Tube size strength information.

[Ant]

Starting to look at my IRS and building a new subframe and A Arms.

The Certification people here require a plan with tubes sizes etc so we can go through the design phase and get approval before construction. They specify a minimum size e.g. a lower rear A Arm is 7/8" diameter tube with a wall thickness of 5/32" for generally speaking a heavy weight sportscar.

I am thinking of using 4130 tube 1-1/4" diameter x 0.080" WT for the lower wishbones and would like to compare the strength to their minimum specifications. There must be a calculator or for people like me that aren't that good at Mathematics a formula to calculate.

Feed back appreciated.

[Silverback51]

Sorry, I'm an engineer and I do not know of a table format short cut for you to use.

Just to many variables to try to tabulate.

[mickmate]

Hey Ant what about getting some projected numbers together and seeing if a good mechanics lecturer from AIT might like to look at them. Maybe even as a class project. Think about the weight, acceleration, more importantly deceleration, cornering G's etc. I think decel would be one of the more critical numbers. You're dividing force over length of arms, number of members, spacing etc. We had a couple of really keen and clever car guys when I was there that would love to crunch some numbers on that kind of stuff.

[vector1]

the jbl uses 1.25" dia. tubing for front and rear a arms fyi.

[Ant]

Thanks for the replies,

I spoke to the certifier today and he has asked me to supply information on the Rectangular front lower suspension arms 40mm x 25.40 x 2mm WT, these arms have been used for the best part of 25 years on cars the same as mine that ran in the Cobra Bardhal series early 1990's in France. We have a Hobby manual with minimum sizing and we are able to build aslong as the material selected meets the minimum standard, what I am wondering is why are the asking me to come up with a yield analysis of the rectangle steel when I am paying them to do a job and they must have some basis or knowledge to approve or reject a submission.

One option might be as I did with my single hoop roll bar I had to spend considerable money etc with a consultant Engineer.

Vector1 1.25" appears to be a good diameter for a lower wishbone for an approx 950kg cobra like mine, I guess your arms would be 2mm wall thickness minimum.

[Three Peaks]

The drawings I have for the original Cobra control arms shows 1 1/8" tubing with .120 or .134 walls IIRC. I have some I got from Kirkham that look the same spec that I could measure if you need.
Can't help with the stress analysis though.

Bob

[vector1]

Ant, contact Richard Hudgins via the JBL forum, he should be able to help you on a couple of your questions, i don't know the thickness of the tubing.