Friday, 3 July 2009

Don't Panic!

With that reference to the lord of humour, I'm going to talk today, about braking on wet roads. A lot of people tend to fall while riding on wet roads. This has a lot to do with the manner in which the brakes are applied on a two wheeler. Most people believe that on wet roads you must forgo the use of the front brake and use only the rear brake. This, is a very risky thing to do. I'm going to explain, with the help of a little bit of mechanics, how brakes should be used in the wet (or even dry).

Before we get to the braking though, a few general tips. The water on the road reduces the friction between the road surface and your tyres. While riding on a road with a little bit of water (i.e. not standing water), the water will tend to reduce the friction (or grip) available to you by about 15%. So, for starters, ride about 20% slower than you would on dry roads. Secondly, maintain distance between the vehicle in front of you. On a dry road, I remember rearset saying somewhere that you should maintain a distance to the vehicle in front of you such that you can see the tyres of that vehicle. On a wet road, extending this distance further, as much as a car length is a good idea. Additionally, avoid riding on anything that is not tar/concrete, i.e. painted signs, tiles, metal manhole covers, etc. That 5% difference in grip may be the difference between you being on the bike and on the ground.

Now, on to the braking part. Consider a two wheeler travelling on a stretch of road,


In the picture above, imagine the long straight line to be the body of your two wheeler. Consider four frictional forces in that figure. Fft and Ffb are the frictional forces at the tyre-road interface and brake respectively for the front wheel. Similarly, Frt and and Frb are the frictional forces at the tyre-road interface and brake respectively for the rear wheel.

In order to slow down the bike, without causing a wheel to lock up, the frictional force at the tyre-road interface must exceed the force applied by the brake at all times. As long as Fft exceeds Ffb, the frictional force at the tyre-road interface will force the tyre to keep rotating. If Ffb becomes higher that Fft, the tyre will simply stop rotating and lock up. This would imply that you should apply equal, but limited pressure on both brakes to brake safely. There is another factor though. The moment you start braking, the body of the bike tends to lurch forward due to inertia. This motion compresses the front shock absorbers and allows the rear shocks to expand. So, once you start braking, the picture changes to this,

Shocks are not perfect, and therefore will transmit force (even though they're supposed to absorb it). Therefore, you now have a state where there is a greater load on the front wheel than there is on the rear wheel. This means that Fft now greatly exceeds Frt. It is easy now to lock up the rear wheel, and correspondingly hard to lock up the front wheel, because the limiting values of Ffb and Frb have also changed.

This is the reason why bikes always have a stronger brake on the front wheel. The explanation above holds for dry and wet weather. The correct method for braking therefore, is to start braking with only the rear brake. Once weight transfer to the front begins, slowly start using the front brake, and reduce the pressure on the rear brake. This ensures that you're less likely to lock up either wheel.

Don't Panic
If you understood what I just said, you should be less likely to lock up the front wheel. Rear wheel lock ups are still possible. If you do lock up the rear, whatever you do, don't panic. Because the front wheel still isn't locked, chances are that you'll still be going in a straight line. Gently release the rear brake, more often than not, it'll start rotating again.
Always be prepared to fall. There's no technique in the world that can ensure that you'll never fall. You WILL fall, all you can do is to reduce the frequency. When you are open to the possibility of falling, if you do fall, you'll probably get up, pick up the bike and start riding again. If you believe that you can never fall, when you do, you'll be too stunned to do anything about it.

That does it for my first biking techniques post. Feedback on whether or not that was coherent and understandable is welcome.

6 comments:

abhi said...

nice one there.. very comprehensive also.. this has inspired me to write a similar one for people to understand gears better - or rather just understand them in the first place, and then use them based on knowledge rather than simply on experience! (specially for the rare combo, gaining popularity these days - female riders on manual transmission bikes!)

falconer said...

Nice one.
I had the opportunity to use this knowledge two days ago when the (whats the feminine sense of jerk?) in the Swift in front of me decided she wanted to take a u-turn on FC (F-ing Chaos) Road without using the indicators. Thanks to this technique no mishap occurred.
The fact that I read this post after the incident is immaterial.
Now I feel like writing one on basic traffic-good-manners, but all the people reading my stuff already know them.

A half light said...

Hehe, don't know why I picked up the habit, but on wet roads, I just prefer leaving hold of the accelerator instead of braking and let the bike slow down of its own accord. I have a nagging phobia of braking on wet roads!
Needless to say, the crudest way of driving I guess!
And this has inspired me to write on better things that can happen (sometimes) when you don't take matters into your hands :P

greySith said...

The 'leave everything and pray' approach is a mighty useful one... but only on oil and gravel. On those two, seriously, just pray. Water isn't so bad. You should practice. The rains are the best part of the year when you want to learn how to ride. The stuff you'll learn in order to stay astride on the wet, will help you even more on the dry. At the end of every monsoon, aim to be a better rider. It's time to level up :P

A half light said...

Yeah but the wetness has a tendency of tricking us to believe it's water, has happened a couple of times with my friends, they ended up skidding down the way on oil that they comfortably thought was water :P
That's more of why I don't like braking on wet roads, I end up accelerating and 'leaving and praying' in spurts..
PS: Don't know if I'm a good rider, but my falling count has been a measly 1 till date (which happened quite recently)!! And I'm proud of that! :D

greySith said...

On a dry road, be careful with wet looking spots, when it's raining, it's all water anyway, water washes away all the oil.