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Peter68

Are Strut Braces necessary ?

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Found an interesting article on Scooby.net which I am sure they will not mind being shared here :-

This  is what Prodrive guru Damian Harty had to say:

Strutbrace Q: There is an awful lot of mythology around this stuff that goes back to body-on-chassis beam-axled racers in the 20s - I'm not kidding. There are two effects that are important. Basically, the body structure is like a "fifth spring" between the front and rear suspension. If that spring is not stiff enough then the body relaxes out any redictribution of roll moment that the anti-roll bars were trying to make and so the car is unresponsive to handling balance tuning with springs and bars. However, once the body is "stiff enough" then making it stiffer offers no benefits. A good rule of thumb is that the torsional stiffness of the body (between suspension mount points) needs to be about ten times the roll stiffness of the stiffest suspension end (usually the front). If you chase the numbers through you end up with about 5-7 kNn/degree as the requirement for a body structure. Most modern monocoques comfortably exceed that and the Subaru with its bonded screens both ends does too. Somewhere I have a figure but can't recall it right now. Anything over 10 is good, 15-17 is current "state-of-the-art". So in that case, a strut brace does very little. The second effect is a bit more complicated. The body moves on the suspension but the wheel also moves on the tyre - the tyre is in many ways a "secondary" suspension system. That movement is partially controlled by the tyre and partially by the suspension damper and happens 10 to 15 times a second. The body is a flexible thing that has its own resonances and because of the shape of most cars at the front - they need a hole to put the engine in - it can get quite flexible in just about this frequency region. If the body goes flexible - goes into resonance - then the damper just moves with the body and can't contribute to the control of the tyre and in fact can do something bad called "mass loading" where the tyre is carrying not only itself but also part of the body _while it resonates_ (it's important to separate the static 'weight carrying' from dynamic things in your mind). In those cases, the strut brace can help because if it is a good design then it stiffens the front end usefully.

What all of the above means is that the effectiveness of a strut brace is strongly connected to the stiffness of your suspension. So for a Scoob that is fairly standard, the strut brace probably doesn't do a great deal, but as they get modified and stiffened the brace will contribute more to a well controlled feel over less-than-perfect surfaces.

The final point about strut braces relates to the emporor's new clothes - having bought a flash one, not many people will admit they can't really tell the difference.

Sorry for such a long answer but it isn't straightforward, especially when I'm denied my usual engineering shorthand of "Hz" and "modal damping" and so on..

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It's also car dependent for some of the effects/benefits/downsides as well.

On the Mk1 Clios for example, fitting a strut brace does stiffen the front of the car but when driven properly hard, what it also does is move the flex to somewhere else on the car causing the roof to flex instead. It's only an issue to the cars with a sunroof fitted as the roofs aren't quite as strong with a big hole cut in it and it starts to let water get into the car :lol:

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When I had my 94 Impreza the front brace did naff all, the rear one when eventually fitted made it feel sharper.

I fitted a front one to a mk1 focus and that really made a difference, really turned in well, then fitted coilovers and it was terrible so removed it.

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