The "accurate front suspension" thread has got a slow cos we have all added about 85937826 zillion megs of images to illustrate our suspension problems.

The upshot is that my brackets are in the "wrong" position, but they are perfectly parallel and symetrical, AND the sit well on the lala tubes (sounds like bleeding teletubbies). I don't really want to move them because they look right, and having them half on and half of the upright tubes just does not look right to me.

This leaves be 22mm to find to get the right castor angle (a Cortina only has 1.5 degrees of castor, why do we need 5.5?). I have used my really expensive CAD Program (wooden ruler and a biro, and a son who can use adobe sweatshop) to draw this diagram of an even more asymetrical upper wishbone to give the assumed correct castor angle.

Can anyone see a problem with this, or got a more elegant solution to the problems of RC's crap maths?

Answers on a postcard.......................
Rescued attachment AltWishboneSML.jpg

Mark, the main thing is that your brackets are symmetrical and parallel to the centre line of the chassis.
Castor is contributes (as does KPI) to the "self center" feeling to the steering and the "feel" of the steering in a turn (the resistance you feel acting on your hands in the opposite way to that which you are turning)
Too little castor and you may not have much of a clue as to what the front wheels are doing as the steering will appear "light" and won't weight up when cornering, the car may also wander or feel un-stable or un-settled when running straight.
Too much castor and the opposite happens.
Anything between 1.5 deg and 6 degrees seems to be ok.
The drawing you posted is probhably right for YOUR chassis if you measured it correctly as they all seem to vary considerably.
Don't take 5.5 degrees as gospal a lot of it is up to personal feel.
As long as you know what you've built into your chassis so you have a starting point for adjustments you should be ok.

I was involved in the builds (ie did most of the work) of two book Locosts very early on (within 6 months of the orogional book)

The first was done "by the book" and the second we modified due to the problems we had with the first (front suspension)
The first Chassis had a castor of 2 degrees and to get the second "right" we modded the top wishbone as you propose.
Both cars handled accaptably the second had better steering charaistics but had better (avo) shocks poly bushes and a quick rack so they were not realy like for like comparisons.

AFIK both of my Westfield chassis have 5 degrees of castor but I'd have to check to be certain.

HTH

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(a Cortina only has 1.5 degrees of castor, why do we need 5.5?).

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Hi Mark that drg of the wishbone would set your castor right, but it would foul your coil springs, go for then MK style, ie a full u shape then cut and position your threaded boss where you want it. cheers davef.

I've got a small hand powered bender, it looks like the best solution - thanks

Mark

Just a couple of questions then:

If book two is wromg re. the front suspension geometry is it the same as book one - i.e. is that wrong too?

What about all the people who have completed builds 'by the book' - Have you noticed any problems with the steering geometry?

Phil.

Hi Phil, i don,t think most people will have thier suspension set wrong, it will eventually dawn on them something is not quiet right. when they see the top front bracket does,nt appear to sit right on the front uprights, but you can get round the problem by welding in a gusset like mentioned earlyer.in fact if you look at the picture on page 105 in the 2nd book you can see the top bracket does,nt look to be sited correctly, but it will be. thats why i said to any person just starting out on a new build,they should make the wishbones to book, but make the front chassis member page 49 fig 4.10 to a new measurement of 100mm instead of 76mm , plus shorten top rails j1 and j2 by 25mm and the problem disappeares. cheers davef.

I have decided that adding gussets is not what I want.. so I have uploaded photos in my section so that new builders do not make the same mistake.. not that it was my mistake
The front braket is too far off LA and LB for my liking.

Pretty drastic stuff, but I know where you are coming from, I have gone the other route, I have redesigned the top wishbone to compensate. Let me know how you get on

Mark

Hornet, even though the top wishbone doesn't see the same loads as the bottom one does, the way those top wishbone brackets are attached looks downright dangerous. The "ears" of the brackets need to be properly supported.

Soz Rorty, think i have confused you.. this is a long running debate, My pictures show my top brackets as per the book dimensions. I have now took the bull by the horns and removed the front end and will start again with LA and LB 25mm further back to give a better position for the top brackets.
Cheers.

Hi Hornet just checked your chassis surgery, it,s not that painful is it. cheers davef.

Hornet:

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I have now took the bull by the horns and removed the front end and will start again with LA and LB 25mm further back to give a better position for the top brackets.

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Rorty

Pls read my post on "Accurate front suspension"

Joćo

Here is a pic of the brackets in postion with LA and LB 25mm further back.
Much better area of contact.... you have been warned.