Braking Capabilities of Motorcyclists - A Literature Review
Tolhurst and McKnight tested and compared five methods of braking in a straight line and three methods of braking in a curve [1]. For all eight methods, the rider applied the front brake to the maximum extent possible without locking the wheel. For the straight-line braking tests, which were run from a nominal speed of 40 mph, the level of rear wheel braking varied as follows: no rear wheel braking, light rear wheel braking, locked rear wheel braking, pumping of the rear brake, and heavy rear wheel braking just below the level necessary to lock the wheel. For the tests related to braking in a curve, which were run from a nominal speed of 30 mph, the level of rear wheel braking varied as follows: no rear wheel braking while keeping the motorcycle leaned, heavy rear wheel braking while keeping the motorcycle leaned, and heavy rear wheel braking while righting the motorcycle.
This study utilized three expert riders operating three different motorcycles – a Yamaha FJ1100 (a sport touring bike with an approximately 1,200 cc engine), a Yamaha 550 Vision (a sport touring bike with an approximately 500 cc engine), and a Suzuki GS 550. For the straight-line braking, adding the heavy rear wheel braking to the front wheel braking (below the level necessary to lock the wheel) produced the highest deceleration and the shortest stopping distance. The lowest deceleration and longest stopping distances resulted when only the front brake was applied. This study did not examine rear wheel only braking. For braking in a curve, the highest deceleration and shortest stopping distances were achieved by righting the motorcycle while applying heavy braking to both brakes (without locking the wheels). The lowest deceleration and longest stopping distances were generated by continuing to lean in the curve and not applying any rear brake.
Tolhurst and McKnight noted that there were “highly significant differences among the three [riders]…[these] differences are more easily attributed to differences in the design of motorcycle, particularly the tire ‘footprint,’ than to the skill of the riders.” Unfortunately, they only reported a single average stopping distance for each braking method, and so their article does not enable deeper analysis of motorcycle-to-motorcycle differences.
Prem conducted emergency, straight line braking tests with 59 volunteer riders. He used the Motorcycle Operator Skill Test (MOST) to provide a quantitative assessment of the riders’ skill level [2]. The MOST takes the riders through a series of tasks designed to test their steering and braking performance. The braking maneuver from this test required the riders to brake aggressively to a stop from a speed of 32 kph (20 mph). A red signal light was activated to indicate to the riders when they should begin braking. The motorcycles used by the volunteers were instrumented to record the rider’s front and rear brake-lever force inputs and motorcycle speed. Prem did not report the make and model of the motorcycle used in this testing.
Prem was interested in determining the differences in braking technique between skilled and less-skilled riders. He found that skilled riders applied higher levels of front brake force than the less-skilled riders. Less-skilled riders preferred the use of the rear brake. The skilled riders also modulated the level of front and rear wheel braking to maintain optimum braking as weight shifted towards the front of the motorcycle during heavy braking. The less-skilled riders maintained a generally constant level of pedal pressure independent of the weight shift. More skilled riders also exhibited shorter braking reaction times.
Fries, Smith, and Cronrath performed testing with five different motorcycles to determine the deceleration of the motorcycles when the rider employed the rear brake only and when the rider employed a combination of front and rear wheel braking [3]. They tested a 1968 Harley-Davidson FLH, a 1978 BMW R90, a 1982 Honda XR500R, a 1972 Honda SL350, and a 1972 Honda SL125S trail bike. Each motorcycle was tested at nominal speeds of 20, 30, and 40 mph (32.2, 48.3, and 64.4 kph) on worn asphalt. Overall, the deceleration from rear wheel only braking was less than when heavy front wheel braking was also used. The range of deceleration for rear wheel only braking was 0.31 to 0.52 g. The range of deceleration achieved by the riders when they also employed heavy front wheel braking was between 0.54 and 0.88 g.
These authors further stated that “when faced with an emergency stopping situation, or avoidance situation, a motorcycle [rider] has the decision of whether to stop using the rear brake only, front and rear brakes combined, or by laying the motorcycle down. There are several common misconceptions about motorcycles. One is that they will stop faster if they are laid down on their side…When a motorcycle is stopped by laying it on its side there is a delay in implementing the deceleration…The test results show that laying a motorcycle over and rear wheel braking have very similar deceleration factors. However, when laying a motorcycle over there is an impact and risk of injury when the motorcycle hits the pavement. Also, all control is lost. If the motorcycle is kept upright, it is possible to reduce braking and steer. Front and rear wheel braking provides the best deceleration factors. Our testing also demonstrates that even during hard braking with front and rear brakes, the experienced driver consistently maintained a straight path without causing the motorcycle to fall…When a motorcycle rider is presented with an accident situation, proper use of front and rear brakes will produce the most effective stopping…Laying the bike down results in impact with pavement, total loss of control, and a longer stopping distance.”
Hunter reported acceleration and braking tests conducted by the Washington State Patrol on a dry, level roadway with a 1983 and a 1985 Kawasaki 1000 police motorcycle [4]. For deceleration tests with rear braking only, Hunter reported decelerations between 0.35 and 0.36 g. For deceleration tests with front braking only, Hunter reported decelerations between 0.64 and 0.74 g. For deceleration tests with heavy front and rear braking, Hunter reported decelerations between 0.63 and 0.96 g. For the rapid acceleration tests, Hunter reported accelerations between 0.48 and 0.73 g.
Hugemann and Lange conducted 74 instrumented braking tests with 18 different riders, 15 of whom were riding their own motorcycle [5]. Motorcycle types were not specified. The riders had varying levels of experience (less than 12,500 miles and up to 80,000 miles) and were instructed to brake from 50 kph (31 mph) to a standstill “within the shortest possible distance.” Riders characterized as “skilled” exhibited mean decelerations between 0.70 and 0.81 g’s. Riders characterized as “novice” exhibited decelerations between 0.44 and 0.52 g’s.
Bartlett reported testing with four motorcycles – a Harley-Davidson FXRT, a Yamaha FZ600, a Suzuki Katana 750, and a Kawasaki EX650 [6]. For tests that utilized only the rear brake, the maximum decelerations between these four motorcycles varied between 0.38 and 0.46 g. For tests that utilized only the front brake, the maximum decelerations varied between 0.88 and 0.89 g. Bartlett reported testing with combined front and rear braking only for the Harley-Davidson. This produced a maximum deceleration of 0.96 g. In this testing, the Yamaha brake pads were deteriorated, resulting in metal-to-metal contact. The maximum deceleration produced with the Yamaha with these deteriorated brake pads was 0.75 g.
Ecker and his colleagues conducted a study comprised of approximately 600 tests performed by more than 300 riders of varying levels of experience (novice to 40+ years) operating an instrumented Honda CB500 [7]. As the riders were operating 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 deceleration for all 600 runs was 0.63 g with a standard deviation of 0.12g. Assuming a normal distribution, these figures suggest a 68% confidence interval of 0.51 to 0.75 g. Another interesting conclusion of this study was that there was only a minor correlation between braking ability and riding experience, especially for more than 1 year of experience.
Vavryn [8] examined the influence of rider experience level and the effectiveness of antilock braking systems (ABS). He 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 kph (31 or 37 mph). The subjects performed two tests on their own motorcycle and then two runs on a motorcycle equipped with ABS. One of the ABS-equipped motorcycles was a standard-style BMW and the other was a scooter equipped with linked ABS. The average deceleration for experienced motorcyclists on their own motorcycle was 0.67 g (SD = 0.14 g). When riding the motorcycles equipped with ABS, that number jumped up to 0.80g (SD = 0.11 g).
Eighty five percent of the subjects exhibited improved braking with the ABS-equipped motorcycle and the novice riders achieved almost equal braking decelerations to the experienced riders when operating the ABS-equipped motorcycles. Vavryn also noted that “the deceleration the novice drivers achieved with ABS almost equals the experienced drivers’ deceleration. All of the novices improved their deceleration with ABS.” Without ABS, the novice riders achieved an average deceleration of 0.57 g.
Bartlett, Baxter, and Robar reported hundreds of brake tests from reconstruction classes conducted at the Institute of Police Technology and Management (IPTM) from between 1987 and 2006 [9]. These tests were conducted at various locations around the country with 112 different motorcycles and riders. They were all conducted on dry asphalt or concrete. Initial speeds in the tests were nominally 20, 30, and 40 mph (32.2, 48.3, and 64.4 kph). The riders in these tests were typically motorcycle unit officers or instructors from a police agency. The data in this study included 275 rear brake only tests, 239 front brake only tests, and 221 tests with combined front and rear braking. This data yielded the conclusion that the decelerations were normally distributed with a mean and standard deviation for the rear only braking of 0.37g ± 0.06 g, with front only braking of 0.60g ± 0.16 g, and with combined front and rear wheel braking of 0.74g ± 0.15 g.
Bartlett and Greer [10] presented brake test data from students in a motorcycle training program (Skills Training Advantage for Riders from the State of Idaho) with three skill levels – Basic I, Basic II, and Experienced. The authors noted that “the Basic I program is for riders who are new to motorcycling, with virtually no experience, and is conducted on STAR training motorcycles. These bikes are typically 250cc or smaller, with front disc and rear drum brakes. The Basic II program is for riders who are returning to motorcycling or those who have ridden on dirt, but not on the street, i.e., riders with some experience but not much on street cycles. These riders also use the program’s training motorcycles. The Experienced program is for riders who have been riding for more than one year and is conducted using the riders’ own motorcycles.”
The culmination of each program was a riding skills test, which included a stopping test. Riders were instructed to approach the stopping area at a steady speed between 15 and 20 mph (24.1 and 32.2 kph). Once in the stopping area, they were to stop the motorcycle as quickly as they could with maximum braking. Bartlett reported the results of 288 tests. The results of these tests “were almost indistinguishable” for the three skill levels. The Basic I group produced decelerations with a mean and standard deviation of 0.60g ± 0.16g, the Basic II group produced decelerations of 0.64g ± 0.14g, and the Experienced group produced decelerations of 0.61g ± 0.14g. The authors note: “The application of this work to reconstruction should not be viewed as a means to interpret speed based on skidmarks. Skidding friction values, to be used when there are marks to measure, have been discussed at length in other articles and publications. Rather, this data should be applied to those circumstances when one is attempting to evaluate how a rider performed or could have performed, given situationally appropriate time and distance limitations based on the scene and circumstances of the event under consideration.”
Dunn [11] reported brake test data and tire mark characteristics for three motorcycles – a 1995 BMW R1100RS (sport-touring with antilock brakes), a 2003 Buell XB9R (sport), and a 2005 Harley-Davidson XL 1200 Sportster Custom (cruising/touring). They tested three different braking strategies – best effort front braking only, best effort rear braking only, and best effort front and rear combined braking. Initial speeds for the tests were nominally 25, 45, and 60 mph (40.2, 72.4, and 96.6 kph) and most of the tests were conducted on a flat, dry asphalt surface. One set of tests was conducted on wet asphalt with the BMW, a motorcycle equipped with antilock brakes.
For the BMW, the rear-braking-only strategy produced decelerations between 0.364 and 0.416. The front-braking-only strategy produced decelerations between 0.671 and 0.828. The combined front and rear braking strategy produced decelerations between 0.642 and 0.842. For all three strategies, the decelerations increased with increasing speed. On the wet asphalt surface, the BMW produced decelerations with both brakes between 0.637 and 0.827. For the Buell, the rear-braking-only strategy produced decelerations between 0.345 and 0.380. The front-braking-only strategy produced decelerations between 0.548 and 0.709. The combined front and rear braking strategy produced decelerations between 0.612 and 0.708. Again, for all three strategies, the decelerations increased with increasing speed. For the Harley-Davidson, the rear-braking-only strategy produced a deceleration of 0.386 (this strategy was only tested at 45 mph). The front-braking-only strategy produced a deceleration of 0.518 (this strategy was only tested at 45 mph). The combined front and rear braking strategy (tested at 45 and 60 mph) produced decelerations between 0.658 and 0.674.
Dunn found that “at the extreme, the rear tire of the Buell lifted off the ground in some tests.” Frank [12] noted that “pitch-over events are common in motorcycle accidents, and can be caused by impact to the front wheel and occasionally by hard brake application…Provided there is sufficient tire/road friction, at the limit of the braking capacity of the motorcycle the weight on the rear tire is zero. Though not inevitable, this is the point at which the motorcycle can pitch-over.” Frank conducted 18 sled tests to evaluate the trajectory and velocity of riders and passengers on motorcycles that pitched over due to braking. This testing used target decelerations of 1.0, 1.15, and 1.3g. Target speeds for the testing were 20, 30, and 33.5 mph (32.2, 48.3, and 53.9 kph). The lowest braking deceleration that produced a pitch-over in Frank’s testing was 1.0 g with a test speed of 30.2 mph (48.6 kph).
Fatzinger, Landerville, Bonsall, and Simacek [13] reported a study of motorcycle deceleration for sport motorcycles during over-braking of the front wheel. Testing was conducted with the following motorcycles: a 2002 Kawasaki ZRX1200R, a 2006 Yamaha YZF-R6, and a 2013 Ninja EX300. Thirteen tests were completed, with initial speeds ranging from 50 to 60 mph. All three motorcycles had independently actuated front and rear brakes without antilock brakes. Testing was conducted on a flat asphalt surface. Brake pressure was applied to the front brake lever or the rear brake pedal with elastic straps. Electronically controlled valves installed in each brake line prevented this pressure from being applied to the calipers until the motorcycle was up to speed. Of the 13 tests, 3 were performed with a 6 ft, 1 in and 175 lb dummy on the motorcycle. In some of the tests, rear wheel braking was applied in addition to the front braking, and in some of the tests, no rear braking was applied. Front wheel lockup was achieved in 9 of the tests.
Fatzinger et al reported that the deceleration achieved by the motorcycle with front wheel lockup depended on the lean angle of the motorcycle at the beginning of the braking. They reported that the average deceleration when the initial lean was approximately 2 degrees or less was in the range of 0.69 and 0.8g. The average deceleration when the initial lean was around 3 or 4 degrees was between 0.51 and 0.67g. The average deceleration when the initial lean angle was between 8 and 9 degrees was 0.32 to 0.39g. When the front wheel braking resulted in a pitch-over, the deceleration rate was in the range of 0.8 to 0.86g. Rear brake application did not significantly increase the deceleration of the motorcycles when front wheel lock had been achieved. Also, there were “no significant differences noted in the peak and average decelerations between the tests” with and without the dummies.
Peck, Deyerl, and Rose examined the effect of tire pressure on the deceleration achieved with full application of the rear brake only [14]. This testing utilized a 2003 Suzuki GSF1200 equipped with Michelin Pilot Road radial tires. The tests were run from a nominal speed of 30 mph (48.3 kph) – three tests with the rear tire at 40 psi and three tests with the rear tire at 20 psi. The front tire was inflated to the manufacturer recommended tire pressure of 36 psi for all tests. These authors documented the size of the tire contact patch by using a rear swingarm stand to suspend the rear tire above a piece of brown paper, putting paint on the tire, and then lowering the tire onto the paper. The size of the rear tire contact patch was 46% larger at 20 psi than at 40 psi and the average deceleration was 5% greater at 20 psi than at 40 psi. For the tests at 40 psi, the three tests yielded the following decelerations (g): 0.324, 0.321, and 0.327 (average = 0.324). For the tests at 20 psi, the three tests yielded the following decelerations (g): 0.341, 0.339, and 0.338 (average = 0.339). These findings related to the influence of tire pressure are consistent with results reported by others for passenger cars [15, 16].
What Deceleration Can Motorcyclists Be Expected to Achieve?
Crash reconstructionists are frequently asked to determine how a crash could have been avoided. In conducting this analysis, there will be instances in which an assumption will be made about the level of deceleration a motorcyclist should have been able to achieve. Based on the literature summarized here, motorcyclists would be able to achieve a deceleration of 0.5 g and above on a dry road by utilizing only their front brakes. By utilizing both brakes, most motorcyclists will be able to achieve a deceleration of 0.6 g and above on a dry road. That said, the level of deceleration that can be achieved during a specific emergency must consider conditions present that may affect a rider’s ability to achieve these expected levels. External factors such as roadway conditions, other traffic, the presence of cargo or passengers, or what the specific avoidance decision a rider makes may need to be considered when assigning an expected braking level to a specific crash scenario.
References
Tolhurst, N. and McKnight, A., "Motorcycle Braking Methods," SAE Technical Paper 860020, 1986, doi:10.4271/860020.
Prem, H., “The Emergency Straight-Path Braking Behaviour of Skilled versus Less-skilled Motorcycle Riders,” SAE Technical Paper 871228, 1987, doi:10.4271/871228.
Fries, T.R., Smith, J.R., Cronrath, K.M., “Stopping Characteristics for Motorcycles in Accident Situations,” SAE Technical Paper 890734, 1989, doi:10.4271/890734.
Hunter, J.E., “The Application of the G-Analyst to Motorcycle Acceleration and Deceleration,” SAE Technical Paper 901525, 1990, doi:10.4271/901525.
Hugemann, W., Lange, F., “Braking Performance of Motorcyclists,” 1993.
Bartlett, W., “Motorcycle Braking and Skidmarks,” Mechanical Forensics Engineering Services, LLC., 2000, unpublished article available at https://www.mfes.com/motorcyclebraking.html, accessed on June 1, 2017.
Ecker, H., Wasserman, J., Hauer, G., et al., “Braking Deceleration of Motorcycle Riders,” International Motorcycle Safety Conference, Orlando, FL, March 1-4, 2001.
Vavryn, K., Winkelbauer, M., “Braking Performance of Experienced and Novice Motorcycle Riders – Results of a Field Study,” International Conference on Traffic & Transport Psychology, Nottingham, England, 2004.
Bartlett, W., Baxter, A., Robar, N., “Motorcycle Braking Tests: IPTM Data Through 2006,” Accident Reconstruction Journal, July/August 2007, ISSN: 1057-8153.
Bartlett, W., Greer, C., “Braking Rates for Students in a Motorcycle Training Program,” Accident Reconstruction Journal, Volume 20, No. 6, November/December 2010, ISSN: 1057-8153.
Dunn, A.L., et al., “Analysis of Motorcycle Braking Performance and Associated Braking Marks,” SAE Technical Paper 2012-01-0610, 2012, doi:10.4271/2012-01-0610.
Frank, T., Smith, J., Hansen, D., and Werner, S., "Motorcycle Rider Trajectory in Pitch-Over Brake Applications and Impacts," SAE Int. J. Passeng. Cars - Mech. Syst. 1(1):31-42, 2009, doi:10.4271/2008-01-0164.
Fatzinger, E., Landerville, J., Bonsall, J., and Simacek, D., “An Analysis of Sport Bike Motorcycle Dynamics during Front Wheel Over-Braking,” SAE Technical Paper 2019-01-0426, 2019, doi:10.4271/2019-01-0426.
Peck, L., Deyerl, E., Rose, N., “The Effect of Tire Pressure on the Deceleration Rate of a Motorcycle Under Application of the Rear Brake Only,” Accident Reconstruction Journal, July/August 2017, ISSN: 1057-8153.
Baumann, F.W., Schreier, H., Simmermacher, D., “Tire Mark Analysis of a Modern Passenger Vehicle with Respect to Tire Variation, Tire Pressure and Chassis Control Systems,” SAE Technical Paper 2009-01-0100, doi:10.4271/2009-01-0100.
Rievaj, V., Vrabel, J., Hudak, A., “Tire Inflation Pressure Influence on a Vehicle Stopping Distances,” International Journal of Traffic and Transportation Engineering 2013, 2(2):9-13, doi:10.5923/j.ijtte.20130202.01.