Motorcycle Braking


Motorcycle braking is a topic that's frequently misunderstood in the field of collision reconstruction, and surely beyond. Magazine testing shows that most modern motorcycles are capable of braking at a rate of approximately 1 g or higher. As a result, some reconstructionists evaluate collision avoidability using a potential braking rate approaching 1 g. Something along the lines of: if the motorcyclist was travelling at a speed of 50 mph, and braked at 1.0 g, as Magazine X showed the motorcycle is capable, the rider could have come to a full stop in 158 feet, including 1.3 seconds allotted for perception-response time, thereby avoiding impact. 

Let’s step back for a second and look into what’s required for an optimal quick-stop on a motorcycle. 

  1. Roll off the throttle and simultaneously apply both the front and rear brakes (unless the rider is “covering” the brakes, this will require the rider to move their fingers from the throttle to the front brake lever, and their foot from the peg to the rear brake pedal).
  2. As weight shifts to the front, and from the rear, apply more front brake pressure and less rear brake pressure.
  3. Modulate the front brake to prevent lock-up, and to ensure the rear tire doesn’t lift from the ground (or lift too high, at least).
  4. Modulate the rear brake to prevent the rear wheel from locking (the less weight on the rear tire, the easier it is to lock).
  5. Grip the tank with your knees to maintain body position and keep your butt as far back in the seat as you can to optimize weight distribution and prevent the rear wheel from lifting (on bikes with a higher center of gravity).
  6. If you do lock the front or rear tire during the maneuver, respond accordingly. For the front, release the brake and start again. For the rear, the best bet is to hold it until you come to a stop.
  7. As you come to a stop, downshift to first gear and check your mirrors in case you’re about to be rear-ended. If so, find an escape route.
  8. Oh, and do all of the above in the presence of a life-threatening hazard.

As you can see, and likely already knew, there’s a lot to properly stopping a motorcycle. Sure, those magazine tester people sure can stop a bike quickly, but they’re on a closed track, under no pressure, can run the test multiple times, and are professionals with lots of practice. I don’t really care what they can do, I want to know what a typical rider can do. As a bonus, I’d like to know what a typical rider can do when presented with a dangerous situation. 

  Hugemann et al., 1993. 18 subjects, 74 tests. Skilled avg. 0.77 g's. Novice avg. 0.49 g's. 

Hugemann et al., 1993. 18 subjects, 74 tests. Skilled avg. 0.77 g's. Novice avg. 0.49 g's. 

Okay, so let’s start digging into the available research to see if we can find an answer.  In 1993, Hugemann et al. conducted 74 instrumented braking experiments with 18 different riders, 15 of whom were on their own motorcycle [1]. The riders had varying levels of experience (less than 12,500 mi up to 80,000 mi), and were instructed to brake from 50 kph (31 mph) to a standstill “within the shortest possible distance.” Riders characterized as “skilled” and “novice” exhibited braking rates of 0.77 and 0.49 g’s, respectively. 

  Ecker et al., 2001. 300 subjects, 600 tests. Avg. 0.63 g's. 

Ecker et al., 2001. 300 subjects, 600 tests. Avg. 0.63 g's. 

In 2001, Ecker et al. conducted a study comprised of 600 tests performed by 300 riders of varying experience (novice to 40+ years) operating an instrumented Honda CB500 [2].  As the riders were riding the Honda around a training facility, the test coordinator would trigger a red light mounted to the instrument cluster, signaling the rider to “make a full stop emergency braking maneuver.” The average braking rate for all 600 runs was 0.63 g’s with a standard deviation of 0.12 g’s. So, assuming a normal distribution, these figures suggest a 68% confidence interval of 0.51 g’s to 0.75 g’s. Another interesting conclusion of this study is that there was only a very minor correlation between braking ability and riding experience, especially for more than 1 year of experience. They also found that half of the participants exploited 56% or less of possible performance, and that locking occurred quite often. Not a good combo. 

  Vavryn et al. results. Note, the acceleration is reported in m/s^2 here, not g's. Divide by 9.81 to convert to g's. 

Vavryn et al. results. Note, the acceleration is reported in m/s^2 here, not g's. Divide by 9.81 to convert to g's. 

Seemingly motivated by Ecker's results (I confirmed this was indeed the case, upon meeting Dr. Ecker after a recent presentation of mine), Vavryn et al. conducted a study geared toward analyzing the efficacy of anti-lock braking systems (ABS) [3]. Vavryn et al. reported the results of 800 tests performed with 181 subjects on two different motorcycles. The riders were asked to “come to a complete stop as soon as possible without falling off the vehicle.” Initial speeds were either 50 or 60 km/hr (31 or 37 mph), and the subjects performed two tests on their own motorcycle, and then two runs on a motorcycle equipped with ABS. One of the ABS bikes was a standard BMW, while the other was a scooter equipped with linked ABS. The average braking rate for motorcyclists on their own motorcycle was 0.67 g’s (SD = 0.14 g’s). However, when riding the motorcycles equipped with ABS, that number jumped up to 0.80 g’s (SD = 0.11 g’s), despite that the riders were now on an unfamiliar machine. 85% of the subjects improved braking with the ABS motorcycle and the novice riders achieved almost equal braking rates as the experienced riders when operating the ABS machines. 

On that note, the Insurance Institute for Highway Safety (IIHS) conducted an analysis of fatal collisions involving motorcycles with and without ABS [4]. They found that there were 6.6 fatal collisions per 10k registered motorcycles without ABS and 4.1 per 10k registered motorcycles with ABS, a 38% reduction. Another article will follow on that topic shortly.

  Bartlett, 2010. 288 tests. Overall average about 0.62 g's.

Bartlett, 2010. 288 tests. Overall average about 0.62 g's.

Bartlett reported the results of 288 tests conducted during Idaho’s STARS (Skills Training Advantage for Riders) program [5]. The class caters to three levels of riders (rookies, some experience, and greater than 1 year of riding), and the conclusion of each class involves a stopping test, where the initial speed is 15 to 20 mph. For the three groups mentioned above, the average braking rates were 0.60 g’s (SD = 0.16 g’s), 0.64 g’s (SD = 0.14 g’s), and 0.61 g’s (SD = 0.14 g’s), respectively. Similar to Ecker, there was no notable experiential effect observed here. 

  Dunn et al. results, in part. Three riders, bikes, and initial braking speeds (only two speeds shown here). 

Dunn et al. results, in part. Three riders, bikes, and initial braking speeds (only two speeds shown here). 

Dunn et al. presented the results of braking tests performed with three riders of varying experience (2, 5, and 35 years), three motorcycles (Harley-Davidson XL1200 Sportster, Buell XB9R, and BMW R1100RS), at three initial speeds (25, 45, and 60 mph) [6]. At 45 mph the mean drag factors for all riders were 0.67, 0.66, and 0.73 g's for the Harley-Davidson, Buell, and BMW, respectively. The mean drag factor for the BMW tests is higher, as expected, as that motorcycle was equipped with ABS. The mean drag factors at 60 mph were 0.66, 0.71, and 0.84 g's. The authors of the study opine the observed improvement in braking performance at 60 mph, excepting the Harley-Davidson, is likely due to the time required for the rider to "determine and apply the proper amount of brake force on the controls."

Clearly, the braking numbers presented above are well below those reported in magazines. If you’re currently using motorcycle braking rates approaching 1 g in your analyses, I hope the studies presented above will make you reconsider. It depends on the situation, motorcycle, and rider, but a range of 0.45 to 0.75 g’s seems like a good starting point considering the literature (0.60 average with a SD of 0.15 g’s). Going back to the example in the introduction, if a rider is travelling at 50 mph, the total stopping distance is more like 214 feet, using a braking rate of 0.60 g’s and allotting 1.3 seconds for perception-response time (PRT depends on the situation of course,  a topic for another day). That’s quite different than the aggressive 158 feet.

If the motorcycle is equipped with ABS, or combined ABS, it may be best to rely on research dealing specifically with ABS-equipped motorcycles, like the Vavryn study. Every situation is different, and should be evaluated as such, but hopefully the data presented here will give you a foundation to conduct an informed analysis. 

It should also be taken into consideration that the subjects involved in the studies here were not presented with a life-threatening situation. Who knows how that will affect braking rates. At this point, we have no naturalistic data to answer that question, but it’s coming down the pipe. Braking data from Virginia Tech’s 100 Motorcyclist Naturalistic Study, funded by the MSF, is expected to be available in the Summer or Fall of 2016. Another study funded by the Department of Transportation is expected to produce similar data that should also be available in the Summer or Fall of 2016. I’m very anxious to see the results of those studies, as that will be our first real-world glimpse into the braking capabilities of motorcyclists in the presence of a life-threatening hazard. 

Thanks for reading, 

Lou


  1. Hugemann, W., Lange, F., "Braking Performance of Motorcyclists," 1993. Online here
  2. Ecker, H., Wasserman, J., Hauer, G., et al., "Braking Deceleration of Motorcycle Riders," International Motorcycle Safety Conference, Orlando, 2001. Online here.
  3. Vavryn, K., Winkelbauer, M., "Braking Performance of Experienced and Novice Motorcycle Riders - Results of a Field Study," International Conference on Traffic & Transport Psychology, 2004.
  4. Insurance Institute for Highway Safety (IIHS), Status Report, "If They Need to Stop," Vol 43, No. 9, Oct 22, 2008.
  5. Bartlett, W., Greear C., "Braking Rates for Students in a Motorcycle Training Program," Accident Reconstruction Journal, Vol. 20(6), pp. 19-20, 2010. 
  6. Dunn, A., Dorohoff, M., Bayan, F., et al, "Analysis of Motorcycle Braking Performance and Associated Braking Marks," SAE Technical Paper 2012-01-0610, 2012.