Torsional rigidity--measuring and increasing

[mikedc]

I don't know about you guys, but I've never actually flung around a Bughatti Veyron's 60,000 Nm/deg chassis and tested how it feels compared to 34,000 Nm/deg Fararri F50.


Specific numbers on a few cheaper & older American rides might be a bit more relevant.

[Tony Arnold]

What i noticed from the pictures posted of the chassis stiffners are that they do not provide any triagulation and do not strengthen the chassis where it sees the load. If you were to look at any NASCAR chassis you will see multiple bars going to the spring pockets. This help support the load that the chassis sees at the point it gets loaded. You will also see that most chassis builders will tie both front hoops or spring pockets together with either bolt in k or x bars. Keep in mind these are just my suggestions. One simple thing you could try is make a bar about 1 3/4 in dia and run it across both hoops to tie them together.

[TheBandit]

I stumbled on this thread reading through the stickies today. I'd really be interested to see this kind of testing done for the Hotchkis Handle Bars.



Thanks to all who've contributed to the thread. I will try to get similar measurements before & after on my Nova when the time comes.

[andrewb70]

....I will try to get similar measurements before & after on my Nova when the time comes.

Better late than never :-)

Andrew

[TheBandit]

Better late than never :-)

Wow I forgot all about this thread. Looking at the dates I was still a few years out from having my car back on the road at that time. I recently started a new thread on this topic, but decided to nuke it to keep the conversation going here since there is already a lot of good info.

I am preparing to install subframe connectors and I plan to get a baseline measurement on the torsional rigidity of my car, then see how much it changes. After reading through this thread I have a few ideas on how I'll go about it. Thank you for pointing me back here Andrew!

For reference, in addition to what's described in this thread, I came across another well-documented attempt at this here:
https://www.stangnet.com/mustang-for...-coupe.723029/

[David Pozzi]

I recommend using a dial indicator instead of the angle finder that I used in my tests. Accuracy is rather poor with a .05 resolution angle finder. With a more common .0 resolution angle finder, it's very poor. Many phones can do angles but I think the resolution is not good enough.

[TheBandit]

David I could not find inch on how you constrained, loaded or measured yours. Did you post an explanation here or on your website thanks for any pointers.

[TheBandit]

Found a great video here

[Norm Peterson]

When you're looking for effects in the 5%-ish range, I think you should be hanging barbell plates from a fixed position near the end of that bar. Bags of loose stuff distributed over a foot or more probably won't end up with their weights as evenly distributed from one trial to the next, or even be located in the same places every time.

The door bars can only improve torsional stiffness over their length within the chassis, so they may well have added 8% - 10% to that mid-section portion of the chassis. Everything in front of and behind that section is the same as before, so the overall effect would be one involving "springs in series" math.

But it is a good illustration of concept, despite the mention of strength rather than stiffness.


Norm

[David Pozzi]

David I could not find inch on how you constrained, loaded or measured yours. Did you post an explanation here or on your website thanks for any pointers.

I tested similar to the Porsche video. Used a chain to support the square tube & apply torque. I did not tie down the other end. Just supported it on jack stands. It’s heavy enough That it did not move on a fully built car. On a shell it needs a counter balance Weight or tied down. I tested a Camaro with roll cage & nearly no stiffness improvement! The forward braces stopped near the steering box coupler which was required by the SCCA rules.

[TheBandit]

Thank you David. Where did you position your jack stands? With a fully built car I am thinking both sides under the rear subframe near the front leaf spring perch and one side under the front subframe on the horn extending in front of the suspension. Then a chain over the other horn of the front suspension for the lever bar. Torque would be measured from the single jack stands up front to wherever the weight is applied. I would measure deflection at the unsupported frame horn.

I was thinking maybe instead of using weights, I could use a jack and put a bathroom scale between the jack and the lever arm. That would require chaining the opposite side of the lever arm.