This is more of a curiosity of mine. I've noticed on modern GT3 race cars, bumpstop/packer tuning is becoming very important. What's the reason for this? Why would the manufacture purposely emphasis using bumpstop as tuning tool?
isn't that very imprecise, and the bumpstop rate rises quite fast.
is it solely to control the aero pitch sensitivity at highspeed? do these cars have that much downforce that pitch sensitivity becomes that big of an issue.
GT3 cars can have significant amount of downforce.
Of course, being heavier cars than, say, an F1 or F2, the ratio between downforce and weight is smaller, but they can still produce a lot of downforce.
I can imagine controlling ride heights could be a pretty important tuning aspect, above all in tracks with fast corners in critical parts of the circuit, with respect to lap time.
Beside the absolute amount of downforce, in aero cars controlling ride heights is critical also to keep the Center of Pressure (or aerodynamic balance) in the "right window".
how do they control the bumpstop so that it only touches for purpose of controlling down force.
for ex. lets say a 100mph corner, they tune the packer so that the suspension rides on the bumpstop for controlling aero platform.
now next corner is 40mph corner where you have to jump a curb for the fast line, now the bumpstop also touches although for the wrong reason, rather than controlling aero platform I imagine it would decrease the mechanical grip dramatically
I'll give you my take which means that an actual suspension engineer will be along shortly to correct me...
My first point is that the springs aren't the only elements in the system. The dampers play a huge role in controlling chassis dynamics and would have markedly different characteristics in your two scenarios. Steady state at 100 mph has the dampers not doing anything (Assuming a perfectly smooth surface, etc.), so this is dominated by spring rate. In the second scenario, curb at 40 mph, the damper has a huge effect, greatly increasing the force seen at the wheel. This short term increase can be several times the spring rate.
The second point is that the packers are just another spring. The packers rate is in addition to the regular spring. If you look at any of the racing damper sites you'll see that there is a huge range of packers available so that every aspect can be tuned: Height (When the packer begins to engage.), Rate (How stiff the material is.), and what the spring rate curve looks like (Linear? Progressive? Stepped?). I know there are production cars that are always on their packers, namely some Acura models.
I hope that helps and doesn't further cloud the topic for you. If you chase down a professional suspension tuning text all of this is covered (And then some!).
