Thread engagement - Rod end bearings

[Terrapin]

Promting a discussion here - does anyone have any information on thread engagement of male rod ends?
How far can a rod end safely be wound out of say a suspension wishbone female bush when setting up the suspension.
I have seen some production racers (Brabham, Crossle etc.) where the rod end shaft is over an inch out of the threaded bush (leaving approx an inch in the bush).
As an engineer it looks suspicious but the stress point should be at the point where the lock nut engages.
One guy told me you should have them no more than a few threads out of the female bush.
Any views

[twentyover]

Traditional practice says use 1 1/2 times thread diameter, so, it depends on thread size. Most tech inspectors would be OK if this was a 5/8" threadsize- maybe some may give it up for 3/4 diameter, but most would (I think) baulk at much more, depending on the size and load

[Ian]

I would say quality of the joint is more important than just going up in size and the elimiation of any bending loads being a priority .Ian...

[Terrapin]

Ian, fully agree with you on quality issue.
I am using one of the highest spec ratings you can get for the 3/8" rod ends on my Terrapin (carbon/PTFE - 9900lbs rated)
My question has risen from a need to set the lower front wishbone SRE's out about an inch to get the camber correct.
This leaves just over an inch in the wb bushes.
As an engineer I was always of the mind that 1.5 x thread diameter (in my case 1.5 x 3/8" = 9/16" ) was robust. - It just looks odd - as based on this I could have up to 1.5 inches of thread showing as the SRE's have approx a 2" threaded shank.
Having said that, once I took an interest I see it done on a lot of single seaters.
If uncomfortable I can always make new bottom wb's for peace of mind. I may also find the suspension settles a little more (as you may know with the Terrapin the front suspension camber moves from quite positive at droop and then through negative during compression - all good stuff for handling)
Just wanted some practical experience from the likes of yourself.
Cheers
Rob

[Ian]

Like yourself I have never been a fan of seeing to much rod-end shank exposed ,I always aim for...with the car set up correctly an exposed length beond the locknut of 3/8 on 3/8 shank and 1/2 on 1/2 shank enough to make any small adjustment after first test ...even if this means new wishbones etc, For this reason I never paint or plate without doing a preliminary build....Ian.

[Ian]

Rob, After re-reading your post...Neg camber is not always the answer it is dependent on the severity of the camber curve generated...especially when you start to move into wider rim widths .. Ian.

[Terrapin]

Ian, doing some research on this - any advice on setting up the suspension would be most welcome.
I'm using 8" rims front, 10" at rear - all 13" diameter
rolling radius with tyres - 21.2" front, 22" rear.
Gould plates used at rear
I have made up some adjustable rods with 1/2" increment stops so that I can substitute them for the dampers/springs and measure the suspension set-up through 7 points, from full droop to full compression (based on 3" travel on dampers front and rear).
Rear is not really an issue.
With the car is on wheels & tyres I can then start working around the ride height - spring ratings, length etc. and play with the a/r bars (starting here with relatively light roll resistance using 1/2" OD ENT24 tempered to "T" condition.)
I must admit this is more effort than any of my many previous project which have the great benefit of manufacturers data ;D
But, this is one of the reasons for my build - increasing practical knowledge

Nice to share this techy stuff, it's one thing to calculate what your a/r bars should be - using the maths from a few sources (Allan's other books, Smith etc.) - reality may be slightly different,

[Terrapin]

I found this very interesting

www.auto-ware.com/setup/cam_curv.htm

[Terrapin]

Ian, what's you view on some details I have that indicate that static negative camber is commonly used to counter McPherson strut camber gain due to the geometry of McPherson strut suspensions, there is some camber gain as the suspension compresses, so the static negative camber is being lost as the body roll compresses the suspension. So as much static negative camber as possible is set - within limits - excess negative camber can also increase stopping distances as the tyre tends to be up on its edge during braking, which can cause loss of braking traction.
So in essence it is the rate and amount of negative camber during compression that is of more importance rather than what is set at rest?
In my case when using unequal wishbones where the camber progression has been calculated the exact value at rest is not so important.

Pity this was not the topic of conversation over a bacon butty at FSE when Allan & others were at hand

Hope my rambling is clear

[Ian]

Rob, Allan and myself always check our suspension motion ratio,s with increments of only 0.125 A well designed suspension but with prehaps a manufacturing error can develop camber curve graphs that move both in and out. You are correct in saying that it is un-important to worry to much about static setting all that concerns us is what is happening when dynamic loading is applied...The camber curve should be as little as possible to achieve the the required result ,as you rightly say the knock on effect can be a smaller footprint under braking etc....Ian..

[Terrapin]

Thanks Ian. Much appreciated.

Bump steer next ;D

I'm using the mini (uprated type) arms rather than fabricating double sheer brackets with rod ends - I have however, made the rack itself adjustable (up/down)

[allan]

Original c0-designer Allan Staniforth has now managed to become a Forum member. Queries to Allan

[Cita]

For the UK builders Nick Skidmore has reasonable prices for rod ends.
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