Author Topic: Front Tyres Center Wear  (Read 1003 times)

fka

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Re: Front Tyres Center Wear
« Reply #30 on: 11 May 2019, 10:34:44 PM »
Your edge also looks "polished" the same as mine. I presume this was on a tyre before you sorted out any warn bushes?
I was wondering if that stepping was due to the wheel "skipping" due to a warn damper. Warn bush putting it out of alignment + warn damper causing a bounce that lead to the flat spots? I have always felt some instability/ vibration (not front end) at motorway speeds. Thought this might answer that particular issue?

Pics below of what I ACTUALLY wanted to look at today - the inner arches! Initially I thought they looked really good compared to some of the horror stories that have been posed on the Facebooks recently. Then I looked up and found a tennis ball sized hole masquerading as patch of rust. I didn't have time to look at the other side but this is going to need a cutting out and patching.
Turned out to be an expensive weekend  ::)
« Last Edit: 11 May 2019, 10:44:42 PM by fka »

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Re: Front Tyres Center Wear
« Reply #31 on: 12 May 2019, 12:05:26 AM »
I think the wear is a form of skipping, but more   due to the combination of camber and toe in/out caused by a worn big trailing arm bush. 

Once you get that hole patched, I was recommended to put builders "Flashband" on the plastic wheel arch liner.  That's the self adhesive bitumen strips/rolls from builders merchants for sealing roofs and gutters.  I was going to do this - but OI forgot :o  Put it on the outside, not the inside next to the tyre and exposed to the elements.  Apparently it reduces the road noise a lot especially in wet weather.
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fka

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Re: Front Tyres Center Wear
« Reply #32 on: 12 May 2019, 11:36:31 AM »
I saw that post about the flashing. I must admit to being a little sceptical when I read it.

I'd love another opinion on the videos I posted but I had it jacked up again this morning to wobble the wheels holding at 12 +6 and 3+9. There's some movement but how much is expected? No clunking etc..
« Last Edit: 12 May 2019, 11:39:04 AM by fka »

carrera

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Re: Front Tyres Center Wear
« Reply #33 on: 12 May 2019, 12:04:51 PM »
I don't think I have ever noticed any play on the rear of my 9-5's when preparing for MOT. Is it perhaps some wheel bearing play you can feel, and in which orientation ?

I can have a feel on the breaker car I am currently dismantling for comparison next time I am with it, though of course I don't know how it drove.
9-5 Aero Estates, 2002 Cosmic Blue, 2002 Steel Grey, 2003 Graphite Green, 2003 9-5 Glacier Blue 2.0 saloon

fka

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Re: Front Tyres Center Wear
« Reply #34 on: 12 May 2019, 12:28:51 PM »
I wouldn't say there's any play as such, just a few mm of damped (ie bush) movement when wobbled 12+6 and 3+9 o'clock. Did you have chance to look at the short video I posted?

Basically I don't think anything has failed, I just wonder if the movement I see is enough to cause the edge wear?

Cheers

carrera

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Re: Front Tyres Center Wear
« Reply #35 on: 12 May 2019, 12:40:01 PM »
I have now.

Let me see how that compares to the breaker before i comment, but the direction of movement you are checking isn't the lateral movement that would be necessary to allow camber variation. Mind you, I have replaced rear control arms on a Boxster before now. On the car they twisted, it was only when I had the new ones I realised just how worn they were (from movement and absence of knocking)
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fka

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Re: Front Tyres Center Wear
« Reply #36 on: 12 May 2019, 01:02:37 PM »
Thanks mate, appreciated  :D

carrera

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Re: Front Tyres Center Wear
« Reply #37 on: 12 May 2019, 07:07:54 PM »
I was unexpectedly with the car this afternoon and you made me start dismantling the rear suspension. :)

Well, not that much. First of all I put the pry bar in like you did. I could get some twist, and to be honest, not as much as you did, but I don't go mad with the pry bar.

Then I removed one of the lower air deflectors and put the pry bar upwards so I could try for longitudinal movement. All I could feel was a tiny amount which then sprung back as I released pressure. Watching and feeling carefully I concluded that the movement was in the sides of the arm bending inwards under pressure, the spring backwards was the arm returning to its original profile.

No video, but I hope that helps
9-5 Aero Estates, 2002 Cosmic Blue, 2002 Steel Grey, 2003 Graphite Green, 2003 9-5 Glacier Blue 2.0 saloon

fka

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Re: Front Tyres Center Wear
« Reply #38 on: 12 May 2019, 08:59:27 PM »
It does help a lot, thank you!

The Vector B (same rear suspension.) forums seem to suggest the best method is to grab the wheel at 12 o'clock, with the car on the ground, and see if you can feel any movement. I can't. Also, as you put it, any motion I saw with the wheel off the ground sprung back when I released it.
I don't think there's anything wrong with the rose bushes. A trusted mechanic told me as much about a month ago so I really should have stopped there :)

Having read the rear toe adjustment procedure in WIS which basically involves shifting the position of the bracket that holds the trailing arm bush whilst holding the longitudinal links with a special tool. I do wonder if when the trailing arm bushes were changed, the rear toe was set correctly using this procedure?

Next step is obviously a 4 wheel alignment but I need to find an establishment that has the wherewithal to do the rear toe..

Thank you both again for your help  8)
« Last Edit: 12 May 2019, 09:02:08 PM by fka »

carrera

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Re: Front Tyres Center Wear
« Reply #39 on: 12 May 2019, 09:12:23 PM »
I have done the trailing arm bushes on my Blue Aero and a friends Vectra B. The Saab design /fitment is better, as you would expect. I have a set of tracking gauges so can do the toe checking myself, which does involve additional work when dealing with rear toe as you only measure total toe with them.

In my experience, establishments with the 4 way alignment kit tend not to have a set of spanners that can undo slightly rusty bolts, it seems to be a more widespread problem.

You can measure the existing toe yourself with an axle stand, a length of string, a rule and a bit of trig........ and a couple of hours for practice.
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fka

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Re: Front Tyres Center Wear
« Reply #40 on: 12 May 2019, 09:23:46 PM »
My nearest 4 wheel alignment kit is at the local KwikFit - say no more!

I was unexpectedly with the car this afternoon and you made me start dismantling the rear suspension. :)

Apologies for pushing you towards unnecessary/ unplanned spanner work  ;D

carrera

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Re: Front Tyres Center Wear
« Reply #41 on: 12 May 2019, 09:54:57 PM »
I wouldn't trust Kwik-Fit with a push bike, I'm convinced they would advise 4 new tyres were required. I use "Kwik-Fit school of engineering" as a non complimentary term  ;)

Don't worry about me working on the breaker car today - it's all coming off anyway, probably in one piece though that might be a bit heavy to manhandle  ;D
9-5 Aero Estates, 2002 Cosmic Blue, 2002 Steel Grey, 2003 Graphite Green, 2003 9-5 Glacier Blue 2.0 saloon

fka

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Re: Front Tyres Center Wear
« Reply #42 on: 16 May 2019, 01:10:34 PM »
Took the day off and put the car into Tutts in Dorking, they have a Hofmann 3D imaging alignment hoo-har. Not a Saab specialist but a really nice family run garage.
You can see in the pics the rear is spot on, so I can only assume the wear on the rears is 'inherited' and had started before the rear trailing arms had been done. Or the car is such that they will always wear like that...
Front toe was quite a way out considering it was checked, albeit in an oldskool fashion, two weeks ago. Really noticeable difference on the drive home. It felt good anyway having had the subframe bushes done but really felt more planted powering into the corners, and spot on track cruising along.
I'll go back there again next time, 45 well spent!


carrera

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Re: Front Tyres Center Wear
« Reply #43 on: 16 May 2019, 03:42:47 PM »
That looks pretty good, and I assume your steering wheel is still in the straight ahead position as well - "another driver" kerbed my Aero and knocked the steering out. It was a bit of a pain adjusting each side to bring the steering wheel straight as well as the correct toe in. The car did drive better afterwards.
Assuming you are on 17" sports chassis the spec is I believe as follows

Front - 0.9 degrees +/- 0.5 degrees, or 24' to 1 degree 24'

Rear - 1.1 degrees +/- 0.25 degrees, or 51' to 1 degree 21'

You are running a bit more negative camber than recommended on the rear and on the upper limit on the front, which will be benefiicial to the handling. Just keep an eye on the rear inner edge wear   :Fawlty:

« Last Edit: 16 May 2019, 06:51:43 PM by carrera »
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fka

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Re: Front Tyres Center Wear
« Reply #44 on: 16 May 2019, 06:21:52 PM »
Yep the rear camber is a little out of speck. Front right caster is a borderline too.
Due to pending birth, it wont happen this summer, but we're planning to get a caravan before next summer. I'll do the rear rose bushes and have B12 + new top mounts going on before then. So that lot should help pull most of it back in line..