Suspension Settings - Dialing Out Bump Steer
Discussion
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
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
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?
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
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?
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?
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...
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...
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.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,
Have you tried out the newer Michelin PS3 yet? http://www.michelin.co.uk/tyres/michelin-pilot-spo...
Any impressions?
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...
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...
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. 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 second is more traditional looking and certainly more expensive.
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.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,
Kumho's definitely are a harsher ride and tramline a bit.
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-JimWhen would you notice it is a problem?
Cheers
Mark
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??
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