3.3TT Any disadvantages to a square setup for the track?

[ElChanclo]

TLDR: If I went to 245/35r18 (or 255) tires all around for track days, what effect would that have on handling?

I had a very fun and rewarding track day with all my track focused improvements done (new PB's are always exciting), one of which was the Cup2 tires (235/40r19 front and 265/35r19 rear).
I tracked the wear and tear and found that the fronts wore 1.27mm left & 1.15mm right, while the rears didn't wear at all.

I get the feeling the front OEM tires are undersized for hard braking and cornering, so if I widen those, I might as well meet in the middle with the rears for a square setup. At this rate the rears will probably age out before they wear out, but going to a square 245 or 255 setup would let me rotate the tire's any which way and even out the tread wear.

Was also considering dropping to 18" rims to reduce unsprung mass. Any input would help before I go finding out the hard way .

 

[ElChanclo]

Found some quotes regarding wheel diameter for track days:

"our rule of thumb is to run the smallest diameter possible that still clears the brakes"

"the smaller the wheel, the less the weight and its momentum of inertia. you cant go too small on the wheel however because they have to be large enough to fit over large brakes."

"The wheels need to be big enough to clear the brakes, anything more is extra weight"

"every 1 lb of unsprung weight saved was the equivalent of 4 lbs of sprung weight."

"Since the rubber seems to weigh just as much as the wheel, I'm not sure there's any weight disadvantage to larger wheels..... for the same overal diameter tire."

"the concentration of weight is very important. A heavier rotor will have less of an effect than a heavier tire. Or a wheel with a heavy spider and light rim will accelerate faster than a equal weight wheel with a light center and heavy rim section."

I know for a fact (aka learned the expensive way) that 17s won't fit over the brembos, so a light set of 18" enkeis or rays is on the list. Still questioning the best rim and tire width for a square track setup (most likely AD09 tires)

 

[Volfy]

TLDR: If I went to 245/35r18 (or 255) tires all around for track days, what effect would that have on handling?

For dedicated track wheels/tires, square 245/35R18 or even 255/35R18 makes a lot of sense. The lower profile allows the wheel to better support the tire, which leads to sharper turn-in and more responsive transitions. the shorter sidewall effectively lowers the car, while keeping the same suspension geometries and articulation range. The car's roll centers remain mostly the same, so the car maintains the same level of resistance to lateral weight transfer. This avoids all the compromises of the typical lowering methods of shorter springs and coilovers. I myself have been tempted to doing exactly this and may still do this eventually. I just have too many track tires to wear out before I spend any more $$ on fresh buys.

In addition, your transmission gear ratios will all be slightly reduced, as will the effective final drive ratio. This quickens acceleration, at the expense of a slightly lower top speed, which is likely inconsequential for all but the fastest straights of some tracks. I don't like fast tracks anyway.

Only caveat is that your speedometer might not register correctly, but that is a don't-care for running track.

I had a very fun and rewarding track day with all my track focused improvements done (new PB's are always exciting), one of which was the Cup2 tires (235/40r19 front and 265/35r19 rear).

I tracked the wear and tear and found that the fronts wore 1.27mm left & 1.15mm right, while the rears didn't wear at all.

I get the feeling the front OEM tires are undersized for hard braking and cornering, so if I widen those, I might as well meet in the middle with the rears for a square setup. At this rate the rears will probably age out before they wear out, but going to a square 245 or 255 setup would let me rotate the tire's any which way and even out the tread wear.

Was also considering dropping to 18" rims to reduce unsprung mass. Any input would help before I go finding out the hard way .

Glad to hear you had a great time at the track.

If I may be so frank, the heavy front wear is likely the result of the car pushing into the corner (i.e. understeering). Your chassis is either not set up properly, or... more likely, it is just a fairly typical tendency of a new track rider not loading the front end to load the front end to give the front tires better grip entering the corner, thus pushing going in and scrubbing speed off the front end. Get a GoPro and mount it on the driver's side just behind the front door, so both the driver's steering angle and the front tires' slip angle are in view, along with the track. That will help you diagnose what you're doing and where you can improve. That is what we have been doing for track runs.

What tire pressures were you running? Did you adjust before each session?

For the Stinger/G70 with the OEM Brembo brakes, anything larger than 19's is less than ideal. Running track, you are constantly accelerating or braking, often at the threshold with max effort. Every last lbs of unsprung weight and rotational mass matters. Novice drivers might not be able to tell seat-of-pant difference, but lap times won't lie.

For everyday street riding, run 19's if you like the looks.

 

[ElChanclo]

The lower profile allows the wheel to better support the tire, which leads to sharper turn-in and more responsive transitions. the shorter sidewall effectively lowers the car, while keeping the same suspension geometries and articulation range. The car's roll centers remain mostly the same, so the car maintains the same level of resistance to lateral weight transfer. This avoids all the compromises of the typical lowering methods of shorter springs and coilovers.

This right here is why they pay you the big bucks

If I may be so frank, the heavy front wear is likely the result of the car pushing into the corner (i.e. understeering). Your chassis is either not set up properly, or... more likely, it is just a fairly typical tendency of a new track rider not loading the front end to load the front end to give the front tires better grip entering the corner, thus pushing going in and scrubbing speed off the front end.

Is this the "trail braking" I've heard so much about? Only just started learning about that now that I've sorted out the issue with the brakes and tires.
If only you could've heard those poor stock PS4 tires on my first track day, I'm told they could hear the screeching from across the track and over the roar the NA V8s.

Get a GoPro and mount it on the driver's side just behind the front door, so both the driver's steering angle and the front tires' slip angle are in view, along with the track. That will help you diagnose what you're doing and where you can improve. That is what we have been doing for track runs.

Will do! Already got the gopros, there's just never enough time to set everything up between sessions and chatting.

What tire pressures were you running? Did you adjust before each session?

I deflate them to 36 after the first few sessions and then just keep an eye on em. Some guy in a 718 suggested I do a cool down lap mid session for heat management so I've started doing that. 1 in lap, 2 hot, 1 cool, 2 hot, 1 cool/out. I find the full 8 sessions draining so a mid-cooldown really helps keep everyone happy.
Interestingly (if not predictably), the next morning my pressures are:
32 33 | FL FR
33 34 | RL RR

For everyday street riding, run 19's if you like the looks.

I appreciate the comfort of the GT the other 360 days of the year, so I got a square 18" PSAS4 setup for a more comfortable ride.
Once I run through my 19" track tires I'm selling the aftermarket rims to go 18" on the track and saving the OEM 19's for snow. Bloody things take up a surprising amount of room.

 

[Volfy]

Is this the "trail braking" I've heard so much about? Only just started learning about that now that I've sorted out the issue with the brakes and tires.
If only you could've heard those poor stock PS4 tires on my first track day, I'm told they could hear the screeching from across the track and over the roar the NA V8s.

Yes. It's not easy to do perfectly, and I still struggle to get it done perfectly at every corner, especially when you combine it with threshold braking just prior to transitioning to turn-in and trail braking. The track is the best place to practice it, though, as you get to repeat the same turns over and over again. Best way I've heard it described is to imagine a "slinky" connection between steering wheel and either brake or accel pedal. As you let off pressure the brake pedal, only then should you feed in your steering angle. Add more in one; reduce it in the other. There is only a finite amount of traction for cornering/brake/accel.

The other part of the equation is to set your corner entry speed properly. Going in too hot, and you will just scrub off speed by understeering. Slow down too much, and you loose momentum and your trail braking effectiveness.

Will do! Already got the gopros, there's just never enough time to set everything up between sessions and chatting.

Understood. I've positioned the gopro on top of the roof, inside the cabin, etc. I found the driver's side tells the best story for training purposes.

Also, get a dual suction cup mount. None of the single suction cup mount is strong enough. Don't ask me how I know.

A extender battery is also great to have. I really like my Re-Fuel 9hr, which runs all day, so I don't have to putz with changing batteries. Not sure if it works for the latest GoPro versions though.

I deflate them to 36 after the first few sessions and then just keep an eye on em. Some guy in a 718 suggested I do a cool down lap mid session for heat management so I've started doing that. 1 in lap, 2 hot, 1 cool, 2 hot, 1 cool/out. I find the full 8 sessions draining so a mid-cooldown really helps keep everyone happy.
Interestingly (if not predictably), the next morning my pressures are:
32 33 | FL FR
33 34 | RL RR

Sounds like you got good advice. Next time, bring an infra-red temp gun and check your tire temp across the contact patch. That'll let you fine tune tire pressure. If temp is much hotter on the outside of the contact patch, then increase pressure. If center is hotter, increase.

I appreciate the comfort of the GT the other 360 days of the year, so I got a square 18" PSAS4 setup for a more comfortable ride.
Once I run through my 19" track tires I'm selling the aftermarket rims to go 18" on the track and saving the OEM 19's for snow. Bloody things take up a surprising amount of room.

Tell me about it... I'm up to 9 sets of wheels for our 3 cars. I really need to thin the herd and get rid of the OEM wheels.

As for square setup, as much I like it, there are limitations. Factory chose staggered setup for a reason, and that is power handling for the primary driving tires in the rear. For stock 3.3T, you really don't want anything smaller than 255 for this reason. I can get away with 245 at the track because I'm running 2.0T and 2.5T. Even the 2.5T is getting close to the limits, especially on Map2.

For track, if I run a 3.3T juiced up a bit, say to map2, I'd consider running 245 front and 285 rear, on 8.5" and 10" rims.

Just starting out though, run what you got. The car will talk to you and tell you what it wants.

 

[ElChanclo]

The track is the best place to practice it, though, as you get to repeat the same turns over and over again.

Does practicing on a sim (wheel+pedals) help at all or is it totally different from real world seat time?

The other part of the equation is to set your corner entry speed properly. Going in too hot, and you will just scrub off speed by understeering.

I definitely lean towards overdriving, especially with an AWD I mostly get under steer, but a stiffer rear sway, track tires, and disabling the TCS really helped. It's way more fun letting the rear swing a bit, but I noticed the more comfortable I got with it the slower my lap times.

Next time, bring an infra-red temp gun and check your tire temp across the contact patch. That'll let you fine tune tire pressure. If temp is much hotter on the outside of the contact patch, then increase pressure. If center is hotter, increase.

I brought my thermal camera to check the engine and brakes, but never thought to use it on the tires, that's a great idea. Will add it to the list!

Factory chose staggered setup for a reason, and that is power handling for the primary driving tires in the rear. For stock 3.3T, you really don't want anything smaller than 255 for this reason.

I'm pretty sure the factory specs were chosen with the RWD model in mind. The AWD system feels like an afterthought, only intended for intermittent use when rear traction isn't enough, so I don't think they sized the fronts with constant acceleration in mind. That said the stinger wasn't made to be a track car either. As stock its perfect for long road trips, but if you're taking it to the track you have to adapt it a little.

 

[ElChanclo]

Factory chose staggered setup for a reason, and that is power handling for the primary driving tires in the rear. For stock 3.3T, you really don't want anything smaller than 255 for this reason.

I thought that too, but as I noted at the very top, there was no measurable wear on the rear 265 cup2 tires after a full track day. I know a cheap digital tire gauge isn't the best method, but by my notes the rears actually grew 0.04mm. All the wear was on the fronts, so those are my main concern for now.

And the EBC Blues wore AVG 1.13 mm front and AVG 0.80 rear, which is excellent considering the Z26 street pads burned out after a single track day, so I consider the brake issue solved (thanks to your advice ).

 

[Volfy]

I thought that too, but as I noted at the very top, there was no measurable wear on the rear 265 cup2 tires after a full track day. I know a cheap digital tire gauge isn't the best method, but by my notes the rears actually grew 0.04mm. All the wear was on the fronts, so those are my main concern for now.

My guess that your tire wear difference is due to scrubbing off speed off the front is just that - a guess. An educated one, but a guess nonetheless. Without first hand knowledge, or video footage of what your steering angles vs. slip angles were doing, I wouldn't know for sure.

That said, the fact that yours is an AWD is another indication that lends more weight to my guess. Most drivers think that AWD improves drive out of corner by letting the front wheels help with traction. This is not exactly the correct way of looking at it. Reason is... upon initial acceleration post apex, the chassis begins to transfer weight to the rear as the driver leans into the throttle. The car still has not finished turning, so both front and rear tires still have to devote traction toward cornering load. If you stomp on the loud pedal too fast too early, when the tires do not yet have spare traction for forward acceleration, the applied torque to the wheel will simply overwhelm the tire's available grip.

In a RWD car, this means the rear wheel slip angle will increase dramatically. The car will oversteer. The tail end will swing wide. Some experienced drivers will take delight in the car's response and keep the rear wheel slipping. The result: excessive rear tire wear.

In an AWD car, however, the car will sense the rear slippage and divert some torque to the front. However, the front tires don't yet have enough grip to spare. This combined with the fact that weight transfer tends to reduce front end traction even more, means the applied torque will cause the front end to slip as well. If the chassis balance is ideal, the front and rear will share equal slippage and the AWD car will 4 wheel drift out of the corner. Done right, it is a thing of beauty. So... AWD mostly helps by reducing applied torque to the rear wheels, not so much because the added FWD help the car turn and burn.

In fact, if the chassis balance is less than ideal, the front could get too much torque. Result is heavy understeer and excessive front tire wear. This is why some AWD cars have the reputation of being an understeer fest, especially in the hands of inexperienced drivers.

And the EBC Blues wore AVG 1.13 mm front and AVG 0.80 rear, which is excellent considering the Z26 street pads burned out after a single track day, so I consider the brake issue solved (thanks to your advice ).

Bluestuff is definitely a great track day compound and can handle the heat. Typical street pads cannot and will soften and wear away fast.

Also, part of the bedding-in process involves the right kind of pad material transfer, in which a very small layer of pad material develops uniformly on the rotor surface. When this happens, the brake pads will essentially be wearing against itself, instead of the rotor metal. Not only does this offer the maximum frictional coefficient for optimum braking power, it also reduces wear. There are outfits that offer services to racing teams to pre-bed-in their pads and rotors prior to a race. This way, max braking power and efficiency are guaranteed from lap 1.

if you look closely at your rotors after the track day, you should notice is slight colored hue to them. That is the micro-transfer of pad material coating the rotor surface. See my rotor below after Session4 at MSR Cresson. I would not recommend Bluestuff unless you plan to track though, as the drawbacks might not be worth the benefits.

 

[ElChanclo]

My guess that your tire wear difference is due to scrubbing off speed off the front is just that - a guess. An educated one, but a guess nonetheless. Without first hand knowledge, or video footage of what your steering angles vs. slip angles were doing, I wouldn't know for sure.

I can pretty much confirm this. Too heavy on the pedal trying to "vroom" my way to a faster lap time, but when you turn your wheel and the nose doesn't follow you're just going fast in the wrong direction.
Slow is smooth, smooth is fast... then around lunch I get overconfident and try to push beyond the limits of car mass and tire friction .

Still learning about trail braking and weight transfer, all in good time!

I would not recommend Bluestuff unless you plan to track though, as the drawbacks might not be worth the benefits.

The dust was bad, but despite looking for light color wheels the best staggered fit I could find was Dark Metal Grey. And lucky, as they don't look bad and you couldn't tell they had dust until you made the mistake of touching them. I'm bringing wet wipes and gloves to set my pressures from now on. Besides that, other than a lack of bite and some squeal when cold, they were fine for road driving.


On the topic of the front OEM 225/40r19 tires being undersized;

WRX - 3600lb 271hp - comes in 245/40r18 square
2020 S5 sportback - 3924lb 349hp - 255/35r19 or 265/30zr20 square
M440i GCx - 4169lb 382hp - comes with a variety of 245 & 255 tires in 18,19,20...

So I'm convinced the 4165lb 368hp AWD stinger isn't being served well on the track with 225 up front. Again, a grand tourer, not a track car (despite the marketing).

So if I want 245 up front I'd need 275 at the rear to keep the OD on par. And if I'm understanding correctly, generally speaking, for a 9.5" rim they recommend 245min and 275max. Staggered tires on a square set of rims. Sounds weird but could it work?

 

[Volfy]

On the topic of the front OEM 225/40r19 tires being undersized;

WRX - 3600lb 271hp - comes in 245/40r18 square
2020 S5 sportback - 3924lb 349hp - 255/35r19 or 265/30zr20 square
M440i GCx - 4169lb 382hp - comes with a variety of 245 & 255 tires in 18,19,20...

So I'm convinced the 4165lb 368hp AWD stinger isn't being served well on the track with 225 up front. Again, a grand tourer, not a track car (despite the marketing).

There are no wrong sizing, only wrong applications. If you look at BMW 3-series, they come with near identical tire sizing to G70/Stinger. You are correct that such setups are ideal from a NVH perspective for a GT car.

Then you look at the M3, which comes with 275/40R18 on 9.5" front and 285/35R19 on 10.5" rear. No doubt BMW's suspension tuning on the M cars are very different, but the nearly same tire width front/rear tells an interesting story. Staggered sizing for the rear is really only to make sure the rear tires have sufficient power handling. Then you can stuff as wide a tire as you could shoehorn into the front. Especially for your relatively front-heavy 3.3T AWD, I think there would be definitely advantages going with 9" wide front wheels, or even 9.5". Problem is the G70/Stinger's front end has trouble accommodating wider than 8.5", so that's is the primary constraint.

Before anybody jumps in and say you can absolutely stuff wider wheel up front... let me clarify that we are talking about maximizing handling prowess and track worthiness. Not how the car's stance looks cruising down Sunset Blvd. If you look at BMW's front sizing:

3-Series 225/45R18 on 18x7.5 ET25
M3 Comp 275/40R18 on 18x9.5 ET20

They kept the offset within 5mm of each other. This is, of course, to maintain/optimize scrub radius on two cars that are mostly based on the same chassis & suspension layout. If I could do that on the Stinger/G70, you bet your ass I'll go wider than 8.5" front.

So if I want 245 up front I'd need 275 at the rear to keep the OD on par. And if I'm understanding correctly, generally speaking, for a 9.5" rim they recommend 245min and 275max. Staggered tires on a square set of rims. Sounds weird but could it work?

It's for sure better than the other way around... same size tires on staggered F/R wheels. That makes zero sense.

 

[ElChanclo]

They kept the offset within 5mm of each other. This is, of course, to maintain/optimize scrub radius on two cars that are mostly based on the same chassis & suspension layout. If I could do that on the Stinger/G70, you bet your ass I'll go wider than 8.5" front.

It's for sure better than the other way around... same size tires on staggered F/R wheels. That makes zero sense.

Now there's a term I've never heard before. So lets say you swapped the 225 8.0" fronts to 255 on 10" (r19), while keeping the original inner wheel to strut spacing so all the "extra wheel" is poking outside, what would that do on the track and how would that feel?

It's for sure better than the other way around... same size tires on staggered F/R wheels. That makes zero sense.

I actually watched the video below on tire stretch and this thought crossed my mind, maybe you can tell me exactly why it's a bad idea. Lets say you were given a container full of brand new 235/40r18 track tires. If I was set on using them on the track, it looks like more stretch = better lap times (but more dangerous and less forgiving). So if you wanted more response up front and more compliance at the rear, a 9.0" front rim and 8.0" rear would be the best rim layout on our imaginary scenario, no? Goofy as it may look...

The car tested was much lighter and RWD, but the trend is consistent on dry pavement:

I was also convinced not to go any wider than my 235 AS4 for wet performance.

 

[Volfy]

Now there's a term I've never heard before. So lets say you swapped the 225 8.0" fronts to 255 on 10" (r19), while keeping the original inner wheel to strut spacing so all the "extra wheel" is poking outside, what would that do on the track and how would that feel?

Ah yes. If you want to get the most out of your HPDE by experimenting with various tire/wheel setups, you owe it to yourself to know the concept of scrub radius. Same way roll center is important if you want to play with suspension ride height. There are lots of online resources addressing these topics, so there is no need to draft an essay here. This is a good starter for Scrub radius. Once you understand it more, you begin to appreciate why BMW went up only 5mm on the M3 Comp's front offset. Most RWD (or RWD-biased AWD) cars have a modest amount of negative scrub radius, as I'm sure the regular 3-series and our Stinger/G70 do. Pushing it toward zero scrub radius or even beyond that will start to cause braking instability and steering issues like mid-corner bump steer. Cruising perfectly straight on dry smooth hwy, you probably won't notice much effect. On a track where you are working your suspension to the extremes, or driving in inclement weather over broken rough pavement... that'd be another story.

I actually watched the video below on tire stretch and this thought crossed my mind, maybe you can tell me exactly why it's a bad idea. Lets say you were given a container full of brand new 235/40r18 track tires. If I was set on using them on the track, it looks like more stretch = better lap times (but more dangerous and less forgiving). So if you wanted more response up front and more compliance at the rear, a 9.0" front rim and 8.0" rear would be the best rim layout on our imaginary scenario, no? Goofy as it may look...

The car tested was much lighter and RWD, but the trend is consistent on dry pavement:

I was also convinced not to go any wider than my 235 AS4 for wet performance.

It's best not to think of "tire stretch" but how well the wheel supports the tire. Bear in mind that videos like those - while informative - do have to exaggerate the differences to make a point and they are mostly speaking about ultimate grip (and lap time) from a HPDE perspective. The importantly take away is that tire/wheel setup is an integral part of your suspension system. As such, changing it affect a lot of factors relating to handling, ride quality and NVH... more than just how fast it goes around the track. Optimizing one factor invariably worsens others. It is a balancing act. What is the best compromise can be different for different drivers and different car setups, for different usage cases. What I prefer for how I drive my 3600lbs G70 6MT 2.0T RWD might not be to your liking on your 4000lbs Stinger 3.3T AWD and how you drive it... despite the fact that they share exactly the same suspension design.

I know this might sound like a cop-out, but I'm merely stressing the intricacies of suspension tuning. It is a fascinating subject and a challenging endeavor. One that requires a good understanding of ground vehicle dynamics. To me, that is why I enjoy it far more than spending $$$ on HP.

 

[AlphaNav]

Running square for the most part only has benefits ie: longer tire life with rotatability. Another benefit (depending on the driver really) is going to be a change in turning behavior (especially at the limit) towards a more neutral turn in feel, rather than understeer-y. A lot of people with heavier cars find benefits in doing this, just obviously being careful if you have lots of power when you're back on the throttle to prevent oversteer from taking over.

(Stock/OEM stagger is .5 inch from front to rear, rear being the wider wheel)

 

[ElChanclo]

Ah yes. If you want to get the most out of your HPDE by experimenting with various tire/wheel setups, you owe it to yourself to know the concept of scrub radius. Same way roll center is important if you want to play with suspension ride height. There are lots of online resources addressing these topics, so there is no need to draft an essay here. This is a good starter for Scrub radius. Once you understand it more, you begin to appreciate why BMW went up only 5mm on the M3 Comp's front offset. Most RWD (or RWD-biased AWD) cars have a modest amount of negative scrub radius, as I'm sure the regular 3-series and our Stinger/G70 do. Pushing it toward zero scrub radius or even beyond that will start to cause braking instability and steering issues like mid-corner bump steer. Cruising perfectly straight on dry smooth hwy, you probably won't notice much effect. On a track where you are working your suspension to the extremes, or driving in inclement weather over broken rough pavement... that'd be another story.

Where can you find the stock scrub radius for the stinger? The only thing google brings up is "turn radius" and older posts of yours.
So if we have negative scrub to begin with, it looks like more poke outward just gives you more negative scrub, you're not crossing to zero or positive by going wider if I'm reading that right.

It's best not to think of "tire stretch" but how well the wheel supports the tire. Bear in mind that videos like those - while informative - do have to exaggerate the differences to make a point and they are mostly speaking about ultimate grip (and lap time) from a HPDE perspective. The importantly take away is that tire/wheel setup is an integral part of your suspension system. As such, changing it affect a lot of factors relating to handling, ride quality and NVH... more than just how fast it goes around the track. Optimizing one factor invariably worsens others. It is a balancing act. What is the best compromise can be different for different drivers and different car setups, for different usage cases. What I prefer for how I drive my 3600lbs G70 6MT 2.0T RWD might not be to your liking on your 4000lbs Stinger 3.3T AWD and how you drive it... despite the fact that they share exactly the same suspension design.

I know this might sound like a cop-out, but I'm merely stressing the intricacies of suspension tuning. It is a fascinating subject and a challenging endeavor. One that requires a good understanding of ground vehicle dynamics. To me, that is why I enjoy it far more than spending $$$ on HP.

It all begins to do your head in after a while, but I understand it's important to keep those factors in mind when you go changing up the factory setup.

The real conundrum to me, is if I want to go 245 up front staggered, I'd need to go 275 rear, and that would be on 9.5" & 10" rims respectively, which feels like too much deviation from the factory 8.0 & 8.5, and too much tire at the rear (can that be a bad thing?)
Which is where the idea of identical tires on wider front rims and narrower rear rims came from.

I'm using this chart as reference:

So assuming the stock configuration of stretch at the front (225 on 8.0) and pinch at the rear (255 on 8.5) is the goal, it would mean a 245 square setup would need 9.5" up front for the stretch, but a more pinched 8.5" at the rear. The logic seems to work, but wider rims at the front feels off .

Those are my options as I understand it:
245x9.5 front & 275x10" rear (1.5" poke out vs stock and too much rear tire).
Or 245x9.5 front & 245x8.5" rear (looks completely ass backwards).

If I'm not modifying anything else, which is the best track setup (3.3 AWD)?

 

[Volfy]

Where can you find the stock scrub radius for the stinger?

It won't be listed for any car. Like roll centers, these are parameters crucial in the original suspension design. Once put into production, they are not typically something that most owners need to to know or worry about. That, unfortunately, is why few enthusiasts are aware of them, even though modifying suspension do affect these parameters and, in turn, how the chassis behaves.

To find the scrub radius on a MacPherson strut car is pretty straightforward. You simply follow the centerline of the strut down to where it intercept the ground plane with the car at ride height. This is easy to estimate, but measuring it precisely would be a bit tough. It is more practical to assume most RWD cars have some amount of negative scrub radius, and operate from that assumption.

I have amassed quite a few spacers (3, 5, 8, 10mm) and wheels of various offsets (34, 35, 38, 39, 40mm), so it is easy for me to experiment with different offsets to get a feel of the chassis response, then correlate that with the expected chassis behavior at -ve, 0, and +ve scrub radius.

For example, I have been daily driving mostly on my 18x7.5 ET39 with no spacers. This has 5mm more negative than the stock 34mm. As expected, the car's steering effort is a bit higher, but the front end felt like it tracks better, especially on corner exit when returning to straight. biggest difference is when hitting standing water, which around these parts is a regular occurrence with flash floods. Overall, probably not my favorite for a "fun" setup, but excellent for safe everyday driving on public roads.

OTOH, for AutoX, I typically run 18x8.5ET40 or 18x8.5ET38 with 10mm spacers. This changes effective offset to 28 or 30mm. The biggest difference is the steering effort, which is dramatically lighter than my street setup, even though I run wider and sticker track compound tires. Turn-in is faster and steering feel is enhanced (this one is also affected by other factors). I avoid running these tires in the wet, for obvious reasons, and the track is typically fairly smooth, so the negative effects have less chance of getting me in trouble. Center finding on corner exit is less precise, but with AutoX, you are turning constantly, so that's not a big deal either. For running Track Days at higher speeds and longer straights, I might dial the offset back closer to stock 34mm.

So if we have negative scrub to begin with, it looks like more poke outward just gives you more negative scrub, you're not crossing to zero or positive by going wider if I'm reading that right.

No. More positive. See diagrams above. MacPherson strut cars typically run negative scrub radius.

The real conundrum to me, is if I want to go 245 up front staggered, I'd need to go 275 rear, and that would be on 9.5" & 10" rims respectively, which feels like too much deviation from the factory 8.0 & 8.5, and too much tire at the rear (can that be a bad thing?)
Which is where the idea of identical tires on wider front rims and narrower rear rims came from.

I'm using this chart as reference:
View attachment 86881
So assuming the stock configuration of stretch at the front (225 on 8.0) and pinch at the rear (255 on 8.5) is the goal, it would mean a 245 square setup would need 9.5" up front for the stretch, but a more pinched 8.5" at the rear. The logic seems to work, but wider rims at the front feels off .

Too many folks let their pre-conceived notions color their judgement. There is nothing wrong with wider rim up front. Remember from above example of the M3, which has 275/40R18 on 18x9.5 up front.

Problem with the Stinger/G70 is that the front has trouble clearing aftermarket wheels wider than 8.5". Not at reasonably affordable prices anyway. If I could find an 9" front that would fit, I would be running that in a heartbeat.

Those are my options as I understand it:
245x9.5 front & 275x10" rear (1.5" poke out vs stock and too much rear tire).
Or 245x9.5 front & 245x8.5" rear (looks completely ass backwards).

If I'm not modifying anything else, which is the best track setup (3.3 AWD)?

245x9.5 front & 245x8.5" rear sounds like a terrible idea, driven solely on giving the rear more compliance on a square setup. While those are legitimate factors to consider, they should not be the only one.

245x9.5 front & 275x10" rear would be okay, if you can find a 9.5 with proper offset that would fit the front. I think 245 or 255 on 9" rim would be a more realistic target for front. Again, assuming you can find one with proper offset that'll fit. Even that will be a tough find, but not impossible.

 

[ElChanclo]

Problem with the Stinger/G70 is that the front has trouble clearing aftermarket wheels wider than 8.5". Not at reasonably affordable prices anyway. If I could find an 9" front that would fit, I would be running that in a heartbeat.

245x9.5 front & 275x10" rear would be okay, if you can find a 9.5 with proper offset that would fit the front. I think 245 or 255 on 9" rim would be a more realistic target for front. Again, assuming you can find one with proper offset that'll fit. Even that will be a tough find, but not impossible.

Just a quick reply, there's a set of rims for sale nearby:

Enkei T6S black - set of 4 $500usd​

NO TIRES​

5x114.3​

18x9.5 +15mm​

Super lightweight for their size​

Wheels only no tires​

Clearance looks good, but poke is +38.1mm (1.5") so VE is probably 0 or positive?


I could run 245 up front and 275 285 rear on those (or try 255 square etc). I'd do a test fit up front to make sure the spokes clear the calipers, but would you recommend a setup like that?

EDIT: Actually that would be 285 rear, too much pinch for track use?
EDIT2: ADVAN NEOVA® AD09:
245/35R18 92W = Rim Width (Appr.) 8.0 - 9.5
285/30R18 97W = Rim Width (Appr.) 9.5 - 10.5
OD is 24.8" vs 26.1" stock, but again, for track it's probably a good thing.

 

[ElChanclo]

dupe

 

[Volfy]

Just a quick reply, there's a set of rims for sale nearby:

Enkei T6S black - set of 4 $500usd​

NO TIRES​

5x114.3​

18x9.5 +15mm​

Super lightweight for their size​

Wheels only no tires​

Clearance looks good, but poke is +38.1mm (1.5") so VE is probably 0 or positive?

I love that wheel! If the offset was at least +30mm, I'll say go for it. Still not my preferred buy, but might be worth a try. Bring a floor jack and trial fit before you hand over the cash. I've done that before.

+15mm... I wouldn't put them on my Stinger/G70 even if they are super cheap. 21mm outward will for sure push the wheel centerline past the zero scrub radius point and introduce all manners of handling woes. Plus the tires will likely hit the fender, even without lowering.

Generally, I prefer to buy aftermarket wheels with offset slightly greater than stock. This way, I have the option of tweaking the offset on either side of the stock ET, depending on the usage case.

But, it's your car, your money, your call.

 

[Volfy]

I could run 245 up front and 275 285 rear on those (or try 255 square etc). I'd do a test fit up front to make sure the spokes clear the calipers, but would you recommend a setup like that?

EDIT: Actually that would be 285 rear, too much pinch for track use?
EDIT2: ADVAN NEOVA® AD09:
245/35R18 92W = Rim Width (Appr.) 8.0 - 9.5
285/30R18 97W = Rim Width (Appr.) 9.5 - 10.5
OD is 24.8" vs 26.1" stock, but again, for track it's probably a good thing.

If we disregard the 15mm offset, I actually like that tire setup on square 9.5 for track-only. Properly sized for 3.3T, and might even be suitable for a hopped-up 2.5T.

Those Yok's and RE-71 are probably 2 of the most popular AutoX/Track tires.

Of course, ultimately, you'll need to thrash it about the track and play with tire pressures to know if it is a good match for your car.

 

[ElChanclo]

+15mm... I wouldn't put them on my Stinger/G70 even if they are super cheap. 21mm outward will for sure push the wheel centerline past the zero scrub radius point and introduce all manners of handling woes.

But, it's your car, your money, your call.

Glad you pointed that out, I'll definitely pass on these. Handling woes is not the effect I'm looking for , but I'm a bit lost on the 9.5" rim offset issue...

If we disregard the 15mm offset, I actually like that tire setup on square 9.5 for track-only.

I saw an old post of yours "We run 18x8.5 ET38 Enkei TFR with 255/40R18 and they bolt right on no problem. Clearance to the strut was tight, with only a few mm's gap, but they do clear." so that looks like the limit for inset, according to WillTheyFit.com is "10.4mm closer to the suspension strut." vs the factory 225s.

So taking the ET15 offset +10mm, would a 18x9.5 ET25 rim work? There's no more room to move closer to the strut, but that's still 28.1mm of poke vs factory. And if that's too much, then you just can't fit a 9.5" rim up front without crossing the scrub centerline, right?