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BTW Its my mom's low mile tip I'm thinking about taking out of mothballs for my daily doody. These days when you can get a model 3 that does 60 in two seconds.. you would think people would be over the whole moar pwer thing. And I think I am. Wants are something comfortable that dances. Don't think I need 1.15g cornering or 398hp to cover those bases really.
 

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It's unclear to me what your objective is, and your plan of attack to achieve it. Do you intend to run the same 225/45 tires all around, using the stock staggered wheels, but swap the front wherls to the rear axle, and vice versa? If so, I'd advise against the axle swap. Assuming they'd fit (I'd be concerned with using the 8"wide, 40mm offset wheels in the front), the car would tend to oversteer significantly. Mid-engine cars tend spin quickly once they start to rotate. But if you leave the wheels on their original axles, everything will fit without requiring spacers, and you'd still dial out some of the inherent understeer.
Please clarify, if I've misunderstood.

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No you're right. Thinking 225 50 all around. Objective is comfort and yes less under steer. In my experience a narrow wheel will absorb bumps better than the same tire on a wide wheel. I would want that in back, and the sharp steering response of a wide wheel up front.

The width of the contact patch should be the same front and rear. Only difference should be the sidewall characteristics of a narrow wheel versus on a wide one. 1" spacers in the rear should mean all four wheels move outward 1/2".

Maybe even 205 55..
 

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I'd srongly suggest that you keep the wheels on their original axles. But it can't hurt to experiment with different fitments in an empty lot, to get a feel for the different handling characteristics at and beyond the limits of traction, before potentially endangering yourself and others on public roadways.

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No you're right. Thinking 225 50 all around. Objective is comfort and yes less under steer. In my experience a narrow wheel will absorb bumps better than the same tire on a wide wheel. I would want that in back, and the sharp steering response of a wide wheel up front.

The width of the contact patch should be the same front and rear. Only difference should be the sidewall characteristics of a narrow wheel versus on a wide one. 1" spacers in the rear should mean all four wheels move outward 1/2".

Maybe even 205 55..
You cant use the same size and aspect ratio tire on all four corners . The 987 and 981 both use a staggered rear and front rolling circumference that must be maintained within certain limits. The rear is typically around 1 inch wider diameter than the front and screwing with this ratio will cause ABS and traction control issues with the system which expects to see that stagger and difference in speed between the front/rear wheels. The PSM can be fooled into thinking the tires are slipping because the system isnt seeing the wheel speeds they expect so the ABS and traction control may abruptly activate during normal driving and braking

Its no problem to use smaller rims and wider sidewall for a softer ride assuming they clear, but refer to this calculator to compare what tire size and sidewall profile is needed compared to what the car was using from the factory ro make sure you are not screwing up the front/rear rolling ratio

 

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You cant use the same size and aspect ratio tire on all four corners . The 987 and 981 both use a staggered rear and front rolling circumference that must be maintained within certain limits. The rear is typically around 1 inch wider diameter than the front and screwing with this ratio will cause ABS and traction control issues with the system which expects to see that stagger and difference in speed between the front/rear wheels. The PSM can be fooled into thinking the tires are slipping because the system isnt seeing the wheel speeds they expect so the ABS and traction control may abruptly activate during normal driving and braking

Its no problem to use smaller rims and wider sidewall for a softer ride assuming they clear, but refer to this calculator to compare what tire size and sidewall profile is needed compared to what the car was using from the factory ro make sure you are not screwing up the front/rear rolling ratio

I actually did run winter 225/45 tires all around, on the factory staggered wheels, on my '07 Cayman. I never had a PSM or ABS issue or warning from doing so. The speedometer was a little "optimistic", however. It was great fun to drive in the snow, with a Guard LSD, Nokian Hakkapeliita R tires, and a Cayman R-like suspension!

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I actually did run winter 225/45 tires all around, on the factory staggered wheels, on my '07 Cayman. I never had a PSM or ABS issue or warning from doing so. The speedometer was a little "optimistic", however. It was great fun to drive in the snow, with a Guard LSD, Nokian Hakkapeliita R tires, and a Cayman R-like suspension!

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Your say staggered "wheels" so do you mean you have different diameter wheels front to back? If not I wonder if its just a 987.2 thing then? I know the 986 used equal diameter tire values all around as I had one, and my 987.2 was staggered like my 981 is (tires sidewall only, rims are all the same diameter) and you will definitely get issues if you wander too far out of bounds. The guys at BGB claim the factory diameter delta is about .9 or a rolling circumference difference of about 2.5 inches front/back. They say about 1.1 delta or 3 inches circumference is the limits before it will cause issues, but maybe this applies only to increasing the stagger difference and not going less?
 

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This is the type of excellent discussion I was hoping to get here. So I guess I should research if that 1.1 to 3 delta is specific to 987.2 or not.

Additional reason it would be nice to go 50 all around is to swap back to front for wear/handling reasons.. but I did wonder about ABS PSM issues. I don't foresee a handling issue solely due to wheel width, but who knows. It would be nice to be able to swap back to 'normal' wheel stagger at will, without dismounting tires.

The more I think about how fun an FRS BRZ is to drive- the more it makes me think I should even go square 205 rather than 225.
 

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Would love to know what you find out. I have always assumed the ratio applied in both directions, but its possible I was incorrect and maybe increasing the delta causes issues but reducing it does not? Ive read others say this delta is programmed into the car and can be changed with a Piwis, so I just assumed that breaking out of it in either direction would confuse the system
 

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Could swap the stock setup front to back to find that out.

Far as endangerment, don't think its possible to make this car as dangerous as some of the other stuff out of the roadways... no matter what tires you put where.
 

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Could swap the stock setup front to back to find that out.

Far as endangerment, don't think its possible to make this car as dangerous as some of the other stuff out of the roadways... no matter what tires you put where.
Good luck, and please kept us posted with your results.

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Would love to know what you find out. I have always assumed the ratio applied in both directions, but its possible I was incorrect and maybe increasing the delta causes issues but reducing it does not? Ive read others say this delta is programmed into the car and can be changed with a Piwis, so I just assumed that breaking out of it in either direction would confuse the system
I only drove the car in the winter one year with this setup. It most certainly might have "upset" the ABS/PSM in other conditions. For example, I once mounted a set of 2nd hand Hoosier slicks,with a "reduced delta" tire diameter ratio, at a DE event. It was the only time that I ever experienced the dreaded "ice pedal", so maybe the increased traction from the slicks, as opposed to the decreased winter traction, pushed the system over the edge. In any case, when you mess with the factory setup, you risk experiencing unintended consequences.

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Gotcha, I do have an appreciation for what you're saying. For sure will do any experimenting within a safe methodology. Will look up ice pedal.
 

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I'll save you the effort. It's a situation where the ABS gets overwhelmed under maximum braking. The pedal is firm, but the braking effort is diminished no matter how much force is applied by the driver. The remedy is to quickly pump the brake pedal to reset, or "unfreeze", the ABS system.

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I only drove the car in the winter one year with this setup. It most certainly might have "upset" the ABS/PSM in other conditions. For example, I once mounted a set of 2nd hand Hoosier slicks,with a "reduced delta" tire diameter ratio, at a DE event. It was the only time that I ever experienced the dreaded "ice pedal", so maybe the increased traction from the slicks, as opposed to the decreased winter traction, pushed the system over the edge. In any case, when you mess with the factory setup, you risk experiencing unintended consequences.

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Good to know and Ive heard of the ice pedal but luckily never experienced it before. I'm sure it can be quite terrifying going into a turn over 100 mph and the brakes aren't there no matter how hard you press the pedal. The one time was able to induce rolling ratio issues on my 987.2 was after a tire swap and overdid it in the back. The car would drive ok on the highway or in town stuff, but would act up when driving in the mountains on the twisties or with wide sweeping turns like a 180* exit off the highway. I was not fully aware back then that I had to maintain a certain stagger ratio and learned the hard way. Your advice is best that we probably should not be second guessing the engineers that design our cars:)
 
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