If you cut out a sectional profile of any rim, you will find there are two horizontal walls creating a chamber, an outer wall of material, and an inner wall of material (the tube well). On any traditional rim, both of these walls are concave. Meaning they both curve inward like a bowl. Note: It’s easy to find sectional profile drawings on any rim maker’s website. Now, take a look at the Oohbah profile on the attached photo. The inner wall is curved outward, or it is convex. This is very important. The effect of one concave wall and one convex wall create a second feature of “hoop strength” in the sectional profile. In essence this allows the rim to approach a toroidal shape, which has the lowest mass and highest stiffness on all planes. This adds immense additional rigidity to the rim as a whole. It creates a positive force of resistance to deformation of the rims straightness and sidewalls (vertical walls), as well as lending further stiffness to the rim, (which improves performance). Think of it this way…If you take an egg, and apply equal force to two sides, it is remarkably strong. Now, if you took two haves of the same shell, and put them together, both in the same direction, they could withstand very little force without caving in. The incredible stiffness and strength that results allows us to reduce the thickness of the material, reducing weight.
It is also worth noting that the “wave” shape of the inner tube well wall on an Oohbah rim, is also far stronger than an traditional design flat or curved wall. A great analogy to explain this is corrugated steel roofing, which can easily support your weight if you walk across a roof. Flat sheet metal of the same thickness would buckle and fail immediately under the same force. On other rims, as the curved tube well bends downward under pressure, it pulls the sidewalls inward causing them to fail and eventually collapse. Oohbah tube wells stay stable and support the side walls, maintaining the form of the rim.
Having a lighter, stronger design affords us a really cool opportunity. It allows us to create wider rims than anyone else at equal or lower weights. The wider a rim’s material, the more rigid the hoop is. Rigidity means less of your energy goes into flex, and more to the ground and your cornering and braking performance are improved. Wider rims also mean greater “tire spread”, meaning more of your tire’s treads are in contact with the ground, and your “traction” or grip on the ground improves. So, wide rims equal better stiffness and traction. If you look at any of our competitors’ rims, compare weights to find similar models, and then compare widths, ours are usually 5 mm or more wider, (and often still lighter).
The second major feature is the addition of a second set of “beadnips”, on the inner wall of the rim. Beadnips hold the tire’s bead in place (the bead-seat) when you are riding. Almost all rims have one on each side of the rim, at the top of the vertical walls. They keep the tire’s bead from slipping upward and coming off the rim. That is very important. However, there is a second type of flat that called snake bites, or pinch flats. This is when the bead of the tire slips inward, out of the bead-seat, toward the center of the rim. Then the sidewall of the tire collapses, and the tube is pinched, creating two holes (top and bottom of tube), and a flat tire. We have added a second set of beadnips, on the inside of the bead-seat. This keeps the tire in the correct position, even when riding at very low air pressures. Anyone who rides will understand that sometimes, especially on rough and loose terrain, that lower tire pressures improve traction and comfort. With other rims, when you lower your air pressure you run a high risk of pinch flats. Spank rims can run much lower air pressures with significantly reduced fear of flats! That’s Oobah!”
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