Theory
You do several things when you set the static ride height:
The roll center (or sometimes, roll axis)
is the an imaginary point about which the car rolls
left and right. It's usually below the ground.
There will be one roll center for each end of the car.
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In general, you want to set the ride height to be as low as possible, to get the CoG as low as possible. A lower CoG produces less lateral load transfer (so you can corner harder before you overload the tires), less longitudinal load transfer (so you can brake harder before you overload the tires) and less body roll (because the CoG is not as far above the roll center(s)). It's a leverage thing - imagine a pole sticking vertically out the top of your car. Waggle the pole around. The longer the pole, the more leverage you can get on it, and the easier it is to move the car around on its suspension. A shorter pole will require more force on it to move the car around. Now imagine a pole extending upward from the roll center to the CoG; having a higher CoG is just like having a longer pole.
However, there are times when a higher ride height will produce a better performing car:
Altering the difference between the front and rear ride heights can be used to alter the balance of the car. Lowering the front in relation to the back creates an angle of rake.
Increasing the rake angle decreases corner entry understeer, but decreases traction available at corner exit. How does this work? Well, lowering the front in relation to the rear lowers the CoG of the front, decreasing the amount of roll leverage acting about the front roll center, effectively stiffening the roll resistance of the front, leading to less weight transfer from the inside wheel to the outside during cornering. Since the weight is now distributed more evenly between the two front wheels, the front of the car will get a little more grip. Also, lowering the front moves the CoG of the car forward a little, giving more initial grip before roll transition.
Conversely, decreasing the rake angle can make the car understeer a little into the corners, but gives great traction out of the corners.
Application to GPL
I think that low ride heights, while not cheating, are not in the spirit of the simulation and I feel guilty when I use them. The AI cars don't have 1" ride heights and neither did the real cars in 1967. Plus, they can make the cars too hard to drive, and if higher frequency bumps were modelled, then (I believe) 1" ride heights would be unusable. I'm relieved that they have been outlawed by the 1.1.0.3 patch from Papyrus; now we don't have to argue about it anymore.
Wolfgang Woeger, from Schubi's forum: I'm not sure how much slower you really are with the higher setups. I tested it ... and found the higher setups way easier to drive ... Cars go easier over the bumps and even braking and accelerating is easier (not faster) ... I did my 3:13 laps in Spa all with a low (1,0 inch) setup, but I tried a high one (2,5 inch+) too, and could also get a 3:13:9x after 5 laps.
Ian Lake, from the APEX forum: Low ride heights do not make you that much faster ... the difference in times by running 1 inch to 3 inch setup is about 2 tenths of a second (averaged over a 1 minute period, say the glen)... That's not very much is it?
Even the new minimum ride height, 2.50", is too low. Folks are finding that at 1.00", they're on the bump rubber all the time, and that's effective. But at 2.50" they're impacting the bump rubber too often and too hard. Ian Lake, again: I was experimenting with a new 2.5inch setup, as well as my 4inch setup. I stayed with my 2.5inch setup right up until qualification, when I switched back to my old setup because the 2.5 one felt really bad through some sections. I took the 4 inch setup out and picked off a time of 7m58s. And the corners I had trouble with (actually some of the fast sweepers), were actually easier to drive. I can't really describe it, but it felt like 2.5inches was slower than a 4inch setup.
I've come to the same conclusion myself at the bumpier and twistier tracks: for example at Zandvoort I found that a 2.50" setup was about 0.4s slower than the same setup raised to 3.50". It was because the higher setup let the suspension smooth over the bumps, which let you use more throttle in the corners. Also, the higher CoG meant that more weight was being transfered to the rear wheels under acceleration, which gave more traction out of slower corners. These effects overcame any loss of performance from the raised CoG, resulting in a faster average lap time.
Even at smoother tracks, a SRH of 2.50" requires fast, accurate inputs in order to keep it on the edge of traction all the way through a corner. With a SRH of 3.50", the car requires slower inputs to keep it on the edge of traction, so therefore it can be kept on the edge more consistently, so therefore it spends a greater percentage of it's cornering time at or near the edge of it's traction budget.
I went along to the Donington Grand Prix Collection, and stuck a ruler underneath their Brabham, BRM, Eagle and Lotus 49. They were all about 4-5" off the ground (the Brabham was little less) and all slightly lower at the front than the back. I know this is hardly conclusive - they may well not have raced like that - but it ought to give a ball park figure. The point is that they certainly weren't 1 or even 2 inches off the ground.
Using a 4-5" ride height in GPL just doesn't look right, so I usually set the static ride height at around 3-4", which looks about the same as the AI cars, the period photographs and the footage in the introductory AVI file. (the wheel rims were 15" in diameter front and back, the tyres were 9.5" wide at the front and 12" wide at the back, if you want points of reference, but remember to allow for rolling and pitching).
The 'proper' ground clearance certainly makes for easier driving. The importance of this in a race cannot be overstated; when mixing it with several other cars into a corner, you just do not have time to baby the car. Also - when coupled with the softer springs that the suspension travel now allows - you can use the kerbs more liberally; you can run over them at Kyalami/Barbeque, Monaco/*, Rouen/Paradis, Silverstone/Chapel and Silverstone/Abbey without ending your race.
How do you chose the static ride height? This will largely have been decided by the designer of the car. For any car, there will be a 'natural' ride height that permits the suspension maximum movement in bump and rebound. In GPL, this height is easy to spot: look at each car from behind, and adjust the height up and down until the drive shafts are parallel to the ground.
In '67, you would tune your car with sway bars, springs and shocks.
The designed OPTIMUM suspension geometry dictates a specific ride height.
The designer would settle on a suspension geometry that gives the best camber curve
and roll center height that he thinks would do the job.
Initially, springs and roll bars are selected from the roll center height
and center of gravity height, weight bias, anti squat, anti dive, etc.
Then the driver would go and sort the mess out.
Generally you would settle at a ride height somewhere near what the designer intended,
unless excessive bottoming is occuring at certain tracks.
A large change in ride height means that a basic suspension design error has occured.
Necessitating a major rethink or rebuild.
-- ‘brian’
The 'natural' ride heights for the GPL cars are about:
"Ah but", I hear you say, "the AI cars don't run at those ride heights, do they?" True, they always run a little lower than the 'natural chassis height'; see the cars data table for more details.
After setting the car to this 'natural' ride height, do one of the following:
...and/or one of the following:
However, you always set the ride height in conjunction with setting the wheel rate; the two are closely linked. I use a simple rule of thumb for co-ordinating the two.
In 1967 the cars would all have had some +ve rake (front of car lower than back of car), so that airflow under the car would generate some downforce. Since airflow under the car isn't modelled in GPL, you can use zero or even -ve rake without losing any downforce.
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Dr Bunsen Honeydew experiments... We know that, while lower ride height can increase aerodynamic downforce, a higher ride height will reduce aerodynamic drag along a straight due to better airflow under the car. (Which might explain why a higher setup is so quick at Spa, where top speed is critical.) I tested this theory by measuring Vmax at fixed points at the end of the longest straights. The result? The same Vmax, whatever the ride height. So I guess airflow under the car isn't modelled. |
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