Geometry and Castle Combe (again)

[Fishy Dave]

On Saturday I had a tinker with my car ahead of a trackday afternoon at Castle Combe yesterday. Oil and filter change (again), spanner check and then a full geometry set up using the old fashioned but accurate string method. It helps having the use of a 4 post lift, but it's a right pain finding things to replicate my weight in the drivers seat and footwell (and I'm not that chunky!).

I fitted longer, 30mm 10.9 bolts through the damper base into the front uprights, with a slim washer to give me more negative camber (around -2.5 deg). If it helps, the standard bolts are no.3 in the diagram and the washers go between part 1 and 2 http://www.realoem.com/bmw/enUS/showparts?id=BT92-EUR-09-2006-E85-BMW-Z4_M32&diagId=31_0758

The front toe was good with the tiniest tweaking to parallel.

The rear toe surprised me with both rear wheels toeing out by 4mm. Adjusting this is a pain, but I managed to get both rears to run parallel.

To Castle Combe yesterday for the afternoon only and the car felt fractionally down on power, but I put this down to the warmer weather and carrying passengers for most sessions. Understeer was very noticeable through Quarry and Tower, making it necessary to heavily trail brake, losing me time. This time I just couldn't keep up with Tom (video to follow), probably for a few reasons (excuses). I think Tom is driving faster, I had a passenger, my understeer, Tom is on track compound NS2R (I'm on 'street') and towards the end of the day a possible reason for being down on power a warning light with the code showing a TPS error. The car drove home fine so will get it the TPS swapped over and see how it feels. Not sure if I have disturbed something when unplugging the front sensor to change the oil filter at the weekend?
Still I enjoyed giving Toms mate some pointers from the passenger seat of his E46 M3. Also good to meet James, a Z4 2.2 owner who was out on track for the morning only. Both Tom and I gave him passenger laps which he seemed to enjoy Get involved on here James if you're reading let us know about your car.
I am going to order some new RTABs, fit the limiters I've already bought and try again with the rear geo. Does anyone else run toe out on the rear or should I play it safe with parallel?

Cheers, Dave

 

[Argenta]

I just had my RTAB's changed with AKG Motorsport limiters.
Put it all back in std pos and it was (with Eibach's) camber -2deg and toe-in 2mm at the rear.

Not yet happy as it actually became 'floaty' at the back, coming out of certain bends.
Don't know what I did wrong.. Maybe I should've gone for 0 toe as you? Less camber?

I imagine running toe out would make things much worse for me anyway.

 

[Fishy Dave]

Thanks Per.

I've changed my RTABs for Meyle HD and added ECS Tuning limiters and then took some time to set the car up again, deciding on 2mm toe out at the rear.

The guys at Amspeed say they run a tiny amount of toe out on their race cars to help eliminate understeer which is reassuring.
The old bushes actually looked perfect, with no splits of any size in the rubber.

The rear toe out was immediately noticeable, making the car feel just how I like it on the drive home. It doesn't wander or tramline but does turn in crisply and seems more willing to play at the rear.
I'm going to try to get an hour or two at Thruxton next week to see what it's like.

I changed the TPS sensor at the front but can't feel any difference, then again the warning light only appeared on track and I have no pending codes showing? Thruxton will soon show up if it is the other TPS instead.

 

[Fishy Dave]

Finally got around to adding the footage to Youtube, not very exciting but does go to show how adjustable the handling can be by altering rear geometry alone (in this case I'd really ruined it!). Tom had some very good onboard footage he sent me but after trying for a couple of evenings I've admitted defeat, something about it crashes my editing software.

[youtube]https://youtu.be/SPB_wAXa9e0[/youtube]

https://youtu.be/SPB_wAXa9e0

I drove Thruxton last week for an hour in the Z4M (and a Ginetta G20 race car thanks to a CSCC driver) and showed that the TPS fault has gone away with full power returning. Adding rear toe out has restored my preferred handling balance, more on this plus a bit of video to follow.

 

[Beedub]

bloody hell that looked fast ! lol