Downforce question

[Superjet800]

Hi real quick how many lbs of downforce do these cars create at the highest df setting and the lowest df setting at 100mph?

[David Ferguson]

I would say between 100 and 600 lbF total.

[S Lathrop]

I would say between 100 and 600 lbF total.

David is correct in his estimation. I have actually measured down force at and above 600 pound and in the 120 mph and up speed range.

Remember, down force is directly related to speed and it is a a non-linear relation. Double the speed and down force goes up by a much larger amount.

The big trick is to keep the gain in down force balanced between the front and rear of the car as speed increases. It is way too easy to gain at one end and go out of balance as speed changes.

[Superjet800]

Appreciate the info guys ! Exactly how does one measure the downforce at speed?

[BeerBudgetRacing]

Appreciate the info guys ! Exactly how does one measure the downforce at speed?

Load sensors on the suspension.

[Purple Frog]

Or... if you are building the next great FC car... rolling platform wind tunnel...

[S Lathrop]

Appreciate the info guys ! Exactly how does one measure the downforce at speed?

On the car we did the testing, we had rotary post mounted in the bell cranks. They were geared so we had something like 100 degrees or more of rotation for 1 inch of wheel travel. This gave very good resolution of chassis movement with speed.

We were lucky enough to be able to use the taxi way at a nearby airport to do coast down tests. That is when you accelerate to car to a certain speed and then shift to neutral and let it coast down to a much slower speed. We were interested in how the down force changed with speed.

[Jim Edmonds]

There was a fun and well written article in the February 1961 Road & Track on using coast down and differential equations to develop a formula estimating car drag in pounds at all the intervening speeds. Wrote a Fortran program in 1963 using the resultant drag equation to estimate acceleration curves for a H Production race car. It worked exceptionally well.

A good high school student who has taken high school calc could do that now in Excel. Fun project. Almost flunked out that semester working on the program's punch cards instead of studying, Ha.

Jim

RF95 FC
RF01 FF
MV Agusta F3 track day bike