BEAVIS' White Track Car

[beavis]

Phillip Island
Out at Phillip Island today with the WRX folks and the MX-5 club.

I had some troubles with all my electronic gadgetry... batteries, power, bluetooth, plugs etc... but in the end that didn't stop the car from doing its thing. It did mean i couldn't get my RaceChrono to work properly, so lap times weren't recorded.
The new radiator seemed to keep temps down, definitely looked to be running cooler than the car used to. I might put in a 'colder' thermostat when I get a chance. Apparently coolant running closer to 80degC is best for power.

Met a few new people today which is always interesting and fun... the bloke in the Yellow 911 Turbo was interesting, followed him for a few laps and he was getting the ass of the car out pretty slidey a few times, amusing to watch.
Good to see Chris from P1 was out taking pics, keep an eye out for them, they may take a few days to get online: http://p1racephotography.smugmug.com/Motorsport
Was also cool to meet the dude from circuit threads.... hopefully he does a write up of the day: http://www.circuitthreads.com/

Interesting GIF
I took some footage from the rear of the car looking forward toward the left rear shock.
I made this interesting GIF showing the difference in ride height between the static car, and at about 180km/h. There is a noticeable drop in ride height, presumably due to 'downforce'. If you have the skills to work out how many kg's of downforce the car is generating based on that GIF, then I am interested to hear your opinion.



Video
And, here's my quickest lap for the day.
New best time, a 1:50.4. There is still more time to be made, just need one of those trouble free days with nice conditions and no traffic..... A 1:49 is not far away.

[hks_kansei]

DOwnforce weight should be as simple as taking into account the spring rate, the amount of deflection, and multiplying by 2 (because 2 wheels at the back)


so a 6kg/mm spring, with the control arm deflecting 20mm at the shock base, would have taken 12kg to push that far.
2 wheels would suggest then 24kg of downforce at the rear.


I think anyway, no guarantees I havent stuffed something up in my thoughts

[lightyear]

Put stuff in the boot till the suspension is compressed the same amount, then weight that stuff?

[beavis]

DOwnforce weight should be as simple as taking into account the spring rate, the amount of deflection, and multiplying by 2 (because 2 wheels at the back)


so a 6kg/mm spring, with the control arm deflecting 20mm at the shock base, would have taken 12kg to push that far.
2 wheels would suggest then 24kg of downforce at the rear.


I think anyway, no guarantees I havent stuffed something up in my thoughts

You are almost right, except it would be 240kg, not 24.

[davekmoore]

That is a great instructional video for anyone wanting to get quickly round PI.

It would also be fascinating to see what happens to my rear suspension at a similar speed. Suspect there would be nil or negative downforce?

[beavis]

That is a great instructional video for anyone wanting to get quickly round PI.

It would also be fascinating to see what happens to my rear suspension at a similar speed. Suspect there would be nil or negative downforce?

Almost certain there would be lift.

[davekmoore]

... and is there a short list of known cost effective solutions, with no doubt lower ride height being one of them?

[beavis]

... and is there a short list of known cost effective solutions, with no doubt lower ride height being one of them?

Lowered ride height wont really help and will hinder suspension geometry.

Consider that a car is shaped kind of like an airplane wing:

To convert the above picture into words: as air flowing over the car travels a greater distance than the air flowing under the car, the the air flowing over travels faster than the air travelling under, resulting in a difference in pressure.

You could:
Reduce the amount of air flowing under the car (with a splitter/air dam)
Counteract the affects of lift with downforce (with a wing/boot spoiler)
Increase the speed of airflow under the car (with a flat undertray)
Reduce air pressure under the car (rear diffuser/ground effects)

Note, the fastback on my car actually increases lift (that's bad), but reduces drag (that's good).

Also note, I may actually know nothing about aerodynamics.

[orx626]

DOwnforce weight should be as simple as taking into account the spring rate, the amount of deflection, and multiplying by 2 (because 2 wheels at the back)


so a 6kg/mm spring, with the control arm deflecting 20mm at the shock base, would have taken 12kg to push that far.
2 wheels would suggest then 24kg of downforce at the rear.


I think anyway, no guarantees I havent stuffed something up in my thoughts

You are almost right, except it would be 240kg, not 24.

...and don't forget to factor in the suspension lever ratio.

[beavis]

...and don't forget to factor in the suspension lever ratio.

So, multiply by 0.735 for the rear, or 0.66 for the front.

[orx626]

So, multiply by 0.735 for the rear, or 0.66 for the front.

[greenMachine]

So, multiply by 0.735 for the rear, or 0.66 for the front.

Errr ... no. Have another read of hks' post ...

[beavis]

So, multiply by 0.735 for the rear, or 0.66 for the front.

Errr ... no. Have another read of hks' post ...

True... "At the shock base"

Note the red lines in my gif go to the end of the arm, not to the shock base.

[davekmoore]

... and is there a short list of known cost effective solutions, with no doubt lower ride height being one of them?

Lowered ride height wont really help and will hinder suspension geometry.
You could:
Reduce the amount of air flowing under the car (with a splitter/air dam)
Counteract the affects of lift with downforce (with a wing/boot spoiler)
Increase the speed of airflow under the car (with a flat undertray)
Reduce air pressure under the car (rear diffuser/ground effects)
Note, the fastback on my car actually increases lift (that's bad), but reduces drag (that's good).
Also note, I may actually know nothing about aerodynamics.

So, if I did something like number 3 in post 124 of this link in order to reduce lift (for track only), will it reduce airflow under the car so much it causes overheating of gearbox or diff? I'm thinking plastic garden edging for a cheap material. http://www.miataturbo.net/race-prep-75/ ... 612/page7/

[beavis]

I highly doubt you would have adverse effects with just an extended lower lip.