The evolution of the Sarma Naran carbon fat bike rim

Jul 11, 2016

 

 


Sarma Bikes - a company with roots from Siberia. Not only do we get the pleasure of producing and riding our bikes and components, we also try to develop and improve our products using a group of the best engineers from the aerospace industry.

In this article we would like to tell you about our progress in improving the design and how often seemingly minor changes can significantly improve the product.

We released the first Naran 80 carbon rim in November 2013. Since the start of production our engineers have constantly looked at ways to improve the product and in the last two years we have identified several important steps for improving the function and performance of our rims.

1. Prototypes.

It all begins with the prototyping and the design of the rim during a six month period prior to the start of production. This is a job that is carried out by a group of engineers with extensive experience in the manufacture of composite products for the aerospace industry. 

At that time it was decided to work with the double-walled embodiment of torsional rigidity and overall strength as the main focus of design. Our desire was to create a rim resistant to the stress of year round use. A double-walled rim design can be slightly heavier than using a single-walled rim however it is much stronger and of better torsional quality.

2. Changes to the profile geometry

After production of the first batch based on a review of the actual operation we realized that it is possible to raise the strength of the rim due to small changes in the angles on the walls of the rim (or profile geometry). The rim profile has become more rounded which in turn enables the rim to better dampen and absorb direct strikes. (for example, if your rim comes into contact with set in rocks or is accidentally struck by a flying stone) it then distributes the load of impact on the entire structure, not just concentrating it on the bead hook area or point of contact.

3. Changes to the inner part of the rim.

This is perhaps the most unobtrusive to the customer without a change of engineering education however still very important.
bigquotes In the production of the first versions of the rims, we used a special plastic bag to create pressure inside the rim when baked in the oven.
The rim was placed in a metal matrix, and the air bag is then inflated to contact the inside walls of the rim. After heating the matrix and the rim to a specified temperature the pressure inside the rim is no longer required and the remains are removed through a small opening. This technology is proven, but not perfect. There were cases when inside the rim formed small waves visible to the eye.

It was then decided to change the process and use a new technology.
Using this new technology we have achieved a significant improvement in quality of the inner surface of the rim which in turn increased the overall strength by 10-15% while maintaining the same weight. Also changed was the internal profile of the bead shelf to provide a better mounting and seal of tubeless tires.

In the development of the first rim the tubeless concept was a top priority. It was also important to find a compromise for the design of a special trough in the middle of the rim also known as the drop center which allows the tire to be easily mounted and removed by placing the tire beads in the drop. The profile of the drop is very important to allow the tire when inflated to move outward toward the bead lock which makes mounting and changing tires very easy to do. In the first version it worked well however after more experience mounting tires from the many manufacturers with different TPI and tire construction, slight alterations were made to the angle as well as the depth of the drop to make the rim function even better.

4. The introduction of a metal matrix and the use of a hookless bead.

The most significant improvement made however the hardest part of the production to change. It requires the use of highly skilled engineers as well as a significant investment in the manufacturing process.

Considering the difference in production with the rims produced being "baked" in a rim oven. 
The appearance of it in this state little resembled the rim itself. Then the upper part of the Carboniferous was cut and the silicone removed .
This approach had a number of shortcomings. Firstly, cutting of the fibers. Secondly, the silicone material being soft did not always form the grooves in the bead shelve area consistantly which sometimes led to rejecting the rim.

With the new process there is no use of silicone or cutting of the rim wall.
Based on extensive experience it is now possible to accurately calculate the amount of pressure that the metal matrix then applies to the wall of the rim when heated.
With the help of this method of production we have improved virtually all important components of the rim.
Metal matrix produces a very precise forming of the rim which gives a number of advantages. Firstly, the rim has become much more resistant to higher pressures. We were able to increase the maximum recommended pressure of 15 PSI to 20 PSI, however tests have shown an increase in the maximum pressure more than 100%!
Secondly, the surface became considerably smoother which now makes beading tubeless tires even easier!


We have come a long way to improve our products and the end is not yet. We hope that you get as much pleasure from riding as we enjoyed the process to achieve the best results to provide you with the very best products!
 

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