8. feb. 2014

Rolling Resistance Of Bike tires

Earlier we wrote about how the air resistance increases heavily when increasing your speed. Now we will look on the rolling resistance developed between the tires and the road surface. I will try to make you understand how this works. First, we will have to look on how the rolling resistance is found. That can be done by using equation 1 below:

The equation that shows how great the rolling resistance is. The variables are:
  • P is the power needed from the rider to keep the velocity. This power is measured in Watt [W].
  • Crr is the rolling resistance. This value varies greatly from tire to tire and from the surface being used. There are some few numbers below here from Wikipedia:

Specific tire        
Minimum value
Maximum value
Production bike tires at 8,3 bar on rollers
Typical BMX tires

  • N is the normal force of the bike and its rider against gravity. This force is measured in Newton [N], and can be found by the following equation, equation 2:

In this equation, we have the following variables:
  1. m is the mass of you and your bike. This is measured in kilograms [kg].
  2. g is the gravitational force. This force is 9,8 m/s2.
  3. Cos(θ) is Cosine to the horizontal angle. If you are riding on a flat road that would be 0 degrees which equals 1. So on a flat road this is nothing to worry about. But of your are climbing on a mountain or hill, or descending, it has to be taken into consideration.

But as we already saw with the drag, the power needed is different than the force you are experiencing. The equation for the power required is shown below in equation 3:

There is only one variable that we have not met before. That one is:

  1. V is the velocity you are doing. This is easily measured by your bikecomputer http://www.cyclingtipsonline.com/test/bikecomputer-reviews/ . This is measured in meters per second [m/s]. If you want to convert your speed from kilometers per hour to meters per second just divide by 3,6. If you want to change it from meters per second to kilometers per hour, multiply by 3,6.

What this simple equation got, is the rolling resistance multiplied with the velocity. That means that we can put it in equation 1, along with equation 3, and therefore can make it into a single equation, if you want to find the power required at variable speeds. That gives us equation 4:

Calculation of examples

Lets make a few examples at different speeds. We will take 20 km/h, 30 km/h, 40 km/h and 50 km/h. We say that the rider weighs 70 kg, which is a decent average. The road is also 100% flat. The rolling resistance coefficient of the tires will be 0,003.

If we start off at the 20 km/h, that equals 5,556 m/s. So the equation will be:

As we can see, the rolling resistance will account 11,43 Watt. 
At 30 km/h, the equation will be:

Now it has become 17,15 Watt. In a 50 % speed increase, it has increased around 50 % too. At 40 km/h it will be

The value has now increased to 22,87 Watt. As you can see, that is about the double of the value than it was at 20 km/h. So the power required increases linearly with the speed. If you double your speed, you double the power required to overcome the rolling resistance.
However, what if we are having some nice tailwind? How much power will we need to overcome at 50 km/h? That can be found in the equation below:

At 50 km/h the tires are now creating a resistance so great, that you now need to power 28,58 Watt in order to maintain your speed.

Nevertheless, remember, these numbers does not account for much more than just theory. Every tire acts different, and even the smallest difference in production of the same brand of tire can give them two different friction coefficients. And the drag you will experience because of the wind accounts for a much larger value than the tires rolling resistance. Nevertheless, if you want speed, try checking the Continental GP4000S out. They were the fastest clincher tires in the German magazine “Tour” test.
If you want to decrease the rolling resistance as much as possible, ride with a high pressure in your tubes. The higher the pressure the lower the rolling resistance. That is due to the harder the tire will bounce over just the smallest roughness in the surface. But that is different on a mountainbike. On a mountainbike in the forest, a low pressure would actually make you go faster. 
But try to read here why you should focuse on buying good tires before spending much more on a pair of wheelset. You will actually be able to win more speed by changing your tires than your wheels!

Written by René

Read more: http://www.cyclingtipsonline.com/news/rolling-resistance-of-bike-tires/

2. feb. 2014

Craft Elite Jersey Test

Craft is one of the biggest producers of cycling clothes around the world, and sponsors the World Tour team Trek, which includes Fabian Cancellara, Jens Voigt, The Schleck-brothers, etc. The Swedish based company has produced sport related clothes since 1977, and is known to deliver clothes in great quality.

(Note, the jersey's design is from my bike club)

On the road
I have been testing the Shirt, which according to Craft, should be aerodynamic, light, and have a great fit. Well, I can certainly say that they seem to be aerodynamic, because you are able to see every gram of overweight on your torso if you wear the shirt correctly. It is very comfortable though. The fabrics got a great stretching-ability making sure that it fits all different kind of body types. No matter if a rider needs a size medium, and either got big muscularly arms or small mountainrider-ish arms, the same size of the shirt can fit you. I am in the last group, but guys with much larger arms fits the same jersey just as good as me.

The shirt got a total zipper from the neck to the bottom, so it is easy to take on and off, unlike some other shirts that only have a half zipper, or none at all. It makes it a lot easier to put on and take off, along with you can zip it a bit down on hot days if needed.

Since the fabrics are not that thick, sweat transportation is almost impossible. Therefore, you would need a sweat-absorbing shirt underneath the Craft-shirt to make that problem go away. However, on super-hot days, it is really nice to wear because overheating won’t become a problem. It lets a nice amount of wind cool you down. I personally find temperatures above 16-17 degrees Celsius, on a sunny day, fine for this jersey.

The shirt got four pockets on the back. Three of them easily accessible, while one is placed on top of the middle pocket, with a zipper. Therefore, you can put valuable stuff in the pocket with the zipper, and do not have to be nervous if it falls out of the pocket during the workout. A nice feature I have been using a lot for my cellphone and money for a pit stop during the ride. Nevertheless, the three other pockets are easily deep enough to stop stuff from falling out of them 999 out of 1000 times.

The verdict
This is a nice shirt! Craft have really done a great job designing this. They have thought of about almost everything and every detail, to make this shirt great in all different kind of scenarios. It is both aerodynamic, comfortable, and practical, and even after a long time, the colors of the fabrics have not faded at all. So if you want the best of the best, these may be the pair you should take a look on.

Written by René

Read more: http://www.cyclingtipsonline.com/news/craft-elite-jersey-review/

1. feb. 2014

Beetroots, mustard, and chocolate milk can make you go faster

You are what you eat. That is a sentence you have heard a few times already in your life. Your diet is important and it does matter what you put in your mouth at the dinner table – especially when you are training. Protein is great for the muscles and carbohydrates are great for longer training sessions. However, did you know that there are a few things that will be almost as efficient as doping?

The mustard plant contains natural steroids
The mustard plant contains the same materials that makes anabolic steroids efficient, but without all the drawbacks. The specific type of steroid the mustard plant contains, is called the Brassinosteroid. Studies from North Carolina State University in the United States of America showed that mice that was given mustard increased their protein synthesis, which means that it increased their fat burning and muscle power compared to mice that did not get any mustard. That means that you can build up stronger muscles in the same amount of time, along with lowering your amount of fat. For any bike rider that can be a massive gain, especially in hilly races.

Beetroots will increase your endurance
However, if you are not a big fan of strong tasting stuff like mustard, there are other solutions. Beetroots are another fine example. They do not help you with building muscles, but will give you some extra stamina that can make you intensify you training sessions. A study from Exeter University in the United Kingdom showed that a group of younger men who was given beetroot juice were able to train for a 16% longer time, and could cover the same distance 2% faster compared to not getting any beetroot juice. Their blood pressure were also lowered by drinking the beetroot juice. Speculations are that the Oxygen absorption in your body lowers when given Nictric Oxide from the beetroot juice, giving your body an extra amount of Oxygen in surplus for when needed. It is like a car with 99 octane petrol will always be able to go longer and faster on the same amount of fuel, than if it was given 92 octane.

Chocolate milk will make you recover faster
But that is just something you can do when you want to. Another thing you can, which probably most will like, is that after each training session you should drink a glass of chocolate milk. Studies from James Madison University found out that low-fat chocolate milk was superior to any carbohydrate beverage when it goes down to getting the muscles to recover as fast as possible. The studies found that the 13 males that were tested had lower levels of creatine kinase than the people who did not drink chocolate milk after each training. Creatine kinase is an indicator of muscle damage, so the lower the level of creatine kinase is, the more recovered are the muscles. Milk alone is also efficient, but the chocolate milk got some extra nutrition’s that will lower the recovery time even more. Recovered muscles are very important in order to get the maximum out of your next training session, and if you do not make your muscles recover, you will not gain any additional muscles until they get to recover probably. 

Nevertheless, what is your routine? Do you do anything like this at all? Do you have any additional types of food that also will make you a stronger athlete? Please tell us in a comment below!

Written by René

Read more: http://www.cyclingtipsonline.com/news/beetroots-mustard-and-chocolate-milk-can-make-you-go-faster/