Frog arms or butterfly brace?

[NitroDann]

I would be so keen, but.. would the market?

Typically I dont believe in adding material to increase stiffness unless its obvious triangulation or an obvious design flaw, weld in simple parts I can get behind.

Any reason you dont just weld in bolt in's?

Dann

[davekmoore]

Don't think it's a design flaw as such, but all three of the MX5s I've owned have had the interior lights come on when going over decent sized bumps. This has never happened with any non-soft top car apart from an Austin Allegro and suggests a floppy body which seems difficult to avoid while only having one thin connection point between the front and back of the car compared with a car which also has a roof connecting the front to the back. While there's supposed to be more stiffness in later cars my 04 SE suffers no less than my earlier two cars (although the SE may be affected by having more power than the others).

A full welded in cage would obviously help the connection and the stiffness.

But for a car that's used on the road as well as on the track, is it worth looking at door bars and/or frog arms and/or something else which does the job but doesn't attract the sort of attention a cage would?

[NitroDann]

Well that is the question isnt it.

One thing is to decide if the stiffness offsets the weight in a performance application.

I have decided to compare braces to mufflers. (example uses na6)

With mufflers one person will say "my car sounds different with this on and I prefer it.
Another will say "my car sounds better AND it makes the car heaps faster". Which is BS.

With braces one person will say "my car feels different with this on and I prefer it.
Another will say "my car feels better AND it makes the car heaps faster". Which is very debatable and 100% unprovable.

See where I am going with this? Some braces MAY stiffen the car enough to improve performance. Welding a bar across the top of the door opening and then a diagonal across the cabin is definitely a cheap easy effective way of fixing a design flaw (no roof), adding material to a frame rail (by adding 'frame rails) just doesnt make sense to me.

Any engineer who has seen an FM butterfly brace would just laugh. Its laughably poorly designed and flimsy. It may change the feel and some may prefer it.

Dann

EDIT, my example of welding the door opening closed is what door bars hope to achieve, also frog arms appear to make sense in the way they are loaded and can be manufactured. All of the braces add mass so change the harmonics of vibration often called scuttle shake, again, some people may prefer the feel, but it would be silly to assume a noticeable change was an improvement rather than just a change.

[davekmoore]

I'm going to make the chassis seem way stiffer by deactivating or removing the door-open plungers and just relying on the dome light switch. What's the best way to do this? I prefer to remove the plungers as this'll save a heap of weight.

Or maybe I could seam weld the back edges of the doors to the front of the rear wings? That's got to be a heap of stiffness right there. Might even weld the front edge of the doors to the back of the front wings as well and remove the hinges to save even more weight. Perhaps weld across the bottom of the doors too? A decent bodyshop could make it look stealthy. Some issues with getting in and out of the car though, especially for an old dude. Might need an hydraulic seat. Certainly need the roof down and not to ever use a hardtop, but then I've just had to sell the hardtop to help fund the end of the motor rebuild, so that all works out ok.

[kazama]

nb coupe body rigidity would be delicious id imagine. maybe similar to rx7 level?

[sailaholic]

Done any engineering courses Dann?

I know a few engineers that agree with frame rail braces. And a few that have looked at the butterfly brace and not laughed.

I've been told if you have a good look under the NC there is a structure similar to a butterfly brace.

Similarly they have questioned the design of the frog arms.

I also seem to remember you arguing strongly that a factory hardtop couldn't add stiffness but then Danny went and proved that it does.

I agree you need to weigh (pun not intended) the "advantage" of braces against their weight.

I would agree that people get caught up with bracing "hype" and the need for a stiffer car.

But maybe be a bit more careful when throwing big statements around.

Dave I've never had problems with my lights, I'll have to make sure I they are on door for the next couple of drives.


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[NitroDann]

I don't have an issue with the concept of the aftermarket butterfly brace. I have an issue with the execution. Put a butterfly brace in their hands and ask.

I know full well adding depth and mass to the rails will add stiffness but I see no performance benefit.

I doubt I ever said these ideas (the xoncwpts not necessarily the aftermarket executions) couldn't add stiffness but I stand by them not adding quantifiable performance. See the muffler example.

Of I said the hardtop Adds no stiffness and I may have. I was wrong.

[JLDM]

Garage star sell their own fender braces and they aren't too expensive.

[malibu Q]

I have both. Installed the frog arms first and didn't think they made hardly any difference. I installed a Carbing three point front strut brace prior to the frog arms though. The front strut brace only made a small difference too.
The FM rails and butterfly brace made a huge difference that was apparent immediately. I could feel it as I was taking the car off the hoist after fitment. Makes the car feel much tighter.

[revhead]

i would be keen on some functional bracing! whether it is functional in the fact that is helps me get around a corner cleaner, or functional in that it removes some annoying rattles/vibration (without adding a heap of weight that is), i would be keen
light weight + handling performance and/or vibration killer = useful bracing (to me anyway)

if you start a pre buy special on off the shelf "frog arms" or custom made arms, let me know. thank you.

[davekmoore]

i would be keen on some functional bracing! whether it is functional in the fact that is helps me get around a corner cleaner, or functional in that it removes some annoying rattles/vibration (without adding a heap of weight that is), i would be keen
light weight + handling performance and/or vibration killer = useful bracing (to me anyway)

if you start a pre buy special on off the shelf "frog arms" or custom made arms, let me know. thank you.

Here you go ......

viewtopic.php?f=82&t=63654

[revhead]

Thank you! I put my name down and following the thread. Cheers

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