DESIGN OF LOW PROFILE FRAMES (Jim Cook MCEI)

Summary of changes to rider’s position and education.

 It is sometimes difficult to get the rider to accept major changes to his position, because he, like the vast majority have been fed a diet of garbage by the cycling press and amateur coaches, who in the words of one of the best “could not teach frogs to jump”.

• 1. Move rider forward over the B/Brkt this will increase GME by approx. 2%-3%.
• 2. Position Tri-Bar pad height and width to eliminate neck and shoulder problems. ( the rider usually wants to ride as low as Chris Boardman, remind him that he is not Chris) too low is as bad as too high, ( this is pretty hard for the rider to grasp)
• 3. Explain that pulling on the bars only increases pulse rate not linear speed.
• Again the principle of muscles not engaged in propulsion should be in a relaxed state. Modern swimming techniques in the American crawl has the legs in almost a passive role, the major groups for propulsion are the arms.
• 4. Reduce frontal area, show rider video shots from the side and front of new and old positions. The upper body and arms should now be almost parallel to the induced airflow.
• 5. Get the rider to conduct his own roll down tests, ( it lays the aerodynamic crap to rest ) now is a good time to test the scoop effect of his old position. He can also measure the over stated effect of various components.
• 6. Introduce the rider to breathing control. ( see Breathplay Web site )
• 7. Remind him that riding a 100 T/T one week is not speed training for a 10 P/B the next week. When was the last time Linford Christie run a marathon in training for the 100 yards?

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Tubing and Construction of Low Profile Frames.

I must confess a preference for Columbus NIVACROM steel Tubing, As the design calls for seat angles of 78—85 degrees the frames are fillet brazed using 9% Nickel Bronze. (Lugs and bottom bracket shells are produced for standard 73 degree angles) The fillet size through the throat should be 3-4 times the thickness of the parent material with a leg length of times 7 to give 100% joint efficiency. I prefer to use the type” L “ 50X32 Megatube as the down tube, it’s a good aero shape, also the D/T is main structural member in the front triangle, this gives the frame its inherent stiffness.

  The front triangle is completed in the multi jig, by this method as opposed to only tack brazing in the jig, perfect alignment is maintained. Cold setting of the finished frame is eliminated resulting in a stress free structure.

Setting of the rear triangle is with a true dished wheel and fore/aft jig rails. Rear vertical dropouts are polished investment cast stainless steel, they are stronger than the normal steel types and less prone to stripped threads on the gear hanger. After painting I treat the frame internally with a rust inhibitor. The whole process from start to finish takes about 60-70 hours.

 The mechanical characteristics of the Nivacrom tubing are retained following the brazing process; this is achieved by the addition of Vanadium and Niobium. These elements prevent the formation of chromium carbides and refine the grain structure in the parent material. This prevents brittle fracture in the heat-affected zone and increases fatigue life of the finished frame.

 The tubing material is designed specifically for bike frames and the various welding /brazing processes applied to frame manufacture. In the Welding Industry, weld procedures are developed to produce mechanical properties equal to the parent material, the real clever bit is to design an alloy steel (Nivacrom) that after the joining process the original mechanical properties are retained without further thermal treatment. The chemical composition has a minimal effect on the actual performance of the frame, tube diameter, tube length and wall thickness are the determining factors in frame rigidity. Again the cycling scribes write some utter nonsense about tube types and aerodynamics, but their description of welding and brazing methods are hilarious, they must be extracts from their favourite comic book.