating, I pressed more was thrown off.

It seems that you were braking only with the rear brake and used front as an emergency. This is the least effective way how to slow down. I often brake with rear wheel sliding, sometimes locked.

When braking, the most of the energy is absorbed by front brakes. The deceleration puts mass to the front wheel and remove it from the rear wheel.

The best way for braking is brake more with the front brakes, brace againts the handlebars and move the centre of mass as far as possible to the rear and low. This will reduce the risk of throwing off. For long descents it is better to brake hard and then release, then brake hard again.

But, sometimes the best way is to find a soft place to land.

Answer 7

Under suboptimal condition, tyre will lost traction and slide even under slow walking speed (4km/h) when you apply brakes. Ironically, you need to release the brake in order to regain traction, quickly re-apply it to slow down. And this is how Anti-lock Braking System(ABS) works.

Few people are trained to deal with rear wheel slide : most of us went panic and apply the front brake, cause both wheel locked up and the weight shift just throw us out.

Unfortunately, "ABS simulation" is not an easy skill to acquired. What we can do is slow down to walking speed to reduce the impact damage.

Answer 8

I'm not 100% confident in this as an answer, but I do have a bit of experience. I don't know anything about over-heating breaks.

I commute year-round, and part of this ride is on a small hill on a quiet road. Snow provides the perfect conditions to ask "What can my bike do?"

So, I'm going straight down an icy hill and lock the back wheel... The back of the bike instantly whips towards the front. The distance between the front and rear obviously has to stay the same, so the bike becomes sideways in the road (sometimes, with me still on it). The best course of action seems to be exactly what you would do in a car, turn the handlebars to keep the front wheel in the direction of your movement and release the breaks. The difference with a bike is that you also have to keep your weight over it, so don't resist your bike going sideways or it will slide out from under you.

As a side note: I don't know why the rear of the bike goes do much faster than the front, but it's significant. It could be that the lack of traction causes the back to slide out from your weight, but then the front still has enough to transfer that sideways force to forwards. I'm no physicist, just a guy locking his wheel. :)

I've always had better luck slowing the bike down by using only the front break.

Turns are not easy. When I'm on ice, leaning into a turn will cause instant crashing. I take a turn slow enough that I can do it by turning the handlebar alone.

Winter is coming up here, I'll be thinking about this.