Suspension Settings - Dialing Out Bump Steer
Discussion
hi jonny, thanks for your input much apriciated,when you spend circa 50 to 70k on a car like this you expect an amount of time given over to how the car performs at high speed by the factory there seems to be a bit of a cover up of the failings in this area instead of some difinative answer that most of us want.i understand that tire choice is helpfull but those of us with the [wrong choice]are left with the job and expence of trying to sort this out on our own.have spoke to the factory a number of times even given them my bump steer readings which they say are well with in there guide lines ,then am told to change the tires that they supplied previously at my own expence.it seems to me that no enough has been done to nail this issue once and for all.i know that with a change of wishbones,change of wheel offset,and tires,this could be cleared up but at what expence 2 to 3 k or there abouts,for something thats in my mind a factory issue. just my opinion-jmwram
And to the next update, in this ever evolving saga....
As reported in Dec, the steering rack mod made a big difference, but it didn't fully resolve the handling issues and I was planning a geo setup. I finally got round to sorting the geo recently and things took another leap forwards. As I'd expected, with all the messing around over the last 18mths, all 4 wheels were pointing in different directions, so this was a necessary step.
Ride heights were reset (F: 100mm, R: 160mm), camber adjusted (F: -1deg, R: 0deg) and toe set (F: 2mm out, R: 1mm in). The camber is in line with factory recommendations, but the extra rake and toe out on the front are not. On the evidence of 250miles+ driven since the new geo, I can honestly say the setup is working nicely so far. The car turns in keenly and is much more stable in acceleration, braking & high speed runs. As noted, while the car was originally set to factory specs after IVA, a lot has changed since then, so it's not a back-to-back comparison and I am not knocking the factory specs.
So, we're nearly there, but not quite. Despite the car showing the sort of promise I've always hoped for, there's still some bump steer left, which is more evident on the worst surfaces. Moving the rack up & down isn't killing it, so next up is an adjustable outer tie rod setup (as discussed on the previous page of this thread). It's hoped / expected that these will give a much finer final adjustment on the steering geometry (vs moving the rack) and allow us to get the last of the bump steer dialled out. Just for good measure a set of firmer springs are going on too.
Hopefully all this will be done at the end of April, so I'll be able to report back in a month or so. I'll close out by saying that while everything discussed in this thread has helped my car, this may not be for everyone. Maybe I'm more sensitive to fine suspension adjustments than others, I don't know... all I can say is that for me, these changes are really working out and giving me the handling characteristics I wanted from the car.
As reported in Dec, the steering rack mod made a big difference, but it didn't fully resolve the handling issues and I was planning a geo setup. I finally got round to sorting the geo recently and things took another leap forwards. As I'd expected, with all the messing around over the last 18mths, all 4 wheels were pointing in different directions, so this was a necessary step.
Ride heights were reset (F: 100mm, R: 160mm), camber adjusted (F: -1deg, R: 0deg) and toe set (F: 2mm out, R: 1mm in). The camber is in line with factory recommendations, but the extra rake and toe out on the front are not. On the evidence of 250miles+ driven since the new geo, I can honestly say the setup is working nicely so far. The car turns in keenly and is much more stable in acceleration, braking & high speed runs. As noted, while the car was originally set to factory specs after IVA, a lot has changed since then, so it's not a back-to-back comparison and I am not knocking the factory specs.
So, we're nearly there, but not quite. Despite the car showing the sort of promise I've always hoped for, there's still some bump steer left, which is more evident on the worst surfaces. Moving the rack up & down isn't killing it, so next up is an adjustable outer tie rod setup (as discussed on the previous page of this thread). It's hoped / expected that these will give a much finer final adjustment on the steering geometry (vs moving the rack) and allow us to get the last of the bump steer dialled out. Just for good measure a set of firmer springs are going on too.
Hopefully all this will be done at the end of April, so I'll be able to report back in a month or so. I'll close out by saying that while everything discussed in this thread has helped my car, this may not be for everyone. Maybe I'm more sensitive to fine suspension adjustments than others, I don't know... all I can say is that for me, these changes are really working out and giving me the handling characteristics I wanted from the car.
Hi Mark
Thanks for your comments and thoughtful approach to resolving this problem. I was considering the longer wishbone and different wheel option and was half hoping you had gone that route and it had helped. I have rose joint suspension and have had a Steve Smith geo set up. This has calmed it down but not eliminated it. If you have read Dave Hodges report in 'Complete Kit Car Magazine' you will see he has reduced both front and rear tyre and wheel widths and says this has cured his issues. Are missing something here with tyre and wheel widths? I will be interested to see how increasing the spring rates affects the issue and general handling especially on the road.
Roj
Thanks for your comments and thoughtful approach to resolving this problem. I was considering the longer wishbone and different wheel option and was half hoping you had gone that route and it had helped. I have rose joint suspension and have had a Steve Smith geo set up. This has calmed it down but not eliminated it. If you have read Dave Hodges report in 'Complete Kit Car Magazine' you will see he has reduced both front and rear tyre and wheel widths and says this has cured his issues. Are missing something here with tyre and wheel widths? I will be interested to see how increasing the spring rates affects the issue and general handling especially on the road.
Roj
Racingroj said:
Hi Mark
Thanks for your comments and thoughtful approach to resolving this problem. I was considering the longer wishbone and different wheel option and was half hoping you had gone that route and it had helped. I have rose joint suspension and have had a Steve Smith geo set up. This has calmed it down but not eliminated it. If you have read Dave Hodges report in 'Complete Kit Car Magazine' you will see he has reduced both front and rear tyre and wheel widths and says this has cured his issues. Are missing something here with tyre and wheel widths? I will be interested to see how increasing the spring rates affects the issue and general handling especially on the road.
Roj
Hi Roj. No worries, a lot of time & effort has gone into this, so if it helps, I'm pleased! I had considered longer wishbones and yes, this would calm bump steer by virtue of the wheel travel will lessen the tie rod movement vs std. I chose not to go this route, as we believe the residual effects can be dialled out with an adjustable outer tie rod setup. This is something we can do quickly and being a more cost effective route, provides scope to experiment Thanks for your comments and thoughtful approach to resolving this problem. I was considering the longer wishbone and different wheel option and was half hoping you had gone that route and it had helped. I have rose joint suspension and have had a Steve Smith geo set up. This has calmed it down but not eliminated it. If you have read Dave Hodges report in 'Complete Kit Car Magazine' you will see he has reduced both front and rear tyre and wheel widths and says this has cured his issues. Are missing something here with tyre and wheel widths? I will be interested to see how increasing the spring rates affects the issue and general handling especially on the road.
Roj
Wheels & tyres will have an overall handling impact of course and front wheel width / offset changes will also impact steering feel & to a small degree, bump steer. I've had an offline chat with Dave and I am considering a possible wheel change too... the jury's out on that one at the moment, but the lure of a wider & cheaper tyre choice is swaying me, regardless of anything else!
356Speedster said:
Racingroj said:
Hi Mark
Thanks for your comments and thoughtful approach to resolving this problem. I was considering the longer wishbone and different wheel option and was half hoping you had gone that route and it had helped. I have rose joint suspension and have had a Steve Smith geo set up. This has calmed it down but not eliminated it. If you have read Dave Hodges report in 'Complete Kit Car Magazine' you will see he has reduced both front and rear tyre and wheel widths and says this has cured his issues. Are missing something here with tyre and wheel widths? I will be interested to see how increasing the spring rates affects the issue and general handling especially on the road.
Roj
Hi Roj. No worries, a lot of time & effort has gone into this, so if it helps, I'm pleased! I had considered longer wishbones and yes, this would calm bump steer by virtue of the wheel travel will lessen the tie rod movement vs std. I chose not to go this route, as we believe the residual effects can be dialled out with an adjustable outer tie rod setup. This is something we can do quickly and being a more cost effective route, provides scope to experiment Thanks for your comments and thoughtful approach to resolving this problem. I was considering the longer wishbone and different wheel option and was half hoping you had gone that route and it had helped. I have rose joint suspension and have had a Steve Smith geo set up. This has calmed it down but not eliminated it. If you have read Dave Hodges report in 'Complete Kit Car Magazine' you will see he has reduced both front and rear tyre and wheel widths and says this has cured his issues. Are missing something here with tyre and wheel widths? I will be interested to see how increasing the spring rates affects the issue and general handling especially on the road.
Roj
Wheels & tyres will have an overall handling impact of course and front wheel width / offset changes will also impact steering feel & to a small degree, bump steer. I've had an offline chat with Dave and I am considering a possible wheel change too... the jury's out on that one at the moment, but the lure of a wider & cheaper tyre choice is swaying me, regardless of anything else!
Paul
deadscoob said:
Didn't Dave change the tyres at the same time as the wheels? So to get a true comparison we need a lback to back test with normal bs thinner wheels but both with same tyres
Yes he did. I was looking around last night and 305/30/19 tyres are plentiful & almost half the price of 335/30/18s. With so much choice in that size, it's making a wheel change look like a very interesting option.I'm having exactly the same thoughts, had a brief chat with Richard about it to.
Richard did send me a link and the U.S. have more choice than we do thanks to Vipers. But, you can get a 305/30/19 super sport or pilot cup 2 in that size and being a porsche size supply is likely to be good for a while. Or get a gen 2 RS size of 325/25/19.
Problem for me is I don't fancy paying forgelines 2015 prices, they seem to have gone a little crazy.
In the meantime I've just replaced with Kumhos - and to add, anyone that is after these, don't bother shopping around, the factory price and delivery is the best by some way.
Richard did send me a link and the U.S. have more choice than we do thanks to Vipers. But, you can get a 305/30/19 super sport or pilot cup 2 in that size and being a porsche size supply is likely to be good for a while. Or get a gen 2 RS size of 325/25/19.
Problem for me is I don't fancy paying forgelines 2015 prices, they seem to have gone a little crazy.
In the meantime I've just replaced with Kumhos - and to add, anyone that is after these, don't bother shopping around, the factory price and delivery is the best by some way.
well
i finally now have Mitchelin PS2 tyres front and back and omg what a difference.
the last few years have been a nightmare with the kumos on the front and i seriously thought i had a handling problem
camber left at 1.5 degrees, toe in total 2mm and the car has transfered into a normal car.
to make matters worse a visit to Brunters on Sunday for the SCD secret supercar meet, it was lashing it down with standing water everywhere and the car drove without fault
so if you want to dial out bump steer, may i suggest think about tyres too?
ps... Whos was the Kawasaki Green Ultima there too on Sunday
dom
i finally now have Mitchelin PS2 tyres front and back and omg what a difference.
the last few years have been a nightmare with the kumos on the front and i seriously thought i had a handling problem
camber left at 1.5 degrees, toe in total 2mm and the car has transfered into a normal car.
to make matters worse a visit to Brunters on Sunday for the SCD secret supercar meet, it was lashing it down with standing water everywhere and the car drove without fault
so if you want to dial out bump steer, may i suggest think about tyres too?
ps... Whos was the Kawasaki Green Ultima there too on Sunday
dom
deadscoob said:
What's the grip level like Dom?
I really wish michelin would make the super sports in our sizes, great on track, great on road.
i ran it in the wet and it was very impressive. i have to admit i wasnt hooning it as i tend to bed in tyres anyway and allow all the oils in the rubber to go..I really wish michelin would make the super sports in our sizes, great on track, great on road.
1st impressions after dunlops and kumo were 9/10
im off out again tonight in cold damp roads and will see again
for the price of £121 each side, i feel its money well spent
i was told by mitchelin not to mix super sport front with ps2 rear and also, due to my gearing , he would rather have ps2 on mine, as if i did high speed runs the ps2 has a stiffer tyre construction
dom
356Speedster said:
And to the next update, in this ever evolving saga....
As reported in Dec, the steering rack mod made a big difference, but it didn't fully resolve the handling issues and I was planning a geo setup. I finally got round to sorting the geo recently and things took another leap forwards. As I'd expected, with all the messing around over the last 18mths, all 4 wheels were pointing in different directions, so this was a necessary step.
Ride heights were reset (F: 100mm, R: 160mm), camber adjusted (F: -1deg, R: 0deg) and toe set (F: 2mm out, R: 1mm in). The camber is in line with factory recommendations, but the extra rake and toe out on the front are not. On the evidence of 250miles+ driven since the new geo, I can honestly say the setup is working nicely so far. The car turns in keenly and is much more stable in acceleration, braking & high speed runs. As noted, while the car was originally set to factory specs after IVA, a lot has changed since then, so it's not a back-to-back comparison and I am not knocking the factory specs.
So, we're nearly there, but not quite. Despite the car showing the sort of promise I've always hoped for, there's still some bump steer left, which is more evident on the worst surfaces. Moving the rack up & down isn't killing it, so next up is an adjustable outer tie rod setup (as discussed on the previous page of this thread). It's hoped / expected that these will give a much finer final adjustment on the steering geometry (vs moving the rack) and allow us to get the last of the bump steer dialled out. Just for good measure a set of firmer springs are going on too.
Hopefully all this will be done at the end of April, so I'll be able to report back in a month or so. I'll close out by saying that while everything discussed in this thread has helped my car, this may not be for everyone. Maybe I'm more sensitive to fine suspension adjustments than others, I don't know... all I can say is that for me, these changes are really working out and giving me the handling characteristics I wanted from the car.
interesting readingAs reported in Dec, the steering rack mod made a big difference, but it didn't fully resolve the handling issues and I was planning a geo setup. I finally got round to sorting the geo recently and things took another leap forwards. As I'd expected, with all the messing around over the last 18mths, all 4 wheels were pointing in different directions, so this was a necessary step.
Ride heights were reset (F: 100mm, R: 160mm), camber adjusted (F: -1deg, R: 0deg) and toe set (F: 2mm out, R: 1mm in). The camber is in line with factory recommendations, but the extra rake and toe out on the front are not. On the evidence of 250miles+ driven since the new geo, I can honestly say the setup is working nicely so far. The car turns in keenly and is much more stable in acceleration, braking & high speed runs. As noted, while the car was originally set to factory specs after IVA, a lot has changed since then, so it's not a back-to-back comparison and I am not knocking the factory specs.
So, we're nearly there, but not quite. Despite the car showing the sort of promise I've always hoped for, there's still some bump steer left, which is more evident on the worst surfaces. Moving the rack up & down isn't killing it, so next up is an adjustable outer tie rod setup (as discussed on the previous page of this thread). It's hoped / expected that these will give a much finer final adjustment on the steering geometry (vs moving the rack) and allow us to get the last of the bump steer dialled out. Just for good measure a set of firmer springs are going on too.
Hopefully all this will be done at the end of April, so I'll be able to report back in a month or so. I'll close out by saying that while everything discussed in this thread has helped my car, this may not be for everyone. Maybe I'm more sensitive to fine suspension adjustments than others, I don't know... all I can say is that for me, these changes are really working out and giving me the handling characteristics I wanted from the car.
i have a few questions
if you are running 100mm fr and 160mm rear ride height, then the car is low at the front and the caster will be different to normal..... has this change helped or have you readjusted caster to compensate ride height differnces?
Since making the changes i notice you still have some bump steer... have you removed the rack again as altering caster and camber will alter the tseering rod angles too so the rack will need moving again?
interesting how you are running toe out at the front.... ive found on rear wheel drive cars, this tends to want the car to lead you in straight line rather than naturally want to go straight... may i ask why you have gone this way rather than toe in? what differences it made
also what tyres are you running...
thanks dom
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