Bumpsteer elimination

[thehelix112]

Wow.  Lots of good information here, lots of not so good information too.

 

Modifying the front roll centre for a race-car is not necessarily bad, its just another tuning tool.  NZeder is right in as much as changing only the front one alters the relationship between front and rear, again, another tuning tool.  The downside of course is that its far more difficult to alter the rear roll centre so you become limited in what you should do with the front by the rear.

 

Other thing that perhaps bears mentioning is that you may be limited in how much you can space the outer tie-rod end attachment to the steering arm by your wheels.  I have 14" wheels on my zed in the states, and its awfully close:

 

Also, I fail to see a reason why you can't use both the strut-spacers and adjust the inner LCA pivot.  The spacers adjust where in the bump-steer curve the suspension travels, the inner LCA pivot alters the bump-steer curve.

 

NZeder is on the money.  Make something to test the bump-steer and test it.  I need to, just haven't gotten around to it.  Excited to see what I might find.

 

Dave

[NZeder]

A mate emailed this link today - this is very well written and I recommend those interested in bump steer should have a read.

 

http://www.speedwaymotors.com/images/pdf/910-82700.pdf

[Riceburner]

Thread revival!!!

 

After seeing this linked in Vorns thread I went through it again twice, it becomes confusing with no conclusion.

 

My questions are:

1) Can you run roll centre spacers and raise the inner control arm pivot point? They do exactly the same thing don't they

2) If you raise the inner pivot point will you need longer arms to retain the same camber setting?

3) Are adjustable steering arms part of the solution to try and get them on the same arc as the control arm?

4) If yes to question three, are these suitable? http://www.zccjdm.com/catalog.php/azcarbum/dt93255/pd1827536/Z.C.C.___IMSA__RACE_ADJ._OUTER_TIE_RODS_

[mossy]

I'm interested in this answer too, the only thing I think I understood is you can't run the spacers and raise the LCA together, it has to be one or the other.  Maybe Mike can post a pic of the part he installed?

[Riceburner]

I'm interested in this answer too, the only thing I think I understood is you can't run the spacers and raise the LCA together, it has to be one or the other.  Maybe Mike can post a pic of the part he installed?

 

Re-reading again, I see Helix says the inner pivot alters the bump steer curve. The spacers alter where in the curve the suspension travels.

 

So, doing both the spacer and inner pivot you will move the bump steer curve further than the original setup which was not ideal to begin with? But also perhaps a tie rod similar to the type pictured above to match the new angles.

 

There's also the question of control arm length, as I understand it if you go higher on the crossmember this will increase the distance from the inner pivot to the bottom of the strut. This would require a longer control arm to keep the same camber you had prior to the mod  :-\

 

[PeterAllen]

... This would require a longer control arm ...

 

The nominal relocation of the pivot bolt holes is not only18mm higher but also 6mm outwards, negating the need for longer arms. As 'Enzo' stated you are best to decide on the ride height and wheel/tyre setup of your particular car and then determine where to drill the new hole.

[Riceburner]

Thanks Peter.

 

Also is there a way to determine what height the shims need to be on the modified steering arms pictured above?

[mossy]

Thinking about getting some of these from Nagisa Auto in Japan

 

http://www.nagisa-auto.com/products/nissan/gc10_s30_130z.html

 

I think this is what they look like though

 

http://www.jdmjunkies.ch/wordpress/2011-10-05/240z-nagisa-auto-nams-tierod-end-links-arrived-here/

http://minkara.carview.co.jp/en/userid/357364/blog/31281257/

[PeterAllen]

I drilled another cross-member today and took some photos of the process:

 

Mounted the cross-member on the mill.

Drilled new holes 19mm higher and 6mm outwards.

Made and fitted new spreader plates - the old ones were mangled when chiscelled off.

Filled the old holes with weld.

 

I still need to dress it all and have it media blasted prior to painting.

[Riceburner]

Thanks Peter, It's always nice to have some pictures for the simpletons(me) amongst us 

[YosemiteZed]

Hi Peter

Again thanks for the live (photo) details.

For your measurement what size wheels/tyres is this mod for and is there details/experience for other rims that have to be taken into account when re-drilling the holes

Cheers

Phil

[PeterAllen]

Phil

 

Those dimensions are not really based on a specific setup, they come about by being the maximum adjustment before the control arm (Datsun call them a 'transverse link') will foul on the cross-member. In fact you have to grind away a bit - Note: not as much as I have indicated in the photo.

 

I think my setup might be unique in that I'm running 26" dia front tyres (29"rears) on 6" rims because I was after a period look for the GTO. I think I will actually get away with fitting the spacers under the hub carriers as well but I'll probably have to make up a spacer for the steering arm also.

 

With this modification you can lower the front 19mm and still have the control arm horizontal - if fitted with original wheel/tyres. If you are lowering any more you should consider an aditional spacer.

 

You really need to check your own car to see how horizontal it is with your ride height/wheels/tyres and go from there.

[PET240]

I have been looking at tube crossmembers to give me adjustable pivot points, but really think this may save some cash. Not upset about that, looking for minimal bumpsteer and a roll centre adjustment would be nice.

Going to have to find old Fred's book here somewhere....... figure out how to sort the rear....though I have some ideas.

Thankyou gents!