It was an interesting coincidence that you should feature the Lotus Mark IX in the same issue of your magazine as the Vanwall, because these cars have a firm historical link. As helper to Colin Chapman on the design side I remember that the Vanwall’s rear suspension was just a scaled-up version of the Lotus, and your articles reminded me of an incident…
The same type of jig for the de Dion tube that we had used for the Lotus IX was used on the redesigned Vanwall. I did the drawing for this, and Colin asked me to come to the Vandervell works in Acton where the Vanwall was being built. Colin explained that the Vandervell people were very concerned that no limits had been shown for the overall length of the piece of channel section Rolled Steel Joist (RSJ) that I had specified. In fact, it would not have made the slightest difference if it had been three inches longer or shorter, but Colin thought we would have a bit of fun.
He waited until they asked the question again, and turned to me. “What do you think, Peter?” After some moments thought I replied, “Well, plus 10 minus zero, I would say”, meaning that it would have to be cut to a tolerance of 10-thousandths of an inch. “That’s fine” they replied, happy now to be able to carry on!
To elaborate on the difference between the production Lotus Mark IX frame and the works spaceframe, the one shown in your cutaway drawing is the frame that Frank Costin had told Colin was “too heavy” when they had first met. It had 1.875in diameter lower tubes which were far bigger than needed to take the load. Frank said he was only interested in “aircraft design principles”.
The ‘works’ Mark IXs, which were known as P4s, had a completely different chassis frame designed by Mac McIntosh to full aircraft design principles, with tubes of only 1in diameter top and bottom, and one even had a detachable member across the top of the engine bay. Two of them were made, the first, with magnesium body, for the 1500cc car, and the second, with thin-gauge aluminium body, for the 1100cc car which ran at Le Mans. They were the forerunner of the frame of the Lotus XI which came out the following year.
I am, yours etc,
Peter Ross, Historic Lotus Register, Falmouth