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Do you break out into a cold sweat when someone asks you what your total reaction distance at X km/h is?
Then I’ve got bad news – you’re most likely going to get this question when you take your theory test.
But the good news is that you don’t have to memorize the result for every single speed limit – you can figure out your reaction, braking, and stopping distance by doing some math.
It’s not rocket science either – just basic arithmetic.
Tune in to learn:
- The definitions for the reaction distance, braking distance, and stopping distance
- 3 easy formulas to determine your reaction, braking, and stopping distance
Hello, and welcome to the 30 minute motorcycling podcast, where you’ll learn something new about motorcycles and other two wheelers in 30 minutes or less.
What’s your reaction distance at 40 kilometers an hour? How about your braking distance? And total stopping distance?
Usually, this is one of the common theory questions you might get on your exam, You might get a even get the exact same question that I just mentioned.
But how do you answer that?
Now, you can either memorize every distance for every conceivable speed limit, but that’s way more trouble than its worth.
Or you can learn 3 simple mathematical formula that would make things a lot easier for you.
And that’s what I’m going to teach you in this episode. Before we get started however, I have a disclaimer that I need to get out of the way.
These formulas are for the metric system – in other words, we’re going to talk about kilometers and meters. I might do a future episode for the Imperial system, but for now, let’s stick to the metric system.
Let’s begin with the reaction distance.
The reaction distance is the time it takes for you to recognize a potential hazard in the road such as:
a plank of wood in the road,
a child running out from behind a parked car or
even a car door opening in front of you.
You can’t swerve around it – you have no other choice but to stop.
So how do we calculate the reaction distance?
We take your current speed, remove the last digit, and multiply the remaining number by 3.
For example, let’s say we’re traveling at 40 km/h. Once we’ve removed the “0” from the number 40 – that leaves us with “4”
We then take that 4 and multiply it by 3 – which gives a final result of 12.
So in other words, your reaction distance at 40 km/h is 12 – 12 meters, that is.
So what about the braking distance?
The braking distance is how far you travel between the point where you begin to apply the brakes to the point where you’ve come to a complete stop.
So far, everything seems straightforward, but it’s more difficult to get calculate the braking distance with 100% accuracy since it’s affected by things like:
- The road conditions
- The condition of your tires
- The condition of your brakes
Your braking distance even varies if you just one of the brakes as opposed to both of them together.
To make this calculation as easy as possible, we’re going to assume that the road conditions are good, your brakes and tires are both in good condition, and you’re using both the front and rear brake.
So how do you calculate your braking distance. Once again, you remove the final digit of your current speed. Then, you take the remaining number and multiply that number by itself.
So if we’re travelling at 40 km/h, we’ll remove the “0” digit, which leaves us with the number “4”
We then multiply that “4” with itself – and 4×4=16
But wait – we’re not done yet. We then take that result and multiply it by 0.4
So if we multiply 16 by 0.4 – we get 6.4
So the braking distance at 40 km/h is 6.4 meters 6.4
And finally, the stopping distance is the combined distance of the reaction and the braking distance.
So it’s pretty easy to figure out your stopping distance – you just add your reaction distance and braking distance together and you’ll get your stopping distance.
So if our reaction distance and braking distance at 40 km/h are 12 meters and 6.4 meters respectively, our total stopping distance will be 18.4 m, since
12+6.4 = 18.4
And those are the formulas for your reaction, braking, and stopping distance – for the metric system.
If you’d like a helpful resource to remember these formulas, I’ve provided a link in the show notes to a blog post on The Dual Wheel Journey which includes a free downloadable cheat sheet.
So the next time someone asks you what your total stopping distance is at 40 km/h, you’ll be able to say 18.4 meters with your head held high and without batting an eyelid.
And that concludes this week’s episode of 30 Minute Motorcycling.
Until next time, keep your helmet on and your eyes on the road. Bye!