Gaz Shocks ?

[dave]

How it all works.
To stop a car getting bump steer:-
Lines A C and B D are centre lines of top and bottom ball joint and inner wishbone pivot points.
If the steering rack has its joints along those lines and the rack is positioned so that it is equally proportioned between the two sets of pivots ie; if the rack is mounted 1/3 rd of the way up between D and B then the track rod end pivot should be at 1/3 rd of the way up between C and A you will get zero bump steer.

This all gets even more complicated when you try to incorporate the reduction of tyre scrub on tight bends.
If you can make sense of the "Plan" sketch it shows (In two colours ( Representing upper and lower wishbones)) the line in the other plane that the T>R>E needs to be fixed.
If the rack is fitted behind the axle then the T>R>E's need to be set slightly more inboard than if they are mounted in front of the axle where they are best suited if they are slightly outboard. It's all to do with making the inner wheel on a bend take a tighter turn.
If you play around with this setup you will find that it is not possible to fit the rack in front of the axle because the T>R>E will hit the brake disc. This is not the end of the world because your car may benefit from some tyre scrub/ under steer to counteract an otherwise tail happy car but the closer to the disc the better.
I could go into more detail but i'd be here all night. If anyone wants to know more ring me.

[kdavies3]

OOH! Stop it you're making my head hurt!!!
:+ :+
But seriously folks I've driven the Dax with tracking out and it's jumps about all over the place with bump steer.

But when it's setup properly it's fine!!

[BenBaron]

I know Im thick but whats bump steer?

and also how do you set the tracking right?¦-0

[Miket]

Ben

Bump steer is when the wheels are steered by the suspension as it moves up and down, this is obviously an undesirable feature.

Tracking is better done at a tyre fitting company or garage and have it set up on a laser tracking machine, you will obviously have to get the correct settings from Dax or Dave B.

[osgood]

Contrary Mary

Hope this helps, Eric

[dave]

So you have a copy of "How to make your car handle" too it would seem.

[osgood]

Contrary Mary

Yes Dave, as a retired motor engineer I have many books, little rusty perhaps but always prepared to learn when the opportunity arises, with ONC & HNC certificates to match. May I just mention at this point, bump steer was never mentioned as the original question.

All I was suggesting was if Graham altered his ride height on the front it may be necessary to re set the tracking to its original setting. I am aware that early Dax suspension points were in the wrong place anyway, but I don't think Grahams car is one of these. All confirmed by Cheng Lim who had two first the week end before last, and probably another this week end at Brands; I think, he also won the championship last year. You have put another theory forward which I am quite willing to accept as I said (never too old to learn). Have learned a lot on this site re Cobras with many tips from yourself which I have noted for further reference. Don't know it all Dave, but if I am wrong I stand corrected, especially from someone like yourself that does the business for a living. The name is Eric not Andy :+

[dave]

Hi Eric.
I got into geometry some time ago when i "Dare i say" copied a chassis from a Cobra and found the handling horrible, so the next time i made a chassis i borrowed the "Handling" book from a friend and sat in front of the chassis on the floor with the book on my lap reading and re-reading and looking at the chassis for 2 days until i thought i understood.
Then i made a to scale working template with bits of card and drawing pins and pinned it to my drawing board (Chassis end)and moved things around. After much fiddling about the "Penny dropped" so to speak and worked out what it was all about.
And the example with the piano hinge that you attached to check for bump steer i made one just like it..............Including usind a battery to hold it to the floor.
Some people read Shakespear or Orwell to shape their lives but not me, i read the "How to make your car handle" book by...........I can't remember.
If you have this book could you let me have the numbers off the back so that i can order it from Amazon cos i gave back the copy i had to a friend who has since lost it..........The book that is.

[osgood]

Contrary Mary

Hi Dave, Yes I am a bit of a cardboard man myself mate! Only problem is when I have made a template for something I put it down & can never remember where I put it I spend more time looking at a job these days than getting on with the job!! Senile I think they call it!

However I digress, I know the book you mean but I too lent it out but too whom I know not. I have sent you an email copy I had of http://www.motorbooks.com if you go to there site map, plum for other products, then repair manuals I think there are loads of stuff. For example chassis engineering & car suspension at work etc. Its a American company but a useful site for info on all sorts of books, regards Eric.

[dave]

Cheers Eric, i'll take a look.