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Did you modified your suspension? Are those the "S" model tips or you did an upgrade there too? What´s the size of the tires? Sorry for so many questions!!
All you guys that are just adding spacers to factory wheels aren't doing your research on scrub radius and how offsets and spacers effect how the suspension works.
In order to preserve the suspension's designed scrub radius for optimal handling, you have to keep the center of the front wheel where Porsche put it. That means to achieve the look you're going for, you really need to run a wider wheel if you're going to adjust the offset - a spacer essentially adjusts the offset.
From a stock 8" wheel with say 55 offset, if you're adding a 7mm spacer to this, you've essentially created an 8" wheel with a 48mm offset. That means you've moved the scrob radius from a neutral or zero to a positive one.
If you went to an 8.5" wheel with the same offset of 55 that moves the inner lip in 6mm and the outer lip out 6mm, but keeps the scrub radius the same. If you had 8.5" wide wheels from the factory and want them further out, move up to 9" wheels with the same offset. That will move them out 6mm but preserve your handling. The right way to stance the front of a 997, or any car for that matter, is to widen the wheel, but keep the offset the same so the center of the contact patch still intersects with the kingpin or ball joint angle at the original position right in the center of the contact patch where it meets the road.
Do. Some research on how scrub radius effects handling dynamics, but going to a positive scrub radius makes the car push through turns as the steering geometry requires the tire to "scrub" through the turn instead of roll through the turn. It also creates instability in wet weather when one wheel hits a puddle by causing the other side to pull instead of track naturally straight. Widening the rear track actually helps the control aspect.
When you hear people complain about their front end grip but love the "stance" of their car, now you know why. Most cars have a small negative scrub radius from the factory for safety.
I personally experienced this when I put a set of 8.5" et42 wheels on my 997 and the handling became very twitchy and unstable. When I went back to my other wheels with an et53 the stability and proper handling was back. At the time I didn't understand why, but since have learned how scrub radius impacts cornering and stability and now know why those happened.
Also, lowering the car moves the scrub radius to more positive since it changes the kingpin angle. Then to fill the wheel wells, adding spacers moves it even more positive, so those two common things done together are the worst possible combination. You can fix it a little with camber but not much.
If anyone knows the scrub radius Porsche uses on the 997 that would be helpful information to know. Most rear wheel drive cars have a slightly positive scrub radius because the acceleration and braking forces force the front dire deflection out toward positive. You don't want a zero scrub radius because the car feels like it wanders and pulls under braking. Setting a rear wheel drive car to have negative scrub radius and then the forces pushing it near zero would make it unstable. Front wheel drive cars tend to have a negative scrub radius to minimize torque steer.
Is an acceptable way to keep scrub radius the same to measure the width between the center of both front or rear tires. Then as you make wheel offset, spacer and tire size changes to keep the same width?
Last edited by platinum997; 08-08-2021 at 09:13 AM.
Is an acceptable way to keep scrub radius the same to measure the width between the center of both front or rear tires. Then as you make wheel offset, spacer and tire size changes to keep the same width?
No, scrub radius has to do with the front wheels and what happens to the arcs of them relative to the suspension and each other as you're turning. The rears just go straight so spacing them out is fine. It effects front to rear track, but that's not a critical handling factor.
i have a 2008 C4S with OEM lobster 19 x 8 front wheels with a 57 mm ET. I am looking at possibly trading the stock wheels for 2006 Turbo OEM wheels that are 19 x 8.5 with a 56 ET. Will this create problems?
i have a 2008 C4S with OEM lobster 19 x 8 front wheels with a 57 mm ET. I am looking at possibly trading the stock wheels for 2006 Turbo OEM wheels that are 19 x 8.5 with a 56 ET. Will this create problems?
Nope. The offset is nearly identical so the center of the contact patch will be in exactly the same spot (well, 1mm different). You'll just have 6mm more wheel further in from thr current wheel edge and 6mm more wheel.further out than the current wheel edge, but there's plenty of space for that.
No, scrub radius has to do with the front wheels and what happens to the arcs of them relative to the suspension and each other as you're turning. The rears just go straight so spacing them out is fine. It effects front to rear track, but that's not a critical handling factor.
ok.. so no for the rears but that should work for the fronts, right. If the width between the center of the fronts is say 100. I make a bunch of changes but the net effect is still 100.. should be the same right ?
ok.. so no for the rears but that should work for the fronts, right. If the width between the center of the fronts is say 100. I make a bunch of changes but the net effect is still 100.. should be the same right ?
100 is a made up number obviously.
Maybe just easier to keep net offset the same?
I don't think yuu have to worry about the tracking offset from the front to the rear changing from say 100 to 90. The rear will still just follow the front and a wider rear probably helps with the rear engine 911 platform.
i have a 2008 C4S with OEM lobster 19 x 8 front wheels with a 57 mm ET. I am looking at possibly trading the stock wheels for 2006 Turbo OEM wheels that are 19 x 8.5 with a 56 ET. Will this create problems?
Use this calculator and it'll tell you exactly how much further (or indeed less) the wheels will protrude both the face and the back
It's worth noting Porsche have fitted thin (5-7mm thick) spacers to their cars previously. The Mk1 996 GT3 and Boxster 550 Anniversary (IIRC) are two examples.
It's worth noting Porsche have fitted thin (5-7mm thick) spacers to their cars previously. The Mk1 996 GT3 and Boxster 550 Anniversary (IIRC) are two examples.
Those stance calculators don't factor in scrub radius at all. It's possible that the cars with OEM factory spacers have different suspension geometry and why they add spacers for scrub radius. Hardly anyone pays attention to or understands this concept. It's all about how far out can I pull a wheel and how wide a tire can I put on it without it rubbing the fenders.
08-06-2021, 12:19 PM
