August 7, 2011
FLO Cycling - Component Series Part 4 - FLO WIDE RIDE Rims
In Part 4 of our Component Series we are going to discuss our 24.4mm wide FLO WIDE RIDE rims. We will discuss the benefits of a wider rim vs. a standard 19mm rim.
You can read earlier parts of our component series in the links below.
FLO WIDE RIDE Rims
Why use a wider rim? For most, that is the first question that comes to mind. There are a few reasons why we chose to use a wider rim on FLO wheels:
- Contact Patch/Rolling Resistance
As most of you know, we wanted to design our wheels as an aerodynamic system. The aerodynamic advantage gained by our fairing shape means nothing if the rims and tires erase it. Let's start with rims.
For many years the standard rim width has been 19mm (for aluminum clincher wheels). If you take a look at the picture below you can see the standard 19mm rim on the right and our 24.4mm FLO WIDE RIDE rim on the left.
|24.4mm FLO WIDE RIDE Rim (left) - 19mm Standard Rim (right)|
Many of the more popular clincher tires on the market are available in 20-23mm widths. If we place a 23mm tire on a standard 19mm wide rim, the tire balloons out wider than the rim. You can see this in the picture below. On the right we have a standard 19mm rim and a 23mm tire. You can see the tire is wider than the rim. On the left we have the FLO WIDE RIDE rim and a 23mm tire. The rim width is nearly identical to the tire width.
When we think about aerodynamics and air flow over the wheel, we want a smooth path for the air to follow. If we were to use a standard 19mm rim, the air sees the "buldge" of the tire. This is not very aerodynamic. If instead we use a wider rim, the "path" from tire to rim to fairing is nearly flat and as a result more aerodynamic. You can see the result in the picture below. This is our FLO 60 with a 23mm Michelin Pro 3 Race tire.
|FLO 60 with 23mm Michelin Pro 3 Race Tire - Photo by TriRig.com|
A contact patch is the "patch" of tire that makes contact with the road. There are a few factors that effect this:
- Tire Pressure
- Force (weight)
- Object Shape
Tire Pressure and Force
The equation for the area of a contact patch is as follows...
- Area = Force/Pressure
Envision a bicycle tire while we explain this equation. When you get on your bike and apply your weight (a force) the tire flattens out a little bit. As the tire flattens out, more rubber contacts the road and the "contact patch" becomes larger.
Pressure in the above equation is the amount of air pressure in your tires. Typically between 100-120psi. As pressure goes up, your contact patch area becomes smaller. As pressure goes down the contact patch area becomes larger. Now imagine a flat tire. A flat tire has 0psi inside. This means a bigger contact patch. Take a look at the size of the contact patch on the flat tire in the picture below.
|Flat Tire with Large Contact Patch|
Shape of the Object
The shape directly effects the shape of the contact patch. A round object like a basketball has a round contact patch, and a football would have an oblong contact patch.
What it all Means
We'll start by looking at the rim and tire picture again. The wider FLO rim effects the overall shape of the tire. To accomodate the wider rim the tire becomes both shorter and wider.
Assume that we pump both tires up to the exact same pressure and place an equal force/weight on each tire. The above equation tells us the contact patch area (in number of square inches) will be equal. Since the tire on the FLO WIDE RIDE rim is wider, it's contact patch will also be wider and as a result shorter. Take a look at the picture below.
|Contact Patch Comparison|
In our opinion a shorter and wider contact patch is beneficial for the following reasons.
- Better Handling/Cornering/Stability
- Improved Rolling Resistance
Imagine a friend asks you to stand with your feet together and then tries to push you over. We all know it won't take much effort to push you over. If instead your friend asks you to widen your stance before trying to push you over, your friend will have a much harder time doing so. This is because widening your stance helps to lower your center of gravity and creates a bigger moment about your center of gravity. The same goes for wheels. A wider contact patch will increase stability. This increased stability helps improve overall handling and cornering.
Rolling resistance is defined as the resistance that occurs when a round object such as a ball or tire rolls on a flat surface, in steady velocity straight line motion. There are many factors that effect rolling resistance but we are only going to focus on one for the purpose of this article. That factor is known as the deformation or in our case the contact patch.
Assuming all other variables are equal, the length of a contact patch can increase or decrease your rolling resistance. Take a look at a picture below to help with the explanation.
|Rolling Resistance vs. Contact Patch Length|
The contact patch creates a flat section in the tire. As the wheel rolls forward it has to continually overcome this flat section. The force created by the flat section "F" creates a moment about the hub in the opposite direction of travel. Since the moment is equal F x D, it is in our interest to make D as small as possible. Since the FLO contact patch on the left is shorter (D1) the rolling resistance is less than the rolling resistance of the longer contact patch (D2) of the standard rim.
As engineers we seldom like to talk about our feelings, especially when we can't validate them with numbers or equations. But there are times when things just feel better. In our opinion, and in the opinion of all of our test riders, wider rims just feel better. They roll better, are more comfortable and compliant, corner better, experience fewer pinch flats and simply give you a feeling of stability. You almost feel like you are on rails. When I started cycling years ago I road a standard 19mm rim. The day I switched to wider rims was the day I knew I would never go back.
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All the best,