chiark

Hi there

I have a set of P1 wheels on my MY00 and, apparently, the offset is wrong. I've just been in to have my geometry "done", and the guys doing it told me the offset was wrong.

How they knew this was to strap their kit onto the front and back wheels and move the steering wheel a quarter turn. The wheel moves more one way than the other for the same lock - apparently showing the offset is wrong. A mate with an evo had his geometry done, and his offset was right so they showed me what the difference was.

I am a little surprised by this.

Could someone in the know comment???

Ta,

Nick
(btw, I'm running P1 wheels with 215/40R17 tyres as opposed to 205/45R17s which are the standard if this makes any difference... Not that it should as the 5mm extra will be on "both" sides )

SPEN555

Nick,

Lee P has P1 wheels on his MY00 and had the geometry done at Falkland Performance along with eibachs fitting and I've not heard him mention there is anything wrong with his. He has also done a couple of track days since.

Damian.

JonW

Cripes Nick... Ive just got me a set of these...

Surely though if these wheels dont catch on lock etc then they are the right offset. how can they be more out on one side than the other?

Jon.

Mickle

Maybe chiark's got a wonky set or his car's been in a smash

Ray T

got um on my my00, had a four wheel alingment done at power engineering, they did'nt mention any problems.

ray t

chiark

Car is mine from new. Never been in a smash.

However, they also told me that a wishbone was bent, probably from being through a pot-hole... I wonder if this could be the problem...

It doesn't rub on anything, but that's not apparently the real test of offset. The chap who did my setup appeared to know what he was talking about, explaining *lots* about things to me, including why the offset would affect handling. He does the set-up for everything from the Ultima GT-Rs that a colleague builds (I saw it), through to rally set-ups, through to Ferraris, porsches, lotus (loti? ) for the JCT600 franchises and, bizarrely, volvos too.

chiark

Sorry, I'll explain exactly what led him to this conclusion.

Strap laser alignment thingy to front wheel.
Strap "ruler" to rear wheel.
Move steering wheel half a turn left, then right. The deviation from left to right should be equal. It wasn't.

Swap over to other side of car.

Find same, but in reverse if you see what I mean - the opposite direction produced more turning than the first side. In other words, it's straight, but the wheel offsets are wrong as the tyres aren't in the centre of the suspension. Think about it and it makes sense. I think

Pete Croney

Chiark

Offset is often determined by what fits, not by the optimum castor or king pin alignment.

carl

Let's get this straight:

Half a turn to the left, back to centre, then half a turn to the right?

The deviation won't be the same because that's how Ackermann steering works. The wheel on the inside turns more than the one on the outside.

Logically, if half a turn to the right turns the right wheel as much as half a turn to the left turns the left wheel, then half a turn to the right must turn the left wheel less than this because the outside wheel has to follow a larger circle.

chiark

Pete,

Thanks for that!

I think that could be where the bloke was coming from. He seemed to know his onions, and showed me the difference on the Evo we had tracked at the same time.

I guess it ain't optimal, but what it looks like you're saying is that "if it fits and doesn't rub, the offset's ok".

I can live with that.

It just rather surprised me that he was saying they were wrong given that they're prodrive wheels

Ta for putting my mind at rest.

Nick.

chiark

Carl, I thought that too. And it looked the same on the evo, too, to a certain extent but not nearly as pronounced...

As mentioned, this guy does everything from Volvo->Ferrari so I guess he sees the lot.

Another subaru was there too. I left before he'd got his checked, but he was running 18" oz's...

mutant_matt

Nick,

If they are "wrong" for your car then I would imagine they are wrong for a P1 too!!! I would guess that it's got more to do with your bent control arm than the wheels?

You could also give PS a call (seeing as you're going there soon) and check with them as I would trust their advice when it comes to suspension/handling/geom....

Matt

ScoobySnack

Have a MY00 with P1's on........ Never had a problem

Also... from SIDC

"One important point to bear in mind when shopping for new wheels is that the recommended offset (the distance between centre of the rim and the mounting face) for Impreza wheels is unusually high, at between 52 and 55mm depending on the model. Using more common, smaller, offsets will increase the track (width) of the car, which may cause the tyres to foul the arches, and will have an adverse effect on handling (by increasing the leverage of uneven roads and cornering forces on the suspension and steering components). One knowledgeable wheel retailer claims that anywhere from 45-55mm is fine (even going so far as to say that 55mm is excessive!), whilst a Subaru dealer insists that 55mm is essential and anything else wrecks the handling. It's probably worth pointing out that the standard wheels are 52.5mm offset, and the Speedline Competition 2, sold by Prodrive through your Subaru dealership, is 48mm!"

J

SG

I have them on my MY00, had a four wheel alingment done at the Local Subaru Dealer. No probs.

kwack

Somewhere on the inside of the wheel will be the offset stamped. From memory they are 52. I have them on MY99 with zero probs


Kwack

SimonH

Have also got them on my MY00. The car's been in to PS a couple of times (bumpsteer, eibachs etc etc) and has had the geometry done there twice. No problems to report

CrisPDuk

Get your wishbone checked, and if necessary changed. If it has been bent backwards the castor angle will change, without affecting either the camber or the tracking when the wheels are straight.
I have just had the nearside replaced on mine, because the castor was way out, and what a difference it made. An error in the castor angle does have a marked knock on effect on the camber and tracking when lock is applied, which will explain your alignment being incorrect.
Apparently (and this makes sense), the wishbone is the 'weak' link in the suspension, it is designed to give slightly under extreme loadings, i.e. big potholes, crunching kerbs (the wife?), etc, to prevent the load being transferred into the chassis.
If you regularly drive the same car you will adapt subconsciously to developing faults and consequently not notice them. It was only after I had not driven mine for a while, then got back into it that I felt something was wrong.

chiark

Cheers Chris. How do I get it checked?

I feel a trip to TSL coming on, as they seem to know what they're talking about.