Running at 40mm

[Larry J-Croft]

Right, another chance to air my ignorance, maybe generate some debate and hopefully gain some useful intelligence.

Mono F3 cars at 40mm - a well aired topic and I don't want to discuss the pros and cons - its been done to death elsewhere. My question is, on the basis that you have to comply - how to mitigate the effects as much as possible? The problem seems, that if you start mucking about with a good setup (albiet at 15mm) too many variables enter the equation and without recourse to some serious time, money and testing you may lose more than you gain.

Some initial thoughts:

a. dual rate springs which would allow the car to run at 40mm statically but compress lots as soon as the wings cut in. Not too sure about this as without wind tunnel data you won't know how much force is generated at various speeds so a enormous amount of empirical testing would be needed not to mention cost and time. plus camber change issues, varying dynamic roll centres etc etc.

b. some form of variable geometry pivots for the pushrods - same argument as above would apply I think.

c. I have seen elsewhere on the forum, the idea of 'softer' springs but why? what about static wheel rate? would this include anti roll bars? what about losing the ability to negate droop using preload? what about effect on camber as the springs will allow much more body movement and hence camber change? aaarrrgghhhhhh

Could throw in more ideas but I know some of you know far more than me!!!!!

[TEAM78]

whats the rocker ratio??

how much is the aero package affected by ride height, i.e what happens to lift and drag as the ride height is varied.

I feel a little test in the MIRA wind tunnel coming on

[MikeBz]

Originally Posted by Larry J-Croft

c. I have seen elsewhere on the forum, the idea of 'softer' springs but why?

Maybe the aero advantages of running at 10-15mm are such that it's worth taking the compromise of a stiffer-than-optimal spring in order to minimise contact with the track surface? Just a thought.

Mike

[Larry J-Croft]

Wish I could afford a wind tunnel!! I think I am going to have to get a set of varous springs and just experiment - guess that is the difference between the professionals and us hard up, time limited amatuers.

[TEAM78]

read some SAE papers on all this, they are very good

[kbooth1]

Originally Posted by Larry J-Croft

c. I have seen elsewhere on the forum, the idea of 'softer' springs but why? what about static wheel rate? would this include anti roll bars? what about losing the ability to negate droop using preload? what about effect on camber as the springs will allow much more body movement and hence camber change? aaarrrgghhhhhh

Could throw in more ideas but I know some of you know far more than me!!!!!

The monoshock suspension on an F3 car seperates the bump and roll dynamics of the car. This means the spring only has to control bump and can be softer to provide a 'comfortable' ride for driver and aerodynamics. The roll is controlled usually by bevel washers which form a spring and has the same effects as an ARB.

[Larry J-Croft]

Yes - but I dont have a monoshock system. I have pushrods with one shock per wheel and anti roll bars. Still I think a more comfortable ride and the chance for the car to squat more at high speed has got to be worth a try.

[DAE]

If you were to run a very soft tender or helper spring (eibach supply these) in series with your existing front springs, this could go coil bound under very little load. You could play around in your workshop and find one which would maintain the static 40mm ride height, but would compress under a few pounds load to ensure that your dynamic height and cambers would be as you need them.

[TEAM78]

Originally Posted by Larry J-Croft

Yes - but I dont have a monoshock system. I have pushrods with one shock per wheel and anti roll bars. Still I think a more comfortable ride and the chance for the car to squat more at high speed has got to be worth a try.

if I was you I would do my best to lay my hands on some aero data for your car and see how ride height affects the rear diffuser, search the net hard! you be surprised what you can uncover.
Also its the stop watch that counts not whether the ride feels nice, poor test drivers usually end up setting up cars which ride nice but are slow.

[THR]

personally.. i think soft shocks are no way to go.
all the energy goes into making the spring compress rather than making the car go foraward.
so u should run the stiffest springs so as the car doesnt skip over bumps

hillclimbing cars are a right one for that.. they are all soft cos of the bumps but they nearly all squat off the line.. the cars that dont squat.. are FTD cars!!

[Larry J-Croft]

Originally Posted by DAE

If you were to run a very soft tender or helper spring (eibach supply these) in series with your existing front springs, this could go coil bound under very little load. You could play around in your workshop and find one which would maintain the static 40mm ride height, but would compress under a few pounds load to ensure that your dynamic height and cambers would be as you need them.

I've looked at this and also progressive springs. The corner weight of a wheel is about 150kg (or 330lbs) all up, so it will have to be stiff helper springs!. Also I need to preload the spring to eliminate droop, consequenlty I cannot see this working - also no-one else is doing it which is always a good clue!!

THR - the logic of the softer spring and 'squat' was not an 'off the line' issue more allowing the car to settle lower under aerodynamic load at high speed and getting some of the ride height reduced - along the same lines of logic of that above.

[Splatz the Cow]

Mercedes used this idea on their FIA GT cars. I can't remember if it was 1997 or 1998 or both. But it had a significant effect on topspeed and downforce. The faster the car went, more dowforce pushed the car down lower, which reduced the drag etc. However, at slower speeds with less downforce the car naturally sat higher. I don't know how they controlled the car otherwise on bumpy stuff. I don't lnow if it was used on the 1999 CLR at Le Mans.

For your use, have you thought about how it would be in different conditions,in the wet, or in traffic?

[andy97]

Surely any attempt to run the car in Mono at ride heights lower than 40mm by the use of softer springs, or any other method come to that, is against the spirit of the regs (he says naively!!).

[Larry J-Croft]

Andy, By definition, a car running at 40mm statically, that generates downforce will be at less than 40mm on the track - unless it has infinitely stiff springs!!! The debate is really whther we can maximise the effect.

[maddogf3]

Originally Posted by Larry J-Croft

Andy, By definition, a car running at 40mm statically, that generates downforce will be at less than 40mm on the track - unless it has infinitely stiff springs!!! The debate is really whther we can maximise the effect.

Seeing as our old F3 ran 15mm and had quite stiff springs but I still had to use packer's and ran it on the bump stops ( Koni ) ones. it ran at 30mm at rear and did bottom out even with 1000 lb springs but not with any packer's in we even tried 1200 but didn't see any improvment in times so went back to 1000 If we were to run at 40 mm I think I would try super soft springs with loads of preload to get the ride height back These older cars with flat bottoms need to be kissing the ground nearly, to generate suction "Depression" by speeding up the airflow under the floorpan . Take it from me they are very drivable on the bump stops and most of our circuits are quite smooth but keep away from the lift off the kerbs 40mm suddenly means little underfloor generated downforce ( you still have the wings ) As for comments about " not being in the spirit of things " My comment would be this is motor racing its what we do within the rules and still get an advantage if we can . I hope I dont get any flak from my veiws I usualy do !!!!