Crazy idea #5672 - front stiffening

[widebody911]

Mulling over how I can stiffen up my car, I struck upon this idea. I haven't really done a lot of homework on it, but I'll lay it out here anyway.

My idea is to triangulate the front of the car not just between the shock towers, but to the front A-arm pickup points as well. My contraption would consist of a couple of pieces of something like 1/2" 4130 attached topside from the strut bar or some place near it, down to the pickup point. Yeah, that's been done already; here's the crazy part: I would extend the hole that holds the cover plate for the A-arm protector, so the bolt would extend into the trunk, giving a removable attachment point. A tab could be welded onto the strut bar, enabling one to make a removable brace.

What do you think? Do I need to go back on my meds?

[Chuck Moreland]

You have the sickness, but you're not crazy.

I've looked into this exact idea. It can work, but a couple thoughts to keep in mind.

- The X brace tubes will intersect in the middle. This complicates fabrication and fitment.

- Though the bolts may protrude up from the A-arm mount, you want it to be firmly attached top-side. Otherwise you have a bolt 2-3 inches long sticking up and flexing.

Keep us posted.

[project935]

Maybe come up with a bolt-able connection at the intersection.

Double-shear the A-arm mount attachment.

Send me some rough dimensions and some pics of the attachment areas and I'll see what I can whip up in CAD if you like. PM me if interested.

[jluetjen]

How stiff is your car torsionally (front to back)? Oh yeah -- it's a cab -- it's not. It may not hurt to do what you are suggesting. But if your car is as soft as a wet noodle between the rear wheels and the front wheels, stiffening up the front may not make a whole lot of difference when compared to the additional weight of the tubing.

Have you ever tried measuring the torsional stiffness of your car? It's pretty straight forward (although I've never done it yet). Basically you attach the rear of the car (ideally close to the suspension mounts) firmly to some some jack stands. You also support the front of the car on the centerline. You then apply a known torque to one side of the front suspension mounts (Say the weight of hefty friend) a known distance from the centerline of the car and measure how much the suspension mounts move vertically. You then work the math and voila -- the torsional stiffness. Now try adding your brace and see how much of a difference it makes.

Having played around some with cage designs and FAE software, I suspect that you'll find the change is negligable.

[project935]

I agree - overall torsional rigidity won't change much in a full vehicle CAE analysis ... esp with a cab.

You'll certainly locate the front of the A-arm mount better with respect to the shock tower. Probably keep things in alignment better in the case of an accidental off-track excursion.

Thom - do you have any fore/aft connections between the towers and your interior cage? Obviously needs to go thru the dash. That would be your best bang-for-the-$.

[kach22i]

Originally posted by widebody911
Do I need to go back on my meds?

No, but I'll be saving this quote for the O.T. section.

Nice to see you think about your car in the same way you do other topics- outside the box.

[banjomike]

I looked at your car website. Do you race or DE? Lots of racing classes limit suspension pick-up point reinforcement or tie-ins. You wouldn't want to bump yourself into a faster class.

Another question... What kind of stiffness are you trying to add to here? I can see how this could add to longitudinal stiffness but how much flex could a 911 have between the strut tower and the a-arm mount? It might prevent the strut towers from moving forward and back relative to each other (like one moves forward while the other back), but there is already lots of structure preventing that. I can't see it adding any torsional stiffness. I suppose this would make sense if you tied it into a rollcage, then you might be looking at increased torsional stiffness, which is a good thing. I guess I just have my doubts that this would add much (or any) to the structure beyond what a triangulated strut tower brace will add.

If there was any flex that this would stiffen then welding tabs somewhere along the strut brace would introduce a bending force in the strut brace where the diagonal was attached. You'd probably want to tie into the strut tower itself.

Finally it looks to me like the gas tank and battery are in the way (unless you've moved your battery). I located the top of the a-arm brace just by feeling it, and I could be way off.

[Bill Verburg]

Like this?


IMO w/o a full cage tied to all the suspension points it won't be effective

[banjomike]

Gee while I was writing my reply a few others beat me to the same points. And even worse I looked at the pics and didn't notice it was a cabrio!?!!? From the pics it looks like you have a roll bar but not a cage, a roll cage will work miracles for your car's overall stiffness. A Cabrio has big deficits of longitudinal and torsional stiffness. Just think about how easy it is to flex a flat piece of cardboard versus a taped up cardboard box. The cabrio isn't much more than a flat sheet between the A pillar and the B pillar.

I photoshopped up a photo of your car to show what a cabrio's structure looks like.

d'oh!

best solution for adding stiffness to a cabrio, buy a coupe.

[banjomike]

I looked at your car website. Do you race or DE? Lots of racing classes limit suspension pick-up point reinforcement or tie-ins. You wouldn't want to bump yourself into a faster class.

Another question... What kind of stiffness are you trying to add to here? I can see how this could add to longitudinal stiffness but how much flex could a 911 have between the strut tower and the a-arm mount? It might prevent the strut towers from moving forward and back relative to each other (like one moves forward while the other back), but there is already lots of structure preventing that. I can't see it adding any torsional stiffness. I suppose this would make sense if you tied it into a rollcage, then you might be looking at increased torsional stiffness, which is a good thing. I guess I just have my doubts that this would add much (or any) to the structure beyond what a triangulated strut tower brace will add.

If there was any flex that this would stiffen then welding tabs somewhere along the strut brace would introduce a bending force in the strut brace where the diagonal was attached. You'd probably want to tie into the strut tower itself.

Finally it looks to me like the gas tank and battery are in the way (unless you've moved your battery). I located the top of the a-arm brace just by feeling it, and I could be way off.

[widebody911]

No, Bill - the other way, downward. I do need to do something upward eventually, though.

I already have longitudinal braces; see pic below.

One of my near-term plans was to get one of those lightweight batteries and relocate it to the smuggler's boot.

[Paul Thomas]

How about this? 934 at RR2.

[widebody911]

Originally posted by Paul Thomas
How about this? 934 at RR2.

Next time give me a "NSFW" warning!

Yes, like that

[john70t]

banjomike seems to have condensed it with a single pic.
The front (empty trunk with heavy tank) can be stiffened to a rock... and roll well on smooth track....but there's still twist in the middle without a swing/lockable bar along the top of the door panel.

Kind of like a human spine. 6inch diameter bicepts are no good when there's a couple tweaked vertebrae in the middle.

[SpeedracerIndy]

I think this is a much better idea for stiffening the front: Training wheels on my Porsche

Plus it has the added benefit of protecting the bottom of the car! Sorry, couldn't resist.

[RSBob]

Crazy idea #5672 - front stiffening

Thank god this is about cars and not another guy who took too much Viagra and needs to go to the ER for a woodectomy.

Many guys use X braces inside the doors to add ridigity to coupes as well as cabs. You might consider something like
---
X
---

Crude, but you get the idea.

[aturboman]

This is my version of front end reinforcement. I have made a x-brace as you've discussed. It is fastened in with some trick Titanium bolts, I've shown a close-up of the intersection of the X that is welded. Hope this is is what you were talking about.

[john70t]

Thanks for the pics. Definitly impressive and well made, but with that much bracing it's now endo-skeleton instead of exo-skeleton.

That heavy steel shell could be replaced with Nascar fiberglass.

[aturboman]

I agree it is a bit of overkill but it's hell for strong and not as heavy as you might think. I can easily lift front of the empty shell off the dolly by a foot, and I'm not very strong.