Hello People.

I've mentioned before about building my own chassis using Sierra Running gear. However I have a fear of bump steer on the resulting car.

I have got Jim McSorleys drawings and another CAD drawing for a Sierra running gear chassis. Trouble is that there is no steering rack mentioned and no places for it to fit.

Does anyone have any tips or measurements of a Sierra based machine's front end? Surely someone must have done it and got it to work with zero bump steer.

If not.... can anyone recommend a book that I could purchase which would give me all I need to understand before taking on the formidable task of designing the front end myself.

Regards
Vince.

design the front wishbones for sierra then when making the rack mount aim for the rack arms to be as horizontal as possible. then you won't find problems with bump steer

as for a book try either alan stantford's
books or one by des hammil

tim

Hi Vince,

Tim is correct about keeping the arms horizontal. What you also need to do is make sure that the joint of the track rod arm is inline with the pivot point of the wishbones.
To explain better:
for each side of the car draw a diagonal line between the top and bottom wishbone. Where this line intersects with the horizontal line of the steering rack is where you want the track rod arm joint.

The MKIndy uses a cut down Sierra rack to do this. They chop out the middle section of the rack (this bring the joints into line and also brings the mount points and pinion insie the car!) and then add a section to each track rod arm to compensate.

Hope this helps,

James

Thanks for that guys. So you don't think it's a problem then obviously.

I was considering doing the chassis that I have a drawing of then using MK for bits anyway. I'm sure they will supply me with their modified rack????

Regards
Vince.

Vince

IIRC, you want the arms to follow the angle of the lower wishbones, ie at rest the lower w/bones are horizontal, so are steering arms (this determines "vertical location" of steering rack). As w/bones rise, arms follow angle of inclination, and vice versa.

For longitudinal location - believe you will be wanting a straight a line as possible between both upright/steering arm ball joints (with rack in the middle), if you see what I mean.

ATB

Simon

"Photo Archive
Building: 3 stage moving stairs
posted on 28/1/03 at 21:17

here is one i posted earlier
"tech site on suspension

don't know wether this is news to you but found some nice info on bumpsteer and more importantly how to reduse it.
http://www.rebcoperformance.com/articles/artcat.asp?CATID=2
"
an old post have a look

I can't say if the method described by timf and supported by James will work or not. By some fluke it must do if they say so. Asuming it does just happen to work correctly on their cars, it would then require your ride height, wishbones, uprights, tyre diameter etc to be identical, for it to work on your car too.
There are more scientific means to establish the correct rack position, though I can't comment on the site mentioned above, as I haven't looked at it yet. I haven't read the books that timf recommends either, but I believe their authors are gurus within the fraternity.
There's some guff on the topic of rack location and bump steer on my site if you're interested, or if you need any clarification on rack location, let me know, and I'll happily explain the three most standard methods.

Rorty

I'm intrigued now, the method myself and james advocate is the one outlined in alan stantfords books also the theory is the same one on the website posted by fastenuff.

can you give a brief overview as to the way you say to do it. It may be that its better and easier to set up/ achive

Tim

Oh Sugar.... worm can now fully opened.

Just my Fear...

VinceG
Cobra Seller
Locost Builder (soon honest)

the whole point of the forum is to share info some people have there own opinions if ocasionally the worms wern't let out they would no way of coming up with new ways of doing things.

Absolutely Tim. The sharing of my fears has now shown me that there's nothing to fear except fear itself. I now have much more of an undersanding of the concept, and when I come to do it, (which I will now definately do) I will bear in mind what everyone has said.

Regards
Vince.

I have been thinking about this.

Is this

'geometricophobia'

:

atb

steve

Stephen,

I suspect you, as do I have far too much free time at work to contemplate such matters!!

Ned.

I don't recall Staniforth stating that the track rod arm should be parallel with anything!

What I do understand from reading his books is that the track rod inner pivot should be in line with the upper and lower inner A-arm pivots, and should also be the same height in proportion to outer pivots.
What this means is that if the outer track rod pivot is 1/3 of the distance from the top pivot to the bottom pivot then it should be the same on the inner pivots.

eg. if distance top to bottom outer pivots is 5inches and the track rod pivot outer is 2inches below top and 3inches above bottom; therefore the inner should be, if top to bottom is 10inches, 4inches below top and 6inches above bottom.

Hope this makes sense!

Terry


ps; unless of coarse your outer steering pivot is exactly halfway betwen top and bottom pivots, then youMAY find the track arm parallel to the ground or horizontal.

[Edited on 10/7/03 by Spyderman]

No Terry. Sorry it doesn't make sense. Then again. does anything make sense to me. Probably not.

Regards
Vince.

quote:

---

Originally posted by ned
Stephen,

I suspect you, as do I have far too much free time at work to contemplate such matters!!

Ned.

---

The only thing I would add which I've read somewhere, is to try to build some form of adjustment into the steering mounts. This can be in the form of slotted mounting holes or shims. Obviously try to get it as close as possible by design but in the case I read about it was something like 1/16 inch of vertical adjustment corrected 3/8inch of bump steer. I might have read this in Alan Staniforth's book.

All in theory mind 'cause I've not tackled steering yet...
Cheers,
Craig.

timf:

quote:

---

the method myself and james advocate is the one outlined in alan stantfords books

---

You could look at this thread too.
I did a really arty picture to illustrate!

http://forum.locostbuilders.co.uk/xmb/viewthread.php?tid=5983

This is what I mean.

A and C are the chassis pivot or inner pivots.
X and Z are the outer pivots or ball joints.
B Y is the track rod or track control arm.

The distance A to B must be the same proportionately as X to Y.
If Y falls at 75% of distance XZ the B must be 75% of distance AC.

Clear now?

Terry
Rescued attachment no bump steer.jpg

Absolutely spot on. Thanks for that. And to think, I've just gone and spent 15 quid on the book above. Should be interesting reading though.

Regards
Vince.