Why do motorcycles go so fast?
Why can motorcycles accelerate faster than cars?
The answer may seem obvious: ‘because they’re less massive’. But what’s the correct physics relationship here? If two identical engines were fitted in a bike (say, 200kg) and a car (1000kg), will they: a) put out identical energy over a given time. So, when converted to kinetic energy via $E_k=fracmv^2$ the bike’s velocity after a given period will be faster than the car’s by a factor of the square root of five because $v=sqrt< 2E_k/m>$. Or, will the two identical engines b) put out identical instantaneous force? So, when converted to acceleration via $F=ma$, the bike will accelerate five times faster $a=F/m$. There’s also a wind resistance element, so we could assume the bike has one quarter of the font-facing surface area (ignoring any streamlining design). I assume this is part of the equation that would govern top speed. (Would love a pointer to how to calculate this given known torque (and thus force at tyre) and drag.) Some aspects of this question relate to engineering. Eg, the tendency for bike engines to be over-engineered cf similarly-priced car engines. There may also be an effect of the bike’s power being applied to the wheel/the ground more directly than the car’s. But I’m really asking about the physics of the situation. Assume same engine in each vehicle. Assume bike is a fifth the mass of the car. Will acceleration of the bike be five times that of the car, or square root of five? I’m kinda interested in difference in braking ability too, assuming half the contact on the road and one fifth of the momentum at equivalent velocity.
asked Mar 15, 2018 at 6:35
Errol Hunt Errol Hunt
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$begingroup$ Note that you must not confuse acceleration with maximum speed. If you look at this video you will realise that there is no easy answer to your question. youtube.com/watch?v=bfLqa4vlmFI The maximum torque relates to the maximum acceleration whilst the maximum power relates to the maximum speed as you can arrange the gear ratios to achieve a very high acceleration whilst the maximum speed is comparatively low. As the video points out power, aerodynamics and gearing for the motorcycle are all significant factors. $endgroup$
Mar 15, 2018 at 9:41
$begingroup$ Fascinating race, but not quite apples and apples, as the car engines have five times the power of the bike’s engine and nine times the torque. Thanks for your notes about power (determines max speed) vs torque (determines acceleration) — good point! This link explains it quite well: physics.stackexchange.com/questions/163263/… $endgroup$
Mar 15, 2018 at 12:38
$begingroup$ I have just remembered this answer. physics.stackexchange.com/a/352498/104696 $endgroup$
Mar 15, 2018 at 12:40
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There are two important points to be made in the performance of a vehicle
- Power over Weight is directly proportional to acceleration. In fact acceleration (without air resistance) is exactly power over momentum $$ a= frac$$ So in the comparison between a car and a motorcycle consider that the power to weight ratio (and hence power over mass) is much higher for a motorcycle. This plays a role at mid speeds. At lower speeds traction is important and at higher speeds aerodynamic forces become significant.
- Traction forces acceleration to be very similar in 1st gear for most vehicles (with the caveat that motorcycles can do wheelies which increases traction). So if initially acceleration is limited to some $a=mu g$ what differs between vehicles is the speed at which acceleration is due to power only happens. Let us call this $v_1$ , and it usually corresponds to the top speed in first gear. $$ v_1 = frac
$$ Again, the higher the power to weight ratio is the higher speed can be achieved in first gear (in general). A semi-truck for example might shift from 1st to 2nd gear at 10mph, while a passenger car might at 40mph and a motorcycle at 70mph.
So a motorcycle can accelerate at the maximum traction limit to a higher speed and then transition to acceleration under power. Of course, there are many factors that go into designing drivetrains and the above is a very coarse simplification.
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answered Mar 16, 2018 at 18:28
John Alexiou John Alexiou
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$begingroup$ This is a wonderful answer, thank you. I have more questions though, to understand these relationships. 1a) Can you tell me why $a=P/mv$? What is that derived from? And 1b), I assume that means $a$ drops off as $v$ increases (even ignoring air resistance)? $endgroup$
Mar 17, 2018 at 16:22
$begingroup$ Also, it’s a fascinating note that initially $a$ is dependent on traction. 2a) Can you tell me why traction causes $a$ to be very similar in 1st gear? Ie, why does changing from 1st to 2nd gear correspond with when $a$ becomes dependent on power/weight, not traction? 2b) Does a motorbike’s reduced number of wheels reduce it’s traction and thus $a$ in this first phase? 2c) how does pulling a wheelie help with traction? $endgroup$
Mar 17, 2018 at 16:22
$begingroup$ The definition of power is $P = F,v$ and force is $F=m a$. Combined they result in $a = frac
$. When considering air resistance the general form is $$ a = frac
— beta v^2 $$ where the coefficient $beta$ depends on many factors. $endgroup$
Mar 18, 2018 at 12:53
$begingroup$ Traction depends on the % of weight on the driving wheels. Compare a moto with a RWD car and you have more % weight on the back on a moto. If a moto pops a wheelie, all the weight goes to the rear wheel increasing traction. Car designers generally don’t want their cars to overpower the wheels in 1st gear because it leads to less acceleration, tire wear and possible loss of control. Why have a 300hp engine, if the traction control limits it to 200hp in 1st gear (I am looking at you dodge caliber SRT4). $endgroup$
Mar 19, 2018 at 0:53
the maximum acceleration rate of any vehicle is determined by its power-to-weight ratio. It’s common to have sportbikes these days that weigh 500-600 pounds (with rider) that contain 100HP engines, and so they can out-accelerate almost any street-legal car. In fact, because of this even a Honda CM450 can out-accelerate a Porsche 912.
The top speed is set by the power-to-drag ratio. The dominant term in the drag sum is projected frontal area which is small for a bike and large for cars, which is why the superbike class of sportbikes (150HP+) can do almost 150MPH on 150HP.
answered Mar 15, 2018 at 17:44
niels nielsen niels nielsen
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$begingroup$ Guy Martin vs. F1: youtube.com/watch?v=7tlxG1-aWtI $endgroup$
Mar 15, 2018 at 19:36
Power to weight ratio is one factor, but another key factor for 0 to 60 mph of a motorcycle versus a front or rear wheel drive car is the motorcycle’s relatively high center of mass means that more weight is transferred to the rear tire, or all of the weight in the case of a wheelie, which in turn allows for more relative friction at the driven wheel, typically resulting in over 1 g of acceleration on higher end motorcycles.
The situation may have changed with some all wheel drive hybrid cars like the Tesla Model S P100D, with a launch controlled acceleration of 0 to 60 mph in 2.5 seconds, provided there’s enough traction (probably a drag racing track with VHT is needed). The Ferrari LaFerari takes 2.4 seconds and the Porsche 918 Spyder 2.2 seconds. This matches or exceeds the fastest bikes with the best riders hunched down over the tank to reduce the wheelie factor. Some bike testing is done with the front end strapped down and the rear shocks set to max stiffness and height or locked into position.
In a street situation, it seems unlikely that even with smooth torque applied by the electric motors to all 4 wheels, there simply won’t be enough traction for the cars to achieve sub 3 second 0 to 60 mph times.
However, once past 60 mph, or more like 80 mph, since that’s 1st gear on the high end bikes, the bike accelerate harder than almost all cars, due to power to weight ratio.
As for the bikes, the high end bikes are around 200 hp now (Ducati V4R is 230 hp with optional exhaust), but due to wheelie factor, 0 to 60 mph times haven’t improved much, stuck at around 2.5 to 2.6 seconds. For example the 175 hp first generation Suzuki Hayabusa matches the 0 to 60 mph time of the 200 hp current ZX-14R, which is 40 lbs heavier, and possibly with a center of mass that is further back and/or higher. The ZX-14R is about 0.25 second quicker than the Busa in a 1/4 mile run (9.5 versus 9.75 with a pro rider on a good track).
5 Reasons Riding a Motorcycle Makes You Happy
Melissa «The Maverick» Anderson : Apr 18, 2023 10:38:01 AM
We hear about the dangers of riding a motorcycle all too often but rarely are the physical and, more importantly, the mental benefits spoken about. Riding a motorcycle comes with a lot of mental and physical benefits. For starters, it helps to clear your mind and provides a great way to relieve stress. Additionally, it gets you outside and forces you to take in some fresh air and vitamin D. Furthermore, it’s a great form of exercise that helps to improve your cardiovascular health and strengthens your leg muscles. And lastly, it’s just a fun activity that can help to improve your mood and overall sense of well-being.
Top Physical & Mental Health Benefits Of Riding A Motorcycle
5. Positive Outlook
That feeling of pure joy after a long ride is something every motorcyclist can relate to. The reason we feel so happy is pretty simple; every twist of the wrist releases adrenaline which, in turn, releases endorphins. These ‘feel good’ hormones improve our mood, increase pleasure and minimize pain.
So, endorphins give us that joyous feeling but, after a ride, there’s also that sense of relief, like a weight has been lifted.
This is similar to mindfulness meditation: Body position, speed, road position – on a motorcycle you’re constantly analyzing and adjusting depending on the situation. This ties us into the present moment, and means our minds have no room for worries about money, jobs or any other day-to-day problems.
You’re fully engaged while riding. This is why your mind is like a blank slate when you throw your leg off after a long ride.
4. Cognitive Function
Riding a motorcycle can help to increase cognitive function as it requires the rider to be constantly aware of their surroundings and to make quick decisions. This can help to improve reaction times and increase the rider’s ability to think on their feet. Additionally, the act of riding a motorcycle can help to clear the mind and allow the rider to focus on the task at hand, which can lead to improved concentration and focus.
But a scientific study, conducted by Ryuta Kawashima, who partnered with Yamaha Japan and Tohoku University, found exactly that. Riding a motorcycle improves your cognitive function, by as much as 50%.
This is down to the fact that riding a motorcycle requires a high level of alertness and rapid problem-solving. According to Kawashima, “the driver’s brain gets activated by riding motorbikes.”
3. Core and Neck Strength
The day after their first long ride, many motorcyclists report the same aches and pains – muscles in our necks are always at the top of the list. Wearing a helmet for a few hours a day would strengthen your neck regardless, throw windblast into the equation and you’ve got a real neck workout.
This is especially true for those who ride without a windshield. You still need to make sure your motorcycle fits you correctly, as constantly cranking or straining your neck will have a negative impact in the long run.
This means checking the handlebars, seating position, and foot pegs are right for your measurements. Riding a motorcycle requires lots of muscles to work together but your core ties everything together.
Every maneuver you make on a motorcycle involves the use of your core, especially low-speed maneuvers. The movements are low-impact and relatively low-intensity so it’s something you may not notice but, if you’ve been riding for a while, your core will be stronger.
2. No More Squats
Riding a motorcycle requires you to constantly move around on the bike, gripping with your thighs and knees. These movements strengthen your thighs and in turn, strengthen your knees.
The muscles in the thighs are used to keep the patella and other bones in the knee in place. Since the movements are low-impact, people who suffer knee or thigh pains describe riding a motorcycle as a kind of physical therapy.
For those lucky enough not to have those problems, riding can help you stay injury free.
1. Burn Some Calories
Yes, you can burn a substantial number of calories while a riding a motorcycle – the gift that just keeps giving.
Those who like to get dirty can burn up to 600 calories per hour of intense motocross riding. Stick to the streets and you can burn between 200-300 calories per hour, especially if you ride with some vigor.
Even passengers on sports bikes can burn up to 50 calories per hour. But, unfortunately, passengers on cruisers and tourers aren’t likely to see their calorie expenditure go up.
Overall, riding a motorcycle can increase cognitive function because it allows a person to use both sides of their brain at the same time. It also increases the level of dopamine in the brain, which has been linked to improved cognitive function. While riding a motorcycle comes with a lot of risks, there are also a lot of mental and physical benefits that are good to consider.
Share the Road with Motorcyclists and Keep Them Safe
In 2020, 5,579 motorcyclists were involved in fatal traffic accidents. There are many reasons this number is so high, but most of the accidents are due to other drivers. By putting an end to bad habits like distracted driving or not giving motorcyclists enough space, drivers can help motorcyclists stay safe on their rides.
12 Ways Drivers Can Help Motorcyclists Stay Safe on the Road
1. Put Away Your Phone
The easiest way to make a motorcyclist feel safer is to put away your phone. You shouldn’t be using it while driving in the first place, as it is the most common form of distracted driving.
2. Only Drive Sober
This speaks for itself. Never drive with alcohol in your system. It slows down your reaction time, reduces your concentration, and substantially impairs your vehicle control. You need full control of your car, especially when driving near motorcycles.
3. Give Motorcyclists Extra Space
It’s common to misjudge the speed and distance of a motorcycle compared to a car. Always give bikes an extra cushion to prevent rear-ending them if you have to come to a quick stop. While a collision may just be a fender bender to a car, it could kill a motorcyclist.
4. Adjust Your Mirrors
Your mirrors should be adjusted to minimize blind spots. Cars are usually easy to see, but a much smaller motorcycle can sneak into a blind spot.
5. Talk to Young Drivers about Motorcycles
Newer drivers might not be aware of the damage they can cause to a motorcyclist if they make a mistake while driving. Inform them that they need to share the roads and always be alert to their surroundings.
6. Open Doors Cautiously
If you park on a road with heavy traffic, be sure to look behind you when you open the door. You could open your door and clip a motorcyclist if you aren’t paying attention.
7. Slow Down at Intersections
Forty-two percent of fatal collisions involving vehicles and motorcycles occurred while a motorcyclist was making a left turn and a vehicle was going straight through an intersection. Always slow down when going through an intersection, especially if you have any obstructed vision.
8. Have Your Passengers Watch for Motorcyclists
Your passengers can see different parts of the road that are a blindspot to you. Have them alert you if they see a motorcycle approaching in case you missed it.
9. Pay Attention in Construction Zones
Operating a motorcycle in a construction zone can be challenging, especially if there are rough patches, obstacles, or grade or surface changes. Give them extra space in case they have to make a quick stop or turn.
10. Be Careful in Inclement Weather
While you are in the comfort of your vehicle in inclement weather, a motorcyclist has to deal with the rain directly. It’s harder to drive in inclement weather, so give them extra time and space. Their vision is likely affected and they need more stopping distance.
11. Turn Down the Volume
Usually, you can hear a motorcycle long before you see it — unless you’re blasting music in your car. Try to keep your volume at a reasonable level so that you can hear a motorcycle approaching.
12. Don’t Rely on Turn Signals
You can’t always trust a driver to properly use their turn siwgnals. Keep in mind that a motorcycle could potentially cut in front of you without a signal.
Keep Motorcyclists Safe on Their Ride
It’s up to automobile drivers to do their part to keep motorcyclists safe on the road. Never drive distracted or drunk, and keep full attention to your surroundings. One additional way to stay safe on the road is by taking a defensive driving course. They are available for both teens and adults and will go more in-depth about driver safety.