Has anyone experimented with lowering the ride height of their Radical, and if yes, how does this affect handling and other chassis geometry settings?
According to race car engineers (e.g. Carroll Smith), the motivation to lowering the ride height is to reduce the amount of roll that occurs during a turn, thus reducing the amount of vertical load on the outside tires; vertical load decreases a rubber tire's coefficient of friction, so by lowering the car there should be less roll in a corner, which distributes the vertical load more evenly across all four tires, resulting in overall more traction and therefore more lateral load capacity of the four tires.
This is my current theoretical understanding of why it is beneficial to lower a race car up to a limit -- the limit being that bottoming the chassis against the race track surface interrupts the ability for a tires and suspension to do their job and also eventually leads to the chassis being ground down and compromised. For a Radical, the chassis is about 25mm higher than the side pods and diffusers, so the bodywork will scrape and wear before the chassis bottoms out, but the same limit applies -- we don't want to prevent the suspension from doing its job due to body parts bottoming out on the track surface.
On my SR3, I have about 46mm of static clearance at the lowest point which is at the front splitter due to the rake. I like to maintain about 45mm to 50mm of clearance at the front because otherwise I am scraping the track too often and wearing down my splitter. By adjusting the splitter stays, it can be raised and the chassis can be lowered a bit. I am considering lowering by 5mm the front and rear, maintaining the 18mm of rake. I would do this all by maintaining the same preload in the springs, and adjusting each of the four pushrods to be shorter by an amount to achieve the desired drop heights front and rear. The Radical Cup technical regulations require that the car has at least 40mm of clearance everywhere with the exception of the fuel hose vent, so lowering the ride height by 5mm should be possible.
My questions:
1) Is 5mm lower ride height sufficient to observe a performance increase in cornering?
2) And should the camber be modified from the factory setup guidelines when reducing the ride height? I would imagine if lowering results in less roll while cornering, then less camber is required.
I think you will definitely notice the difference in 5 mm of drop. Not a professional or anything, but I feel the car is sensitive to both ride height and rake - more from aero than roll center though.
I think you will feel more difference with the roll bars for weight transfer than you will from ride height.
This idea did not work out because the pushrods are too long to allow a ride height drop of 5mm. To get around that I would have to either shorten the existing pushrods or replace with shorter pushrods. Reducing the pushrods to their minimum length reduces the ride height about 4mm/3mm drop in the front/back, however one needs a mm or two of adjustment to corner weight the car.
Sounds like you need a heavier driver to lower the car 🙂 I have no trouble getting a 40mm ride height in the front with the standard pushrods.
In any case, I think you should run what you are comfortable running from a wear perspective. The lower the better, and you know the serious Radical teams are all at 40mm - especially since at least one car every weekend gets a penalty for violating the minimum ride height. But if it means you have to shell out for new wear pads and do fiberglass every weekend to me that wouldn't be worth it.
The "factory setup" assumes a ride height of 40mm with the associated camber settings, so I would start there and adjust as tire temps and the track indicate what the tire needs.
According to race car engineers (e.g. Carroll Smith), the motivation to lowering the ride height is to reduce the amount of roll that occurs during a turn, thus reducing the amount of vertical load on the outside tires
Correction on the above -- it is not the chassis roll which causes higher vertical load on the outside tires, but the load transfer from inner to outer tires in a turn, similar to load transfer that occurs on front tires during braking and rear tires during acceleration.
"One of the most widespread misconceptions in racing is that the amount of load transfer taking place is directly related to chassis roll." -- Carroll Smith
Even vehicles without dampers such as go karts experience load transfer which is described by this equation:
load transfer = (lateral acceleration * weight * cg height) / track width
Based on this, Carroll Smith wrote: "never lose an opportunity to lower the c.g. or remove weight."
I did my best and lowered the chassis by 3mm. I think even if there was an opportunity to lower the chassis a more significant amount, other issues would surface such as loss of suspension travel and the front diffuser can only be raised so much before the nose does not fit well.
