Do any of you road racers or time trial guys use a strut tower bar?

[CSG Mike]

Originally Posted by ROADRACER

So are you saying stiffer springs will not increase the force exerted on the strut tower?

It does not.

Lets say you have a scale, and you put a spring on it and tare it, and then stand on the spring. Now, you change that spring for a different rate spring, tare it again, and again, stand on the spring.

Does the scale read a different weight for you?

[rice_classic]

Originally Posted by CSG Mike

It does not.

Lets say you have a scale, and you put a spring on it and tare it, and then stand on the spring. Now, you change that spring for a different rate spring, tare it again, and again, stand on the spring.

Does the scale read a different weight for you?

I disagree. Your example is good for static load but not for when an external force is applied.

Force over time is what's at play. It's the same principle behind crumple zones, safer barriers and Hans devices. The force is reduced if spread over time.

So if I clip a tall curb at the apex which applies 1500lbs of external force to my suspension, the force transferred to my shock tower is a function of how much of loading is spread over time. A 2000lb spring will spread that loading over less time vs a 500lb spring and thus transfer more force to the tower/body.

The amount of external force that is transferred to the chassis is directly related to the amount of force that can be absorbed. Stiffer springs exactly means that more force is transferred to the chassis.

edit: The best terminology is the word impact. A stiffer spring means that hitting a curb transfers more of the impact to the body.

[chaoskaze]

Originally Posted by Pat

Yeah, I think I'll pass on getting one now.
But I do wonder, after the chassis has 150,000 hard miles on it, would the strut tower brace be more noticeable and effective?

I don't think so? But If you get the Subaru flex bar + straw stiffener. (They are designed as a pair that works together instead of a giant bar) I'm sure if will have a positive effect over long term.


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[CSG Mike]

Originally Posted by rice_classic

I disagree. Your example is good for static load but not for when an external force is applied.

Force over time is what's at play. It's the same principle behind crumple zones, safer barriers and Hans devices. The force is reduced if spread over time.

So if I clip a tall curb at the apex which applies 1500lbs of external force to my suspension, the force transferred to my shock tower is a function of how much of loading is spread over time. A 2000lb spring will spread that loading over less time vs a 500lb spring and thus transfer more force to the tower/body.

The amount of external force that is transferred to the chassis is directly related to the amount of force that can be absorbed. Stiffer springs exactly means that more force is transferred to the chassis.

edit: The best terminology is the word impact. A stiffer spring means that hitting a curb transfers more of the impact to the body.

That's where the damper comes in

[rice_classic]

Originally Posted by CSG Mike

That's where the damper comes in

Affirmative. Same principle still applies. Force over time.

[nikitopo]

Exactly. All these are well known properties discussed in forums a long time ago. Damian Harty (Prodrive) gave once some good feedback:

"the effectiveness of a strut brace is strongly connected to the stiffness of your suspension."

[nikitopo]

Originally Posted by gramicci101

Rather listen to someone who's graduated high school already, thanks.

He is 26 years old and he is a mechanical engineer. He has already worked for an automotive company designing a hybrid.

[Yoshoobaroo]

Originally Posted by CSG Mike

I guess this car needed a strut tower brace. It's a Porsche GT4.

A strut tower brace would not have saved this.



MAYBE a strut tower reinforcement plate like pictured above would have, but I still doubt it. These are used in E46s. (early 2000 BMW 3series) as their shock towers were on the thin side. They will stiffen them and thus help prevent a fatigue fracture.

On this Porsche it looks like the vertical impact was just too much for the sheetmetal. That's not a fatigue failure. A brace does not transfer vertical forces well, only lateral forces, so it wouldn't have helped.

-Josh

[gramicci101]

Originally Posted by nikitopo

He is 26 years old and he is a mechanical engineer. He has already worked for an automotive company designing a hybrid.

Whoopty doo. Does he have any experience racing this car beyond the theoretical? You said yourself that how effective these things are is very vehicle dependent, so why is it so hard to accept that on this specific chassis, they really add no value? Theory is great, math is great, but in the end I'll listen to the people who race this specific car and have tried everything in search of faster times. You seem to be dead set on the idea that all of these people, who have many many more track miles in this car than wonderboy engineer does, are wrong. Why? Because strut bars make a difference on other cars? Because they mathematically add some fraction of a percentage of stiffness? Show me practical unbiased results, not theory.

[Yoshoobaroo]

Originally Posted by gramicci101

Whoopty doo. Does he have any experience racing this car beyond the theoretical? You said yourself that how effective these things are is very vehicle dependent, so why is it so hard to accept that on this specific chassis, they really add no value? Theory is great, math is great, but in the end I'll listen to the people who race this specific car and have tried everything in search of faster times. You seem to be dead set on the idea that all of these people, who have many many more track miles in this car than wonderboy engineer does, are wrong. Why? Because strut bars make a difference on other cars? Because they mathematically add some fraction of a percentage of stiffness? Show me practical unbiased results, not theory.

The math will tell you much more than people's first hand experiences. Humans are shit data collecting devices. We can't figure out placebo from any real effects, especially when changes are subtle (like with a strut bar). Look at grimmspeed's data for their bar. Sure looks like it's effective, bravo them, it's an effective part and they met their design goals. But a lot of people still don't feel the difference.

-Josh

[gramicci101]

Mathematical differences can also be too small to provide any practical effect, which is what I think is happening here. Sure, any bracing will make the chassis stiffer to some extent. But to what extent? In this case, not very much. Not enough to be worth the money. On another car with different construction? Yes, absolutely.

[Sleepless]

Originally Posted by Yoshoobaroo

A strut tower brace would not have saved this.

...

On this Porsche it looks like the vertical impact was just too much for the sheetmetal. That's not a fatigue failure. A brace does not transfer vertical forces well, only lateral forces, so it wouldn't have helped.

-Josh

Strut bars do transfer some of the vertical force to the opposing tower so I don't think we can conclusively say a bar would not have saved the Cayman's tower.

[Sleepless]

Originally Posted by gramicci101

Mathematical differences can also be too small to provide any practical effect, which is what I think is happening here. Sure, any bracing will make the chassis stiffer to some extent. But to what extent? In this case, not very much. Not enough to be worth the money. On another car with different construction? Yes, absolutely.

Given that at least one of the "experts" is wrong about the forces exerted on the towers when going with a stiffer suspension, I'd rather go with sound theory personally, and I did and can feel the difference. Am I faster? Hardly. But the car feels better to me.

[gramicci101]

You sure it isn't a placebo effect? I'd want something I spent money on to make a difference too. So how much stiffer does a strut bar make the chassis on this car?