Originally Posted By: BoleCailey
Originally Posted By: SteveSRT8
Many race cars (not just F1) use the underbody to direct airflow.
This means ride height is both a suspension adjustment and an aerodynamic adjustment.
The differences can be dramatic in high speed cars like F1.
Yes, I know, but in a street cars/track cars and most race cars, ride height is set at the lowest point that allows the suspension to work on a given surface while allowing for the lowest center of gravity possible. When you get into high downforce cars, ride height certainly has an effect on underbody aerodynamics, but in our applications it is pretty much irrelevant other than a lower ride height reduces drag.
Yeah, the main advantage to lowering the car (apart from the obvious advantages inherent to highly-adjustable rebound/compression coilovers) is that the CoG is lower, thus the car "tips" less through turns (again, assisted somewhat by the significantly stiffer shocks/springs). A set of very thick and stiff sway bars made body-lean literally non-existant in my car on any public road. Also, switching out the factory roof (with sunroof) for a full Vorsteiner Carbon Fiber roof dropped over 80lbs from the highest point of the car, and didn't disrupt the 50/50 front/rear weight balance one bit.
However, with the addition of front splitters, full front undertray, functional rear diffuser (the "slots" cover the majority of the fuel tank), and the CSL trunk lid (integrated yet very aggressive "lip-style" spoiler), I have noticed that my car feels significantly more planted at speed. Over 120mph with a strong crosswind and it doesn't disrupt my car the way it would have when the body was stock. Plus, Vorsteiner is known for making the highest quality carbon fiber parts available (ever) for BMW's, with their CSL-replica-parts being 100% identical in every way, down to the weave, of the OE parts (except you can't buy the CSL CF roof from BMW), and as the aero parts were good enough for BMW's "Holy Grail" M3 (excluding the practically-extinct GTR), they surely are functional.
That said, they aren't creating downforce like some parts can (properly-done big rear wing, etc), but at the same time it would stand to reason that they would also not be "working against me" as much when it comes to the car's top speed.
Part of the reason I went with the 3.23:1 diff ratio as opposed to the more common 3.46:1 (which is common for those with the 6spd manual as it has far less impact on highway engine speed) was actually fourfold:
1) I can hit 102km/h in 2nd gear at 6970rpm (rev limiter is currently at 7200rpm; will be 8000rpm with fuel cut-off at 8200rpm when I install the forged Pistons, as right now it's only forged rods; fortunately, my entire drivetrain was replaced with all Titanium parts, where applicable, and "ported" valves, and is rated for 10,000rpm)
2) I can hit 100mph while in 3rd gear at 7110rpm (90rpm before my current fuel shutoff, so I don't run that high unless I am doing a "pull" against another car)
3) Cruising on the highway at 85mph in 6th gear keeps my engine well below 2500rpm yet with the twin-screw supercharger, I have 100% of peak torque on tap at the press of a pedal, all ~400ft*lbs@rw
4) It does not limit top speed as with the gear spacing (ratios) of the 6spd transmission and stock 2.91:1 rear diff, the gear-limited top-speed would be 211mph, so going to a 3.23:1 keeps it in the 190's while going to a 3.46 would have dropped it down to the high-170's (theoretical, of course)
But, I don't have a few miles of straight, open, non-public road where I could ever test this out; but I can say that the car still pulls HARD above 145mph (and still has 2 gears to go through).
In terms of downforce, I would estimate a couple hundred pounds at most; however, that's significantly more than any stock BMW, so I am happy. It does it's job on the track; since the bodywork (with no suspension changes), I can take a turn at 80mph that I used to have to take at 65mph. The limited-slip helps there a lot too...
