Electric Bicycle Road Racing Theory

Electric Bicycle Road Racing Theory

The idea of this thread is to start with some basic principles and realities and build the sport of EBRR up from the roots. Along the way I will attempt to recreate existing arguments about electric bicycles that seem to recur regularly. This is to be made as a sort of college course... even though it's not really going to be taught anywhere. (well, you never know, I can remember some college courses at about this same level)

Physics

We begin with a review of bicycle physics.

An ordinary human being can (at best) produce 400 watts of power over a sustained period by pedaling. For short durations it's possible for peak athletes to achieve 750 watts of power going out the rear wheel. At about 30 mph the primary losses are due to air resistance, so it's very difficult to go faster than 30 mph by pedal power alone in an upright bicycle.

The electric bicycle was created as a "bicycle" replacement or enhancement. In order to retain a definition of "bicycle" we need to accept that motor power cannot significantly exceed human power. This sets a realistic upper limit of 750 watts (1 hp) as the boundry.

The first major point is that even BEFORE we look at the laws pertaining to electric bicycles we are already more or less bound to a limit of 750 watts simply because it what makes us within the definition of a "bicycle". Going significantly above this level and you are into motorcycle or moped territory.

Present Laws

Europe - 250 watts output
Canada - 500 watts output
USA - 750 watts output

The USA is allowing the logical maximum for a "bicycle" while the other nations seem to cut the limit down to something less than is within the accepted understanding of a "bicycle". This is unfortunate, but what we have to work with.

Since we are discussing "pure forms" in the abstract and we see that in the most pure sense 750 watts is the logical limit for an ebike we simply state that 750 watts is the "proper" level to establish as a worldwide standard for Electric Bicycle Road Racing. Since racing would be done on Go Kart tracks and these are not regulated by street laws there is no reason not to set the level worldwide as 750 watts. (that way in the future if you have the World Cup equivalent of EBRR then everyone is using the same limits)

So the "bottom line" is that laws exist and some are compatible with racing while others are not. In the USA it should be easier to produce machines that can be used on the street as well as the track, but in much of the world these machines would be sold as "off road only".

Motor Input verses Output

We know that at tax time we report our income and then deduct certain things before we actually calculate our taxes. Motor Input verses Output works the same way. Laws are written to limit the "Output" of a motor, but make no reference to what "Input" was required to get there.

A typical motor is about 75% efficient. This means that if you start with 1000 watts of Input power that you will get approximately 750 watts of real Output at the rear wheel.

Given the physics involved and also that fact that it's nearly impossible to limit Output directly (it's always something that is arrived at "after losses") the logical way to organize racing is around an Input side restriction.

So if we want approximately 750 watts Output, then we limit the Input to 1000 watts and we simply allow that through the process of motor losses we arrive at the desired result.

This is a critical insight, because if it's possible to electronically calibrate the precise amount of power going INTO the motor we can have a class of racing that is fair. With a simple meter on the Input it's possible to define a class of racing very tightly.

1000 watts of Input is the logical definition of EBRR.

Other Arguments

It's always important to review each and every other argument for how to organize racing classes.

Unlimited Power

The most natural urge is to want to allow Electric Bicycle Road Racing to use as much power in the motors as the designer can achieve. On the surface this even seems like a good idea until you start to anticipate where the designs will naturally progress. If you can increase motor power on an unlimited basis you will also need to increase battery capacity to feed this higher power level. More battery means more weight and that means a stronger frame and possibly suspension to make it usable. At some point the machine resembles a motorcycle only it retains "faux pedals" to satisfy the bicycle definition. An acronym PINO (Pedals In Name Only - "Pee No") describes this type of machine.

The next logical step is to limit the overall weight of such an overpowered machine so that a limited battery weight places a self induced restriction on effective power usage. Let's say the bike is limited to 100 lbs overall. You now have a situation where a 150 lb racer has a 50 lb advantage over a 200 lb racer because the bikes are limited to a fixed amount of weight.

In order to still try to salvage this approach you have to figure out some sort of indexed relationship of power, body weight, and bike weight to equalize things. It simply gets too complicated and no one will perceive it as being fair.

With a 1000 watt power restriction the rider's pedal strength will tend to match their weight (if they are athletes) so the heavier rider can compensate by being stronger. This nullifies weight differences during accelleration. (though when it comes to top speed aerodynamics the smaller rider probably glides better)

Battery Capacity Limits

Another approach to equalizing the racing is to set a limit on the battery capacity without regard to it's physical weight. This allows all the bikes an equal overall quantity of power but alters the way people will operate their machines in a race. Rather than an all out sprint where the racer applies full throttle whenever they can the Battery Capacity Limited racing will favor those with a smoother riding approach so that less energy is wasted getting around the track. While we can applaud the ideal of increased efficiency, if the effect is to take the passion from the racing experience the psychological negatives tend to make this less attractive. However, there are special cases where this could make sense. (fragile streamliner recumbents for instance)

To date these are the main alternative approaches to ebike racing.

Public Perceptions

There are several broad categories of people that have fairly clearly defined perceptions and opinions about ebikes.

The Cyclist

The pure cyclist simply will not allow a single thought towards electric bikes because it's a violation of everything that the cyclist holds dear.

The Senior Citizen

Many Senior Citizens view the electric bike as a "mobility device" for those who are by now too frail to get around under their own power. In this view the electric bike is a sort of wheelchair. This person will guard the low speed image of ebikes and oppose anything that gives a racing perception.

The Outlaw

The outlaw is someone that knows the laws on the street, but just completely disregards them in favor of whatever power they can achieve by their own bike modifications. When presented complicated issues about how high powered ebikes fit into the larger scheme of things their response is "I do whatever I can get away with." This person might race, but possibly in some other racing category. To the outlaw having a 1 hp power limit seems confining.

The Parent

If you are shopping at WalMart for childrens toys you will come to realize that within the store bicycles are classified as "toys". They sell some electric "toys" such as scooters, pocket bikes and even ebikes. The parental perspective is that ebikes are more or less silly toys that you get your child for xmas, but that they will grow out of them quickly so you shouldn't pay too much or worry too much about quality. The parent will be a little worried about something that appears too fast, so the 1 hp power limitation will provide some comfort to help them decide to purchase an EBRR bike for their child.

...the target demographic for Electric Bicycle Road Racing begins at about the age of twelve and fades out at about thirty much the same as in BMX. (this isn't to say that some older folks might not like it too)

The Passion

What will make Electric Bicycle Road Racing unique?

Cycling already provides numerous excellent racing styles that demand athletic performance of their racers. Motorcycle road racing already gives the rider skill thrills of riding at the edge of traction.

Part of the reason that newer sports like Mixed Martial Arts have taken hold is that they took the best of several other sports and blended them into something that brings out the best of all of them. That same mindset needs to be used in EBRR in that the top level racers need to have mastered all elements of the sport to succeed. There can be no room for the out of shape racer if EBRR is to be considered a real sport.

Walk Through A Race

Let's walk through a typical race...

At the start riders are lined up in rows of two (ideally) based on heat races or best lap times which were decided in advance. The faster riders are placed at the front. To get a fast start the rider needs to stand up and pedal explosively off the line because below 30 mph aerodynamic effects are small. Once the rider gets up to about 25-30 mph it makes sense to drop down onto the seat and tuck behind the fairing to increase top speed to near 40 mph. This is taking place on a Go Kart track that isn't going to allow top speeds for very long, so just as you are hitting your top speed you quickly need to brake for the upcoming corner. In the corner you ride the very edge of traction and both tires may drift a little. Depending on how much speed you lost in the corner you would either stay in the tuck and use all motor power or you might stand up again and get another burst of pedal power.

Different Go Kart tracks are going to stress different racing styles as the tighter tracks will reward more frequent bursts of acceleration coming out of the turns while other faster tracks will reward more time in a tuck for faster top end speed.

Drafting will be a big factor in this sport as it is in Cycling because at 40 mph the aerodynamic wake is much larger than at the 30 mph level that most Cyclists are used to. This means that the rider in second place on a straight away will almost always have passing power coming into the next turn. This means that the racing will be very intense with a lot of chances for passing.

At this point it's important to bring up the notion of "fair play".

You simply cannot allow dirty tactics into a sport like this because it's simply too easy to disrupt another rider and cause a crash. While in many cases the dirty rider goes down with the innocent anyway the sport suffers if there is no authority to penalize foul play. Riders should be stripped of any win if they intentionally cause another rider to crash and if they repeat that behavior that rider should be banned from the sport.

Penalties

What about doping?

I don't think that doping would be a big issue in this sport. Even if some guy is using steroids it will only benefit in the acceleration portion of the sport and that is not so dominant as to make for instant success. While there might be problems down the road with doping it doesn't seem important for now.

Electrical Cheating?

There will be an absolute need for precise power limiting circuitry to ensure that no one exceeds the 1000 watt input limit. Anyone caught tampering with the circuit (which needs to be supplied by the racing organization) would get an instant penalty of some sort. For the early days of the sport there will be the need to accept less precise limiting techniques (like just using known 1000 watt controllers) but over time that will need to be made more strict to ensure fairness. (*see next posting)

Distance and Duration

The length of the race needs to be compatible with the amount of battery that is used. We calculate battery size:

Power input restricted to 1000 watts per second = 1000 watt / hour (Wh)

So if the race lasted a full hour at full throttle you would need a battery that was something like 48 volts and 21 Ah. In order to lower the battery requirement it would be preferred to shorten the race to about half an hour which would drop the battery required to:

1000Wh / 2 = 500Wh

...and this can be achieved with a 48 volt and 11 Ah battery.

Lead Acid (SLA) ~ 50 lbs (Peukert's Effect requires 20Ah)

NiCads ~ 30 lbs

NiMh ~ 20 lbs

LiFePO4 ~ 15 lbs

Assuming:

Rider ~ 175 lbs

Bike ~ 55 lbs

SLA = 50 / ( 55 + 175 ) = 22%

LiFePO4 = 15 / ( 55 + 175 ) = 7%

As long as the race duration is kept low the battery is reduced in it's influence on the race outcome. However, just like with being overweight the more athletic rider and the lower weight battery will have an advantage. As with Cycling the quest for lighter and lighter machines will guide technological progress in the sport, but the shorter distance will tend to place a cap on battery costs. The sport needs high technology, but should not only be about technology.

How far is half an hour?

We assume that the average speed is about 30 mph. Half of 30 miles is 15 miles so we calculate that the maximum distance should be LESS than 15 miles.

A realistic track length would be 10-15 miles.

A realistic race duration would be 20-30 minutes.