Wheels and tires or sway bars for understeer

[MartinNoHo]

Took my car out for some overly spirited driving and something doesn't feel right or "planted", when I enter corners I'm fighting with my car (i.e. you can feel load going to the opposing side of my steering input, maybe understeer?), currently I have a SR strut tower brace and St coilovers. I'm still on stock black accent package rims w/ 255/40/19 pirelli run flats [suck] and stock sway bars. Would it be better to go straight to wheels and tires or upgrade the sway bars, maybe even a K brace?

Sponsored

 

[Norm Peterson]

In any corner, load is always transferring off of the inside wheels (the wheels on the side you're steering toward) onto the outboard wheels. No matter what springs, bars, or shocks/struts your car is running, or what tires it sits on. In any given corner at any given speed, this cannot be avoided, eliminated, or even reduced no matter what you do to the car. All you can do is change how the total load transfer gets distributed, front vs rear.

I'm not at all sure what you're feeling here, so I'm guessing (with some basis) that it's because you just got done driving this car in its present "new, improved" form a good bit harder through the corners than you've ever had much experience doing before. That would more than anything make it a 'perception thing', and I'm going to guess it may have been exaggerated by being overly hasty at cranking the steering wheel over into the turns.

This isn't particularly a slam on you, but it is common for people to be a bit surprised to find that their car feels different when cornering at, say, 0.6g, than during their normal 0.3g-and-under cornering. Among the things they tend to notice is body roll, which they find a bit disconcerting mainly because it's outside their normal experience. At 0.6g, you should be at least subliminally feeling the tires operating at slip angles, which is a feeling not exactly the same as when you're driving straight ahead. When you're cornering down under 0.3g it's not enough different from straight ahead to feel any different.


Norm

 

[Radiation Joe]

Since you stated you're on coil-overs, all bets are off.
First thing I would do is check that your ride height isn't too far off from stock, since geometry changes will significantly affect the handling near the limits.
Second, check your corner weighting. Coil-overs can be significantly "off"; meaning the balance going from left to right can be quite different from right to left.
But to your original question, wider rims and tires in the front are going to help reduce understeer up to the point where geometry screws you over. At that point a larger front bar, may help.

 

[NightmareMoon]

My advice is always to start with tires. They're the main source of mechanical grip. Nothing else on the car has as much effect on grip as the tires do. Ever heard the saying "where the rubber meets the road"?

If you have crappy and/or old hard tires, no amount of springs, swaybars, shocks, or anything else is going to help much at all. You want to upgrade from big things to small things and the tires are the #1 more significant part of the car's handling.

Stiffer swaybars will actually reduce mechanical grip (but increase response). Our cars aren't so sensitive to body roll where you need stiffer swaybars to keep the geometry from getting so far out of its ideal zone where you start to loose much grip. Even if stiffening the swaybars somehow added grip (and no, that's not how it generally works), tires would still be a much more significant change.

What swaybars can do is change the bias of front vs rear grip, which can make a car more suitable to an individual's driving style, but having personally tried increasing swaybar stiffness on only the rear, only the front, and both axles, swaybars do change what grip is available in reserve during different phases of the corner, but overall grip isn't really affected much, swaybars just shift the grip around a little. Getting the under/oversteer bias right for your driving habits take a little experimenting.

The stock cars do understeer a bit at the limit (steady state cornering, not corner entry), due in part to the stock swaybar balance and factory alignments, but with your coilovers we can't really say if your car is understeering or not, or if swaybars would make it more neutral or easier for you to drive at all. Also, problems with corner entry understeer is most often a problem with ... you guessed it... tire grip, and in particular the driver asking more of the front tires than they can give. Dial back the aggressiveness, learn to use weight transfer to better transition from braking to cornering more effectively (without exceeding the available limits), and look for more front tire grip by going to wider, stickier tires.

 

[Bluemustang]

learn to use weight transfer to better transition from braking to cornering more effectively

Nightmare, can you explain this a bit further? I was wondering what your typical approach to a corner is.
Do you typically try to stay on the brake through corner entry (or through to near the apex) and then transition to throttle out through exit? Or do you try to get pretty much all your braking completed before corner entry and the start of steering input?

 

[NightmareMoon]

Nightmare, can you explain this a bit further? I was wondering what your typical approach to a corner is.
Do you typically try to stay on the brake through corner entry (or through to near the apex) and then transition to throttle out through exit? Or do you try to get pretty much all your braking completed before corner entry and the start of steering input?

How long you're on the brakes and if you coast at all does depend on the corner.

With lots of space and a sharp single point corner you'll probably be trailing the brakes all the way down to the apex and immediately on the gas at the apex. For a longer road course corner you might be trail braking down and then coast for a while (maintenance throttle only) before picking up the gas and leaving the inside track edge at the apex. It just depends on how constrained your line choices are, meaning how wide the track, how big the corner radius is, and how much angle the corner is changing your direction.

Once you've bled off enough speed to turn in for the corner, the fastest line will still always be overlapping braking and turning for a portion of the corner to use the whole available friction circle. You should be at the limit for the entire corner, which means fading break pressure as your steering is increasing to keep at your maximum Gs in the diagonal directions as you're increasing your steering angle. Trail braking is hard to master tho, and many novices will just blow the corner with a massive understeer skid and miss the apex by a mile if they try to trail brake too much.

Braking in a straight line does apply to bleeding off speed from the straightaway before turning in, but doing all your braking in a straight line and the usual late apex line/advice is only really applicable from novice through intermediate levels, or as a general best practice to leave some room for error on track out. More advanced lines (corner entry AND exit) are spirals.

Now, if you're on the brakes very hard right at the apex and then immediately on the gas, you might be over-slowing right before the apex (don't do that). Trying to spend a moment or two coasting or w/ maintenance throttle right before the apex is probably closer to correct for the average road course (or street) 90 degree corner. For sharper corners with more room on entry and exit, you might not do this. For wide long corners with a narrower available track, or constrained lines on entry and/or exit you might spend more significant time holding the inside line and waiting to spot your exit apex and out-spiral.

 

[Bluemustang]

Thanks @NightmareMoon a lot to digest in this post. I fall into more novice category but am starting to realize I can carry more speed by braking later and carrying that through corner entry and up to just before the apex. This seems in line what you are saying for a typical/straight 90 degree corner. Obviously depending on the corner the strategy might be different, involving some maintenance throttle in order to keep speed up, or use the safer approach of doing all the braking in a straight line if there is concern about overshooting the corner.

 

[MartinNoHo]

Also just to add onto this could it have been TC or SC, because I was on sport + the entire time and I believe in race mode traction is off and ESC is "dumbed" down, maybe I was fighting with TC or ESC. Any thoughts on this?

Thanks to everyone who posted, it was really thoughtful and interesting.

 

[Roadway 5.0]

I like fighting steering in a corner. It means I’m going fast.

If it’s an awkwardness you feel then it’s probably due to lowering. How low did you go? Roll center correction kits are available.

Thinking understeer? Maybe, maybe not. If you held your line then you’re probably good. Get better tires that aren’t threatening to break loose or flex under pressure.

Lastly, double check your alignment. If you have globs of toe-out you’ll be fighting steering ‘round the clock.

 

[MartinNoHo]

How low did you go?

Thinking understeer? Maybe, maybe not. If you held your line then you’re probably good. Get better tires that aren’t threatening to break loose or flex under pressure.

1.5 inch all corners, my alignment is good, i don't have a camber kit but I have -1.8 camber on the front can't remember the rears when i was at the alignment shop. I can keep the line, I just want to go faster, and faster. Toe was OEM spec.

 

[Mikepol2]

Something not a lot of people think about is wheel offset. The GT350 front wheels have a much larger offset than the stock PP1 wheels and poke out of the front fenders a little, but the impact they made on cornering was unbelievable. Between the wheel offset and the 295/35-19 front tires, understeer is a thing of the past.

 

[NightmareMoon]

Advancetrak can definitely feel like its fighting you in a corner. Of course its fighting to keep you from loosing it.

If your tires are shot, the computer is going to intervene more often. If you’re tipping those limits on the street, dial it back a couple notches and address the tires. The computer is telling you you’re at or past the limits. On a closed course, you can turn off the nannies if you like and find out how much more is available past the computer’s comfort zone.

yeah the AdvanceTrak nannies are a little less intrusive in Sport and then Track mode, but try not to trigger them at all. The twitchy throttle response in Track mode is fun, but its not a good thing for handling or control, its too twitchy and can quickly lead to power-on oversteer mistakes when you start getting on the gas coming out of a corner. Anytime you are adding throttle at the limit you must also be unwinding (straightening) the steering wheel, or the rear will try to get away from you.

 

[Norm Peterson]

Also just to add onto this could it have been TC or SC, because I was on sport + the entire time and I believe in race mode traction is off and ESC is "dumbed" down, maybe I was fighting with TC or ESC. Any thoughts on this?

If either TC or AdvanceTrac was still active - even if at reduced sensitivity - you were probably fighting one or the other of those. And it can be a bit frustrating, you trying to make the car do what you know it to be capable of, and it's not going there for you. Sound about right? While my '08 GT does not have AdvanceTrac (and its TC is pretty much worthless as far as what it's supposed to do is concerned), I do have a little stability control experience in other cars. ***

Until you have safely found out for sure that your car can do that much, one or the other of those nannies was probably saving you from yourself. Once this corona crap has died down and autocrossing has started back up, do yourself a favor and run a few autocrosses. Even if you've driven other cars pretty hard in the past, you still need high performance seat time in your Mustang in order to find out where the limits at least "kind of" lie and what it takes from you to get up there without blowing clear through them.

I don't think you should ever feel like you're fighting the car - if you do, you're probably overdriving it. You're either coming in to the corner too hot, or you're trying to use too much brake for the amount of cornering g's somewhere between entry and apex. Even cornering in the dry at 0.75g on those run-flats, you should be able to relax and just drive the corner.



*** the car being unwilling to do what's asked of it is pretty much what I've felt in the WRX and the LGT before it when I've forgotten to turn its stability control completely off. This has happened only when a combination of throttle, gear choice, and cornering g's happened that the system didn't care for, even though I knew it was within the car's performance envelope. You can't successfully bully it into doing what you want; all you can do is ride it out and wait for the kind of response you're looking for to return.


Norm

 

[Norm Peterson]

I like fighting steering in a corner. It means I’m going fast.

If I'm fighting the steering in a corner it means I screwed up.

I was just driving the corners in these shots, no fighting the wheel or the car, no seat-puckering, just turning the wheel over and back out again like I might during a brisk-paced drive out in the country but still a good bit shy of "race pace". Street driving should be at g's half these or less, but even at the 2/3 level you should not have to be working very hard to make it happen and keep it smooth.

Norm

 

[Norm Peterson]

1.5 inch all corners, my alignment is good, i don't have a camber kit but I have -1.8 camber on the front can't remember the rears when i was at the alignment shop. I can keep the line, I just want to go faster, and faster. Toe was OEM spec.

Too low.

Lowering makes it easier to get an aggressive static camber setting, but it puts you in a less helpful region of the camber gain curve. Meaning that you get less camber compensation coming from compression of the outside suspensions. What you gain is less than what either the increased spring rate or the lowered appearance suggests you should have gotten.

Your front geometric roll center drops from something like a couple of inches above the ground to a similar amount below it. This can be corrected, except that then you'll need the bumpsteer correction kit to undo the bumpsteer increase brought on by the roll center correction kit.


Norm

Sponsored