Suspension and aero question(s)

[Magpie]

When people have been doing aero (splitter/wing/diffuser/skirts) mods was any consideration given to the spring rates and/or other suspension components? If people did how did they arrive at the spring rates/other suspension modifications? Did the aero mods change understeer/oversteer characteristics and if so how were these managed? Was it through trial/error or a calculated/planned/ride heights?

I have noticed with my rear wing at the moment that at high speeds there is a very obvious lightening of the front end and at lower speeds (when accelerating after the apex of a corner) there is a bit of understeer (there is no splitter at the moment). It does have a very large angle of attack (15 deg) which in turn causes drag, however the wings’ effect at below say 80 kmh might not be the reason for the understeer. The rebound setting on the shocks is such that there is not an instantaneous transfer of weight from the front to the rear when accelerating out of a corner. Therefore as there is a progressive weight transfer from front to back the front tyres still should have grip so the main reason for the understeer is more than likely that there is no rear sway and not an effect from the aero. Note I’m putting the rear sway back on soon.

My concern is that, is it possible to use most of your suspension travel up through downforce alone and have little travel left for road conditions (especially at high speeds) if you don't consider your spring rates when building aero mods?

Aero mods is my next project/focus as my engine is now being built and I want to understand how it all works together.

[JBT]

Without some way to measure resulting forces from any aerodynamic devices, I guess it's all guess work for the initial setup and then by trial/test to fine tune.

If there is enough down force, you could very well use up a lot, if not all, your suspension travel and be on the bump stops. It would be the same as putting that down force as a load in the car

[project.r.racing]

Sounds like you have just over increased the grip in the rear end. Limiting the amount of steering you can do with the throttle. Any reason for this? Running 200hp or more? Loosing traction exiting corners?

If no - then put the sway bar back in and use a less aggressive wing setting.

[Magpie]

...If no - then put the sway bar back in and use a less aggressive wing setting.

Thanks, I have already been thinking about doing that.

[zoomzoom]

My suggestions would be the following:

Fit rear swaybar, this will lessen understeer/increase oversteer

Reduce wing AOA, your wing will still work at 0deg. From memory you have a GTC-300, at 80MPH for example (which is probably around about your average speed at LS) by running 15deg you get around 23% increase in downforce and about 110% increase in drag over 0deg, ie you have an air brake on the back.

If you still have understeer after the rear sway is back on try increasing the front damper rate as this will slow weight transfer to the rear and help keep traction.

As far as the wing using up the displacement of the suspension, unless you are basically on the bump stops to start with then no. I cant recall exactly but the stock from memory is a little under 3kg/mm, at 80mph the GTC300 even at 15deg is published to have 830N of downforce, about 85kg. Assuming even split that would be about 42kg each spring, even at 3kg/mmthat would be 14mm. You would more than likely be running much harder springs and in the real world probably less downforce than the free-stream CFD results show.

Cheers,

Tim

[Magpie]

Thanks zoomzoom (and others) your suggestions have been taken on board. I just need a way to measure it all. Drag can be done by doing some coast downs and I'm working on a plan for measuring the downforce/suspension use with the aero.

[lightyear]

With a big wing I get under steer from about 80kmh. And over the bumpy sweeper at winton there is a noticeable amount of bottoming out at the rear. I agree start at 0*. As the air meeting the wing is already at an angle.