• Kevin Williams / Survival Skills

How quickly can a modern bike stop?

Something that I have repeatedly stated over the last decade or so is that motorcycles CAN stop a lot quicker than we're regularly told is possible. I know that because I've conducted my own tests.


From 20 mph (30 kph), I can stop in two bike lengths - around four metres.


From 30 mph (50 kph), I can stop in somewhere around five bike lengths - about ten metres.


I've done some higher speed tests, but let's stick with those as they represent the typical urban limit speeds where most junction collisions happen.


Those figures were achieved using two different 600s, one with ABS and the other without, just triggering the rear ABS on the Yamaha and lifting the rear wheel slightly on the Honda.


Both bikes were fitted with part-worn original equipment pads, neither had the brakes freshly serviced and both were wearing mid-life sport-touring compound tyres.


In other words, typical of the kind of bike that the average rider on the road is likely to be using, rather than a factory development model, a brand-new, off the shelf bike being road-tested by a magazine, or even the kind of health-and-safety prepared bike that's almost certain to be used by road safety researchers.


And also representative of the surfaces we have to ride on, rather than a proving ground or a race track, the surface was a typical supermarket car park.


My only concession to 'testing' was that I started gently and built up speed and braking force. I didn't simply go for broke the first time, which of course is what we'd all have to do in an emergency.


And after a few runs building up pressure, I was able to achieve a good level of consistency. The only thing I would say worked in my favour is that I practice e-stops every spring, and I regularly demo e-stops throughout the year.


Now, I ran those figures through a stopping distance calculator.


Assuming a reaction time of 0 (because I knew I was going to stop and was already covering the brakes)...


- a 4 metre stopping distance from 30 kph generates a deceleration of -8.68 m/s. That's actually 0.885 g.


- a 10 metre stopping distance from 50 kph generates a deceleration of

-9.65 m/s. And that's 0.984 g...


...which explains why the rear wheel was starting to lift.


Why didn't I get to quite the same level of deceleration from 20 mph / 30 kph? My guess is that even though I was braking as rapidly as I could, it still takes measurable time to build the braking pressure. With less speed to get rid of, this 'building' phase lasts more of the overall time the brakes are actually applied.


Can YOU get that good?


Well, I believe you can, although it does take a bit of practice And various research papers suggest that it's not impossible.


For example, a recent study on braking performance found that the mean braking forces (in m/s) generated by four different skill groups were as follows:


  • Novice - 3.83

  • Intermediate 5.28

  • Advanced - 6.79

  • Expert 8.03


These are the results averaged out. And one of the expert riders actually managed a peak rate of deceleration of 9.82 m/s. That's actually a bit better than my calculated rate of deceleration.


The scary bit is just how much better the advanced and expert riders where than the novice rider.


Plugging that 3.83 m/s rate of deceleration into the stopping distance calculator, it would have taken that rider just over 9 metres to stop from 30 kph, and just over 25 metres to stop from 50 kph.


Now, remember braking isn't linear but we lose around one QUARTER of our speed in THREE QUARTERS of our braking distance. Imagine an incident where I JUST stopped as a car turned across me. At what speed would the novice hit the car? The answers are:


  • over 15 mph at a starting speed of 20 mph

  • over 23 mph at a starting speed of 30 mph


And it's that poor braking ability which at least partly explains why so many less-experienced riders are caught at by junction collisions. Not only are they less aware of the problem in the first place - so more likely to either freeze or panic-brake and fall off before they get anywhere near the car (see 'No Surprise' for an explanation), if they do manage to get the brakes on, they don't use them effectively.


And that's why US researcher James Ouellet puts the 'at risk' zone at a junction on an urban road as three seconds out. At 30 mph, we'll cover 40 metres in three seconds. If it takes just ONE SECOND to recognise the threat AND react, we'll travel 13,4 metres. And if our braking is in the novice category, it'll take another 25 metres to stop. We'll avoid a collision by just 1.6 metres.


The fact is, we rarely have the luxury of three seconds warning, and that's why so many riders have junction collisions.


And just in case you think that the bikes they were using were some kind of escapee from the MotoGP paddock, it was in fact it was a 300cc Piaggio Beverly scooter with automatic power transmission and standard brakes independently actuated - no anti-lock braking system (ABS) or combined braking system (CBS) - by two hand levers.


It was chosen as being most representative of the small-to-medium sized scooters (150-300cc) most frequently sold in Italy.


Here's the reference:


"Emergency braking performance of motorcycle riders: skill identification in a real-life perception-action task designed for training purposes": P. Huertas-Leyva et al


Read the full PDF here:


https://flore.unifi.it/retrieve/handle/2158/1167406/576326/TRF_2019_HuertasLeyva_et_al_EmergencyBraking%20%28AM%29.pdf


Stopping distance calculator


https://www.johannes-strommer.com/en/calculators/stopping-distance-acceleration-speed/


g force calculator

https://convertlive.com/u/convert/metres-per-second-squared/to/g-units#9.645



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