Bump steer despite geometry set up - videos added

[gizlaroc]

Oh, don't tweak it yourself unless you know what you're doing and use some fishing line or something.

a 1/8th turn to adjust toe can move it from 0.07 toe in to 0.07 toe out (example plucked out the sky, but you get my point.).

Just take it back and say the steering wheel is not straight and needs to be sorted. Tell them a smidge more toe in would be OK as well if that is easier to get it set up equally.

 

[gizlaroc]

One thing you have not mentioned is what tyres you are running?

This can make a massive difference to bump steer.

My car does it far less on Michelins, but still a fair bit. It is called communication.

 

[Moko]

To follow up on my alignment adventures....after the first alignment which I wrote about above the car felt very twitchy following cambers / white lines now after finishing the rear suspension refresh (all new arms, drop links & anti roll bar bushes etc).

Well I took the car to Jaz Porsche for it's alignment and this time the car feels amazing back to its old self (well actually loads better with no slop in the arms )

Attached is the setup it's currently running for those that understand these things.

 

[gizlaroc]

That looks spot on mate.

My god, whatever were the alignment guys doing previously?

No wonder it felt the way it did with the settings like that. 0.16 toe out and 0.06 toe in is unreal.

It just shows how much difference a decent alignment makes though.

 

[Mezgerite]

Total toe out is what makes it jittery. Also run as much negative camber as is physically possible, which is not a lot on a standard height 997 turbo, but will help with understeer hugely. Standard geo settings make for a very understeering car.

 

[kp278]

Hello! The place I used should be quite good, it's Myalloys in Basingstoke, they came recommended, they only deal with alignments and refurbs so figured they'd be better at it than most places. They had a few sports cars there so I was in good company.

I kind of miss the sharp turn in (mostly on roundabouts given the right was at 0.00 before) so I'll either go to 0.02 on both sides or even 0.01 if that doesn't work for me. I wouldn't want to dull it anymore than it already is.

Re: rear toe and drifting, I probably don't drive it fast enough on corners to find the limit, but it feels settled.

Tyres are Eagle F1 all round (although Asym 2 at the rear and Asym 6 at the front as they don't do an Asym 2 for the front).

I've taken a couple of videos - here it is on the motorway
https://www.youtube.com/shorts/4mvnECLSzF0

Here it is on a terrible B road
https://www.youtube.com/shorts/Jy7KnWex2tI

 

[kp278]

bump (pun unintended)

 

[remarklima]

I ended up going 0.01 toe in on the front - with the instructions As close to 0 as possible but on the positive (in) side - must be even both sides

As much camber but even.

Then rear was -1.5 deg camber and 0.10 toe in - again with the note Must be even both sides


Last track day it tracked lovely, great turn in and loads of adjustability - on PS4S tyres.

 

[kp278]

I cranked the left tie rod half a turn out so now I have steering wheel straight ahead, still need to check for even threads either side.

Still interested to know what folk think about the two videos I posted.

 

[gizlaroc]

But all you have done is pushed the left side toe completely out of spec. to straighten the wheel.

It doesn't matter where the wheel is, the geo is done with it presumed to be in the correct position.

How does it feel when you are going say 30mph and turn the wheel to say 10pm and then 2pm? Does it feel the same, turn the same?


I would have been back there and asked them to straighten the wheel personally.


These cars completely change how the feel with the smallest of changes to toe and camber.
Also, the threads on the toe arms won't be the same regardless, even less so if the wheel is off centre when they started doing the geo.