What gauge/type tubing has everyone used for making their wishbones. I was planning on using .090" 1" OD 4130. I was wondering if I could get away with .065" for the top front wishbones. A buddy who builds race cars is going to TIG weld them for me.

I'd say 0.065" was fine, especially Cromoly and Tigged....

What does you race car builder buddy think?

I suppose it depends whether he builds lightweight road racers.....or NASCAR tanks........

The cars he build are powered by big V8's. Not quite Nascar heavyweights at around 2400 lbs. He suggested .090" all around. I have quite long wishbones especially at the rear (about 16". He was a bit worried about them folding if made from 0.065". Plus the motor will be about 270hp fitted with a turbo. Approx 165 ft/lbs of torque. So it needs to be strong enough to cope with the loadings.

PS I seem to have an attack of the smiley faces. Guess I need to be carefore with my use of " and .

[Edited on 26/5/03 by ProjectLMP]

Yeah, I'd guess 16" sways the choice a bit...I was picturing top fronts about 7" or 8" long....

Hey Alan I like the new Avatar!

Terry

Hi Terry,

It's cool isn't it?

Merlin did it for me.....it's better than my cheesy grin staring at you..

yeah, but have you changed that shirt yet alan?

I guess you'll never know......

That may be a good thing......

Rorty, do you have an opinion on what gauge of 4130 to use for my wishbones? Approx lengths of wisbones are:

Front top 11"
Front bottom 15"
Rear top 14.5"
Rear bottom 16.5"

The car is expected to weigh close to 1100 lbs

PLMP, OK, let me see...carry the zero....multiply by Yank....equals....1" X .083 for them all, though you could drop down to .065 wall for the top wishbones. I presume you'll brace them properly etc? You should be able to buy ready made ferules for those sizes too, though for bush tubes, you'd obviously have to use thicker wall stuff.

This is when you need to research the "column strength" of the tubing you want to use. Wall thickness, diameter, and length all matter, with diameter being the most important. Approximate the maximum force you'll encounter, which will probably be pot holes. (This drove me nuts, because just what forces do you encounter from a "standard" pot hole?)

Also, I believe you must heat treat 4130. 4130 is no miracle material, just stiffer. The reason it's used is so a smaller tube can be used for the same strength, which is where the weight savings comes from. I didn't want really stiff arms - I want them to fold in an impact, not break. FWIW, I'm using plain old ERW 0.065" wall, 1" diameter tubing everywhere except the lower rear, where it is 1.25". Then again my car will be less than 1700lbs fully loaded including driver.

[Edited on 7/7/03 by kb58]

As far as I am aware all steels are the same stiffness just about. However, 4130 is tougher than mild steel and has a higher yield strength. I don't think you have to heat treat normalized tubing. However to get maximum strength you do. The downside is that it will make it more brittle and prone to breaking as apposed to bending. I also hear that 4130 is less susceptible to bending fatigue which can't be a bad thing in this situation.

I really didn't have a clue how to model the complex forces that act on the suspension arms (given the added complication of downforce just to make things more interesting). Hence I am going for a bit of a belt and braces approach.

Thanks Rorty. I am not sure if I can get 0.083" may be stuck with 0.095". I plan on using A type braces on all arms and a gusset where the two tubes join at the outer joints. I am thinking I will go with 0.095" (or 0.083" if I can get it) on the lower arms and 0.065" on the upper ones.

0.095" will definitely be belt and braces. It'll also be a bit nicer to weld.
I did use CDS/DOM at one stage, but always use CroMo for the bottom 'bones period.
I've even mashed 25.4 X 2.6 ( 1' X 0.102" ) CDS bottoms before. I must admit though, I nearly always use CDS for the top 'bones. Admittedly, on the buggies, the bones are about 500mm/20" long.
I think you'll be pretty safe with the sizes you've settled on.