Ariel Atom suspension technical question

[Alfanatic]

Hi all,

I was just looking at the picture of the Ariel Atom V8 on the cover of Evo, and in particular the front suspension, with the springs and dampers being anchored to the top crossmember of the, um, dashboard, and the units being actuated by pushrods and rockers.

Now my layman's technical level tells me that in formula racing the suspension units were moved inboard and actuated by pushrods to get them out of the airflow, but in the Atom, famous for its lack of bodywork, that would seem like wasted effort as the car has so many bits and pieces hanging out and exposed to airflow that it's hard to imagine moving the suspension inboard would make a difference.

So my question is, in the case of the Atom, is there any benefit to having pushrod operated spring / damper units instead of just siting them in the classic position (where the pushrods currently are, with of course appropriate hardpoints on the chassis)?

Here's a pic of the Atom that shows the layout I am talking about.

[PhillipM]

It lets them alter the rate of the spring and damper through the travel of the suspension.

Unfortunately, with the mounts being so close the bellcrank pivot, it also intoduces a lot of friction and makes the ride fidgety.
And and I don't know if they've sorted it since, but the Mk1 car had a tendancy to go over centre on the rocker arm and jam the entire suspension and bend the pushrod if the car hit a kerb/huge pothole

[Alfanatic]

Aha! Do you mean that by altering the geometry on the rocker they can multiply the torque applied or, for want of a better word, change the ratio on the suspension (small deflection of wheel = big compression on spring etc)?

EDITED: Actually, I suppose both options are inseparable. Oh, and ratio would probably be a better word than gearing

Edited by Alfanatic on Saturday 16th October 19:28

[tuffer]

Un-sprung weight.....but I'm no chassis guru.

[PhillipM]

Alfanatic said:

Aha! Do you mean that by altering the geometry on the rocker they can multiply the torque applied or, for want of a better word, change the ratio on the suspension (small deflection of wheel = big compression on spring etc)?

EDITED: Actually, I suppose both options are inseparable. Oh, and ratio would probably be a better word than gearing

Bingo, but it also alters it in different parts of the travel as the suspension moves and the pivots change position.

Edited by PhillipM on Saturday 16th October 19:55

[Alfanatic]

Brilliant, thanks for the responses!

[LaurenceFrost]

Following on from PhilipM, there are 3 big advantages to doing it, and unsprung weight is not really a major one since some dampers are so light these days - every little helps though I guess.

The big reasons behind it are:

1) Rising rate - most conventional suspension gets softer the more the wheel compresses, due to the damper angle increasing during bump. You can change this with correct fitment of the rockers, so the suspension gets firmer through its stroke.

2) Fitted ratio - look at where the push rod meets the lower wishbone. It's basically in the wheel. With a thin push-rod you can get the pushrod right out to the wheel, giving a much smaller fitted ratio of wheel to bell-crank. This is not always achievable with a damper.

3) Damper travel (movement ratio) - dampers need to move quite a bit to do their job well, but you can effectively double the movement of the damper for the same amount of given wheel travel. This is a real advantage when trying to control the wheel. More movement = more control over the wheel.

[Alfanatic]

Thanks for the additional information LaurenceFrost, very interesting reading and it all makes a lot of sense!

[thegreenhell]

tuffer said:

Un-sprung weight.....but I'm no chassis guru.

This layout would surely increase unprung weight? The pushrod and the rotational element of the bellcrank's mass are on the unsprung side of things, in addition to the usual bottom half of the damper. Admittedly they would only add a small percentage of the total in relation to the wheel, tyre, brakes, hub and upright.