SEPTEMBER 2019 http://www.racecar-engineering.com 89The next step was to dial in the cornering
speeds. Since ChassisSim is transient lap time
simulation your ports of call are the following;
altitude and road camber; bump scale factors for
the corners; local grip scale factors.
The first and last points are pretty self
explanatory. The middle bit reflects that while
the ChassisSim bump profiling toolbox is good,
it’s not perfect. The bump scale factors help you
fine-tune what the bumps are doing. Typically
0.6 to 0.7 gets you out of trouble and you focuson that when the corner speed deltas (simulated
vs real) are greater then 10km/h. The end result
of all this is shown in Figure 2.
The scales in this chart are speed, RPM,
steered angle (at the wheel), throttle and g
forces. While this isn’t perfect, fundamentally it
is functional and representative – and when you
get to this point you are good to go.
The next step, once the initial correlation
had been dialled in, was to make sure that in
the high speed corners we were in the aerothe front left and right dampers) and rear pitch
(average of the rear left and right dampers). As
always, since this is live data all scalings and
numbers are blacked out. In order to get this
correlation there were some bump rubber gaps
that needed to be corrected. Before and after
aero coefficients are shown in Table 1.Delta force
Again, since this is a live racecar I can’t give you
the absolute numbers, which is why I’ve given
you the deltas instead in Table 1. The magnitude
of these deltas does not surprise me. For
something that has seen a combination of wind
tunnel/CFD these offsets are pretty typical. The
why of this I discussed in my last article, which
focussed on how you should treat your dyno
results (see the August issue, V29N8).Table 1: Global aero coefficients – baseline compared to final model
Item Baseline Final
CLA Max Bline -9%
CDA Max Bline 0%
Aero balance offset Bline +4%Figure1: Endof straightaerocorrelation
Figure2: Finalbaselinecorrelation