Carbon Fiber Frame Conversion
A couple of months ago Steve called me and asked if JBobs could be used for carbon fiber frames. He had been searching for couplings that he could use on his frame but wasn't having any luck with the well known sources until he found the GroupJ website. I told Steve I thought JBobs would work well but that we had not yet done a conversion. But, if he was willing to participate in an experiment, I would be willing to convert his frame in exchange for engineering data on how well the conversion worked. Steve did not hesitate, and within a week or so I had a nice used Scattanti CFR frame delivered via UPS.
The frame has nominally round tubes with the top tube at 31.75mm and the down tube at 39.6mm. There was significant taper in the down tube as it approached the bottom bracket, which dictated the BFC location.
The stainless steel JBobs are joined to the carbon fiber tube (CFT) using high shear 100% solid epoxy and techniques developed in sail boat and motorsports applications. Before cutting Steve's frame in half, we ran some tests to insure that the metal-to-CFT bond was stronger that the parent tube. Test were run on a 26mm diameter CFT bonded to to a -8 STD JBob, subjected to a cantilever bending moment. The test demonstrated that the CFT collapsed under bearing load with the metal-to-CFT bond in tact.
Steve's frame, while not new, was in nice shape so I wanted to demonstrate that JBobs could be installed without damaging the paint and clear coat. A potential advantage to carbon fiber frame conversion is elimination of the need to repaint the frame. A technique was developed to incrementally fit the couplings such that the prepped tube never extended beyond the coupling.
Stay tuned as Steve tests his new travel frame and we learn how well the bonding technique holds up.
My first impression when I took it out of the box was how the silver couplings contrasted with the black of the carbon fiber frame and I really loved the contrast it brought out... a uniqueness of the frame and I truly loved it. Also the weight of the frame seemed essentially the same although I didn't have a before and after weight. I was surprised at the joining of the coupling to the frame in the sense that my mind has this impression of welds from a steel frame but this was so clean, not a bump or scratch. At first I was skeptical about the couplings themselves, I expected that one coupling would mate with the other with more than just a few millimeters of tubing inside the other but when I removed one clamp the frame itself was fairly firm with great alignment. I did get a Ritchy torque wrench to prevent me from overtightning but certainly it is a solid frame with these couplings. I loved the way the brake cable runs, maintaining the routing through the top tube. But I still have not built it up with components and ridden it to see and get the feel of it on the road but I will surely let you know. Again the look of it is so one of a kind I tempt myself to use it as my regular bike .I also have been shopping for a travel case and how it fits in the case is another issue but right now I love it. Thanks again. Steve
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Al James, Founder GroupJ Engineering