ST-X

So I'm looking for some pointers on what to change with the geo of my car to dial out some handling traits that have only appeared after a number of recent-ish changes I've made. The car is a Blob WRX with c290bhp.
- Koni dampers with Prodrive S05 front/RB320 LE07 rear springs (inc 10mm saggy butt spacers)
- ALK + 19mm OEM FARB / Stock 22mm WL RARB set to softest
- 17" 7.5" wheels with F1 AS5's at 35psi all round
- newage quick rack
- 369mm F arch height, 376mm R arch height
- 2pot's front bump stops are fitted but I'm waiting until I pull the back end of the car apart this winter to get the rears installed.

I've been through the original WRX suspension, STI takeoffs, BC's and then went to this. With this setup originally I found the front end would wander wide on turn in, not scrubbing the tyres as such but just the feeling that the back end was failing to rotate, so you would add more lock than was required that you would then need to back off mid corner. Fitting the 22mm rear bar smoothed out the different phases of the corner but it still leaves the car wandering wide on medium sweepers unless you square them off more and get the back end loaded up or hard on the throttle when it really hooks and finds its rails. Is this just something I need to get used to again after many years on the BC's (I don't remember this trait with the STI suspension/ALK which were both fitted and not then aligned).

This is the geo chart from when it was aligned recently using some suggestions from on here as a starting point. I'd prefer sharper turn in without sacrificing the stability. Is this possible or are these handling characteristics something I just need to deal with? If so, what needs adjusting on the geo? Is it something that would be helped by the removal of the saggy butt spacers, or changing back to the OEM RARB despite the improvements it gave initially? Ignore the before position below for the front as that was after a full front end strip down and new rack etc. The back end was as it was.



Any and all help is appreciated!

Cheers

Croney

I what tyre pressures are you running try? Try adjust tire pressures keep the rear 2 or 3 psi below the front, if that's not giving you the rotation your rear toe, try to match both sides at a positive toe angle aim for +0.05 at the minute you have one positive one negative. I'm no expert just what I found works and based from advice from others.

ST-X

While tyre pressures can be used to fine tune it’s definitely not the root cause here as I’ve run between 34-36psi evenly all round for years, the exception being when I was on 888’s which were lower.

I think you’re looking at the initial figures, the rear is reasonably balanced at 6-7 minutes toe in per side.

bonesetter

iTrader: (9)

Geometry looks fine.
Easiest adjustment/test is to switch to middle hole on the rear ARB to increase front grip & increase rotation.

I've always set my cars to rotate RIGHT under the driver's seat :-)

2pot

iTrader: (3)

I wouldn't adjust anything until you've fitted the stiffer rear stops.
You could play with these to simulate stiffer rear stops:

plenty

iTrader: (13)

I never ran higher than 32 psi on my newage cars. High pressures tend to induce the washing-out you describe.

Also worth going to 2 degrees camber up front. Will tramline more but you'll be able to lean on the front end harder.

bonesetter

iTrader: (9)

I 'cold set' my pressures so they'll be what I want at working temperature, just like you see being done at TD's

I could see pressures going into the 40's on a hot summer's day, form a low 30's 'cold set'

I have also used a IR temperature sensor to see what's happening across the tyre too which was interesting at varying temperatures

ST-X

Okay, will do. I was planning to do that after the winter but will try to find the time to get them fitted before I park it up for the strip down.

1.6 deg was as much as we could get while keeping it all even. When I have it apart again over the winter I plan to take the struts out and slightly elongate the holes to maximise camber, as well as giving everything a good pry to make sure that everything's going to give the max camber results.

All tyres are different but I've definitely always run equal pressure all round and around about the 35psi mark for years without this trait which is why I'm suspecting setup, alignment etc rather than the tyres.

Yup, cold set for me too. It's interesting seeing the TPMS figures on the Beemer as I have the MPS4S's set to 2.7 bar cold and can see 3.2-3.3 if I'm really pushing them hard.

I do like the car to rotate, but equally don't like the continuation of that rotation that it feels like it's got at the moment at times which is why I was reluctant to increase the stiffness of the RARB further. When you turn in harder under power (and I'm not inclined to really make the back end twitchier at this point) it just rails but it's the sweeping corners where it feels like the front end is just rotating on a wider arc than the rear (although it doesn't feel like it's a scrubby, no front end grip type scenario, just a different rotation radius!). Now, if increasing the RARB removed this without then making it twitchy in faster stuff then that's an easy win, but I'll take 2pot's suggestion of pulling my finger out over the rear stops at the moment.

2pot

iTrader: (3)

You could run zero front toe. Turn-in would be less instant, but less wash mid-corner.
You could also drill out the top holes on the rear strut lower bracket, to 16mm. Then reduce the rear camber in comparison to the front. Does depend on how conscientious the alignment operative is though!
Your front camber is neg 2deg - it's in degrees minutes - not degrees.

ST-X

Okay, that's certainly easy enough to play about with. I guess as a quick gauge of how it feels is just to mark the arms where they are just now and add 1/4 turn per side in the right direction at a time to see if I like what it does. So toe is basically adding sharpness at the expense of mid corner? I'll still try to do the stops first though before the salt starts getting laid down on the road.

I've not got any issue with stepping the holes out slightly, although I do also have a set of Whiteline camber bolts which were on the car with the BC's. Aside from the utter PITA they are to get out the hub I could use them again? The local place I've found is really good actually, they're all pretty young but do a lot of stuff on track and drift cars so are reasonably happy to do what you ask them to do. The downside is that they're not to the degree of a particular specialist who knows all the individual tricks to maximise each number. That said I think they're more than good enough for what I'm trying to achieve, and they're good guys which goes a long way in my book.

And good point, very big blonde moment. 1.85deg is certainly pretty close to 2.0, certainly not to the degree(!) I'd notice. One side did get to 2.5 but the other was miles away so we settled for this as the max even number we could get.

2pot

iTrader: (3)

Yes. You can go further if required: toe out 3mins each side, if the steering is too responsive/twitchy.[/QUOTE]

Not a big fan of the thinner aftermarket camber bolts. Torque is nowhere near the gd/gg stock - 175N/m front, 197N/m rear.
Try to reduce the rear camber to neg 1deg 15mins to neg 1 deg 30mins, if using the enlarged rear upper holes.
Rear toe in at 3 mins each side is enough rear slip angle.

You did better than that neg 1.9 degrees and neg 1.96 degrees at the front.

ST-X

Good advice, thanks. I generally like the front of the car to feel hooked in, same with bikes, so I suspect with some playing I should be able to get it feeling sharp at the front without the back end feeling too much like it wants to carry on rotating. I don't massively mind the back being twitchy, it was the sensation of it wanting to continue rotating as you backed off steering that I don't find massively confidence inspiring when pushing on.

Cool, enlarged holes and a pry bar it is! I'm guessing you essentially enlarge them eccentrically inwards towards the strut body itself, rather than simply increasing the diameter with a step drill?

Do you reckon the rear toe in is too much then as I've currently got it and, if so, what handling characteristics is that likely to be giving? As you can tell (and from past conversations we've had) I like to understand what each bit is contributing to the overall system.

I was looking at the rear. Apparently I can't read which end of the car is which, as well as mis-reading minutes as points! We did get one of the fronts to over 2 deg but couldn't balance it.

Thanks again!

2pot

iTrader: (3)

You could elongate the rear upper hole inwards. For simplicity, I just drill it out to 16mm, as it's clamping force that holds the strut in place: and your not looking for a big adjustment.

As a test, it would be useful to try zero front toe and 3mins positive toe-in, per side, at the rear. Just to see if that helps you to get closer to, or further from, the balance you want - you may not feel a discernable difference, but tyre wear would be less.

ST-X

I'll see if I can try that before stripping it all down this winter, and before the salt starts getting put down. What would you expect me to feel by doing this?

No worries on the 16mm hole, I like the idea of keeping it simple if it works!