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# Rolling Resistance Calculator

Rolling resistance - basicsTire rolling resistanceWhat is rolling resistance caused by?How to calculate rolling resistance using the rolling resistance calculator?Rolling resistance and drag: how to reduce fuel consumption?Car and bicycle rolling resistanceSummary: What you should have learned from this calculator?

Calculating rolling resistance was difficult... until we created this rolling resistance calculator! You don't need to do all the science and research to know how to calculate rolling resistance, we did it all for you.

Here you can figure out if you should buy those fancy low rolling resistance tires to save gas in your car or to improve your cycling wattage output.

## Rolling resistance - basics

People usually don't understand rolling resistance well, but everyone seems to have an idea of what it means. It has to do with your wheels when you're driving. Generally, you want the least rolling resistance possible and you can reduce it if you buy low rolling resistance tires. Some of you might even know that rolling resistance is a type of friction-force that slows you down.

All of that is correct, but we are here to help you go deeper. Did you know that rolling resistance doesn't depend on your tire size, but it does depend on the weight of your car/bike/train? The best way to explain it is to learn the physics behind it. The easiest way is just to use this rolling resistance calculator to check how each factor affects, e.g., the bike tire rolling resistance. We will try to strike a sensible balance between the factors too. Shall we?

## Tire rolling resistance

We often mention rolling resistance in relation to tires in vehicles. That because the tire's contact with the road, and the way they react to each other, is what causes rolling resistance. Changing the tires is the easiest, cheapest, and fastest way to change the rolling resistance of your car or bike.

Nowadays, you can even buy low rolling resistance tires that help minimize the energy lost to the road when driving around. These are generally more expensive and don't make economical sense for the average user. However, in performance applications, the difference between a regular tire and a low rolling resistance tire can mean the difference between first and last.

But don't let this confuse you, rolling resistance is not something inherent to tires only. Anytime you have an object rolling on top of a surface, you get rolling resistance. Let's see why!

## What is rolling resistance caused by?

As we have mentioned, rolling resistance occurs between a rolling object and a surface. For practical purposes, we can stick to wheels as our round objects, since that's how all transportation on land works. For example, trains have solid metal wheels rolling on rails, and they too have rolling resistance slowing the train down.

If we look at the simplest version of rolling resistance, we can see that there are only two important quantities for the rolling resistance formula, $\mathrm{RR}$:

$\mathrm{RR} = \mu\cdot N$

where,

• $\mu$ is the coefficient of friction; and
• $N$ is the normal force, which is the vertical weight of the object: find out more about it at our normal force calculator.

In reality, the situation is much more complex than it seems, since determining the value of $\mu$ is very tricky. In general, $\mu$ depends on the surfaces touching (wheel and tarmac/rail/ground...) but in many cases $\mu$ might even depend on the speed, pressure, temperature, lubrication, and many other factors.

So, in answering the question "What is rolling resistance caused by?", the simplest answer is the calculated friction between the wheels and the surface. The longer, and more precise, answer is that rolling resistance is caused by anything in the wheel or the surface that takes energy away from the forward movement of the vehicle. I'm sure you can see how something so vague can get so utterly complex.

And that's exactly the reason why we have created this rolling resistance calculator, so that you don't have to do all that research yourself.

## How to calculate rolling resistance using the rolling resistance calculator?

In this rolling resistance calculator, we provide you with all the common values you might need to calculate the rolling resistance of common vehicles, e.g., bicycle rolling resistance. Given how variable $\mu$ is, and the many ways in which we can calculate it, we provide you with a bunch of presets as well as two different methods for how to calculate rolling resistance.

Since you came here for simplicity and not to spend hours figuring out how to use the tool, here is a step-by-step guide on how to calculate rolling resistance using Omni's rolling resistance calculator.

1. Select how you want to calculate rolling resistance (e.g.: Standard "car tires on asphalt").
2. Input the necessary fields as they appear (in this example this is the weight of the car).
3. Watch the result appear in the field "Rolling resistance".
4. Compute again using different data, or a different method.

When you're selecting your method of calculation (in the field Calculate from), you will see three options presented. The simplest one is the given coefficient of friction where you simply input the value of $\mu$ and weight of the vehicle. Then the calculator solves the equation mentioned above.

If you know the coefficient of rolling friction (rolling $\mu$), you can select "know wheel/surface". There you simply input the radius of the wheel, both surfaces' coefficient of rolling friction, and the weight of the vehicle, and the calculator takes care of all the computations using the equation:

$\mu = \frac{\mathrm{rolling}\ \mu}{\mathrm{radius}}$

You can also calculate for a standard car tire and a standard road, as in the example, or you can go for the simplest route, which is using one of our 13 other presets of different wheel-surface combinations, so that you don't have to look for any numbers online.

## Rolling resistance and drag: how to reduce fuel consumption?

When we're trying to cover the distance from point A to point B, anything that steals energy from that movement is bad. Rolling resistance is one of those things, and that's the reason a lot of people turn to low rolling resistance tires as a way to save fuel.

However, in most applications, tire rolling resistance is a very small factor compared to drag or other inefficiencies somewhere in the vehicle. In a car, for example, the air resistance, or drag, is much more important at cruising speeds that rolling resistance could ever be. You can learn how to calculate the entity of the drag force at our drag equation calculator! So designing aerodynamically optimized shapes is crucial.

On the owner side, a well maintained, well-lubricated engine will save more gas than low rolling resistance tires. So, if you want to reduce the cost of owning a car, you are better off ditching those expensive tires in favor of frequent and thorough maintenance.

There is one application in which low rolling resistance tires make a lot of sense, and that is competition and racing. If it's pure speed you are after, you're better off buying racing specific tires. And this advice applies not just to cars, but for bikes as well. In fact, bicycle rolling resistance can be even more significant than in cars, let us explain why in the next section.

## Car and bicycle rolling resistance

When we are talking about car vs. bike, we have to take into account the most important differences between them. These are (for our purposes) shape, weight, and speed. For a bike, speeds rarely exceed $40\ \mathrm{km/h}$ ($25\ \mathrm{mph}$) for an average person. In fact, the typical average speed of a bicycle in a city is around $20\ \mathrm{km/h}$ ($\sim13\ \mathrm{mph}$). At those speeds, bike tire rolling resistance is as important as aerodynamic drag.

So, if you want to cycle as fast as you can with the least amount of effort, spending money on reducing your bike's tires rolling resistance could be a good idea. As you level and speed increases, aerodynamics play a more and more important role, making a perfect bike fit a must-have for professionals. For everyone else, we recommend the bike size calculator to give you a good starting point for free.

All that said, there are many people that just do cycling for weight loss. In that case, you're much more interested in putting effort in than you are in how fast or far you can go. So, it will not matter what tires you use, if you put the effort and the hours in, you will see get your results! 💪

## Summary: What you should have learned from this calculator?

Here is a short summary of rolling resistance, to make sure you learned everything you could.

• Rolling resistance is the result of the friction between the road and the wheels. It slows you down;
• Different materials have different rolling resistance coefficients (which can depend on the pressure, temperature, or speed);
• The rolling resistance calculator helps you calculate the tire rolling resistance of any vehicle in a few clicks;
• Low rolling resistance tires are not recommended outside of competition, as there are better ways to save fuel and money; and
• In everyday use, bike tire rolling resistance can have a bigger impact than in cars.