Okay gang, I'm seeing, more or less, the sort of responses that I was expecting to get so, here's what I've been working on...
As we know, by reviewing telemetry data, front end camber is affected by several things. Of course there's the obvious static camber that we adjust at the top of our alignment tuning screen. Then, there are dynamic changes to camber while on the track, caused by weight transfer/body roll. These forces cause the outside wheel's suspension to compress and the inside wheel's suspension to extend during cornering. ARBs would also have an effect on camber due to the way they push against the suspension during these cornering motions. Both wheels are affected in tandem under the forces of acceration and deceleration as well. Due to the geometry of the mounting points of the suspension components, this movement causes changes in the camber angles and generally speaking, the softer the suspension, the more substantial the change in the camber angles from it's static setting due to this increased suspension movement.
So, let's say that we're test driving and tuning up a car, watching the telemetry, looking at the camber of that outside wheel. If we like our springs, dampers and bars where they are, then this is where we all have traditionally used static camber to fine tune that all important contact patch. We've no doubt noticed that the outside wheel gains positive camber as the suspension compresses but, how much attention has been paid to the inside wheel? Well, the inside wheel is gaining negative camber and that, coupled with the static negative camber setting can mean that wheel angles during cornering of -1.0 to -3.0 are typical, which would seem to be better suited to turning the car in the opposite direction and reduces the contact patch noticeably.
Herein lies our opportunity to make use of caster. I took a car with 0.0 static camber to a track and while completely stopped on a flat section, measured changes in camber angles up to full wheel lock with different levels of caster.
Caster Outside Wheel Inside Wheel
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1.0 -0.53 +0.70
2.0 -1.02 +1.33
3.0 -1.55 +2.00
4.0 -2.05 +2.65
5.0 -2.55 +3.30
6.0 -3.05 +3.95
7.0 -3.56 +4.62
Now, you'll note that this is at full steering lock and while most wheel users probably don't turn that far, some controller users probably do. What we see is that for every 'degree' of caster approximately -0.5 of camber is added to the outside wheel and +0.65 is added to the inside one.
At this point I started to think that maybe I could use static camber to get me in the ballpark for weight transfer under accel and decel and use caster to handle the camber changes to both the outside and inside wheels during cornering. Well, I've been pretty successful with some 6.0 caster tunes as of late but, figured if I was going to present this information to the group, I ought to have something a little more tangible to work with.
So last night, after running the TT at Mugello Short as a 'warmup', I took the R3 Ferrari F430 back out onto the track for some more testing. I ran the car in default trim with the exception of aero which was @ 198/400 and braking @ 46/100 and while the results were not as definitive as I would have liked, there was a noticeable trend. I checked the telemetry at the same point in turn one with the aid of a couple of small buildings at the left side of the track. Note the significant improvement to the camber on the inside wheel, even at less than half of total lock.
Caster Camber Outside Inside Total Camber
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3.5 -0.7 -0.4 -1.7 -2.1
4.0 -0.6 -0.4 -1.6 -2.0
4.5 -0.6 -0.3 -1.5 -1.8
5.0 -0.5 -0.3 -1.3 -1.6
5.5 -0.4 -0.3 -1.1 -1.4
6.0 -0.3 -0.2 -1.0 -1.2
6.5 -0.2 -0.2 -0.8 -1.0
I began my runs with the default -0.5 camber 5.0 caster and then worked my way up thru 6.5 caster. Then, I worked down from the default to 3.5 and finally, returned to 6.0. I was able to post times in the 51.7s for all of the runs from 5.0 to 6.5 with 51.6s at 6.0. The runs with caster below 5.0 got progressively slower until the 3.5 run which I could only get into the upper 51.9s. When i returned to 6.0, I was able to get back to a 51.8 on only my second lap. It should be noted that in the lower caster runs, the steering felt great. It had a very linear, hooked up feel to it but, it was also clearly slowing the car down and the higher static camber was also reducing braking efficiency. The higher caster runs did not have the same positive feel but, seemed to get the car turning with less actual steering input and the improvement to the camber on the inside wheel seemed to be making a difference in cornering speeds which was accompanied by improved braking due to the overall lower static camber.
Since I am still not able to get the inside wheel camber down as low as I'd like to see it, this did not turn out to be the complete solution that I had hoped it would be. For that, I'm afraid that having the ability to customize the suspension geometry or, independant adjustments for all four wheels would be necessary.
Due to the progressive nature of the camber gain due to caster, the tighter the corner, the more the effect. Keep this in mind when doing a telemetry/tuning run. It may be to our advantage to actually tune the contact patch for a corner radius range that takes into account the types of corners that are the most critical for success at a particular track ( if you have track specific tunes like I do ).
Running lower static camber and higher caster is helping me to improve my laptimes due to the improved front end cornering grip and braking ability so, it might be worth a little experimentation to see if it helps you too. It always helps to have another tool in the box and if you should happen to play around with this a bit, I'd love to hear what you find.
J
