Ferrari F92A front suspension

[auteoch]

[auteoch]

single shock absorber

[Tim.Wright]

Yup.

[Manoah2u]

but how. and why?

[auteoch]

[bill shoe]

I believe mono-shocks are out of favor now because a typical setup can't provide damping in roll. The washer-spring things provide a tunable spring element in roll, but even if the suspension (excluding tires) is perfectly rigid in roll, the tires will still allow roll motion and therefore could benefit from some damping to dissipate the resulting energy. Of course using a suspension damper to dissipate energy that was created in the tires requires that the suspension itself is not locked up...

[DaveW]

I believe mono-shocks are out of favor now because a typical setup can't provide damping in roll...

Not for WSBR vehicles. A mono-shock is mandated for that series.

This is a sample gathered from simulated kerb strike applied during a rig test. The vehicle is unrestrained, apart from simulated aero down-force. The four contact patch load time histories are shown, with steady state values manipulated to protect the customer. The input was a 25mm haversine applied to the left front tyre starting at around 1.22 seconds and lasting 0.22 seconds. The input travels down the car, striking the left rear tyre at around 1.34 seconds. Hence for 0.12 seconds after the hit, the only input is the front left. There are no inputs after 1.57 seconds.

I hope that you can deduce that the body rolls, allowing the front wheels to be controlled by the rear dampers. They don't do a bad job, really, because the response has more or less decayed by 2.1 seconds (with the front slight better controlled than the rear, arguably).

[Facts Only]

Mono-Shocks were/are sometimes used on hillclimb cars with massive aero that run on quite bumpy surfaces. Its seems to be falling out of favour even there though.

In reality it seems to throw up more drawbacks than benefits.

[DaveW]

In reality it seems to throw up more drawbacks than benefits.

F3's can be used in either form (although some series do mandate mono-shocks, I believe to reduce costs). The commonly held view is that there is no gain in lap time to be had either way, but a twin shock layout is easier to drive competitively.

I think aero hill climb cars are a special case. Static ride height rules mean that they use low rate springs supported by bump rubbers to control dynamic ride height (or they did the last time I looked).

[bill shoe]

Always educational to have actual data thrown in a discussion, thanks. Looks like right-rear corner was providing the damping for the left-front, which is logical once I think about it. Lots of subtleties to see, I'm still working on it.

Wish there was "equivalent" twin-front damper data for comparison.

[DaveW]

Wish there was "equivalent" twin-front damper data for comparison.

Here is the equivalent plot for a GP2 vehicle, taken more or less at random...

Time bases have been aligned, the input was identical, and the offsets adjusted (roughly) to be similar to the previous post. The continuing oscillation is interesting. It is:

a) typical for the test,
b) typical of similar vehicles,
c) it is a roll mode, perhaps with some lateral translation,
d) Its frequency (around 6 Hz) suggests it is a rigid body mode, probably with a roll centre below the ground and with the suspension locked up.

I suppose the difference between the examples could be vehicle related, suspension layout related, or (possibly) caused by differences in the tyres - they are from different manufacturers.

Edit: Plot X scale now fixed...

[PlatinumZealot]

So Dave, you said the right rear shocks do some work for the left front in roll. Now, that begs the question, when does the front mono-shock work? only in dive?

[DaveW]

So Dave, you said the right rear shocks do some work for the left front in roll. Now, that begs the question, when does the front mono-shock work? only in dive?

My example was extracted from a simulated kerbing input, which excites heave, pitch, roll & warp modes.

With a pure warp input, the centre damper movement is negligible. The movement was around 0.2 % of the rear dampers - in phase with the rear left, as it happens - implying that the movement was due to a slight asymmetry in the vehicle.

I would conclude that the centre front damper responds to heave and pitch inputs (inertial or road), but not to roll or warp inputs.

[Madrok]

I apologise, but you could not paint little bit more in detail.

[DaveW]

I apologise, but you could not paint little bit more in detail.

I am not sure I can. But this thesis should introduce you to the basics. I've not read it thoroughly, but I don't think it covers mono-shock fronts, or even roll response, particularly, but it is a start. It introduces the reader to the concept of over, and under-damped response, see figure 4.1. for example.

With the basics out of the way, I can state that most 4+ damped open-wheeled race cars are over-damped in roll. A mono-damped front suspension can therefore often improve contact patch load control.

However, the structure of the chassis causes a small delay in the rear damper forces arriving at the front wheels, which, in turn, causes a lack of steering "feel". In my view, this is why a mono-shock layout is said to be more difficult to drive.