Dutton Kit Cars and their owners
It seems completely unnecessary and the mounting points stop the front from tipping up properly
I'm also interested in castor adjustment
So, has anyone done the removal of the Escort Mk 2 thing?
I can see you can get a thing called a compression strut for Escorts that replaces it and faces backwards - might not fit a phaeton chassis...
Otherwise it's custom lower wishbones I guess......
If anyone has done this I'd be most interested.....
Thanks James. Yes the camber change due to caster will be less at 20degs than it would be at 30. However as caster figures are seemingly always quoted at +/- 20degs that would not be an apples for apples comparison.
I think someone already pointed out that 20degs is probably a figure that all cars can manage, which is reason enough for choosing it as a standard benchmark figure.
Over 20 and you would be at parking speed, so not to worried about camber and caster. I think that's how I read it anyway :-)
Caster is an absolute figure, The way I'm visualising it is as the angle between the ball joints when viewed from the side (basicallly the hub normally needs to lean backwards to provide self centring etc).
The problem is that it's very difficult to measure it as you cant get to the centres of the ball joints with a protractor or plumbline or whatever, so camber change is used as an equivalent that you can measure easily
While having the whole thing in bits again this afternoon I took the opportunity to see if I could get a figure of true caster angle from looking at the ball joints. It's hard tell exactly where the swivels are inside the ball joints so I did a rough estimate by looking directly down from the top ball joint to the lower, to see how much further forward it is compared to the distance between them.
Remembering that the current figure was measured using the turntables +/- 20degs method to be 5degs - it looks to me that the lower joint is currently about 4cm in front of the upper and that the two are 16cm apart
A bit of trigonometry reveals that this should be an angle of ATAN(4/16) which equals around 14 degrees! Even with my rough and ready measurements I don't think I am going to be 10degs out!
I always thought it looks bigger than the turntable method showed - and even with my rough and ready measurements I don't think I am going to be 10degs out.
So am concluding that established 'figures of merit' for caster measurements are actually based on the camber change with +/- 20degs steering angle rather than the 'true' caster angle between the ball joints.
But then it's so hard to measure the true figure accurately, that that is fair enough.
You might be able to measure the angle with a protractor on your screen if you take a photo looking side on.
If you got a measurement of 5 degrees using the 20 degree method then that'd mean a true castor of 7.3 degrees.
Just so I understand this correctly, the 5 degrees is the difference between the camber at +20 degrees and the camber at -20 degrees?
James I don't know how you arrived at 7.3. Was that your 30deg thing? If so I don't think it's the correct approach. As I mentioned I reckon it could be closer to 15.
The real problem with photos, protractors, plumb bobs etc is that all of it would need to be done from the inside of the wheel. I guess you could take the disc off to see but a dissembled state doesn't allow the weight of the car to be applied with correct ride height etc.
This is why I reckon the 20deg method is used. Alot easier to measure camber (yes it's the change in camber between the 20deg angles).
I strongly suspect now that stated camber figures assume this method rather than true camber.
As I think I mentioned before, what you measure as a camber change between +/- 20 degrees is 68% of the 'true' caster figure. So I divided the 5 by 0.68 to get 7.3 as the 'real' caster angle.
Seeing as your measurement was about half of what you thought by eye then I was interested in whether the 5 degrees that you measured was only the difference between 0 degrees and +20 degrees, which would halve the measurement. So that if you took the difference between +20 and -20 then instead of getting 5 degrees you would get 10 degrees (and instead of 7.3 I would get 14.6). That would make it all make sense.
At the risk of being a bore ... I had a look online and found the method that you are using described on the Driftworks site. The original questioner had the right formula (which the answerer seemed to ignore).
That formula is a simplified formula which comes from an SAE paper which has the full derivation. The SAE paper expects to use smaller angles than 20 degrees but the approximate formula is pretty accurate even at 20 degrees.
I think that you can get special camber gauges (in the kit?) that have the 'correction factor' already built in to the graduations so they read high to compensate for the 20 degrees.
A bit of musing in the bath reveals that altering the lower wishbone has probably already altered the relationship between the top and bottom arm axes and the steering rack trackrod. So we may already be into the realms of bump steer.
There was quite a long section in Project Binky about this (ep 11 https://www.youtube.com/watch?v=ob-FUF0Sh_E starting at minute 4 and again at 5:10)
Not sure we have the resources to go into it in such detail but a couple of relevant points are that even they did not manage to get perfection and that the Phaeton being a low road car with limited suspension travel may be less affected anyway.
So I thinks it's time to get back in the garage and just try some things out. Will that be today? Time will tell.....
Further musing together with another look outside has made me realise that the reason for this problem is nothing to do with subtle suspension geometry changes during bump and rebound. It's just that (guess what) the steering rack moves from side to side. Which considering that the rack rack rod droops from the horizontal was always going to be a problem!
Why did we not notice this before? Because we also have a temporary problem with the steering lock/key and weren't able to test it. D'oh!
So I've had second thoughts about simply providing more clearance between the wishbone and the steering rack track rod. Especially since we only have one wishbone so far.
I'm thinking that it may be possible to create a cranked forward link to the wishbone bracket satisfactorily after all. I think a strong angled joint can be created even in round tube with a solid plate filleted into a slot in the tubes and welded up . The plate would be in the same plane as the angled join and it could be larger than the tube itself.
Watch this space.....