Hi Machin, I was thinking about the way to manage such downforce in real cars. Wich realistic stiffness value could have each suspension spring? O roughly considered the ride height and the df near the maximum speed (320km). I guess 40-50 N/mm, what do you thing about?
Note that this is "wheel rate" and not "spring rate"... to find spring rate from wheel rate you need to divide by the motion ratio, where the motion ratio is the ratio of compression of the spring versus the movement of the wheel... that changes depending in the suspension design, and isn't fixed even for a given design: it changes as the wheel moves...
"Sprung mass" is the mass of the car supported at that corner minus the mass of the wheel, tyre, brake disc, brake caliper, half the suspension arms, etc
For a high downforce car (like the KVRC ones) the wheel frequency typically used is 4.5Hz upwards... Road cars have wheel frequencies under 2Hz... which gives better mechanical grip and better compliance over curbs... the problem is that this doesn't give a nice stable platform for consistent aerodynamics, and also it leads to too much suspension compression as the car's speed rises... hence the need to go to 4.5Hz or above when you have high downforce.... that makes the ride harsher and compliance over bumps worse.... As you can see its all a compromise...
Last edited by machin on 25 Nov 2015, 16:52, edited 1 time in total.
I don't have the actual numbers that I used for the KVRC to hand, but our overall weight is around 975kg with driver and fluids, making about 243kg per corner (average) minus an unsprung weight per corner of about 30kg. To achieve a wheel frequency of around 4.5Hz would need a wheel rate of around 20kg/mm... If you know your motion ratio you could figure out a spring rate (I don't go into that detail in the Virtual Stopwatch simulation).
EDIT: I'm not sure what purpose you're using the numbers, but remember that the wheel rate is designed to increase as the suspension compresses; either by suspension and linkage geometry and/or using a progressive spring itself. This means that on something like an F1 car (or KVRC car) the total wheel displacement will never be more than about 30-50mm even under high downforce conditions. This progressive rate means you can have better compliance over bumps (though not as good as a road car!) whilst avoiding the car bottoming out at top speed.
I have put the image into Inkscape which can 'trace' the image and turn it into a vector that can be export as dxf so I now have the profiles in Sketchup
Finally... I got around to compiling this stuff into an "Introduction to Racecar Aerodynamics Guide".... its aimed at KVRC beginners and doesn't have any maths in it!
Top work Richard! You have done a good job of putting all that work into an easy to understand guide, reading through I have come up with some ideas for the 2016 car!
Thanks.. It's not really aimed at either of you guys though... I would love to read a Variante aerodynamics design guide (as would much of the grid I would guess!)
Its still helped me think about how I am going to approach this seasons car. I think it is written well, should be easy to follow for newbies. If you remember back, I posted that I found all the talk at the start if this thread hard to decipher, what you have done with this guide is made the language a lot easier to understand and obviously it helps a lot.
Last edited by RicME85 on 14 Feb 2016, 17:07, edited 2 times in total.
