Wheel Alignment Question, Car Feeling More Skittish

[Duncan]

lol lighten up bud......everyone's nice in the Suspension section....all the argumentative, opinionated members live in Forced Induction

[Nismo 3.2ish]

haha , if I was any lighter I would float away

Chill

[MozzMann]

Sounds like this True Track know their stuff trouble is they are a bit of a drive from here, I need to get both our cars attended to before the Winter season , . the front end is quite good but the rear is scrubbing the inside indicating to me that there is excessive toe in rather than the usual toe out on the rear.

Anyone got some steering places in Canberra region that are worth talking too re the Stagea suspender's.

[MozzMann]

This may help some here by explaining Steering and Suspension principles

http://www.ozebiz.com.au/racetech/theory/align.html

Edited April 7, 2015 by MozzMann

[Sinista32]

Mozzman - There is only one place worth going to in the ACT

Capital Steering and Suspension in Fyshwick. Peter will look after all your wants

[MozzMann]

Thanks I'll give Peter a Call

[MozzMann]

Booked in with Peter and the gang for Wed next week .

[MozzMann]

Peter and the boys at Capital Suspension very quickly found one issue I was not aware of and that was one camber pin in the rear must have failed and was replaced by a regular bolt.

Getting a full alignment Friday with replacement pin ( hopefully they will have it by then ) and I shall pass on my thoughts then .

And also thanks to "Sinista32" for putting me on to them.

[MozzMann]

OK I can say honestly that the boy's at Capital Steering in Fyshwick. are bloody brilliant , fast efficient, and to be honest brilliant fellas to deal with.so from me a HUGE thumbs up the Peter and the Boys at Capital Steering.

[GTSBoy]

How the hell did Fyshwick end up in a serif font when the rest of the post is Arial?

[MozzMann]

Quite easy I cut and pasted it as I am so tired I couldn't remember how to spell it. done over 2000K's in the last 2 days bud

[Kinks]

I HATE toe-in at the rear

HATE HATE HATE HATE HATE HATE HATE HATE HATE HATE HATE HATE it!!!!

I used to align my R33 "zero zero" front and rear toe and it always drove really nicely. I did this over several alignments. I then went to a place that toed in 2mm at the rear (1mm each side) and he said "you won't even notice it" - well it killed the handling of the car. It became very benign, a safe option for those who don't realise that their right foot can induce oversteer, but it was GOD DAMN BORING to drive. I feel like it became more skittish on the limit because the rear desperately wanted to grip and you had to poke at it to get it to move... but then it wanted to tuck in again. This led to an "all or nothing" personality where you either got it right out or it just stayed in. Not very enjoyable.

My R34 workshop manual says front toe is 0 to IN 2mm. Rear toe is 0 to OUT 5.2mm (yep, toe OUT 5.2mm!!). Wow!!

I have had my R34 toed out 2mm at the rear and front is 0 toe. Drives really well, corners well. Love it.

Also, both of my cars had/have functional HICAS. At high speed HICAS drives the rear wheels in phase with the front steering to promote understeer. You need some initial toe out to help it turn in. And then don't drive like a dickhead and you'll be fine.

I should also note I've done a number of track days and Texi's so I am familiar with how skylines handle. If you're on your first one then just get it toed in, it'll be safer. I can't stand it though.

[GTSBoy]

Also, both of my cars had/have functional HICAS. At high speed HICAS drives the rear wheels in phase with the front steering to promote understeer. You need some initial toe out to help it turn in. And then don't drive like a dickhead and you'll be fine.

That bolded bit is not actually true. The proper explanation of what HICAS does on turn in is as follows....although with a slight detour into what happens without HICAS first.

Tyres generate force to make a car change direction only when they have a slip angle. Slip angle is when the tyre is pointing in a different direction to the direction of travel. The angle is only very small, but it is there.

When you try to turn a conventional 2WS car, you reef on the steering wheel and the front tyres change direction. They are now pointed at some angle to the side, have a slip angle and start to generate turning force. Once that force acts on the road the car starts to rotate around. Assume that the axis of rotation is a point somewhere in front of the rear axle. It is only once the car has started to rotate around this axis that the rear tyres start to take on some slip angle and start to generate turning force.

What HICAS does is turn the rear wheels at the same time as the fronts are turned. This starts to generate slip angle and hence turning force much earlier in the proceedings. It makes the rear end feel lively.

HICAS is good for making cars that are driven on Jap freeways feel much better to drive than their chassis is actually natively set up to feel like. Up to about 7/10ths. Once you start pushing the car really hard on twisty and bumpy roads, HICAS rapidly gets beyond its abilities and starts to interfere with the steering inputs being put in by the driver. There's nothing worse than having a halfwit computer that only knows a fraction of what's actually going on with the car trying to guess what you're doing. Remember, the only real inputs that the HICAS computer has is the steering angle sensor and the speed. There's no G sensor, no rotation sensor. Nothing. Every time you flail away at the wheel trying to mitigate understeer, the HICAS computer sees that as another turn in and makes a probably wrong change to the rear wheel angle.

[V28VX37]

Hi guys,

My R34 has felt a bit more skittish recently, especially on poor or corrugated surface on off camber slopes. It's a bit hard to describe but it feels less planted than I remember, especially on crappier asphalt. Another sensation is this kind of slight 'sideways skip' on a bend if there's reduced grip due to a pothole.

The only thing that's changed is that I had new tyres put on (exact same brand tyre and size as before, Goodyear Early F1 Asym 2) and they did alignment at the same time. Can someone please have a look at the two alignment sheets below and let me know if there's anything suss about the new one?

Thanks heaps!

2013 alignment done at TruTrack to suit my preference:

2014 alignment done at a local shop to whatever their computer threw up by the looks of things:

...

Thread revival, the 'skittish' rear end issue on my R34 is back

I was just driving on M1 towards the city near Richmond/Cremorne, you know the long sweeping bend with a gazillion expansion joints, and it a feels like the rear wants to step out when you hit a joint, at its worst it's like a like a little sideways jolt. This is at a steady 80 km/h staying on the lane. The whole car feel nervous and it's really not a nice feel.

The alignment settings should be pretty close to the TruTrack settings above, however I am thinking of taking it back in for a check up, it's been a while.

Any suggestions on what to check or try? Is one of my swaybars too stiff? Something loose somewhere (I have checked but...)?

Here's the full suspension spec for reference:

• BC Racing BR Type coilovers: 6 kg front, 5 kg rear spring rates - front drop 25mm, rear 30mm
• ARC swaybars: front 28mm hollow, rear 25mm hollow adjustable (at middle setting)
• Hardrace adjustable front radius rods (rubbed bushed)
• KKR adjustable front camber arms (blue)
• NeoTech adjustable rear camber arms (silver)
• Total HICAS eliminator kit (a full conversion to non-HICAS rear, not just a lock bar)

The Goodyear tyres have seen normal road use and one track day, a bit worn on the shoulders but plenty of tread left on them...

[Dale FZ1]

Rear end ride height dropped and running standard rear "traction" arms probably combining to give a bit of bump steer. ie. suspension slightly loaded through the bends you describe, wheel hits the expansion joint and compresses the suspension a bit more. Results in a momentary toe change outwards. Gives nervous feel. On some setups this can be pronounced enough that the car will oversteer.

The test: bring the rear ride height up 20mm and compare (no cost).

The Fix: If that brings general improvement then take it to your suspension specialist, have a set of adjustable traction arms fitted and adjust things so you don't get toe change through your suspension travel.

[V28VX37]

Rear end ride height dropped and running standard rear "traction" arms probably combining to give a bit of bump steer. ie. suspension slightly loaded through the bends you describe, wheel hits the expansion joint and compresses the suspension a bit more. Results in a momentary toe change outwards. Gives nervous feel. On some setups this can be pronounced enough that the car will oversteer.

The test: bring the rear ride height up 20mm and compare (no cost).

The Fix: If that brings general improvement then take it to your suspension specialist, have a set of adjustable traction arms fitted and adjust things so you don't get toe change through your suspension travel.

Thanks Dale this is fantastic! Your description is exactly what it does over bumps, a very unnerving feel. The rear is dropped quite a lot from stock so that's probably why it's so pronounced.

I'm kicking myself for not getting the traction arms together with the camber ones, they're the only non-adjustable arms left in the whole setup (LCA's notwithstanding). Oh well live and lean.

I've just ordered a pair, will chuck them in and get a full alignment & report back, fingers crossed.

[V28VX37]

Quick question, when I put the rear traction arms in should I adjust them longer or shorter than OEM for reduced bump steer?

Here's what I found in an S13 Suspension FAQ:

ADJUSTABLE REAR TRACTION ROD

Rear Bumpsteer Adjustment

When the suspension is lowered, an adjustable rear upper arm is usually installed to reduce the amount of negative camber at the ride height. However, when the rear upper arm is elongated to compensate for the negative camber, this alters the geometry of the rear multiple link and can cause bump-steer. Adjustment of the rear traction rod together with the rear tie rods (Hicas models) or rear toe arm (non-Hicas models), the geometry of the two two arms can be restored to eliminate bump-steer. Typically you want to make the traction rod longer than the OEM unit to reduce bumpsteer. Too much adjustment can cause an unstable change in toe when the suspension bumps. For this reason I suggest that the arm be adjusted minimally.

So is (slightly) longer than OEM the go?

Obviously I'll stilll need to get a proper alignment asap.

[GTSBoy]

Yes longer. But don't just guess.

[hardsteppa]

I suggest lengthening them by the same percentage as you lengthened the rear camber arms, as a starting point.

[V28VX37]

Yes longer. But don't just guess.

I suggest lengthening them by the same percentage as you lengthened the rear camber arms, as a starting point.

Thanks guys, I'll measure the OEM camber arm and compare the current adjustable camber arm setting to that to give me a better guess