In the 1950's & early 60's, most chassis were made from 1" (25mm) o/d mild steel tube. From then to the 1980's the size increased to 1 1/8" (28.5mm) o/d x14swg (2mm) wall thickness tube. Since then the trend has been to use 1 1/4" (32mm) x14swg tube. I would say that throughout this time, the majority of karts were made from "ordinary" CDS/CFS (Cold Drawn/Finished Seamless) tube. A few non-gearbox karts and rather more gearbox karts have used "Chrome Molybdenum" tube, and fewer still the superior T45 spec tube, but chrome moly tube presents difficulties in welding without losing the mechanical properties unless bronze welding. For the home builder the bigger diameter & tougher material presents problems forming the bends unless spending lots of money on bending equipment, cheapest option is a ratchet tube bender.
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