Tube specs for wishbones?

Hi guys, am at the stage (or soon will be!) of making some wishbones, can anyone tell me what sort of sizes are in use regarding the 40`s, I had a mind to use CDS with a wall of 3mm just need a diameter, I bought some 1" but it seems a tad on the small size!!! I will be welding ends in to accept rosejoints.
cheers Chris
 
Chris, dont risk it, take your patterns to Mick at SouthernGT to get the proffessionally made with the correct tube and welding, Frank
 

Russ Noble

GT40s Supporter
Lifetime Supporter
Scratchbuilders tend to do most stuff themselves, that's why they're scratchbuilders! :idea:

Chris, if you feel happy with your ability, and based on your 917 effort I would say you are, then go ahead and do it yourself.

For reference I used ERW tube, 1" x 1/16" for the rear radius rods and front and rear lower arms. 3/4" x 1/16" for the upper front wishbone and the upper rear transverse link. Bronzed with high strength nickel silver bronze. These have been well up to the job.

For details see my build thread from post # 115 on. http://www.gt40s.com/forum/gt40-build-logs/16138-kiwi-scratchbuilt.html

I'm sure your 1" x 3mm will be more than sufficiently robust. Go for it, your 917 build is a credit to you.:thumbsup:
 
Chris, 3mm tubing for front wishbones is definitely plenty strong!! Frankly, 2mm would be plenty. You might want to inquire whether the CDS you're buying for this applicatioin is SAE 1018 (it should be).

I think you'll find that the weakness, if there is one, will be at the welded joint. The upside to a nice thick wall tube like your 3mm is that it'll be easier to weld (less burn through). Presumably you have a good tube cutter so your joint fits are nice and close.

Personally, I'd use 2mm for the tubes and 3mm for the inboard bearing bosses.

Good luck.
 
Thanks Russ and Cliff, I have already read up on your and the incredibly skilled Lim`s exploits, wish I could find someone like him in my workshop!!!
I will go on as I am then, nothing wrong with being a bit agricultral, I can always slim it down later.
The CDS I use is Mechanical - BS 6323 Part 4 and bl**dy expensive!
regards Chris
 

Mike Pass

Supporter
One thing to bear in mind is the bending loads on the lower wishbone. Materials like steel tube are very strong in compression and tension but quite weak in bending. You can show this yourself by trying to bend a very long length of tube - they are quite floppy. Because the weight of the car is applied to the wishbone at a point between the wishbone inner pivot and the suspension swivel joint the bottom wishbone will be subject to strong bending forces and through many cycles due to bumpy roads will fatigue if they flex too much and will break - hopefully at a low speed! This happened to Des Finnan's Tornado at the Donnington track day fortunately without any dire consequences.
The bending load on the lower wishbone will depend on where the suspension strut attaches to the wishbone. The further it is from the outer end the greater the bending load on the wishbone.
Your idea of over engineering it is a good idea. Good strong tube and good quality welding are needed. A £/$ saved is all very well but how do you value your car, your wellbeing and life? The amount you will save in unsprung weight is totally insignificant compared to the mass of wheel, tyre brakes etc.
Have a good look at some tried and tested existing versions and make yours at least as good. Use somebody who can weld to a top standard to weld up the parts you fabricate. These parts take a serious beating on the roads we have here in the UK.

Cheers
Mike
 

Russ Noble

GT40s Supporter
Lifetime Supporter
Mike is right in that the front lowers need to exhibit good design.

I tacked up a couple of preliminary iterations before I settled on the final configuration. Given that I was using light weight tubing I decided to triangulate them in a vertical plane to prevent flexing due to spring loads. The ERW tube I used is just your normal exhaust type tube. Cheap as chips, easy to work and more than adequate for the job.

With 3mm tube, if you feel it needs strengthening, simple strategically placed gussets should suffice.

After you have built them, if you have any concerns, for peace of mind just keep an eye out around the lower shock mount area for signs of cracking. You should see warning signs long before total failure provided you only have one thin spray misted paint coating. Powder coat, chrome or HPC type coatings are a no-no.
 
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