Suspension Settings - Dialing Out Bump Steer

[356Speedster]

Hey peeps... suspension threads come and go, often get hijacked, go down a rabbit hole etc, so at the risk of this happening again, I'd like to ask the group a question: What have you done to dial out bump steer in your Ultima?

Before I went to Le Mans, I had the car setup to the factory's toe / camber / ride height settings. I'm running double adj shocks (set to the factory's settings) and have set the tyres at 16/21psi front / rear. So basically, everything that can be setup is set to factory settings. On my trip, I was quite surprised to find the car quite nervy at speed and that it suffers horribly with bump steer.

Speaking to a few folks, I'm told this is common and hard to eradicate, thanks in part to a lack of caster adj.

In resolving the issue, a few folks have suggested a couple of options:
1. "Shorten" the steering rack and fit longer track rods..... This sounds like major surgery, I've no idea how to go about this one, or if it's overkill?
2. Adjust the height of the steering rack, by "slotting" the mounting holes in the chassis. Apparently this is a setup service offered by the factory?

I'd like the thoughts of the (much more experienced) group on this one pls. Many people talk about the car handling like a big go-kart, but at the moment I'm finding the car to edgy to want to press on and look for that characteristic, especially on great British back roads.

Any thought's on dialing out bump steer would be gratefully received. Thanks, Mark

[V8Dom]

hi

you need to slot the mounting holes for the rack... if memory serves me right about an inch down wards..

adjust so up and down movement is not causing toe in/out.

you can get it very close but there is a massive sudden toe in after a large amount of suspension movement.

Not sure why the factory don't slot them anyway or mount the rack where they do?

Edited by V8Dom on Monday 1st July 19:21

[Spid]

Mines the same had the bump steer done, is great on smooth roads and track, but not great on uneven roads. On my way to work I drive down a dual carriage way used a lot by lorries really doesn't like the inside lane.

[356Speedster]

Thanks chaps.....

Dom - Do you happen to have any settings on the measurements associated with slotting the holes?

Spid - When you say you had your bump steer "done", do you mean by the steering rack mounting modification as discussed above, or by some other means? Who did it and to what specs?

[Spid]

Yep rack mounts slotted and set up by a guy called Charles Dunn

[Spid]

If your not too far from Ultima get them to set it up for you

[Storer]

I have had mine done (same method) but still suffer with some bump steer.

The French roads were much less of a problem but UK B roads are a challenge and a well driven Golf GTI would be able to keep the Ultima in it's sights.


Paul

[3Dee]

So if castor helps bump-steer (does it?), then I understand that the rose-jointed wishbone option might help solve that? Or is it too simplistic?

I remember Jackson Msport (who did a great but expensive job on my geo), asked where the castor adjustment was, since I had the std wishbones... so got me thinking...

[UltimaCH]

I would think that a rose joints suspension set up should cure all alignment problems. I imagine that rose joints wear out faster than the standard poly bushing wishbones. Any real life experience around here?

[UltimaCH]

Ultima factory said:

It is quite simple to dial out all the bump steer on an Ultima by finely adjusting the height of the steering rack. Just contact the factory for an instruction sheet on the procedure or book your car in for the factory to adjust.
The movement required on the rack up or down is usually less than 3mm and in no car that we have tested has there been any large increase in toe in on maximum suspension deflection.
Tyres play a massive part in ride quality on any car and more so on an Ultima. Using different brands front and rear is a recipe for unpredictability and please remember that Kumho tyres are primarily a track tyre designed for smooth tracks that can be used on the road. After extensive testing the factory has found that the optimum tyres for an Ultima are the Michelin Pilot Sport PS2 or the Pirelli P Zero Rosso and fitting these tyres will transform the handling of an Ultima on all road surfaces.


Regards to all,

Thanks Factory for the comments. Nice to know that an instruction sheet is available.
Have you tried out the newer Michelin PS3 yet? http://www.michelin.co.uk/tyres/michelin-pilot-spo...
Any impressions?

[Crazy of Cookham]

Also had mine adjusted by Charles Dunn made a massive difference. He set up suspension geometry with his laser gismo and then Bump steer. Well worth the time and effort.

[ezakimak]

anyone got a set of home alignment jigs or tools

our local club is considering getting some so am asking if there is any rcomendations?

http://www.trackace.co.uk/

or maybe

http://www.merlinmotorsport.co.uk/p4566/DUNLOP-TRA...

[UltimaCH]

ezakimak said:

anyone got a set of home alignment jigs or tools

our local club is considering getting some so am asking if there is any rcomendations?

http://www.trackace.co.uk/

or maybe

http://www.merlinmotorsport.co.uk/p4566/DUNLOP-TRA...

The Trackace looks a very nifty system and also dirt cheap! I may get one.

The second is more traditional looking and certainly more expensive.

[F.C.]

Ultima factory said:

It is quite simple to dial out all the bump steer on an Ultima by finely adjusting the height of the steering rack. Just contact the factory for an instruction sheet on the procedure or book your car in for the factory to adjust.
The movement required on the rack up or down is usually less than 3mm and in no car that we have tested has there been any large increase in toe in on maximum suspension deflection.
Tyres play a massive part in ride quality on any car and more so on an Ultima. Using different brands front and rear is a recipe for unpredictability and please remember that Kumho tyres are primarily a track tyre designed for smooth tracks that can be used on the road. After extensive testing the factory has found that the optimum tyres for an Ultima are the Michelin Pilot Sport PS2 or the Pirelli P Zero Rosso and fitting these tyres will transform the handling of an Ultima on all road surfaces.


Regards to all,

+1 Pirellis for road use, I have zero issues with handling.
Kumho's definitely are a harsher ride and tramline a bit.

[UltimaCH]

I found the P Zeros to tramline a lot when wearing out and certainly more than the Michelins

[mt308]

Fear of exposing my lack of car knowledge here but what are the characteristics of bump steer?

When would you notice it is a problem?

Cheers

Mark

[Graham-P]

mt308 said:

When would you notice it is a problem?
Mark

When you're in a hedge

[Spid]

It's as it sounds, as the front wheels move up and down on the suspension, if not correctly positioned the steering rack will cause the wheels to steer slightly with out any input from the wheel! More noticeable on bumpy back roads with hedges!

[Ult-Jim]

mt308 said:

Fear of exposing my lack of car knowledge here but what are the characteristics of bump steer?

When would you notice it is a problem?

Cheers

Mark

I noticed it while overtaking a tractor on a heavily cambered Norfolk road after only driving the car for the first time for about half an hour. Went to steer back over the correct side of the road after the overtake while accelerating and nearly ended up in the ditch as I wobbled across the centre camber of our typical British bumpy road! One I will never forget. Ult-Jim

[356Speedster]

Ult-Jim said:

I noticed it while overtaking a tractor on a heavily cambered Norfolk road after only driving the car for the first time for about half an hour. Went to steer back over the correct side of the road after the overtake while accelerating and nearly ended up in the ditch as I wobbled across the centre camber of our typical British bumpy road! One I will never forget. Ult-Jim

Yup, it was a similar incident last week on the way back from Le Mans that caused me to ask the question!

Out of interest, has anyone here gone down the steering rack replacement or shortening route? A few folks (offline) have suggested that's a better fix. In line with this, does anyone know who supplies the Ultima std rack? Maybe they have a smaller one off-the-shelf??