Designing the Sun Lover Part 3: Why Bikes Are Safer Than Cars
- Laurence Clarkberg
- Jul 11
- 17 min read
There Are Two Sides to Safety
In part one of this essay I describe the sad state of affairs of transportation today, how people are duped by the automobile and fossil fuel industries into driving unnecessarily heavy dangerous vehicles. I describe how our perceptions about safety have become twisted to only include one side: the safety of the people within the vehicle. The automobile industry has diverted our attention with seat belts, air bags and crash worthiness, etc. which only focus on safety for the people within the car. Have you ever heard an automobile ad describe how their product is safer for pedestrians? Of course not. For any other product, the concept of safety also encompasses a second side: the safety of anyone who is also affected by that product. With cars, that second side of safety includes the safety of pedestrians and bicyclists of course, but also how safe the product is for the environment. Compared to a bicycle, the car as we know it today obviously fails miserably in both of these ways. Cars are unsafe for pedestrians and bicyclists. Cars are a major factor in the climate crisis which is on the verge of bringing unimaginable hardship to millions of people from extreme storms, extreme temperatures, and sea levels rising and flooding coastal areas on a massive scale. Cars are incredibly unsafe.
Driving a car is an incredibly selfish act. By driving you are in effect saying “I’m going to make myself safer while at the same time make everyone else very unsafe.” Why aren’t motorists being held accountable for how dangerous they make our cities? Personally I’ve experienced a weird bias toward myself as a bicyclist. If I tell my friends or family about an unsafe encounter with a car, they go to the idea that somehow it’s my own fault because I choose to ride a bike. They don’t instead see a problem with the motorist choosing to drive a car. They would rather focus on how bicycling might be unsafe for me rather than focusing on how driving a car is unsafe for everyone. They go to “you should stop bicycling” rather than “our roads would be safer if more people biked, motorists should stop driving ridiculously large and heavy vehicles”.
This weird bias often manifests itself when I’m visiting friends and family and I get on my bike to ride home. They look worried and they say “Bike safely!” Frankly I’m offended by the idea implicit in what they think is a kind remark. They are implying that someone riding a bicycle is somehow doing something that is less safe than someone driving a car. But the bicyclist is not threatening anyone’s safety. The motorist is. Instead they should be saying to their friends who are getting into their cars “Don’t hurt anyone!”
Safety of the Sun Lover
In part two of this essay I envision a lighter, narrower, slower vehicle for use within cities. I describe how I became determined to build my own solar-powered vehicle. I describe how I added electric motors and solar panels to an old tandem bicycle to create the Sun Lover. And I describe how while the Sun Lover works great mechanically, I encountered a new problem: my friends and family think the Sun Lover is somehow unsafe. They have voiced three stupid safety concerns: that it’s top heavy, that its light weight makes it more susceptible to sliding on turns, and that the large surface area of the solar array might cause it to lift up at high speeds or be blown over by moderate side winds. Let’s debunk each of these ideas in turn.
Here for the purposes of this essay I invent an imaginary character I call the naysayer, who represents a combination of all my dear friends and family who over my many years of bicycling have questioned the safety of bicycling.
First Safety Concern: It Looks Top Heavy
The idea of “top-heavy” does not apply to bicycles in motion. Period. In order to explain why, I’m afraid I’m going to have to pull out some physics. I will explain how, in order to keep from flipping over on a turn, a bicycle uses a “high center of gravity” strategy along with a balancing mechanism. A car, by contrast, uses a “low center of gravity” strategy and does not provide a balancing mechanism for the driver. But first, for those of you who don’t believe in physics, I want to extend an offer to test these ideas experimentally by actually riding my bike and my trike.
People who are inexperienced with bikes and trikes look at the Sun Lover bicycle with its two inline wheels and the Sun Pony tricycle with its three side-by-side wheels and they automatically assume that the tricycle is more “stable” in some way than the bicycle. In fact, the opposite is true. The only situation in which the trike is more stable than the bike is when the trike and bike are at rest. It’s true that in that situation the bike will fall over while the trike will remain upright. That’s what kickstands are for. But bikes and trikes are meant to be in motion. In the situation of going 15 mph and above, a lightweight bike will always feel more stable than a lightweight trike. You can easily prove this experimentally. I welcome anyone who wants to compare the Sun Lover bike to the Sun Pony trike to take them both down South Hill in Ithaca at 25 mph. You will instantly feel that the Sun Lover bike feels very secure, while the Sun Pony trike feels very scary.
I have a lot of experience putting ebike motors on trikes, and my many customers confirm this low opinion of trike stability. One of my customers, who has a brand of tadpole trike called “TerraTrike,” nicknamed his vehicle “Terror Trike”. (FYI a tadpole trike has two wheels in front whereas a delta trike has one wheel in front.) Another customer, who incidentally was in his 80’s, wanted to increase the wheel size of his tadpole trike. I warned him that doing that would raise the center of gravity and make his trike less stable, and cause it to flip over on tight turns. He responded, “Oh that’s okay, I flip it over all the time! It’s fun!”
For those of you unable to test a trike and a bike in person, allow me to explain their stability mechanisms with some text and diagrams and some simple thought experiments. First let’s look at trikes and quads and in fact any vehicle that has side-by-side wheels, including two-wheeled trailers. The stability of these vehicles is achieved by designing them with a low center of gravity, or by making them wide, or by limiting their speed.
Low CG Strategy
Firstly, what is the “center of gravity,” or “CG,” and why is it important? The center of gravity is the balance point of an object. To find the CG, simply pick up that object and balance it on the tip of your finger. Your finger will be pointing to the CG. The CG is important because it is the point at which gravity and other forces “grab” an object. It is also the point at which an object floating in space will revolve around if you spin it.
We can conduct a simple mental experiment to see how a vehicle behaves during a turn. Imagine a block of wood that is about twice as tall as it is wide sitting on a rubber mat. Now imagine grabbing that block at its center point and pulling it sideways. In this experiment the block represents a top-heavy car going into a turn, and your hand represents the centrifugal force acting on the turning car. In this case, as you pull sideways the block will tip over.
Now imagine a second case in which the block is sitting on its long side. The block in this position represents a car with a low center of gravity. Now when your hand, representing the centrifugal force of a turn, pulls sideways on the block, instead of tipping over the block will slide sideways on the rubber mat!
You can imagine that there is some kind of tipping point between the case in which the block slides and the case in which the block tips over. That tipping point can be determined geometrically by drawing a 45-90-45 degree triangle on the base of the block. (Why 45 degrees? Try the pencil sliding experiment below to find out.) If the center of gravity is within that triangle, the block will slide when it is pulled sideways sufficiently. If the center of gravity is outside of that triangle, the block will tip over when it is pulled sideways sufficiently. This triangle is called the “triangle of stability”. Designing any vehicle with side-by-side wheels has to contend with the triangle of stability. Its CG needs to be within the triangle of stability or it will be dangerous to corner at high speeds. You can see that one design approach would be to add weight to the bottom of the vehicle to bring down its CG. Another approach would be to make the vehicle wider, and so increase the size of the triangle of stability.
To make cars more stable the automobile industry has chosen both of these approaches, adding progressively more weight and width to cars over the years, in order to enable cars to go faster and faster. Cars’ increased weight and width are extremely detrimental to our society. Cars are now so heavy and wide that they require an incredibly expensive and space-consuming infrastructure to support them. We have to ask ourselves, is enabling cars to go 75 mph within our cities worth it? The money and space required to support those speeds could be used instead to feed, house and employ everyone.
One psychological effect of a low CG strategy for vehicle design is that the driver has no ability to balance the vehicle in any way; the stability of the vehicle is determined by the car designer before the driver even gets into the car. This loss of control is what makes a trike scary to drive. While turning you can feel the trike pushing you in the opposite direction of the way you instinctively want to lean. You can feel the trike starting to tip over, and you know deep in your heart that there is nothing you can do to stop it. You feel the terror of the terror trike.
There are other techniques to keep a low CG vehicle from tipping over on turns. For example race car tracks and some highways are banked so that the centrifugal forces of a high speed turn press the car into the road rather than sideways to it. And trains have a clever mechanism for leaning into turns. I remember when I was a boy my grandfather Bill, a renowned engineer in the aerospace industry, teaching me how this works. A train’s steel wheels are actually slightly conically shaped. When traveling straight, the wheels rest in the center of the track so that the diameter of where the wheels are resting on each side of the track is the same. However, when the train comes to a turn, the centrifugal force pushes the train sideways so that the diameter of where the wheel rests on the track is smaller for the wheel on the inside of the turn and larger for the wheel on the outside of the turn. This difference in wheel diameter causes the train to lean slightly into the turn. The train’s wheels and the size of the turns it encounters are carefully designed to work together to be just right to keep the train from tipping over.
High CG Strategy
A “high CG” strategy for a vehicle with two inline wheels keeps a vehicle from tipping over on turns in a completely different way: the vehicle designers give the driver of the vehicle a mechanism for balancing the vehicle. There is no triangle of stability. The concept of “top heavy” does not apply. The driver simply uses the balancing mechanism to line up the vehicle's CG with the forces acting on it. When the vehicle is traveling in a straight line, the driver lines up the CG with the up and down force of gravity. When the vehicle goes into a turn, the driver instinctively lines up the CG with the diagonal forces that are the combination of the downward force of gravity and the sideways centrifugal force. The driver instinctively “leans into” the turn to keep from tipping over.
“But isn’t that hard?” I can hear the naysayer saying. “Doesn’t it take a lot of effort for the driver to figure out the direction of the forces and line up the CG accordingly? Doesn’t that stress out the driver, and make the vehicle unsafe?”
“No,” I reply. “Humans and animals in general have incredible reflexes and powers of balance. In fact, not giving a driver control over the balance of a vehicle causes more stress rather than less. But don’t take my word for it. Try riding a trike and you will instantly realize that this is true.”
“But isn’t the high CG strategy unusual and unnatural and therefore unsafe?” the naysayer continues.
“No,” I reply. “Your own body uses this strategy (if you can think of your body as a vehicle). Your own center of gravity is just below your belly button, so it’s much too high to use a low CG strategy. In fact, it can feel easier to carry a load such as a backpack by placing it above your CG rather than below it. In general it’s easier to balance something by giving it a high CG. If you wanted to balance a broom upright in the palm of your hand, which end would you put in your palm? The heavy end (lowering the CG) or the lighter end (raising the CG)?”
“Um, I’d put the broom handle on my palm with the bristles in the air.”
“Exactly, you’d use a high CG. And a high CG strategy is not unusual, you just think it is because you live in a car-centric society. Most modes of ground transportation have a high center of gravity: walking, bicycling, skateboard riding, skiing, horseback riding. Trains, buses and cars are the only two examples of transportation I can think of that don’t have a high center of gravity.”
“Okay you are right I will just shut up now,” says the naysayer.
“Thank you,” I reply courteously.
Bicyclists can easily adjust to bicycles with an incredible range of CG positions, both high and low and left and right. Look at the example of a tall bike, or a cargo bike with a passenger standing on the back, or an asian merchant carrying hundreds of pounds on a bicycle. Look at these photos of people riding bikes with super high CGs.
“OMG. How is this even possible?” the naysayer asks.
“All I can say is, try it yourself and you will find that it is actually not that hard, but we are just more used to seeing vehicles that use a low CG strategy.”
One last point. The handlebars of a bike are deceptively simple. They are an amazing work of engineering in that they are both a balancing mechanism for implementing a high CG strategy, and a steering mechanism for pointing the bike in the right direction. There are a couple of things bicycle designers can do to adjust the sensitivity of this balancing mechanism, to make it easier to ride a bike that is carrying a lot of weight or is very tall. Basically the designer can make the bike more or less “responsive” by adjusting the bike’s “trail”. Trail is the combination of the bike’s head tube angle with the amount of offset of the bike’s forks. Either increasing the head tube angle or increasing the amount of fork offset, or some combination of these, can make a bike easier to handle. Cargo bikes, touring bikes, and tandems often have increased trail. The trade-off is that the bike will be less maneuverable. Racing bikes will often have less trail to make them more nimble. So with a high CG strategy the bike designer doesn’t need to think about raising or lowering the CG at all, but they should give some thought to adjusting the trail so that it’s appropriate for the intended use of the bike. There probably is an upper limit to how much high weight a bicycle’s balancing mechanism can be made to handle safely, but it is on the order of hundreds of pounds. The Sun Lover’s solar array weighs 26 pounds.
A high CG can challenge beginning bicyclists, particularly when their bicycle is traveling between zero and five miles per hour. At these low speeds the bicycle’s “balancing mechanism” is not as responsive as it is at higher speeds. It can be difficult, for example, for a pair of people riding a tandem to get up to speed at the same time that they are trying to simultaneously hop on their seats and get their feet on their pedals. For this reason tandem bicycles are humorously known as “divorce-makers”. The Sun Lover, however, has a big advantage over traditional divorce-makers. With it’s two powerful electric motors it can easily get up to speed without pedaling.
So Which Is Better, a Low CG or a High CG Strategy?
The simple answer is that neither one is better, they are different approaches to achieving the same goal. But if you ask “Which is better for designing a lightweight vehicle?” then a high CG strategy is clearly the winner, since a low CG strategy can require adding weight or width to a vehicle to make it stable.
Second Safety Concern: Sliding on Turns
So now I’ve explained how vehicle designers resolve the issue of a vehicle flipping over if it turns too tightly or too quickly. I’ve explained that with proper vehicle design, either with a low CG or a high CG strategy, the designer can ensure that the vehicle will slide instead of tip over. But wait a minute, isn’t the vehicle sliding off the road on a turn just as bad as tipping over? Here is where road and tire design comes into the picture. With proper road and tire design there will be enough friction to prevent the vehicle from sliding.
“Ahah!” the naysayer perks up again. “Then won’t a bicycle be less safe than a car because the tires of a bicycle are smaller, and therefore less able to ‘grip’ the road?”
“It certainly sounds plausible to someone trying to find faults with bicycles,” I say. “But the physics of the matter is that friction does not depend on the surface area of the tires, friction only depends on the object's mass, gravity, and the coefficient of friction (which is determined by the materials and shape of the tires, but not their surface area). Although a larger area of contact between the tire and road would create a larger source of frictional forces, it also reduces the pressure between the two surfaces for a given force holding them together. Since pressure equals force divided by the area of contact, it works out that the increase in friction-generating area is exactly offset by the reduction in pressure; the resulting frictional forces, then, are dependent only on the frictional coefficient of the materials and the force holding them together. I remember studying this fact about friction in physics 101 with a simple experiment: a rectangular block sliding down a ramp starts sliding at the same ramp angle no matter which side you place the block on the ramp. Placing the block on a side with more surface area does not increase the sliding angle.”
“Harumph!” grunts the naysayer. But then he gets an idea. “Hold on now! You say the friction depends on the mass of the vehicle. A car has a lot more mass than a bicycle! Therefore the car is less likely to slide on a turn. The car is safer!”
“Wrong again,” I say. I try not to gloat. “It’s true that going into a turn the car’s greater mass creates more friction, which is a good thing. But it’s also true that the car’s greater mass creates a larger centrifugal force pushing the car sideways, which is a bad thing. The physics of the situation is that the benefits of the greater friction exactly cancel the drawbacks of the greater sideways force. Given the same type of tires and road surface, the car and the bicycle have exactly the same likelihood to slide on a turn.”
“Okay well I’d much rather be driving a car when the roads are icy,” says the naysayer. “Everyone knows it’s much safer to drive than bike when the roads are icy.”
“Again, not true,” I respond, “if the bicyclist puts studded tires on their bike. A bike with studded tires has excellent traction even on ice. I have friends who have biked on the frozen Lake Cayuga on bikes with studded tires.”
“Well, I can put studded tires on my car, can’t I?” says the naysayer.
“No,” I say.
“Why not?”
“Because it’s illegal. Cars are so heavy that studded tires act like chainsaws on the roads, tearing them up. City officials don’t like that. But studded tires on a bicycle don’t damage the roads because bicycles weigh so little.”
Third Safety Concern: High Winds Creating Lift
The naysayer would not give up. He had one last safety concern to throw at me: “Your solar array is like a big sail on your bike! I’m afraid that coming down the hill, your bike will lift up and you’ll lose control and crash! Or a truck will pass by too close and the turbulence from it will knock you over! As your friend I can’t in good conscience allow you to ride this bike!”
“Relax,” I tell him. “I’ve already test driven the Sun Lover coming down a steep hill and in moderate side winds and I can verify experimentally that it works fine.” But I agreed to do some calculations to also verify mathematically that the Sun Lover is aerodynamically safe. I find the following online calculator to calculate lift force, which uses the formula CL = 2 × F / (A × ρ × V²). I consider two cases and I enter the following values:
Here I enter a flow speed of 40 mph which is a worst case scenario if, for example, I was coming down South Hill at 30 mph into a 10 mph headwind. I enter a surface area of 16 square feet for my solar array which is two feet wide by eight feet long. I leave the default value for the density of air. Finding the lift coefficient value took a little more research. Apparently this value depends on the cross-section shape of the lifting surface and its angle of attack. The lift coefficient for a flat plate varies from .1 at one degree angle of attack to .8 at fifteen degrees angle of attack. (Above 15 degrees the wing will stall and lift drops dramatically. But that’s a different story.) My solar array is not quite flat, it has a slight camber because cables are pulling it down at each end. So a worst case scenario is that the camber shape is providing some lift. The lift coefficient of a cambered wing can be as high as 1.5. So I enter two values for lift coefficient of .1 and 1.5. I find that the corresponding lift force varies from 29 to 436 Newtons.
Next I want to calculate how many pounds a 29 to 436 Newton force can lift to counteract Earth’s gravitational field using the formula F=ma. Here I set the acceleration “a” to 1g, the acceleration due to gravity, and solve for mass. Here are the results:
The results show that under normal riding conditions, when the solar array is at a one degree angle of attack, even at 40mph the Sun Lover would feel at most 6.52 pounds lighter. Since the Sun Lover weighs 110 pounds unloaded, and I weigh 200 pounds and Judy weighs 113 pounds, for a total of 423 pounds, that 6.52 pounds is not significant enough to cause us to lose control and crash. In a worst case scenario, if the solar array did somehow encounter a 40mph wind that came at it at exactly a 15 degree angle of attack, that wind would at most make the bike feel like it was 98 pounds lighter. For a 423 pound bike, that is still not enough to lift it up and make the driver lose control.
I may redesign the solar array so that it is curved left-to-right rather than along its length. I think a slight curve will help stiffen the solar panels and keep them from flexing. And I may ride with the solar array tilted down a couple of degrees in order to increase traction, like the spoiler on a race car does.
Safety Conclusions
We can conclude that the Sun Lover is safe because:
It is lightweight, narrow and relatively slow so it is less of a danger to pedestrians than a car and it’s easier on the environment.
Unlike a trike, it’s unlikely to ever tip over while turning.
It’s unlikely to slide on a turn any more than any other vehicle.
Winds of 40mph are unable to lift the bike.
2025 Update
As you can see in the photo of the Sun Lover at the top of this post, I did re-design the solar array to be lighter in weight, and I replaced the solar panels with higher-efficiency CIGS panels. To prototype the design I used EMT tubing connected together using Makerpipe brand fittings. The prototype worked so well that I didn't feel it was necessary to make a welded version. I intend someday to make an even lighter weight solar array using carbon fiber tubes. I also used Makerpipe fittings to create a very large kickstand that fits onto the middle seat tube.
Judy and I toured around on the Sun Lover last year (2024) for several day trips. But we found it was exhausting to ride together. It requires a lot of focus to stay upright and pedal in sync. We also had a mishap where a flat tire caused the tandem to tip over very suddenly. So we decided to create a third version of our solar-powered tandem, this time based on a recumbent trike geometry. We purchased a TerraTrike Tandem Pro and this spring I added ebike motors, batteries, and a solar array. We call this vehicle the Honey Cycle. We plan to ride it in the RAGBRAI across Iowa this summer. Judy made a short video about the Honey Cycle here.
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