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Bump steer
darrens - 12/2/08 at 05:57 PM

Trying to iron out a bit of bump steer on the Viento, anyone got any pointers.

Cheers

fesycresy - 12/2/08 at 06:03 PM

The best person I spoke to regarding bump steer was Matt at Procomp.

I would u2u him.

HTH


Lyn

jambojeef - 12/2/08 at 06:05 PM

Can we have some pics of your front susp so we can see what adjustments are possible?

Geoff

nitram38 - 12/2/08 at 06:54 PM

Why have you got bump steer?
Surely the chassis manufacturer should have this stuff sorted?
I have only built one car and used a book to design my car, but no bumpsteer.
I can't believe it when you actually pay for poor design from a manufacturer!

darrens - 12/2/08 at 08:17 PM

Don't get me wrong, it's not bad, but if you hit a big bump it will pull the wheel.

See pic for suspension setup. Have camber and caster adjustment and adjustable shocks.

Cheers Rescued attachment DSCF0502-SMALL.JPG
Rescued attachment DSCF0502-SMALL.JPG

nitram38 - 12/2/08 at 08:27 PM

Where your top and bottom wishbone mounts are inboard, imagine a line running between them (white line in photo).
The steering rack rod end swivel centres need to be somewhere along this line (steering rack centred and straight ahead). (these are the swivel balls under the black gaitors)
You will need to detach the ends of the rack from the uprights and raise or lower the rack until the swivels are somewhere along this line.
Hopefully your trackrod ends will still fit from this new position.

Description
Description



[Edited on 12/2/2008 by nitram38]

darrens - 12/2/08 at 09:13 PM

The rack is moveable in an up/down diagonal fashion, I presume the same could be achieved by moving this to arrive at the centre position.

Cheers

caber - 12/2/08 at 11:13 PM

Hang on a minute I thought bump steer was when the car changed direction as the result of a bump in the road, if you hit a pothole the steering wheel will be pulled whatever you do with the suspension!

Caber

nitram38 - 12/2/08 at 11:23 PM

quote:
Originally posted by caber
Hang on a minute I thought bump steer was when the car changed direction as the result of a bump in the road, if you hit a pothole the steering wheel will be pulled whatever you do with the suspension!

Caber


Bump steer is caused by the trackrod arms on the rack not following the the same arc as the wishbones.
In other words, as you hit a bump the wishbones move but the rack either pulls the wheels inwards or toes them outwards. This means that over bumpy roads your car will try to change direction and leave you sawing at the wheel to keep it straight.
By having the trackrod swivel ball in the same line as the top and bottom wishbone mounts, it will ensure that the trackrods move in the same arc.
Therefore no direction change and a safer car!

darrens, I don't know your car, but you might find that simply putting spacers under your rack, might get it in the correct place.
You really need to take a look square from the front of the car to decide wether it needs to go up or down.
If up, then use spacers, if down, then you need to lower the rack and re-drill the mounts.
It is hard to tell from the angle of the photo.

On my cars I saved myself the hassle by ordering a rack from titan with the distance I wanted between the swivels and by running my trackrods parrallel to my top wishbones.
Here the rack swivels centre on the top bone mounts and my uprights were made by me so that the trackrod lines up with the wishbone:

Rack Mounted
Rack Mounted

[Edited on 12/2/2008 by nitram38]

Phil.J - 13/2/08 at 08:46 AM

Looking at your 'photos I would suggest that it is going to be toeing out on bump?
If so you need to lower the rack or raise the track rod ends, reset the tracking and try measuring again. Small movements can make a dramatic difference to the bumpsteer.
Concentrate on getting it sorted as a sports car with bump steer will feel dreadful on the road.

darrens - 14/2/08 at 06:52 PM

this pic might be better