InTurbo

iTrader: (3)

More news.... Been busy the last few days trying to sort the handling out on the Sti and it's nearly there.

After having the height adjusted in my earlier post. I went for an alignment very near to Bonesetters recommendations, it's now at.
Front toe 0.07
Front camber 1.35
Rear toe 0.08
Rear camber 1.45

The car is better and now giving me a more confidence in it.
It's stable at speed, grips in the corners and tracks straight. But it still looses it's composure at higher speeds on bumpy A/B roads.

Also I think the Goodyear eagle F1 side walls are to soft for the car.

If I run oem pressures the car is squirmy and soft.

If I put them up to 36 34 there still a slight squirm from the rear end on quick direction changes.

If i put them up to 38 36 they a bit better. But Is this over inflating the tyres? Or should I replace them with something with stiffer side walls??

Arnie_1

Tyres are a pretty personal thing. They can be the stickiest things in the world but if they don't give you the feedback and confidence you like, then you'll never be able to drive them to their(or your) max. Bonesetter likes fairly stiff sidewall tyres. For example he never got on with Michelin PS2s, too squirmy feeling, though they are pretty much one the best tyres you can buy. He's moved onto, I believe, Yokohama (correct me if I'm wrong) which have a stiffer sidewall and he's much happier. I personally like a more progressive tyre like the Michelin that has a bit more sidewall flex. I've never got on too well with massively stiff sidewalls. But that's just me. The Goodyears are a good tyre. I wouldn't overinflate as you are just changing the contact patch for the worse. You can either get used to them, or try to sell them off and move onto something like a Bridgestone RE01R or Yokohama Advan Neova AD08.

bonesetter

iTrader: (9)

Oh God, don't get me on tyre sidewalls Arnie

The 'sloppiest' tyre I think I have ever tried were the Toyo T1R's which were quite shocking.

The writing wore off the walls they collapsed over that much

In fact the Proxes were double sloppy - turn in and the wall would collapse (steering had vague nothingness feedback), then the tread blocks would flex & squirm

Steering feel was all over the place

F1's were a little better, but still what has to classed a comfort tyre as far as sidewalls go. Nothing like the Toyo's though



These are the Bridgestones S001 I run on the Forester STi



They give very good feedback, and wear quickly

Really comes down to preference as Arnie says, and also the terrain you drive - rough bumpy mountain roads and you need higher profile, more compliance softer wall etc, fast road with a bit of track, general hooning...

The variables go on and on, but riunning higher pressure is going to reduce grip significantly, and increase wear

Alignment looks good - it's something I do almost immediately on any 'new to me' car so I know where I am

InTurbo

iTrader: (3)

Going to put some new tyres on at the weekend. Not sure what to put on!
Wish they would let you test before buying!!

bonesetter

iTrader: (9)

Ooh, now that's a tricky one

If you're not sure I would say don't rush into anything.

You've made some good changes to your car, that you're happy with. Why not live with the car the way it is for a little while longer, enjoy and get used things - let's face it, none of us know what the weather is going to be doing for the next two or three months -performance tyres like a warmth in the tarmac

Edit: you're in Oxford aren't you, only 40 minutes up the M40 from me - why not come up and try my cars and see how they compare?

InTurbo

iTrader: (3)

Well I've ordered some Yokohama AD08R's as recomended by Simon of chevron. Will be fitting them at the weekend, hopefully this will give me that last bit of stability and control I'm looking for. Just have to be careful with this horrid weather..

bonesetter

iTrader: (9)

Ooh, very very nice - my favourite tyre I have the AD08R's on my Type R

They have the stiffest sidewalls of almost all

BUT - be exceedingly careful...

They really do need some heat in them to perform, and although Yokohama in their speil say the R compound is 'orange oil' and works better in lower temperatures and the wet, they will be very sketchy for the rest of the winter

My Type R sees only 'keeping loose' runs during winter. Needs to be 5°C to go out

During the warmer months they are totally awesome and have grip levels to make you literally lol.

Here's an old worn out set I took off the Type R. See how the shoulders are still completely intact. No other tyre I have ever used has done this

InTurbo

iTrader: (3)

Yeah I fully understand there not suited to the cold weather. I'm not going to push them or try my luck. The Subaru is my weekend toy, I have my Seat for when the weathers bad.
How many miles did you get out of ad08's and do you experience any tramlining with them?

bonesetter

iTrader: (9)

I'm not sure how many miles, but they lasted very well indeed. There seems to be a perception these are a super soft compound tyre, but really they last well

I will say though, they drop off their blistering pace once 2/3ish worn (see pic above), except when totally dry

Zero tramlining

See my 'Staggering' gush here

InTurbo

iTrader: (3)

Lol. I read that yesterday.
Will be good to do a direct comparison between the f1as2 and the ad08r in regards to stability and response.
This is what I'm looking to improve in my car.
Good to hear they don't tramline. I Had Re070s on my last Sti and found them tugging at the wheel quite a bit.

bonesetter

iTrader: (9)

I've not tried RE0-70's, although I did try to (didn't have the size I was after). Sounds like I didn't miss out

Let us know how you get on

InTurbo

iTrader: (3)

Well Ive spend a few days with the Yokohama Ad08r's on the car and I must say so far I'm very impressed! Admittedly it's not been the best of weather the past few days but the tyres have performed excellently.
Ride quality is slightly firmer and I've not had any tramlining from them.

First major improvement is the high speed stability, changing lanes at motorway speeds feels direct with no wallow.

Secondly the squirm during hard direction changes has also gone, even at oem pressure 33f 29r

Drove over 60 miles the other evening on Wiltshire's A roads, The outside temperature was only 2 degrees and the road was wet and they gripped and drove perfect.

Not encountered any standing water in them yet, so can't comment on how they handle that.

Bad points, none really. Road noise has increased ever so slightly that's it.
Can't wait to for some warmer weather to see how they perform.

InTurbo

iTrader: (3)

Edit to my previous post I've had the Ad08r out in greasy conditions and they will push on in corners if provoked but there brake away is very progressive and manageable... Under normal driving there fine. But still not composed on bumpy roads at speed.

InTurbo

iTrader: (3)

Yet another leap forward this weekend.
I replaced the 22mm front and rear roll bars for the original bars and difference is amazing.

Even after driving 100 meters i could tell the ride was a lot better and smoother over speed bumps.

I Took the car down what has been my local test route it's a mix of a/b roads and the car now just flows with the road and gives more confidence. Before it would bounce and crash over bumps and undulations. Really shows that roll bars add to the spring rate and reduce independent suspension movement.

There is slightly more roll but the increase in composure and confidence more that outweighs it.

After now having 24mm then 22mm now oem size bars there is no doubt that a softer bar is more suited to road driving.

The cars been getting better and better the past few weeks, thanks for everyone's comments and help.

bonesetter

iTrader: (9)

Seems you prefer the softer arb's with your BC's.

It's not always the case however, especially when you are using a more compliant damper/spring

BC's are 'good for the money' and I think you would see another leap with the likes of KW V3/Clubsport and their ilk, or even a decent fixed perch (OE) arrangement. Then you would almost certainly see the benefit of more roll resistance

A lot of it is down to preference though, but I think the BC's are your current weakest link

plenty

iTrader: (13)

+1. OP what spring rates are you running on your BCs?

Suspension setup needs to be considered holistically...fatter ARBs can make sense if your struts are sufficiently compliant to begin with.

bonesetter

iTrader: (9)

And for me, I much prefer things that way

2pot

iTrader: (3)

Or, bars always reduce independence and grip.

Use the smallest bars possible.

Unless, you're on smooth roads/track, and maintaining the front camber curve, on the front macpherson struts, with a larger front bar, outweighs the grip reduction.

bonesetter

iTrader: (9)

^ very puzzling post

InTurbo

iTrader: (3)

Im running 5/4 on the BC's. Must be a personal preference but I find the car so much more settled on softer bars.

2pot

iTrader: (3)

What, exactly, are you perplexed by?

GeeDee

iTrader: (2)

I'm running OE struts with some tweaked, more compliant, PCA springs and bump stops and I've had a very similar experiences of changing tyres and reverting back to OE ARBs as InTurbo. I can assure you there was no benefit of more roll resistance on UK roads. In fact, it was downright uncomfortable with a very choppy ride especially when I had standard 91 rated tyres probably made worse by different tyres front and rear creating an imbalance. Currently running Nokian WR A3 XLs all round and actually much more comfortable.

I was also running BCs 5/4 before reverting to OE struts but I didn't get the chance to try them with OE ARBs as I wasn't aware of the ARB problem at that time. They were not comfortable.

You also suggest that the BCs are the weakest link - not convinced. My uprated ARBs came from the Powerstation Stage 3 kit with ASTs and I had similar problems.

Uprated ARBs appear to be a "free upgrade" with regard to all positives and limited negatives but, with hindsight, not so - IN MY OPINION before I get all manner of challenges.

lookout

I think the argument over larger ARBs has to be discussed in 2 ways.

1. Do you want to change the balance of the car?

2. Does the car need more roll resistance?

If you are of the opinion that the Impreza is normally geared slightly towards too much under steer, then a slightly larger rear ARB is one of the easiest compromises. All the other solutions would normally affect the comfort more and have more negative effects.

If you are of the opinion that the Impreza also suffers from ROLL oversteer a tad too much, a slightly larger front ARB is the easiest compromise. If you are aware of the ratios that govern the 4 modes of suspension, it is quite clear that the increase in normal spring rate to achieve the same result would be huge and would be very uncomfortable.

Whether the Impreza actually needs more roll resistance depends on tyres, dampers, springs, body stiffness etc. as well as the road surface. Depending what suspension frequency you want to end up with, but with decent tyres and dampers I would normally expect that a slight increase in roll resistance is needed for driving on dry tarmac.

However, there is no wrong or right here. It is purely personal preference. Just like tyre choices; some prefer a soft side wall, some a stiff side wall.

Normally I would advise people to set the car up according to what the car is used for most of the time. For instance, there is no point to modify the car so it's the quickest when used on a racing circuit if the car spends most of its life on the motorway or A roads.

2pot

iTrader: (3)

3 thoughts:
Add positive caster - can't think of any negatives, unless you add too much.

The prodrive wr99 option suspension used 19mm front and 18mm rear sta bars, with 35N/mm springs front and rear - I wouldn't describe those rates as a huge increase, to completely change the sta bar balance.

I'm now getting to the limits of my suspension knowledge.
Are we using the same definition of roll steer?
On the rear - roll understeer - I understand that on a Impreza - compressed tyre toes out, uncompressed tyre toes in. So start with some toe in unless you want to loosen the rear.
But roll oversteer, on the front? Compressed tyre toes in, uncompressed tyre toes out.
Do Impreza's exhibits roll oversteer - and how would a bigger front bar help?
If it was conventional oversteer, I'd understand a bigger front bar.
I can also see a bigger front bar maintaining the camber curve and reducing suspension travel.
But addressing front roll oversteer with a bigger bar.
Genuinely intrigued.

Hang on, you're not using the word 'roll' to describe the camber curve collapsing, and the loaded tyre edge rolling under; are you??

bonesetter

iTrader: (9)

Roll oversteer, as opposed to traction oversteer, or wash-out oversteer, often happens mid-bend after turn-in, when the outside front wheel is loaded and before the weight transfer to the back happens on throttle application

Insufficient front roll resistance and the car will roll onto the outside front inducing the diagonally opposed, inside rear wheel to unload and loose its weight, resulting in an oversteer

2pot

iTrader: (3)

I wouldn't define that as roll steer, but I understand what you're describing.

Sticking to road use, as per the thread - so likely a 19mm (all roads) to 22mm (smooth/flat roads) front bar.

I'd brake earlier and/or more.

Add front tyre pressure - assuming it didn't spoil the ride quality.

Add positive caster, to get a better line on turn in.

See if I could add more front negative camber - without adversely wearing the road tyres or affecting traction or braking, specifically in wet weather.

And, as were really discussing sta bars, for the vagaries of uk roads, I'd use a smaller rear bar, to keep the unloaded rear inside tyre in contact with the ground.

ditchmyster

iTrader: (7)

Just thought I'd list my set up for anyone who may be interested.

Car is 54 WRX Wagon PPP and AP 4 pots up front.

225 /17 /45 Pirelli Sotto zero winter tyres on standard Sti rims.

Blue Super Pro (I think) polly bushes, on standard bars front and rear, also on the steering rack.

Camber bolts all round, although not taking advantage of them at the moment.

PCA Dynamics Blue springs on standard struts.

Rear alloy drop links.

Cusco rear roll bar brace, this mounts to the same points as the roll bar and goes pretty much in line with it across the underside of the car but has no real flex in it.

Front -1.25 camber
Rear -1.50 camber
Toe -0 01

Caster is around 3.37 had some problems with this but as the next mod is Classic STI Alloy front wishbones and drop links I've not concentrated on it too much.

Going to be heading for about 5 degrees of caster.

Personally I think this set up is good for the road, very stable in all conditions
and when pushing on, good steering feel, direction changes are vastly improved as is cornering speed.

I still have a small amount of understeer which is easily controlled with the gas, either ease off a little and it straightens up or give it some more and the back starts to come round a little, depending on road conditions and speed, but that is me being a little lairy in the wet, turn in is still very good.

Still have a bit of front end roll I'd like to lose and not sure about the understeer as yet but that can be cured via a little more camber or possibly a slightly bigger Front Roll bar (22mm) I'll wait and see how it feels after they Alloy arms are fitted and add 0.5 of neg camber at the front.

I'm currently set up for winter on greasy winding country roads in one of the Mountain Regions of Croatia and you don't really want an over active back end, had that with my last set up and it was a tad hairy for winter.

As above next steps are hopefully going to be the final part to get it exactly where I want it.

I'll be changing to summer rubber soon and add a bit more camber front and rear as I'll be moving a fair bit faster and loading the suspension up more.

As you can tell I'm no expert but in laymans terms this is a good cheap way to get a WRX handling and steering pretty well for about £300 and the ride is still pretty good too.

HTH.

lookout

'Roll over steer' is a normal term in suspension engineering. This happens when a car rolls 'off its rear grip'.

Indeed, extra caster will increase the loading on the inside front wheel during cornering and increase the negative camber on the outside front wheel during cornering. Do pay attention to the camber gain curve when adding caster as on a lot of cars the camber gain is quicker than the loading increase on the outside wheel resulting in the car momentarily only running on part of the front tyre during turn in. This will provide an unsettling feeling, like driving on eggs.

Remember, Subaru fitted ARBs to the Impreza to suit all types of drivers with all types of tyres and all types of road surface. This compromise does favour a safer under steer bias. As enthusiasts might want a slightly different compromise. Even Subaru used a larger rear ARB on some of the more driver orientated specials. In all forms of motorsport ARB adjustment is used to change a car's balance, where permitted in regulation.
In my experience with my Imprezas, the change from Michelin or GoodYear tyres to Bridgestone or Yokodrama has a much larger effect on comfort than changing to a slightly larger diameter rear ARB.

People running cheaper coilovers normally have much larger problems with unloading of the inside rear wheel not only due to reduced rear droop but also increased stiction as well as higher amounts of lower speed rebound allowing the car to 'hold on to its wheels' in roll mode.

I understand that your experience is different. Showing again this is to do with personal preference, not wrong or right.

fpan

iTrader: (11)

They disconnect them in 4x4s to go off road as it allows better wheel articulation but unless you have a massive one I don't see the problem IMHO.

Coming from a 205 GTi (with Bilstein suspension and upgraded ARB and torsion bars) to my first WRX wagon, the car handled like a boat.

Too much roll for my liking and lots of understeer, no lift off oversteer.

After fitting Prodrive springs, ALK and 22mm front and rear ARBs it started being fun.

Saying this, the car was still understeering at the limit and you had to trail brake to make it turn on all fours.

My FSTi also felt too walloy and understeering with its 20mm front and 17mm rear ARB.

After fitting a RB320 22mm rear ARB (on the soft setting) it was perfectly balanced for my liking. I tried it on the hard setting and the front of the car felt too walloy and the car not balanced so back to the soft it was.

The idea came from the RB320 that has a 20mm front ARB and 22mm rear one (I copied this setup in my FSTi and it worked perfectly).

Both cars gave you confidence on wet slippery tarmacs and you could drive them at the limit effortlessly without having to be on your toes.

Just my 2c.

2pot

iTrader: (3)

The RB320 is 20mm front, 21mm road/track adjustable rear (soft setting 20.5mm, hard setting 21.5mm). Due to the softer prodrive suspension for the UK.

I've posted this link already on SN. See if it helps you to see what I'm getting at, with regard to big bars.