Front end instability question
 

I don't normally get much over 80mph but had a wonderful high speed lead on the interstate a few days ago and had somewhere to be so I took advantage of it. As the car got over 90 it felt kind of unsure of itself. At first I figured it was the pavement, then I figured it was the new(ish) tires but over a variety of pavement types it continued. I've pretty much ruled out the tires because on some brand new pavement a little while later it was fine so this leads me to think the struts are worn out. The car has ~115k now so it doesn't surprise me much. Whaddaya think, am I in need of some suspension replacement or is it the tires? General G Max AS05 at 35psi.

instability?
Jumping up and down?
Moving right and left?
Shaking?

More like just vague and doesn't instill much confidence. There was a little bit of lateral movement but that could have been the pavement.

Vague, Like the description of your problem?

Yeah pretty much :( I was just hoping for some insight not definitive answers. Ok, here's a more pointed question. How long is reasonable to expect the stock front struts to last?

Well... that's a pickle. Sounds like it's time to find a jerry can and an empt lot. Time to send her off in a Viking funeral.

But.... if you don't want my logical advice, fine. Here's the "real" stuff:
Might me time for a suspension refresh. I would start with ball joints, tie rod and bushings if need be struts.

Shocks can be expected to need replacement at 80k, so that's probably it right there. That said, you're creeping close to 120k so control arms and tie rods are a good idea while you're down there.

I have the same tires, I drive 80-90mph on the interstate all the time and don't have an issue with any kind of instability. You should replace your struts and have your alignment checked.

What's the alignment, sounds like some toe in would help.

Did the car get unsure of itself …. or, did you get unsure of yourself ..??

Chew on that fer ah spell.

I have found that the older I get, the less stable, at high speeds, my cars get - :iono:

Yep, like said, if it makes you feel better, have your car's suspension updated … or, just don't drive that fast - ;)


humfrz

I'm with strat. Stock package comes together above 90 through 110-ish. Check alignment.

I had the alignment done when I got the tires ~2 months ago but it's entirely possible that with all of the super high quality pavement here in the northeast that I knocked it out again. I guess I'll have it checked again, it's cheaper than suspension components.

A good alignment guy should be able to tell if you need replacement parts.

I didn't suggest you get another alignment, I asked what the alignment was. It's unlikely the alignment slipped in two months of street driving, but sloppy alignments can show green on the machine but be crap at 90 mph. It could slip, don't get me wrong, but if you've got zero toe in the rear and a 1/16 out in the front that will want to go wherever the road and wind want it to go.

I'll try to find the printout and post it up later. I also had to have the tires balanced a few times, maybe they didn't quite nail it.

You'd feel the vibration if it was the tire(s) out of balance.


I'll bet the alignment is slightly wonky and making the car wander.

So actually, I had the same kind of experience in my brand new 2018 a couple months ago. It felt like I had to make too many steering corrections at highway speed (while just going straight)-- not an alignment thing, more like the car was upset by every little crack/groove in the pavement. I definitely couldn't really cruise one-handed on the steering wheel at above 70mph, which was kind of annoying. I was actually having some buyer's remorse during the first 1500 miles because I drive so much freeway out here in CA.

The problem was completely solved when I switched to 18x9.5 wheels with wider and stickier tires. The car is wayyyy more planted now and is easily stable beyond 90+ mph. I can drive one-handed easily and I hardly have to make any steering corrections at all. This is all on stock suspension by the way-- I assume once my coilovers go on it will be even more planted.

Hopefully that helps a bit!

Check your bushings. I kind of felt what you are talking about. Have about 90k miles and stock suspension setup. My front sway bar bushings were dried and nasty looking. Changed to some newer poly bushing and it seems to have helped with high speed stability.

You could try dropping tire pressures 2-3 psi. I can always tell when my pressures are too high if my car feels floaty on the highway.

Here's the alignment printout https://imgur.com/jn52cMx I did ask when I was at that shop again yesterday if they could go a bit more aggressive and the won't. If the car is within spec it's good, they won't do anything but.

That's kind of why I asked the question in the first post, mine is at 115k. I'm going to try and get under there later and get a look at the bushings and see what's what. Thanks.

I guess it's possible that because these tires are a stiffer sidewall than the previous ones that I don't need the psi to be as high. I'll try that.

They also heat up more. The actual right way to do this is to take pressures after driving around. I like mine at ~38-37psi F-R when warm. I have BFG Sport Comp A/S 2 atm. The warm psi translates to ~33.5-32.5 cold, but I adjust a bit based on how I expect ambient temperature to change over the next month.

You can also do the chalk test, ideally when warm as well.

Go to a different shop, you have toe out in the front which I guarantee is a factor in what you're feeling at high speed on anything but a perfect flat road. More rear toe in wouldn't hurt either, I have about 0.03° in the back now iirc but have put as much as ~0.25° (on each wheel), almost always at 0 toe front for me but I'm ok with some highway wandering at speed.

imho on each wheel:
0.00° to +0.03° toe in the front
+0.03° to +0.08° toe in the rear
Maybe you can ask for like +0.01°Front and +0.05°Rear for each wheel? That's what I would try if I had to fix your car.

The more toe-in you have the more stable the car will be at the sacrifice of responsiveness. It seems silly to argue over such little numbers but I guarantee you'll feel it, even at lower speeds, it's not some mushy economy car that can get away with never getting aligned and it feels 'fine' it's whole life.

Edit: seems like a lazy shop to me, bringing in the right rear (toe-ing it in) would help even out the camber and could actually get all the numbers green, but the machine probably tells them camber isn't adjustable and they can't do anything about it even though camber and toe adjustments are interlinked on this car due to the multi-link setup.

Thanks man. I'm going to follow up on this next week, have a couple of big trips to do before that though, 500 miles tomorrow and 600 on Monday. I guess I'll just keep it down to the more reasonable speeds that I usually cruise at :) That was a special circumstance and I got lucky with a great lead that was hauling ass so I took advantage of it, usually I just let them roll by.

Sorry, your stock suspension and wheel/tires should not have any kind of movement... brand new cars can still have alignment issues but nowhere near what you're talking about.

When I got my car new I got it upwards of 90MPH on the way back from Colorado. 3 months later, I got it up to about 110 on a flat/empty/clear stretch of I-15 in Utah (about 10 miles visibility with no other cars on the road, quite odd). Neither of those times did I feel any vibration or instability of any kind.

Wider/stickier tires would make your car track more with the grooves in the pavement, not less.

I dont think 0.02 degrees toe out is gonna affect your stability. I've had 10 times that amount with no instability. I've felt vibration at triple digit speeds but not instability. I'd have them check your suspension for any worn parts/dampers before another alignment. At 115k thats way more likely than -0.02 degrees toe causing it.

I'm with this guy, I've run way more toe and don't have an issue. I'd wager that 100k+ miles of new England roads have worn out the bushings and it's time to do a refresh. The front control arm rear bushing is probably the culprit.


Aftermarket "stock" arms are cheap. You can get them on Amazon or Rock Auto for just over $100. I'm running one on my BRZ and have had no issues.

Camber isn't going to change much in the rear if they bring in the toe ~0.05 or so.

Meanwhile our OP, @gravitylover is out for a test drive after adjusting his tire pressure.

"Ha! Whaddaya know? That did it."

The last time I was up around those speeds I was cruising completely undramatically with two fingers on the wheel.

First thing to check is shocks and alignment.

:slap: now, THAT is for teaching the newbies bad habits!


:D


humfrz

I brought the fronts down 1psi and it seems to have helped but I only got to the mid 80's. I'm going to need another opportunity with someone hauling ass so I can follow a bit behind and run them up to 95 or so to see if that does it.

I wouldn't mess around at that speed. If you aren't obviously rock solid then something is still wrong. Best wishes for a good conclusive fix. :cheers:

There's only one way to find out :confused0068: Suspension bits appear to be alright but the car is almost 7 years old so I bet the bushings are worn and that's really what the problem is. I'll get to them at some point this summer when I have better cash flow, that heart attack and 3 months of lost income put a hurt on us.

Oh, shit! I forgot about that! How the hell have you been?


As sensitive to changes in tire pressure this car is, I can only imagine what worn suspension bits do to the handling. Keeps the sphincter in shape, at least. :slap:

Doing well, thanks. I think it has been a slow recovery but I'm not terribly patient when it comes to being under the weather or injured. I still think I'm 25 and recover in a matter of days :sigh:

Previously I had the Conti EC DWS and had to run them much higher (36/37ft and 34rr) just to get them to be stiff enough not to roll over in corners, these need to be lower (34/35ft) for stability at speed.