Sideways at 110 km/h on 3 wheels is scary.

[DMGT]

I'll post this first. Object: what was left of my RH rear. Location: 50km north of Goondoowindi on the Gore Hwy.

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If you want to know the story read on....

So, the gf and I were on our way from Dubbo to Toowoomba, it way about 5pm and we'd just stopped at Goondoowindi for fuel. The Gore highway is 110km/h, which I'd been sticking to pretty much spot on except for the off overtake, although its a pretty average bit of road. We been driving for about half an hour, as we we coming around a slight left hand bend I for an instant felt that the car felt strange, then all of a sudden we're sideways. With me overcorrecting the car fish tailed about 3-4 times down the road. I applied a bit of brake pressure to slow down (not heaps as I thought it may have been a front tyre that had let go, more on the reason for this later) and managed to get the car under control and eventually off the road. I then sat there and took a few deep breaths. Fu*k.

On getting out of the car it was pretty easy to see what had happened. We got the car up on the jack and got the wheel off, this is what the wheel arch looked like:

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Wanna know what the weird thing was? Earlier that day between Dubbo and Coonabarabran pretty much the same thing happened to the rear left, not as bad a the one later in the afternoon though as in this case the car was in a straight line and never got out of shape, it just felt like a regular flat - which is why in the afternoon when it got so out of control I thought it might have been a front that had gone. At the time I put it down to some heavy wear on the inside shoulder of the tyre (notably this was not present of the right hand rear that let go later in the day) which you can see here:

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After what happened later in the day I doubt the wear on the shoulder had much top do with it. My previous set of tyres were pretty much down to the canvas on the inside shoulder without blowing out like these. I'm really interested to find out how two 4 year old pirelli P7s (not a bad tyre) can fail like that. Top answer a few likely questions:

Car load - yes the car was heavy, us plus about 7 cases or so of wine, plug 2 big bags, maybe 350kg plus fuel, but nowhere near the carrying capacity limit of a wagon.

Load distribution - As we were doing a big trip I wanted the car loaded as evenly as possible, the back seats were down, the wine cases were over or forward of the rear axle and the bags (a bit lighter) were packed last in the boot.

Tyre condition - Pirelli P7s, about 4 years old, about 55000km, well worn but not past the wear markers (except of the inside should on the left rear). I was actually going to replace them as soon as I got to Brisbane.

Tyre pressure - checked by Subaru at the 180,000 km service 3 days prior - safe to say not a factor.

Road condition - pretty average but hey, there are average roads all over the country and I've never seen this happen before.

Rubbing etc causing damage to the tyre - after I replaced the tyres I continued to check their condition, with about 500km more on the right hand one and 1000km more on the left the are in perfect nic, no rubbing or damage at all. The only non-subaru mod to my car on the rear is a whiletline sway bar, the Bilsteins and STI spring are OEM parts. Shocks&springs are only 10,000km old.

Anybody have any idea what was going on here?

Doug.

[Adrian2627]

How does the sway bar look? Has it rubbed against the inner sidewalls?

[fibble]

How does the sway bar look? Has it rubbed against the inner sidewalls?

Agreed - this is where I'd go....

Did the swaybar have "locks" to prevent lateral float in the bushes?

[kiks]

You overloaded the car.
Overheated the inside of the carcass.

And the car is lower than the factory designed geometry allows for (I see some sort of lowered/subaru sti spring there). Seeing as those sti springs are weak as piss, you'd be well beyond the normal range of motion of the hub with that much weight, compounding that with the dynamic camber incurred with the multilink rear end and yeah...money is on overheating the carcass, them being underinflated in the first place, the high camber angle due to load and shitty lowered springs not designed for what you were doing, and possibly a long shot: tyre section too wide causing interference with the wheel well.

Let me get one thing straight. Some 14 year old apprentice checking your tyre pressure is 28 or 30 psi, is not how you should travel with a fully loaded vehicle. I'd have 40-42 in them as a minimum for what you were doing.

Next time, dont put so much shit in the back, bouncing it down the road at 110 with tyres rolling the sidewalls hard instead of being supported by the sidewall, prepare the vehicle properly. You could of killed a family of orphaned leukemia suffering children that never had christmas.

Why the hell are people talking about swaybars, it has no job what so ever in lateral location of the hub. Removing it wouldn't do a thing unless it was just substantially loaded on one corner only. Seeing as it's a wagon carrying so much, and probably also had sedan springs in it too, and the fact the wagon has a narrower track (control arms shorter 5mm)...Its a bunch of cumulative factors.

There are some questions though:
1. OEM wheel?
2. Exact tyre size and brand
3. What modifications to rear suspension. Exactly.
4. How much weight in back in KG.

If you picture a stockish size tyre, with a soft nice comfortable sidewall like a pirelli. Imagine the heat it generates if you compress that sidewall into a bowl shape, then place all of the load on the inside 10-15% of the tyres contact patch, and then rotate that tyre at a few hundred RPM. Just imagine the heat generated from moving that rubber and distorting it hundreds of times per minute.

To prevent this, more tyre pressure for more load. A stock height wagon spring would of been a good idea too if you intend on loading it full of shit all the time to maintain proper safe geometry as per design.

[kiks]

Also for what its worth, I've destroyed a tyre in a gen4 wagon from rubbing on the inner guard.

Similar looking marks but much more focused on one spot. And with a 10" wide semi slick, not a 8" wide section tyre on a stock rim. Im betting on overheat and carcass failure.

[Adrian2627]

Why the hell are people talking about swaybars, it has no job what so ever in lateral location of the hub.

No it doesn't but those Whiteline bars have a tendancy to slide in the bushes unless they are fitted with locks and with the car overloaded could have been rubbing on the sidewall of the tyre. If you look at the pic you can see the corner of the bar has been rubbing.

[HyRax]

No it doesn't but those Whiteline bars have a tendancy to slide in the bushes unless they are fitted with locks and with the car overloaded could have been rubbing on the sidewall of the tyre. If you look at the pic you can see the corner of the bar has been rubbing.

The swaybars do not slide THAT much. The damage to the swaybar is more likely the flailing rubber from the wheel when it blew.

[kiks]

No it doesn't but those Whiteline bars have a tendancy to slide in the bushes unless they are fitted with locks and with the car overloaded could have been rubbing on the sidewall of the tyre. If you look at the pic you can see the corner of the bar has been rubbing.

The swaybars do not slide THAT much. The damage to the swaybar is more likely the flailing rubber from the wheel when it blew.

I've had about 4 different swaybars in the back of my gen4 wagon and changed them dozens of times. I know what moves and how far it moves fairly well, as any sort of qualification to my statement.

Now, if it had two broken links, and was somehow 3 inches wider from you know...magic, then it could interfere. Otherwise no I'd doubt it. Also note the same markings on the trailing arm, this is with a stockish tyre a full inch clear of the sidewall.

What I am more surprised about is the fact the swaybar shackle dropouts aren't snapped off. Looks to be a 20mm or so bar, in a wagon they usually rip that vertical tab in half.

Seams fairly clear cut to me. Too low, too overloaded with weak springs, tyre pressure for commuting not for hauling arse end full of gear up a bumpy country highway putting huge stress on the tyre; exacerbated by the multilink's inherent huge dynamic camber with the quite short upper arms run above parallel.

edited for accuracy!

[bigBADbenny]

Scary and glad you're OK.

Lets see some AVO HD RSB mounts or at the minimum Cusco RSB mounts to reinforce the stock mounts.

Good interpretation of events from esteemed members IMHO.

I recommend a front swaybar to balance out the RSB, for "normal" driving abilities at least.

[kiks]

I wouldn't. Remove the front swaybar completely. Much more fun to drive!

[DMGT]

No it doesn't but those Whiteline bars have a tendancy to slide in the bushes unless they are fitted with locks and with the car overloaded could have been rubbing on the sidewall of the tyre. If you look at the pic you can see the corner of the bar has been rubbing.

The swaybars do not slide THAT much. The damage to the swaybar is more likely the flailing rubber from the wheel when it blew.

HyRax - you are correct. The damage on the swaybar is from the tyre after it failed. There is at least 40mm of clearance between the swaybar and the wheel, in fact the point of least clearance comes from the strut recess where you see in the second photo the tyre damaged the plastic under the wheel arch. The swaybar (and the rest of the suspension for that matter) was installed by professionals - S&J in Adelaide, swaybar locks are fitted. This was not the issue here. Incidentally it was their advice after much research on this forum as to why I didn't get AVO swaybar mounts fitted - they said they weren't required (although I do know of guys who have snapped the OEM mounts) and why I opted initially upgrade the rear bar only. Will be reassessing this decision, particularly the mounts.

Kiks - agree the most likely cause of failure is heat in the tyres. I guess my question really was what do I have to do to stop this happening again. The current situation is absolutely unsatisfactory. Let me explain. I'm a conservative guy. I drive at the speed limit - especially on average roads. My car is a daily driver and I don't just use it to cruise the M1 between the gold coast and Brissie. I put stuff in it, I drive on average roads sometimes, it a family station wagon not a race car, but I would like it to handle just a little better. Hence when I made the decision to upgrade the suspension I went for a OEM package (STI WAGON springs/Bilstein struts) that lowered the car a minimal amount - 15mm, not a diy home job with a hacksaw. I also didn't put 18" wheels on it. The wheels you see on the car are the standard wheel. The tyres are Pirelli P7 214/45 R17 91W - a higher load rating than the OEM tyre and plate on the car (87W).

As for tyre pressure, I acknowledge I didn't personally check the pressure in the tyres before I left, I trusted subaru with this, although I did visually check them after the car was packed to make sure they weren't sagging. However, after the first tyre went I sure as hell did. The remaining 3 tyres were at 40psi - I can only assume the first one that failed was at 40psi as well. I was actually worried that they were 3 psi over that the recommended on the plate for a loaded up vehicle (37psi), I then checked the max inflation pressure on the tyres which was 51psi so I decided this wouldn't be a problem. I don't know, maybe I was wrong?

As for loaded up this is how I looked at it when I packed the car: The total weight in the car was about 350kg (us 160kg + lets say 90 bottles of wine at 1 kg/bottle + 2 x 25kg bags in the boot + 50l of fuel). 350 Kg is equivalent to me and 3 mates - I wouldn't consider that overloaded. Happy to take feedback on this... Lets do some sums here, the car weighs 1500kg dry, lets assume half of that is over the rear wheels (conservative) - that's 750kg. Lets also assume the entire weight of us+cargo was also on the rear wheels only (again very conservative) - that's a total of 1100kg. Each pirelli P7 is rated at 615kg. That's 1230kg carrying capacity of the rear axle. my car was at the absolute absolute most 130kg under the max. In addition I searched the web today for the max carrying capacity - all I could find was for an '06 legacy, note: not a trusted info source, which said 1300lbs ~ 590kg, my car was carrying at least 200kg less than this. Heavily loaded? - yes, overloaded? not in my opinion.

What I didn't realise was the effect of the road and as kiks mentioned the effect the camber must be having on the rear tyres in addition. Subtle - yes, likely to be a significant factor -certainly. So... my question really is how do I ensure this never happens again. I went for an OEM tested suspension setup in order to mitigate risks like this. What happened on the weekend has thrown this into question. In addition if this happened with STI springs fitted what is to say after a few more km the same wouldn't have happened with standard height springs - there's only a 15mm difference, probably less if I took into account how much my old standard height springs had sagged? Does anyone have any info on this? Can the dynamic camber issue be corrected to reduce the stress on the inner sidewall?

I guess I posted this as a bit of a warning. Just shows how by thinking you are being conservative with mods, when doing something slightly different like driving on an average road (not a terrible road I might add, no corrugations, no big pot holes etc, just rough) with a car with a bit of stuff in it, even with keeping to the speed limit things can go pretty wrong.

Thoughts?

[bigBADbenny]

I commiserate, my experience swerving to avoid a roo at 110kph had me fishtailing.
Coilovers, WL rsb and a very expensive setup and alignment can't compensate for a bad descision or apparent lack of driving driving skill in my case.

Your post and the related discussion is a valuable example of the inherent dangers of interstate travel.

[Ben]

Shagged tyres!!!

[kiks]

I can see how it's happened.

Wasn't having a go at you at all. It's good to have the info. That's why I wanted the tyre sizes etc.

Also safe to assume tyres were around right pressure too based on other three. That leaves me thinking about one fix which addresses what you want. A stiffer rear spring.

It'll handle load better.
Reduce total range of movement at the cost of a small amount of comfort (minor).
It'll put that hub in a high -camber position less often.
It will handle significantly better. A rear spring rate 30-50% stiffer than front transforms these cars.

There's a few mobs with higher rate rears, I think swift and prodrive? Would be first thing I would change. In doing so is also move the links all the way to the end of the bar if it's an adjustable sway bar (least torsion).

The sti springs are still quite a weak spring rate wise. If expect a mild change in comfort but hardly noticeable. Just don't go changing rubbers to urethane etc and NVH won't be too different.

[DMGT]

No probs at all mate, no offence taken. Appreciate the info regarding the rear suspension geometry and springs. Anyone want to buy a pair of STI wagon rears?.....