3 shocks at the front.

[Jersey Tom]

I'd say add 'normal' spring & bar to sort the car at low speed like you normally would.. and then at high speed if you need extra ride or pitch support, start adding 3rd spring.

You may not need it at all.

[riff_raff]

How about one shock at the rear?

If you can get a copy of July's Racecar Engineering, there is a photo of the rear suspension on the 2010 Toyota F1 car. The suspension linkage is quite complex, but as far as I can tell it uses one pushrod/rocker/torsion spring per side, a third transverse coil spring over a single dampener coupling the two rockers, a roll bar and linkage coupling the two rockers, and a device coupling the rockers called a "Cambridge inerter" (whatever that is).

[marcush.]

one has to realise ,adding "third"spring will depend highly on how your installion is,those bump rubbers we see in some pics have the benefit of only starting to get involved into the equation when a certain bump travel is reached...but still this is adding a spring in series to the original (corner)springs and adding spring force you are likely to need more damping as well.

[DaveW]

My question is more on setup that anything else.

On the set up of the suspension is it generally accepted that the force of the 3 springs is similiar or do I prodinately want to support the downforce and weight or the car on the 3rd spring? e.g 1000 lbs 3rd spring and 2 500lbs spring for roll?

Suspension settings & set-ups depend on many properties, some deliberate, others not. Aero down force & aero ride height sensitivity, tyre properties, roll centre heights & suspension geometry are (hopefully) deliberate. Roll centre migration, installation stiffness, chassis torsional stiffness, & suspension friction may condition set-up strategy.

It is fair to say that front suspensions usually comprise two dampers & "corner" springs supported by a roll bar & bump rubbers (to control front wing/splitter height at high speeds, either as a 3rd element or as damper travel limiters. An inerter is sometimes included as a front 3rd element.

Rear suspensions usually comprise two corner dampers & "parallel" corner springs supported by a roll bar. A 3rd damper & parallel spring can help to "look after" weak tyres, if necessary. I have seen rear set-ups ranging from no corner springs to no 3rd spring to no roll bar. Bump rubbers are generally used as "crash-out" stops at the rear axle. An inerter is sometimes used as an additional 3rd element.

My advice would be to keep the suspension set-up of your vehicle as simple as possible (4-off dampers, 4-off corner springs and a front & rear roll bar). The more complex the arrangement, the more difficult it will be to understand without detailed modelling tools & hardware-in-the-loop-tests. Keep away from inerters. Try, try, try to keep away from metal-metal travel limiters. They are always "fixes" that can lead into set-up compromises from which it is difficult to escape. Treat pit-lane wisdom & "bolt on speed" solutions with deep suspicion - there is no magic in the real world, only sensible compromise.

[proutyc]

Many thanks all for the comments on supplying me some direction on 3rd springs.

The real reason for looking at this solution is that my car runs ground effects and due to this I want to run the car as close as possible to the ground. (35mm front)

My concern here is that in doing this with a conventional set up would require wheels rate I calculate around 1350lbs per corner (corner weight is 300lbs) which would offer very little bump and mechanical support.

We have a few tracks where we race that have a couple of larger bumps, one track that is rather low grip with a couple low speed sweepers and another track that is high speed, high grip smooth surface track (like a billard table)

Hope this explains why I'm looking down this route. I'm looking to tune the car to a number of differnt circuit needs.

We run dataloggers etc on the car so am comfortable once we start getting data as to whether we need more or less 3rd spring based on tire data, g force etc, just hoping for a little guidance on where you guys would start as a base.

Thanks

[Jersey Tom]

1300 lb/in isn't an unreasonable wheel rate for a car with a lot of downforce and only 4 springs and 2 bars.

As a baseline I'd use that.

You'd have to prove to me that you really need the 3rd spring in the system, and show how it's going to influence the pitch and roll modes of the car (in addition to just heave)... before movin away from a simple setup.

But that's just me.

Edit - Hell for that matter, do you know how much DF this thing makes? How sensitive is it to front ride height? Rear?

[F1_eng]

I don't know when that set-up in the video was ever used, but it's not a Brawn GP set-up.

http://i44.tinypic.com/256vdhy.jpg

Completely different.

[DaveW]

Many thanks all for the comments on supplying me some direction on 3rd springs.

The real reason for looking at this solution is that my car runs ground effects and due to this I want to run the car as close as possible to the ground. (35mm front)

My concern here is that in doing this with a conventional set up would require wheels rate I calculate around 1350lbs per corner (corner weight is 300lbs) which would offer very little bump and mechanical support.

Forgive me, but your first post mentioned "tunnels" & now you state you want to run as close to the ground as possible. The two statements are, for me, incompatible.

The "art" of suspension set-up is compromise. Good lap times for many road circuits are obtained by maximising corner exit speeds from low speed corners. This implies having a good "mechanical" set-up at low airspeeds with relatively low spring rates. However, maintaining stable and consistent operation at high speeds implies accurate control over ride height and rake. A compromise is to use relatively low rate springs supported by, for example, bump rubbers.

For example, a Lotus 91 (serious tunnel aero with soft tyres & poor installation stiffness courtesy of beam rocker suspension) ran (still runs) with around 600/950 wheel rate springs. This works because tunnels are not ultra ride height sensitive. They are, however, rake sensitive (the venturi throats migrate if the vehicle is allowed to pitch). Hence spring rates match the c.g. position fairly accurately. "Corner" bump rubbers are used at both axles to control ride height & rake at high speeds (of course).

An Audi R8 was a serious aero vehicle with stiff tyres and very good structural properties. In this case, however, the aero was developed largely by the flat undertray, so controlling the height of the front splitter was crucial. It ran with around 1250/1150 wheel rate springs, a front 3rd element that progressively increased the front wheel rate up to beyond 1700, & a very soft & long rear 3rd bump rubber to control rake at high speeds (washing off rake with airspeed helped to reduce drag, but the vehicle could become airborne if rake was not limited).

Two serious aero vehicles with very different set-up strategies. I hope the above helps to explain why.

[proutyc]

Many thanks Jersey Tom, Dave

The wheels rate to corner weight is almost 5:1 which on the not so smoth tracks we run on seems rather high.

We believe DF will be in the order 1500 - 1800lbs. The tunnels are derived from a later model Atlantic car but with the growth rate modfied to equate to 12 degrees (Car runs low twin elemnet wing to act as an extractor)

Dave agree hundred percent on different routes. We found alot of what you mention on my sister car that doesn't run third springs this year. runs the same tunnel design. Car's G force increased with lowering the car. We ran either real stiff springs or bump stops and different setups worked at different track. On 2 tracks the bumps are in the highest speed areas and we struggled at times when using bump stops.

Thanks again for your thoughts. and the links

[DaveW]

We believe DF will be in the order 1500 - 1800lbs. The tunnels are derived from a later model Atlantic car but with the growth rate modfied to equate to 12 degrees (Car runs low twin elemnet wing to act as an extractor)

FWIW, Atlantic cars run wheel rates ranging from 600/450 to 1200/950. I guess the higher rates would be for ultra-smooth tracks &/or qualifying.

BTW, an important ratio for mechanical set-up is, for me, Spring_rate/Tyre_rate.

[Jersey Tom]

1800 lbf of downforce is not exactly an awful lot. Let's say for argument's sake that's the value the car will make through the fastest corner, and maybe 1/3 of that (600 lbf) in a slower corner... so a range of 1200 lbf. Mind you this is all ballpark estimation.

If you have 1350 lbf/in at each corner for a total chassis ride rate of 5400 lbf/in.

You're targeting about 0.25" of total squat from downforce?

[proutyc]

Thanks again gents.

Yes was wanting to test minimising squat with aero. I'm hoping to keep the front as stable as possible to maintain a consistent throat for the tunnels. Obviously this will also help minimise front pitch.

100% correct that its not alot of DF, car only has about 260hp

Will obviously baseline the preseason test by not using 3rd springs and then monitor via the data. Just trying to calculate how big a jump in 3rd spring lbs will show significant data comparsions.

Anyone keen to offer suggestions on rake. I've not gone extreme here to date (20-40mm) but am aware from reading RC engineering that similiar ground effect porsche gave best LD ratio with like 70mm.

Thanks again for your thoughts. I'm thinking I'll begin with a 1000lbs 3rd spring and play with different mechancial grip springs. Car has adjustable blades to that dont effect 3rd spring so plenty of data to change and collect to attempt to find a direction to go.