Real Fiero Tech

How much would staggered tire sizes be needed on a 88' duke? Lowered 2" no rear sway bar currently. Was thinking of running 225/45/16s at all 4 corners. No track days, just spirited driving (nothing crazy) on country roads.

If not now, under what circumstances should I go staggered?

My understanding is in theory you should pretty much always be staggered on the Fiero in accordance with your weight distribution. The Fiero is rear weight biased so you should have a wider tire on the back to maintain neutral handling.

In practice, I did one track day in my totally stock 88 duke as a baseline before I started modifying it. At that point it had a square tire setup, a 205/55/16 (because that's what came on it when I bought it). It wasn't scary tail-happy or anything, but it was certainly willing to rotate off-throttle. In a car with stickier tires, stiffer suspension, and more horsepower, that could become some tricky behavior at the limit. Not something that would make it undriveable on the street but just something to keep in mind.

87 Duke with a 5 speed is 43.5% front, 56.5% rear so an ideal stagger would be something like 195 front 255 rear. Given that a front suspension tends to not work as well as rear since it has to turn, you could bump it up to 205 or 215 at the front and probably not be too front-biased.

Jalisurr wrote: ↑Tue Apr 16, 2024 6:06 pm My understanding is in theory you should pretty much always be staggered on the Fiero in accordance with your weight distribution. The Fiero is rear weight biased so you should have a wider tire on the back to maintain neutral handling.

In practice, I did one track day in my totally stock 88 duke as a baseline before I started modifying it. At that point it had a square tire setup, a 205/55/16 (because that's what came on it when I bought it). It wasn't scary tail-happy or anything, but it was certainly willing to rotate off-throttle. In a car with stickier tires, stiffer suspension, and more horsepower, that could become some tricky behavior at the limit. Not something that would make it undriveable on the street but just something to keep in mind.

Series8217 wrote: ↑Wed Apr 17, 2024 3:46 pm 87 Duke with a 5 speed is 43.5% front, 56.5% rear so an ideal stagger would be something like 195 front 255 rear. Given that a front suspension tends to not work as well as rear since it has to turn, you could bump it up to 205 or 215 at the front and probably not be too front-biased.

Appreciate the input, knew in the back of my head it wouldn't be ideal to run square but figured I'd check in anyway. With my current 16x7 wheels, the best I can do is 195/55 and 225/50 with current 16' tire offerings

If you could theoretically get to a 50/50 weight distribution, would you be able to run a square setup? Or should there always be a stagger given the mid engine layout?

I think that this concept of sizing tires according to weight distribution is unrelated to the position of the engine in the car.

NoGoodFiero wrote: ↑Thu Apr 25, 2024 7:59 am If you could theoretically get to a 50/50 weight distribution, would you be able to run a square setup? Or should there always be a stagger given the mid engine layout?

pmbrunelle wrote: ↑Thu Apr 25, 2024 8:13 am I think that this concept of sizing tires according to weight distribution is unrelated to the position of the engine in the car.

Power is a factor as well. C5, C6 & C7 Corvettes are almost exactly 50/50, but run a significant stagger because they have a lot of power. For a low power ride, stagger matching the weight distribution is a great bet.

At the same time, there are a lot of BMW models that leave the factory with stagger for predictable handling (IE, to protect mediocre drivers from themselves), but handle much better--lap times confirm--with a square fitment. They typically have a front-biased weight distribution, though, so a rear biased stagger would be exactly the opposite of what the chassis needs.

There are plenty of FWD autocross cars with significant FRONT stagger.
Many years ago I had a 1990 Pontiac 6000 SE AWD (G000SE). It would take Grand Prix 16x8 wheels up front and otherwise identical Bonneville 16x7's on the rear. With 245/50 front tires and 205/60 rears it was actually quite neutral.

The car has a center of mass. The front-rear position of the center of mass is described by the weight distribution.
The car has a center of traction. The front-rear position of the center of traction is defined by the tire stagger using almost exactly the same math as CG position vs weight distribution.

With the center of traction behind the center of mass, the car will tend toward understeer and be "predictable" as the BMWs I mentioned above.
With the center of traction ahead of the center of mass, the car will tend toward oversteer and be unpredictable. This is the stock Fiero condition, which requires the OEM to deliberately set the suspension up poorly in order to protect mediocre drivers from themselves.

With the center of traction very close to or at the center of mass, the car will be neutral, and can be made to understeer or oversteer by manipulating the rear traction circle with engine power.

Despite what I said about the stock Fiero suspension above, the '88 Formula *with* the rear bar, the slight factory wheel/tire stagger and some tasteful suspension mods handles QUITE WELL on stock sized wheels and tires. I would grade it as excellent to outstanding compared to its contemporary competition.

The Dark Side of Will wrote: ↑Thu Apr 25, 2024 8:51 am Power is a factor as well. C5, C6 & C7 Corvettes are almost exactly 50/50, but run a significant stagger because they have a lot of power. For a low power ride, stagger matching the weight distribution is a great bet.

Like the 50/50 BMWs, the Corvette racers run square for best performance on the track.

Yep, when I was time attacking my C6 the move was always to switch to a square setup (Running 315s front and rear does hurt the tire budget though).

The factory tire stagger is to make the car less likely to oversteer for the typical corvette owner's heavy foot and slow hands, not for ideal track performance.

Series8217 wrote: ↑Thu Apr 25, 2024 9:48 pm
Like the 50/50 BMWs, the Corvette racers run square for best performance on the track.

Jalisurr wrote: ↑Mon Apr 29, 2024 12:19 pm Yep, when I was time attacking my C6 the move was always to switch to a square setup (Running 315s front and rear does hurt the tire budget though).

The factory tire stagger is to make the car less likely to oversteer for the typical corvette owner's heavy foot and slow hands, not for ideal track performance.

I knew Corvettes moved *toward* square in competition... didn't know they got all the way there.
More anecdotal evidence that matching tire distribution to weight distribution is the way to go fast around a course.