The dynamics and the point of fitting a strut brace?
Discussion
My 350Z has one from the factory, I think Nissan realised there was some spare space so decided to fill it with more metal to try and compete with the Discovery 3 on weight 
On most cars it stiffens the front of the shell up, had one on a Golf GTI 5 door and it was a bit of a lost cause as the whole thing would flex along its length, jack a 5 door Golf up at the front and the rear wheels will stay on the floor for ages and the car twists a bit, my 944 cab was hilariously bendy.
I think modern cars are much much stiffer, my Saab 9-3 saloon, you could jack that up and the doors opened as normal, I know that is the whole shell but there must be a knock on to whether a brace makes and difference
On most cars it stiffens the front of the shell up, had one on a Golf GTI 5 door and it was a bit of a lost cause as the whole thing would flex along its length, jack a 5 door Golf up at the front and the rear wheels will stay on the floor for ages and the car twists a bit, my 944 cab was hilariously bendy.
I think modern cars are much much stiffer, my Saab 9-3 saloon, you could jack that up and the doors opened as normal, I know that is the whole shell but there must be a knock on to whether a brace makes and difference
Sensibleboy said:
I believe technically they promote understeer too just like a stiffer front ARB does.
Curious, I'd have expected the opposite. The loaded turret flexing out under hard cornering is going to decrease negative camber, which should decrease front-end cornering grip. Thus a strut brace which reduces the loss of negative camber should reduce understeer.
When I did my suspension refresh on my 306 'shed' a year ago which consisted of some new performance dampers, stiffer springs and some new bushes / drop links I sunk £40 on a used upper strut brace and the associated longer bolts.
It made a noticeable, immediate difference. Mostly to the amount of crashiness, rattles, creaks etc. coming from the windscreen area. I can only theorise that it passed the stresses onto this area of the body and the increased rigidity made it noisier and seemingly bouncier. Worried that I had cocked up the spring selection with the dampers I removed the brace at first opportunity and hey presto; beautiful handling.
It made a noticeable, immediate difference. Mostly to the amount of crashiness, rattles, creaks etc. coming from the windscreen area. I can only theorise that it passed the stresses onto this area of the body and the increased rigidity made it noisier and seemingly bouncier. Worried that I had cocked up the spring selection with the dampers I removed the brace at first opportunity and hey presto; beautiful handling.
Krikkit said:
As kambites said - the strength of the turrets is the key in whether it's worth having one or not, in your case I would definitely fit one.
Some really good and accurate information so far regarding the reasoning and the merits of fitting a proper and functional strut brace.For the OPs E46 M3, it should have had one from the factory, standard fit, however an uprated version wont do any harm. For a track E46 M3, the best thing for he front end would be to tie the struts into the roll cage for max stiffness.
On the rear, the main concern is to reinforce the subframe, and the subframe mounting points onto the car. Fully inspect it for signs of cracking too, as this would be disastrous for the car if it were to fail ..... Its a relatively common problem, however doesn't have to be the huge cost or hassle to remedy if it's done early and done properly. I work for a local race team, and we did mine over a few weekends a few winters ago, and it was much improved afterwards.
SuperchargedVR6 said:
I thought the bulkhead panel 'braced' the front turrets together sufficiently enough, for a road car at least?
For a transverse engined car, it usually will because the turrets are mounted so far back that they're almost in the bulkhead anyway. For a longitudinal engined car like the M3, the turrets are often directly opposite the engine so there's little in the way of bracing between them. TurboHatchback said:
I can't help feeling that if they really improved the handling on a give model by any perceptible degree the manufacturer would have fitted them at the factory (indeed on some cars they have).
I think they are fitted where a manufacturer, or their internal performance sub-brand, have a concern about rigidity or flex.Many cars may benefit from having a stiffer shell around suspension pick up points, however those benefits would need to be weighed up by the bean counters, and considered against the spec that the car is designed to be used for:
There may be gains for a dynamic improvement for a Toyota Camry, however would the local minicab driver be bothered?
Also, the inherent "give" in the shell of the car in certain areas, may protect other areas from excessive stress and potential fatigue ..... Nothing is ever perfectly rigid, and chasing rigidity isn't always ideal. That's why cars have rubber in their bushings, for both compliance and for reduction in vibration and stress in the body (and occupants)
kambites said:
SuperchargedVR6 said:
I thought the bulkhead panel 'braced' the front turrets together sufficiently enough, for a road car at least?
For a transverse engined car, it usually will because the turrets are mounted so far back that they're almost in the bulkhead anyway. For a longitudinal engined car like the M3, the turrets are often directly opposite the engine so there's little in the way of bracing between them. 
The reason that competition cars usually dispense with the rubber mounts and use spherical joints.
VonSenger said:
wow, lots of information here! Thanks. I think the consensus is fit a good one and it cant do any harm.
Pretty much. It can't do much harm (unless the suspension is tuned to take significant strut movement into account, I suppose); whether it will help or not depends on the car and the brace.
kambites said:
Sensibleboy said:
I believe technically they promote understeer too just like a stiffer front ARB does.
Curious, I'd have expected the opposite. The loaded turret flexing out under hard cornering is going to decrease negative camber, which should decrease front-end cornering grip. Thus a strut brace which reduces the loss of negative camber should reduce understeer.
hondansx said:
A strut brace may increase the threshold, but understeer will be more abrupt, so the feel of the car on the limit may make it seem like it is more happy to understeer than before.
Almost anything you do to "improve" the front suspension will have that effect though, wont it? Generally speaking, I've always found the more grip you give an axle the more suddenly it will lose grip when it finally does let go. Old cars with the chassis stiffness of a lump of Brie benefit from them quite nicely. My 180SX is keener to push on at the front without the brace on at lower speeds.
Increasing the stiffness of the chassis allows the suspension components to do their job better. If the chassis is moving around then the suspension is playing second fiddle to the chassis twisting and rotating during corner loading and over bumps etc.
As an example, an F-Type has some additional bracing around the turrets going forward to the slam panel and back towards the firewall. I would imagine it's to bulk up the stiffness and crash performance without adding additional aluminium or an alternative.
Increasing the stiffness of the chassis allows the suspension components to do their job better. If the chassis is moving around then the suspension is playing second fiddle to the chassis twisting and rotating during corner loading and over bumps etc.
As an example, an F-Type has some additional bracing around the turrets going forward to the slam panel and back towards the firewall. I would imagine it's to bulk up the stiffness and crash performance without adding additional aluminium or an alternative.
Edited by zeppelin101 on Monday 30th March 15:44
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