Handling secret sauce?

I’ve been trying to figure out why the 987 platform feels the way it does when driving through mountain twisty roads. It seems like the common refrains are: 1) mid engine (low moment of inertia / easy to rotate) 2) low CG / relatively low weight so stays planted 3) hydraulic steering for good road feel I’m sure all that’s true, but I also wonder about the rear suspension design. When I go around a tight switchback on the mountain road, and start to load up the outside of the car, the back end feels like it is actively helping the car rotate. Does the rear suspension geometry toe the wheels on compression and extension? It seems like it would make sense given that we essentially have very similar McPherson strut assemblies front and rear. I’ve driven very heavy cars with 4 wheel steering, which does a very good job making them feel lighter on their feet and more agile. I guess my question for the day is: What do you think are the ingredients to the 987 handling, and what percentage of the sauce is each ingredient?

I think it's the low polar moment of inertia primarily. The turn in and corrections are just so effortless. The CG being lower than anything else you can find helps. The torsional rigidity of the chassis as well. I am sure there is some designed in toe change in those rear links in response to braking or accelerating loads. Either way it handles way better than the sum of its parts.

Whatever the secret is, it works. I enjoy driving my 987.1 much more than my previous 996.

what an overthought question. just get over it and drive. - or not!’n

If on the limit, the brakes activate differentially as well. I have nothing to compare it with - but I love the way my 987.1S handles. Mine also has: The common Chassis brace Uprated roll bars Cayman R struts/springs Wavetrac LSD I’m not a good enough driver to test its limits - but I’m good enough to enjoy it a lot on a winding mountain road!

Kind of a weird reply as we are on an internet discussion board specifically to chat about these cars? And it is precisely because I do drive it (a lot) that I have these questions.

100% agree. I presently own both and enjoy driving the 987 more. I don’t have an answer to the OP but I think it’s driven by the mid engine layout.

OK - so curiosity got the better of me about the rear suspension kinematics. These are super rough based off an overlay from a few pictures off a website that seemed accurate enough for curiosity purposes. No attention paid to scaling. In this theoretical suspension (angles roughly approximate), the dimensions i'm looking at are the black ones. These will represent changes in toe and camber. In the image below, the toe is not 4.09°, but that is a reference for how the toe changes as the suspension compresses Nominal ride height: Compressed Suspension: When the suspension compresses, the rear wheel toes in and camber increases modestly. Extended Suspension: Just as a sanity check, extending the suspension (unweighting the wheel) toes the wheel out and adds positive camber, as you'd expect. The interesting thing to me is that the amount the wheel toes out on extension is much less than it toes in on compression, and seems kinematically quite intentional by the engineers (again, if you believe this very rough, quick and dirty schematic). The takeaway from me on this point is that lowered cars will have more variable rear toe as it cycles through the travel (although there is less travel, so maybe similar total change in toe?). The change in toe is interesting to me as increased rear toe is generally thought to make the car more "stable", which is consistent with my experience reducing the rear toe on an Audi A3 to extend the lifespan of the rear tires (it is more wandery and darty when pushing it), so I'm inclined to take the rear suspension kinematics off the "it makes things more agile" list and more of a "don't spin the car" tool, but i'm not a suspension setup guru at all, and am curiuos about more experienced interpretations.

I guess my message is that running all season tires will mute somewhat the sharpness of this chassis. If I keep my Boxster long enough to wear out the current tires I will go back to summer tires .

Are you suggesting that the 987 is different from the 981 in this respect? David

Hello, long time lurker but first time poster here. Caylman, I really like your analysis but 4.0° toe change for 25 mm of suspension travel seems like a lot. If I do my trigonometry correctly, that equates to almost two inches across the tire diameter and I would expect to see numbers more in the 1/2” range. To the OP, I don’t know what current industry practice is but in my days many moons ago, as a vehicle dynamics engineer for one of the Detroit big three, rear toe out in suspension compression was a big no-no. The primary consideration was the need to provide the average driver in a relatively softly sprung vehicle with a stable rear end in an emergency lane change situation and one that toes out in compression does exactly the opposite. In that situation, a little bit of rear toe in under compression was considered a good thing. Having driven cars that, due to poor design, had rear toe out in compression, I can assure you that it could be a scary experience. So yes, it’s definitely a “don’t spin the car” thing. That said, tires and suspensions have evolved a lot since then and a Cayman with its typical driver profile presents a somewhat different use case, so maybe things are different now. I also happen to race an open wheel formula car which has full adjustability and we go to considerable effort to adjust toe changes to zero (bump steer is the proper term) in compression and extension on both ends of the car. In that case we’re also concerned with having quick response and good stability at initial turn in but also in eliminating another variable that affects the car’s handling. All of this applies only at the vehicle’s nominal factory ride height so as we deviate from that with lower springs or adjustable coil-overs, the numbers can change quite a bit.

Thanks for chiming in! A vehicle dynamics expert is a welcome addition to this thread. To be clear about the analysis, scaling was completely arbitrary and the “25mm” of compression is a completely arbitrary change that simply looked roughly like something maybe resembling full travel given the arbitrary scale of the image imports. The 4 degree angle in the first image was just an intersection of a static ground plane and a plane defined by the top of the strut, and the 2 ball joints in the rear hub. It is just the change in angle I was looking for, and in this case, it was 1.4 degrees between nominal and “full compression” (maybe?). So that would put it closer to your estimation. I also didn’t factor in the forward control arm pulling the coffin arm forward a little bit which would reduce the amount of toe in on compression, which I justified by figuring the most compliant bushings are in that link (I think?). Thanks for contributing!

Simple to understand. Next time you're in the gym. Go over to the barbell rack, and pick up a 5lb barbell: Hold it in your hand - with the handle horizontal. Rotate it 180 degrees (90 degrees each side)... Then hold it in your hand - holding it by one of the ends so the handle is now vertical, and the barbell is hanging down with the one weight hanging below the other. Rotate it 180 degrees - repeating the first test. ----------------------------------------------------- Now you know why the 987 is such a hoot to drive. It's called inertia . With the weight at the end of the car it requires effort to stop or reverse any turning motions. With the weight in the center of the car - it takes way less force to change the direction of the car (or barbell).. result is a much more responsive (go-cart-feeling) car, no matter what steering system or fancy suspension you put in it. It's simply good design from a physics point of view. It's the same reason every Porsche racecar is now mid-engined. The 911 IMHO is a wonderful example of engineering around an inherently flawed design. I'm surprised Germans keep doing it - they must know mid-engine is the way to go and in my experience, they're typically very practical people.

I swear I can feel the weight of my BMW 128i's 6 cylinder being moved laterally when I turn into a corner in that car. No such sensation in the Cayman. That car rotates around my right jeans pocket effortlessly...