Anyone install coil overs instead of using torsion bars?

Going to install coil over springs in lieu of using my torsion bars on a S1 E.
Has anyone here ever done this or similar?
I want to delete the reactor plate. :skull_and_crossbones:

Thanks in advance

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I believe the coil over conversion has been done before however the reaction plate should not be left out as it is important structural component of the car.

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You’ll probably find it has been covered before if you use the search function to read around the topic.

The torsion bars transfer the bulk of the front suspension load directly into the tub as that is where the back end of the torsion bars is, bolted in via a chunky thick frame called the reaction plate.

By contrast, coil suspension will put all of those forces into the front of the frame tubes, which hitherto have only carried a constant load equal to half the weight of the car. The variable loading here will attempt to twist, bend and buckle the frame tubes more than they were designed to be twisted and fifty years later, that may fatigue the remaining metal more than the original designers anticipated.

You’d really want to sit the car on a jig and look at how both versions move around to see whether that will be an issue in the real world.

kind regards


I think @CliveR can advise you on this: it’s not a simple substitution.

I’ve got to ask, what is the white car in the photo? Would love to see more.

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“Advise” might be too strong a word…I’m not going to contradict those with direct practical experience of this car, as Marek says it’s a long running topic.

Of course I can’t resist a personal surmise, and I surmise that the loads currently applied to the front structure by the dampers are greater than a coil spring would apply at that location (noting that the damper loads in rebound are typically higher than compression, giving a more severe total load cycle than a spring).

The standard jounce bumper adds another level of loading, greater than the spring by definition.

Considering the number of cars now running dampers with higher forces than the original, if they don’t show a pattern of chassis damage then I think it would be low risk to add a coil spring to the front damper.

Detail damper force data is here for those of an inquisitive and numerical bent. (pull up a chair) Getting the best out of standard suspension components for touring driving today

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In place of the TB?

Surely the dampers are only affecting the rate of change of where the force is applied.

Dampers are very easy to compress/extend.

That says, with the spring attached to the tub, only a small force is going into the picture frame, whereas a coilover always has 100% going into the picture frame.

kind regards

edit:- I’m assuming we are dealing with torsion bar versus coilover, not a complementary extra spring onto the picture frame. (The original poster did say “in lieu”.)

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If the goal is to leave the reaction plate off, its a non starter. The plate is too important to the structure.


Absolutely, unquestionably and in the name of the human race

It’s not often I find my antennae tingling, with respect to what an engineer like Clive asserts, but I don’t get it either, how a standard damper exhibits the same force on that front structure as it would holding up the entire weight of the car and the concomitant reaction forces.

Here’s the last time we discussed this:

My conclusion is that a coil spring setup is feasible. The load paths are not as different you think. Plenty of non minor details that would need to be worked out.

Question: Do the S3s use a reaction plate or tie bar?

No: the S3 completely eliminated the reaction plate and has a different scheme for attaching the torsion bars to the chassis.


My take on this is:-

Until either the damper or spring (no matter which type) move, the force has to hammer into the car and move it.

Logic says that if the damper or spring gives a bit, the metal at the other end of the spring or damper doesn’t have to.

So the rate at which the front frame is flexing is lower than at the tub.

kind regards

The s3 has a piece of angle iron going across the front footwell and the torsion bar terminates into there, hence my making references “into the tub”.

kind regards

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My suggestion is that changing the spring medium from a torsion bar to a coil spring, coaxial with the existing damper, does not greatly add to the duty cycle of the surrounding structure. I believe the added spring loads are not large compared with the loads already applied in that area - namely, the damper and jounce bumper.

The damper does not support any static load because it is a velocity-sensitive device - zero load at zero (stroke) speed, loads much higher than spring load when the car encounters a bump. The example chart below shows how quickly those loads can build as the severity of the bump (stroke speed) increases. Bear in mind this test was only run to 250 mm/s stroke speed, where a real-world ridge or pothole can inflict 1500 mm/s or more.

OK: I trust that all your numbers are correct. Then why, if Jaguar felt that that front subframe was robust enough for that, did they not use coilovers rather than the more complicated torsion bar?

I’m not sure I follow you, Marek. The spring and damper will move in response to an input force from the road. The level of damping will determine the output force to the body, but it should always be reduced by some amount - that’s the purpose of the suspension.

I can only surmise they wanted a link with the previous generation racers. Also eye candy & talking points for the frequent occasions the hood would be lifted and the entire front end on display - hence also the pretty but complex wishbone arrangement while the poor damper is hung sadly off the front of same, supported only at one side.

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I know that this thing about dampers only being supported on one side is a big bugaboo for you, but I can also think of about a gazillion other chassis types, from trucks to jeeps to Formula cars, whose dampers were all hung on one side: I don’t know what the problem is there.

It isn’t an absolute perfect application of force, I know, but apparently doing it on one side was OK enough?