Strange Alignment/Sub-frame Issue?

[MSMStannyl]

Hey guys, figured I'd post about this here as I think it's the best place for it. Looking for some insight into a rather strange issue that I recently started noticing.

As my profile states, I have a 2015 GT (non-PP) with the 20" Foundry wheels that I purchased brand new in winter 2014/15. Have some minor bolt-on stuff done but specific to suspension, car is on stock springs/struts/shocks. I do have the Steeda G-Trac front brace on the car as well as their rear subframe IRS braces. Those have been on the car for probably at least 2 years at this point. No issues. The only other thing to mention is that once I burned out the original 265 series Pirelli P-Zero summer tires, I replaced with 275 Conti DWS 06 tires.

Anyway, the issue: This is something I just started noticing maybe in the last month or two. It's mainly on the highway, at higher speeds but seems to be specific to when I'm in a higher torque output (meaning a downshift/lower gear). I might be on a straight section of highway, car tracking straight, then downshift and hit the gas, and it just "feels" like the rear alignment shifts just a tiny bit. I'd equate it to losing traction for a second but I can't fathom that's the case at these speeds, just from getting on the gas a bit.

In my head, it almost feels like the sub-frame is loose and shifts slightly when I hit it. I dunno. Thought I was losing my mind but I can pretty much repeat it at will now so something is definitely off. Just not sure what it is.

I can't say specifically if this started after my last tire rotation (a few months back) but am wondering if that could be the culprit? Maybe some sort of issue with the tires that are now on the rear? I haven't had an alignment done for a while either so maybe it's time for that. I'll probably start there and see what happens. I have also been getting a couple creaks and squeek's from the rear end here and there when starting and stopping but assumed that is just the nature of a car getting older (around 55k miles now).

Anyway, let me know if you've experienced anything similar or have any ideas/suggestions.

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[BmacIL]

@Bluemustang

There's two things:
1) The IRS subframe bushings allow for a TON of deflection under load. BMR and Steeda both offer kits to address this.
2) It's likely your IRS subframe isn't centered and is part of the reason you feel this.

 

[Bluemustang]

Question - when you hit the throttle, does the car track straight or seem to pull to one side? I went through something similar to what you are describing which is why I ask.

 

[NightmareMoon]

Couple of things to check, but first - All-season tires (even tires as good as the DWS) can be pretty much shit for traction once they're aged. two years of use and plenty of road miles and they've likely lost a lot of their initial grip, so getting some wheel spin wouldn't be unexpected (depending on the mileage and years on them). How many miles/years on yours?

1) Check for a loose wheel bearing in the rear. When those go out, sometimes it can feel like the rear end is loose before you get other warning signs (usually a grinding noise, brakes that squeak more than they used to, or a pinging noise on accel/decel at lower speeds). You can check by jacking up a rear wheel, getting a big bear hug arm-full around it the wheel and trying to rock it around. Any play in the hub at all needs to be corrected by replacing the hub before anything else. I'm on my 3rd replacement rear wheel bearing in 45k miles, but I track the car and autox a lot so my car sees more abuse than many.

2) Get an alignment. Alignments don't stick forever, and its usually good to have your alignment corrected when you change tires, or once a year if you are nitpicky about alignments. A rear toe angle that has gone a bit out of whack can cause a loose feeling under acceleration like you describe if you're getting just a little wheelspin from old tires. You'd like your rear toe angles to be slightly toe-in. Any toe out can be squirrelly under hard acceleration.

 

[BmacIL]

Good points by @NightmareMoon

 

[MSMStannyl]

Thanks for the info guys! Regardless of the A/S tires, I would wager to say that I'm about 99.99% sure it isn't wheelspin. This is definitely something else. As was mentioned above it just feels like you're going straight one minute and then you downshift to 4th and hit the gas and for those few moments of excessive gas, the nose of the car pulls to one side (can't recall which side at the moment but I'd say it's the same side each time). It's definitely strong enough that I need to make a quick, pronounced, adjustment in steering to keep the car in the lane. Let off the gas and back to normal. Again, needing to re-adjust steering to keep tracking straight. I'll see if I can maybe get a video of it.

I did pay closer attention and it does seem like to keep in a straight line, my steering wheel is slightly off center so maybe there is an alignment issue afterall. It's just a strange, uncomfortable, feeling. It reminds me of my ex-girlfriends dad's 2001 Honda S2000. He'd let us take it on road trip vacations back in the day and going through some awesome curvy backroads that car would change its track depending on how much gas you were giving it, and not in a good way. If I recall, this was actually a known issue with the first gen S2000.

Anyway, again, appreciate the insight. I'll start with an alignment and see if they can check some of these other issues. Maybe I'll get a bushing kit installed too. I thought the Steeda IRS braces would've kept things in check though.

Thanks again!

EDIT: @Bluemustang Exactly! That's exactly what's happening. What did you do to resolve it?

 

[Bluemustang]

1. Check tire pressure. I had an issue where mine was strangely low on one side.
2. Subframe alignment dowels (this fixed it for me) I bought the Steeda subframe alignment kit for CB005 which is what I have.
3. Also look into an IRS bushing support kit, either BMR or Steeda.

You wouldn't believe it, but the IRS subframe alignment being off makes a difference.

 

[Roadway 5.0]

2) Get an alignment. Alignments don't stick forever, and its usually good to have your alignment corrected when you change tires, or once a year if you are nitpicky about alignments. A rear toe angle that has gone a bit out of whack can cause a loose feeling under acceleration like you describe if you're getting just a little wheelspin from old tires. You'd like your rear toe angles to be slightly toe-in. Any toe out can be squirrelly under hard acceleration.

+1

 

[MSMStannyl]

Man, yesterday, on my way home from work, I had an incident with it that was even worse than before. Definitely scared me a bit. Was getting on the highway, in the right lane. Prius up ahead going below the speed limit. Check the mirror and see I have some space before the car coming up in the middle lane (at decent speed). I'm still accelerating from the merge in 4th so I signal, stomp it down and start moving over. Suddenly that crazy alignment thing happened. Rear end basically snapped one way and then the other. It happened so fast but was pretty scary in that moment. Everything is fine (I am not the Mustang that was spinning out in front of an 18 wheeler! lol) but damn. Definitely need to get to the bottom of this. I'm not liking this one bit...

I'd be really curious what it looks like from behind. To me, behind the wheel, it seems like a pretty pronounced movement/shift, albeit brief. Kinda like you just lose traction for a split second, rear skips over, then catches again. However, as I've said before (and I think @Bluemustang would agree), this is definitely not a loss of traction issue.

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