I recently replaced my 150k mile 1999 Regal GS with an 2008 GP GXP. Part of the reason I got rid of the old GS.....is because the suspension was slap worn out, and my tires were all wearing bald on the insides. Especially the rears.

Fast forward to my 08 GP GXP. I bought it with 38k on the clock, and immediately replaced what appeared to be the factory tires, with a set of BFG G-Force (stock size up front and 235/50/18 rears). The traction of these tires is incredible......but the handling completely sucks compared to the worn out factory ones I replaced them with!! Even with the tires inflated to max pressure, nothing changes. I've tried all different pressure settings with minimal change. It feels like the rear is completely disconnected from the front, as it just slops around like a loose trailer back there. Feels like the sidewalls are rolling in every corner. Very mushy. Even just going down the highway at speed, and sawing the wheel back and forth. Maybe it's the slightly wider size on the narrow rim? All I know is it's freaking horrible.

So I took it back in to Discount Tire to have them checked out.....and low & behold.....the insides of every tire is worn completely bald, especially the rears. This is with about 15k on the tires now. When you look at the rear of the car, it looks like the rear wheels have a ton of negative camber at the top......but that's how every single W Body I've ever seen looks too. I just figured that's normal?

So what's everybody else's experience with the wider rear tires, as well as balding insides of the tires? Thoughts? I'm at a loss. I can't imagine the rear springs are already that worn out on such a low mileage car, or that the alignment would be that far off either. Getting that checked is my next step.

 

Mine were wearing like that so I had it aligned and problem fixed. You can buy special bolts, I have post that has that information if you want to search for it, but my friend who did the alignment said those weren't enough to fix it so he clearanced everything instead and it works great.
As far as the rear traction goes, i've never had any problem. My tires are just hankook ventus V4es, nothing crazy performance. I think it may just feel like that since the front does grip so hard.

 

A 50 series tire is going to feel sloppy. I went from 245-40 to 235-50 and it's a lot worse handling wise.

Now, many W body people have had trouble with keeping camber on the rear. I don't know if there's a fix or not.

 

So what would be the preferred tire size for the rear that others are having good success with? The only reason I averted from the stock size, was because of a lack of good traction options. From reading multiple threads on this site....and many others.....it seemed that the 235/50/18 was the preferred one for the rears. Maybe I read wrong...

Also, is there a link to the thread about the special bolts used on the rear suspension? I've never heard about that, but sounds interesting.

I will say that when I hit a local twisty/turny fun backroad, the Active Handling Control kicks in almost constantly at the peak of every corner, and ruins all my fun. I wish there was a way to disable that... This is taking the corners at speeds LOWER than what I used to take them in my old worn out suspension Regal GS!! To be honest, I've been nothing but totally disappointed with the handling of this car.

 

I plan on going to a 245-45-18. I didn't like the tiny sidewall of the 40, and the 235-50 is just too tall for my taste. The 45 series is just in between, iirc. I'm going to try it and see how I like it.

The GXPs, to my understanding, had the staggered tires as a factory "tuned" suspension. My guess is it was their way of combating understeer. I don't know what to tell you on this. Maybe some GXP guys can chime in.

 

My car had the tires wearing in the rear...
i went to auto zone and got two new rear camber bolts, they claim they make it adjustable from -1 to +1. However, my friend who did the alignment at his shop said with the bolts in, it still didn't suck the tires up enough to stop the wear. He did some clearancing on some parts and got it fixed that way. Now, some of the other gxp guys have used the bolts and said they worked just fine.
As AB eluded to, this was something done on the GXP. I did notice less grace (ever so slightly) in the rear, but it was worth it not to blow through new tires. The system would work great if you traveled on a autocross, but driving back and fourth to work it wasn't working for me.

 

ACDelco camber bolt kit; one kit per wheel.

http://www.rockauto.com/catalog/rafr...&parttype=7542

Traditional HTML (faster loading):

http://www.rockauto.com/catalog/x,ca...,parttype,7542

 

Maybe I'm not understanding....

Is this camber bolt kit referenced above just a replacement bolt for the factory one, or is it some kind of camber-fix-it kit released after a problem was understood by GM?

Thank you all for the help btw. It is helping a great bit!

 

Our camber is not adjustable from the factory (unlike the VE/Zeta). So this camber kit essentially allows camber adjustments. You replace the top bolt with the bolt provided with the kit, thus allowing camber adjustment:



VE/Zeta factory camber adjuster:

 

Completely understood! Thank you for explaining that.

So what is most everyone running for rear tire sizes?

 

No problem.

What I'd like to see is if DavidGXP would swap his wheels so that we could see if the 275s will fit in the rear.

 

The camber bolts might do it but some have had to tweak the strut holes to. Just tell them you want the rears straight instead of whatever the gm spec is.

 

from what i have read a 255 is the biggest that we (GXP's) can go. right now i have 235/50/18's all around and it doesnt handle that bad but it will be alot better when i get the 275/40/18 front and 255/45/18 rear. i had the same problem with it worn on the iside of the rear it is a problem on all w-bodies from what i have heard. what tire pressure are you running now?

 

31 fronts, 40 rears. Anything below max pressure in the rear is super sloppy. Like stupid sloppy. I'll never run that size again! The clearance is very close to the strut tower as well. Not sure how one could run a wider tire back there without rubbing?!

 

I had a problem with my rear tires starting to cup on the inside. I rotated them the other night hopefully they'll last until winter.

 

there are alot of the guys on here running 255's on the rear with no issues. i am running 30 psi at all 4 corners. and it is running good for me. i tried different psi and it had worn the tire unevenly so i tried what the door jam said for the stock sizes and has been fine since that. ever now and then it kicks stability control on but that is because i have really bald tires. once i get good tires on i am pretty sure it wont kick out on me. but that is my opinion.

 

Gonna be a while before she's back on the road.

 

thats all i did was the camber bolt kit had the car alirned and no problem after that, im running the factory size in the rear, but im having other issues right now with the rear of the car

 

Bend some more laterals?

 

no, i need rear tires BADLY the goodyear f1 tires in the rear are sooooooo bad my car feels like im driving the flinstonemobile, i need rear rotors rear pads, and rear strut mounting plates, between the noise of each of those problems is driving me crazy enough to go postal