The 500 cc Racers

I got a real kick out of the last CMRC newsletter story of the return of the JBS 500’s to the track. Mainly, I guess, because a few of these wee racers were still active when I was young and impressionable. The call for more of them to come out and play at set me to thinking. If a retro 500 was built today what would it look like? For sure modern safety requirements would influence the design, but the finished product would still be recognizably a 500.

First up what lessons can we get from history? The first lesson is that despite being the leading manufacturer for the formula over the 10 years or so that it ran Coopers were not always on the leading edge of design. Both JBS and Keift could lay more claim to that role. Even the concept of a Topolino frame with a rear mounted motor cycle engine was first explored by Colin Strang, a kiwi in England. Ladder frames with an upper reinforcing tube were used by Arnotts in England and by JP in Scotland before Cooper picked up the idea. Likewise the four tube frame (JBS) and space frames (Keift) were pioneered by others. What Coopers were very good at was picking up a good idea and taking it a little further down the road. Which means that a study of the evolution of the Coopers is a good basis for our history lesson

The grand-daddy of them all: Colin Strang’s 1946 Fiat Topolino based car.

The general thrust of this seeking of advantage on chassis design can be seen in the progressions below.

Starting with the first production Coopers in 1948.

Here we have a simple ladder frame, based on that of a Topolino (but actually made in house). Suspension, steering and brake components are also largely Fiat sourced. It is an easy concept to copy and many did. But to copy is not to go quicker.

Enter the 1950 JBS. A ladder frame is still there. But its main tubes are smaller than before, with an additional set of even smaller tubes set above them. This is a lighter construction form. Suspension is twin wishbone both ends. This confers more certain geometry and more consistent handling. These were the quick of 1950/51.

But nothing stands still. Next to pop up was the space frame Keift. This has large section light gauge chassis tubes, a 50:50 weight distribution and zero roll resistance rear suspension,. Lighter than the Cooper, and stiffer with better traction and better handling. It was the car to beat for the next three years, and also much copied.

After a couple of false starts Coopers eventual successful response was the not quite space frame all curved tube chassis first seen on their 1954 Mk 8. It used many in house light alloy castings. Lightness was pursued everywhere, and a deliberate move made get a less twitchy high polar moment car. This is a pragmatic frame rather a theoretically perfect one, but with annual detail tweaks it remained virtually unchallenged until the end of the formula.

So where to with a “modern” 500?

Maybe an amalgamation of Cooper and Keift?  But today the very much forward driving  position in the Keift would be frowned upon, as would the over the drivers legs fuel tank on the Cooper. A proper roll cage would also be needed.

I would look at a modified  Kieft frame arrangement with the driver further rearward, a central torque/safety box behind the driver carrying the roll cage, seat belt mounting and a fuel cell. It would look very much like the 1958 Dastle in the photo below.

This even has Keift derived rear suspension, but with roll resistance built in. A good thing really as the zero roll resistance feature of the Keift essentially blocked out the full potential of its very fine and very stiff chassis.

Most period bits and pieces can still be sourced. Say Morris Minor front suspension (ala Arnott). Mini hubs and drive shafts at the rear.  Inboard single disc brake. Manx Nortons are still made at a price, but the late 50’s twin BSA/Triumph maybe not be so pricey. They also have the space saving advantage of a unitary engine and gearbox

This all falls out nice on the drawing board on a 7ft 3 inch wheelbase.

If you really want to escape in reverie for a while check out the “500 Owners Association”. A fascinating website if ever there was one. There you will find, as a final curve ball, that even a bathtub monocoque would be in period. Check out Spike Rhiano’s 1950 Trimax. The Lotus 25 concept to a T, but 12 years earlier.