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YOUR RESEARCHBump steer correction front - setup advise
Leading reported evidence
Install with one additional shim
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Tie rods are installed with one additional shim on top, lowering the tie rod end by 5mm.
Leading evidence: 'Install with one additional shim' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, The most frequently discussed action is 'Adjust after fitting the h&r lowering springs' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Suggestion
Have you had the front and rear wheek alignment adjusted after fitting the H&R lowering springs?
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Suggestion
When cars get lowered a lot this feature of the front suspension kinematics changes unfavourably (into bump steer) when you lower a car more, generally speaking, than what the factory offered as an option.
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Suggestion
When cars get lowered a lot this feature of the front suspension kinematics changes unfavourably (into bump steer) when you lower a car more, generally speaking, than what the factory offered as an option.
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Since the bump steer on my C4S on the B8 / H&R setup is fairly annoying and I won't be changing to the GT3 setup just yet, I got my hands on a set of RSS bump steer tie rod ends.
Is there any general guideline on how the tie rod end should sit with the car on the ground? Are they fully level?
Before going into Trial & Error I'd like to put the rigth spacer in when installing them.
Thanks!
Ben
Hhm that's approximate at best...
Outside front tire is supposed to toe-out under bump when cornering in order to negate lift-off oversteer.
When cars get lowered a lot this feature of the front suspension kinematics changes unfavourably (into bump steer) when you lower a car more, generally speaking, than what the factory offered as an option.
Lots of info in this thread: http://forums.pelicanparts.com/porsche-911-technical-forum/888071-bump-steer-1.html but what it comes down to is that 'tie rod parallel to lower control arms' is not valid for each design of McPherson strut suspension but only for those where the steering rack is at the same height as the lower control arm, which it almost never is but in case of a 996 very close.
The real criterium is: the imaginary line along the tie rod has to intersect with the pole of the front suspension (in front view) at the new ride height.
This pole is also used to find the roll moment center.
Roll centre and instantaneous pole of motion on McPherson strut suspension
To achieve this after lowering you can either move the steering rack up or lower the position of the outer tie-rod end ball joint.
Establishing by how much is the elaborate part in this exercise.
Have you had the front and rear wheek alignment adjusted after fitting the H&R lowering springs?
Yes, the car was aligned. I will get it redone after fitting the new tie rods, hopefully some time next week.
Thanks for detailed explanation. I was already aware of some of the details, such as the fact that I can't really compensate the roll center issue until I switch to the GT3 uprights in the fall.
That's where I was hoping the Tie Rods could provide a termporary solution. I will try the different heights that i can achieve with the RSS Rods and report back.
Yes! I did the trial and error method for now, more to come next winter.
Tie rods are installed with one additional shim on top, lowering the tie rod end by 5mm. Afterwards I had an alignment done.
Don't have the sheet with me in europe but I believe -1.5
� F, -1.8� R, 5' toe front, 35' toe rear, both total. Was hoping to get more camber, but we are maxed out with the stock setup.
Drove the car for about 1,500 miles on backroads and the bump steer is almsot gone. Car feels great, very pointy on turn in, maybe already a bit too nervous.
Next step is the GT3 setup: Coilovers, uniball mounts, wheel carriers, GT3 Control arms, RSR Uniball ends, cup rear tie rods. That should help
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