What suspension issues may cause excessive inner rear tire wear, only on one side?

[Q-DawgVFR]

This is on a 2009 GXP.

Car doesn't pull TOO bad, but does tramline a bit and never drove as well as I remembered GT model I test drove years ago.

Previous owner liked running the tires lower pressure. He said he had initially overinflated them and was wearing the middles too fast and he figured this would even things out.

It's been on my list of things to chase since getting the car in Nov, but I wasn't sure how bad the issue was. Then I also bought a G8 GT this week (long story but deal at auction came up and I couldn't refuse) and it definitely drives better than the GXP. So now I know for sure there's something to chase on the GXP, but I am still not 100% positive it isn't tire management that caused some of this. But wondering what else could be the culprit. Because only ONE of the rear tires is worn hard on the inside.

New rear tires are DEFINITELY in order ASAP. Fronts still look good.

I have plans to upgrade suspension anyway, but want to take care of driveability issues first before I get too carried away with mods.

Any thoughts?

[GXP-G8]

This is on a 2009 GXP.

Car doesn't pull TOO bad, but does TRAMLINE a bit

Because only ONE of the rear tires is worn hard on the inside.

. Fronts still look good.

I have plans to upgrade suspension anyway, but want to take care of driveability issues first before I get too carried away with mods.

Any thoughts?

What is Tramline ? Sounds like my car.

[Q-DawgVFR]

Tramlining is a tendancy for a car to pull to one side or another due to ruts in the road or crown of road and/or low profile tires, etc.

I ran wider tires in my two previous cars ('04 and '11 Audi S4's) and never had these kinds of wandering issues.

My GT feels firmly planted, the way a car should. It also is running on narrower 18" rubber, but I think there are differences in the cars. I do know the GT had some money thrown at control arms and a couple other suspension parts before I bought it, while the GXP didn't see many miles or much work.

The GXP has the tire wear issue, tramlines or pulls a bit, and feels a bit unsettled in the rear when I go over uneven bumps.

[WhatNext]

I would start with getting the alignment checked. But if the strut top bushings are collapsed, that would allow the top of the strut to move fore/aft and left/right resulting in the alignment moving all around. So the alignment will be constantly shifting and getting the car aligned will be a waste of money. Then if the dampers (struts and shocks) have more than 30k on them, they are pretty well worn out so that is what may be causing the rear to feel unsettled.

[Q-DawgVFR]

I would start with getting the alignment checked. But if the strut top bushings are collapsed, that would allow the top of the strut to move fore/aft and left/right resulting in the alignment moving all around. So the alignment will be constantly shifting and getting the car aligned will be a waste of money. Then if the dampers (struts and shocks) have more than 30k on them, they are pretty well worn out so that is what may be causing the rear to feel unsettled.

Thanks. Was thinking of alignment as well, but if something broken or loose could be a complete waste of money like you said.

I read about it a while ago, but I don't think I'm really following what I'm looking for with the strut top bushing being collapsed. I remember a gap being mentioned when I searched about potential issues on thr forums before buying the car. But not sure where to look.

Sent from my SM-N950W using Tapatalk

[WhatNext]

There were picts on both this and the other G8 forum but couldn't find any quickly (the photobucket blowup wiped the picts). Can anyone point to some bushing gap picts?

Here's what to look for: Open the hood, about 3/4 way back from the radiator there is a large horizontal disk (~6 inch dia) on each side of the engine bay above where the strut ends. The disks have a rubber ring on the edge. In a perfect world, the rubber edges would be lightly contacting the top surface of the strut tower. As the strut bushing underneath the strut tower collapses, the disks with the rubber edge get pushed up away from the strut tower surface resulting in a visible gap. If that gap is more than 1/4 inch, then the bushing underneath needs replacing.

[Q-DawgVFR]

Oh mine are definitely shot on the GXP then. The GT has a much smaller gap but I will have to measure

Why the 1/4" gap? Is there always some gap?

Yeah I have actually done a lot of reading on the forums but this photobucket issue has really screwed up every forum I visit. Many of the threads are half useless without the pictures to show what is being discussed. So I appreciate the patience from everyone, as I know I am asking some questions that have been covered.

[WhatNext]

There is always some gap as the bushing squishes a little. The issue is how much squish is acceptable. I said 1/4 inch as I have less than 1/4 inch and its been 7 yrs and 28K miles since I installed poly strut bushings. The gap hasn't changed in a few years. I watched the gap on the factory bushings open from nothing to more than 1/4 in the first 8K miles.

[Q-DawgVFR]

Oh ok that makes sense about the gap. Thanks for the explanation.

I now have a bit of money now to spend on suspension fixes / upgrades: I had a garage sale and sold some stuff from my old car and truck.

It has always been my intention to primarily focus my efforts on handling improvements to the car, so I am researching what to upgrade as I do some repairs.

[WhatNext]

Since the strut bushings on the GXP need to be replaced, the struts have to come out. You should plan on replacing the struts at the same time. So should the rear shocks be replaced to match the front struts. What to go with is a whole other discussion.

Since you are focusing on suspension upgrades, something I observed over the years about our Holdens that I got from this and the other G8 forum, the ride comfort/NVH (Noise, Vibration, Harshness) seems to be very sensitive to suspension items installed to replace the factory stuff. For instance, the strut bushings; a lot of us replaced the factory rubber bushings with tougher poly bushings (only alternative to rubber available in the early years). Some of us had no change in NVH, some noticed an increase, for some the increase in NVH was such that they took the poly bushings out. Similarly PPV replacement struts and shocks, They provide nice tight spring control (after break-in) such that they are perfect for touring with my GT. For others, a lot of complaints from the spouses and rear seat passengers such that some have removed the PPV dampers. No complaints from my wife and I even asked the rear seat passengers about the ride, they only gave me a quizzical look in response. Not that I'm immune: I mounted Michelin Pilot Sport AS3 tires and now get a slight tread hum around 70 mph from the rear. So I am having second thoughts about installing rear cradle inserts which might worsen it. So I highly suggest a cautious approach to replacing the numerous suspension bushings and other components keeping in mind it is very easy to cross over to the dark side with this platform.