I'm looking for advice on A-arm materials. Currently, I plan to use 3/4", .125" DOM. I plan on using heim joints for the suspension. Rather than thread the the male heim joint into the DOM, I want to weld a 4030 threaded tube adaptor. Is this the adviseable materials to use or can I get away with something lighter--ie thinner wall, etc?

Drawn Over Mandrel with tube insets should be fine. If you want to go a bit OTT you can also get them nitotec's as I did.
cheers
Rob

http://www.nitrotec.co.uk/properties/properties_frames.htm

Go up in tube diameter before increasing the wall thickness. The lower wishbone tubes are loaded in bending and the book design relies on that big 1/8 inch plate to stop it from folding up over bumps. Moving the coil pickup closer to the hub is a good thing, check out a Caterham, it gets much closer than the book design and is less loaded as a result.

A one inch 14 gauge tube or 16 gauge tube would be stronger and lighter than the 3/4 inch 1/8 wall tube.

The 16 g tube can take 25% more load and the 14g one can take 33% more load.

Most of my rear suspension links are 1" 16g tube with welded in threaded bungs (1/2-20 UNF).....no bending loads on any though....seem very strong indeed....

well the kit i bought just had normal welded seam tube apparently in 16swg.

Nothing much wrong with ERW (welded tube) IMO.....in 20 years of usage I've never seen a failure (seam split)....I think it is pretty well made these days

certainly hope so! my bones are 16g 3/4 inch round ERW, plus the 3mm plate is a bit chopped about. I think this will be the first thing i replace, cos its not very good...

Spose 15mm copper pipe and yorkshire fittings are out of the question then?

I know of a failure on rear training arms on a Mallock that were 3/4" 1/16g and these had to be beefed up.
However it was pushing out over 200bhp.

Check out the Nitrotec treament I mentioned earlier. I judge at Formula Student and I see it appearing on thinner and thinner gauge tubing all the time!

I honestly do think we are prone to over engineering - but not a bad thing for road use.

I attach an interesting article for interest

PS: Just saw the copper tubing post

Interestingly enough I have seen a prototype chassis made up in 15mm copper and solder fittings - beats wood mock up I suppose!
so there........

Thank you all for the advice. I am now clear as to what the A Arms will be made of. My current plan is to build the suspension out of the 1" DOM. I really want to build this car so I can enjoy it next summer. When it is complete, I will start experimenting with Ti tube and the suggested coating. That is the dream anyhow...

--Thanks all, Chris

We have to over-engineer, or we'll die! As amatuer builders we do one or two cars in a lifetime & there's no way we can do all the analysis and testing Mr Ford does on his new models - it's generally a case of "if it looks right" & make it way too strong. I'm doing an IRS for my locost. OK I can estimate static, sideways and braking forces but my biggest concern is "pothole" stress trying to rip a wheel off, I think all I can do is make it really strong! So I'm putting 1" sq. tube down the transmission tunnel top as well. If I'm still posting here in 3 yrs time then it must be over engineered!
cheers
Bob C

You'll need it over engineered with those roads around Knutsford Bob

ahh you've visited then.....
actually there's some nice roads hereabouts, my commute to congleton is V pleasant (not fast mind you). Too many roads ruined by gatsos & their ilk - the cat&fiddle road has its own police helicopter on nice days!
Bob C

Good to hear BobC is dealing with the pot holes. I'm relying a bit on his suspension design!

I forgot to add that, after all the hard work, it looks like heim joints are not in the cards. For all the material, the cost would be about $100 USD/corner. Not locost at all. So, it looks like Delrin will win out.

[Edited on 11/3/04 by chrisf]