Why should we be interested?
Well, the problem is that the misconceptions of the past still affect us today. Have you heard anything like “maybe if I could get a bit more compliance in the suspension/allow the car to roll more, I could get more feel/better grip/ more heat in the tyres.” This is NOT where would start to fix issues with a car, adapt to a new tyre, or indeed to do a new set-up.
In the 60s, for open wheeler and sports racing cars, you can imagine that there would have been a distinct philosophy at play in guiding designers as to how stiff the cars should be. That philosophy was soft springs make more grip. There must have been NO track testing aimed at disproving this theory.
We can also speak from experience on cross ply tyres of similar construction to tyres in the day, that tyre construction was not a reason to run so much softer.
“Racing and Sports Car Chassis Design” by Costin and Phipps. My copy is a second edition, 1965. In talking about suspension stiffness, “Here the present trend is towards lower frequencies of around 70/80 cycles per minute (CPM).” Now that’s low. I don’t know what cars they’d be referring to. I suspect that the Coopers with the transverse leaf spring couldn’t have physically gone that soft.
It could have been they included the tyre spring rate in the frequency calculation. If so, 70/80 CPM might be equivalent to 90/100 CPM at the wheel centre, as we calculate it.
Recently, we got to see what spring frequencies Lotus was using at the time. Peter Boel from NZ, racer and 1960’s open wheeler aficionado, was using our Weight Transfer Worksheet™ to check the set-up on his two fantastic Lotuses – the Lotus 41 and Lotus 51. Yep, both running around 100 CPM. Wow, lower than I would have guessed.
They weren’t backward about cranking on the anti-roll bar stiffness though – with up to 80 - 90% of the front roll stiffness being done with the anti-roll bars. The designers main concern was keeping roll within reasonable bounds for control of the camber angle. They must have had a complete disconnect in their thinking between the ride stiffness and the total spring stiffness at the tyre, when the car has taken a set in the corner.
Total Stiffness at the Tyre in Roll = Roll Stiffness due to Spring + Roll Stiffness due to Anti-roll Bar).
In racing, of the total stiffness in roll, we want to do as much as is viable with the spring. See our General Suggestions for Spring Frequency below.
The designers would have done the calculations to make the cars stiff enough in torsional twist for the significant anti-roll bars used. So today, we can fit up suitable springs, and know all will be well. The cars are going to be way better everywhere with the extra spring stiffness – more responsive, more grip and less pitch.
A good spring frequency to choose for a modern production car, sports car, sports racing and open wheeler (all non aero cars) is around 150 CPM. Historic cars most probably need to be softer around 135 CPM. We pick up exceptional increase in grip and response by going up in spring frequency.
What happens if you go too stiff? The benefits will taper off. If you have a super stiff front end, the car may turn in great and then wash out into understeer. Then, if you increase rear stiffness to balance it out, it may now work OK. But, you could find the car is still good if you decrease stiffness to the recommended 150 CPM. If it is, then balance adjustment via the anti-roll bars will work better.
To be able to run massive torsional stiffness you have to have a chassis stiff enough, so that the difference in roll stiffness front vs rear can still work. A chassis not stiff enough will dissipate the difference in roll stiffness.
Modern Formula Fords in particular (cars with no aero) can “sneak up” in spring frequency (people think they seem to be better with stiffer springs) to over 200 CPM without proper back to back testing. We recommend to go straight back to around 150 CPM and do a proper back to back test.
With aero, modern sports racing cars, we suggest just work with the maximum suspension travel you think you need. It should not be faster on 220 CPM, for instance, if 180 CPM can keep suspension travel in reasonable bounds for the circuit your racing on ie depends on the downforce you are generating. Time attack cars also.
See the details here: https://www.suspensionsetup.info/store/RcWQdHtt
You can calculate what springs and anti-roll bar you need for best balance. Gives you access to all the Weight Transfer Worksheets™ for 99% of the cars out there.
To help with understanding set-up issues and problems, we show you a full understanding of how the cornering forces are developed at the tyres, and how the driver senses and then controls the motions of the car.
That link again, to check out the course: https://www.suspensionsetup.info/store/RcWQdHtt
In the 1960s and 70s, the way the tyres and driver control worked was not well understood.
The driving of the car was, in most part, instinctive. In other words, any techniques the drivers used were almost entirely self taught. This probably extended to racing team managers as well. They thought the good drivers had an innate skill, but that they were a necessary evil in the process of winning races and demonstrating the superiority of the team's engineering skill and the aura of their brands. Of course, as far as motor racing fans were the concerned, the early great drivers were, and are, amongst our most treasured sporting heroes.
In the 1970s, Australian race car manufacturers dominated the TAA Driver to Europe Formula Ford Series (a national championship), winning every year from 1970 to 1979.
The picture shows my car leading in 1974, a Bowin P4A (see foot note). Running second is Paul Bernasconi in the Mawer (this could have been the first race for the car). The Mawer went on to win two championships with Paul in 1975, and Russell Norden later. Just coming into the picture is Geoff Brabham in a Bowin P6.
All the Australian manufacturers won races and had their time in the sun. These were quick reliable, well engineered race cars in their day. But because of the lack of understanding about
First race of the year (non-series round). First race meeting on Dunlop slick tyres. I gave Skello (previous owner and 1972 Champion in this car) a one off drive in exchange for an engine rebuild by Bruce Richardson. This is the first lap and the race is about to be red flagged. Skello got swamped on the re-start. The car never went on these tyres and their was no help from the factory (not enough knowledge in those days. Also terrible choice of mandated tyre for the series.)
There after the series changed to a road car radial tyre, beginning the dark ages for the Formula. At least the P4As were competitive on road radials, winning a couple of championships with John Smith and then John Wright.
Then in the early 80s, on a proper Formula Ford race tyre, the category started to recover. Stiffer spring frequencies were part of the improvement in lap times in the 1980s.