M3Cavalry

Yeah, yeah, I know. It’s a 911. But I think something is a little wonky with my newly acquired 997.2. It seems nervous at speeds where it should not be, and far more willing to oversteer than it ought. It’s lowered on Eibach springs with 20” wheels with 245 front/305 rear tires. The motor mounts are bad, which may exacerbate the issue. Welcome any input.

Bruce In Philly

2009 C2S 200K miles

Probably an aggressive alignment out of Porsche specs. You will have to go the alignment route first before digging in deeper. Engine mounts are pretty much irrelevant for the type of experience you are having.

Check your front tires for odd wear... especially the inside tread. A common approach to "improving" handling is dial in more negative camber in the front... this will make the car more darty. I did this and when at speed, you really have to drive the car as the car wants to dart around on the interstate. I got wear on the inside tread so I undid my out-of-spec alignment.

Your tires are not Porsche spec'd sizes too... they are bigger, wider, and have a shorter side wall.... well this will exacerbate dartyness given any out of spec alignment. You purchased a tricked out car... it comes with costs... cool to some is weird to others.

Peace
Bruce in Philly (now Atlanta)

evo9

2010 c2s here:

Check age of tires. When I obtained my car, it had old tires that had become hard (perhaps dry rot) and traction was very poor. Stability control was engaging during fast high speed sweepers that scared the bejeezez out of me.

Replaced tires with fresh Bridgestone (any brand would have probably been good) and the odd, disconcerting handling went away/ Fwiw - I have 19" wheels and also run 245 front/305 rear tires

M3Cavalry

that is a fair point, but the tires are new. I’ve had this phenomenon though before, and you’re right—scary as hell.

M3Cavalry

it’s not darty on the highway though. It’s only on curvy back roads. The car was aligned by the shop that did the PPI. They did say the aftermarket, larger wheels impaired them getting in spec but that they got it pretty close.

could motor mounts contribute by having the motor slingshot to the outside of corners?

ALSO: mine is also an 09 C2S. Has 111k. Ang recommendations to reach 200?

Bruce In Philly

I always complained about the engine mounts back when I purchased the car with 26K miles on it. When I would accelerate in a curve and the curve had some humps on it such as road with tree root heaves or whatever, the rear would bob and weave a bit... This is due to, IMO, the mounts allow too much movement... wagging. Later at around 100K miles, I changed them out for new ones (Porsche labeled)... read here: https://rennlist.com/forums/997-foru...s-porsche.html

It really didn't change characteristics much if at all. Others here claim big transformations but not me. It is what it is. Porsche must have recognized there was an issue, because later models had mounts that stiffened/loosened dynamically.... that kinda tells you all you need to know as far as I am concerned.

Given this car has been modded so much, are you sure the mounts are original Porsche parts? Plenty here have swapped them out for stiffer aftermarket. You can try this but they may have some negative consequences such as noise and vibration in the cabin... although with your car modded they way it is I suspect this will not matter to you. On a .1 engine, Jake Raby found that these stiffer aftermarket mounts can retard the ignition as the engine senses false knock. Some have them and love them.

Changing mounts is super easy, plenty of discussions on Rennlist about alt products: https://rennlist.com/forums/997-foru...s-porsche.html

To get to 200K? I dunno... I drive it, Italian tune up if I am just getting groceries too much, Liquimolly 5W Lightlauf with Cera Tec every 5K and throw in a bottle of Techron once a month or so. Use good gas. I am not saying my oil regimen is what did it... no way am I getting into an oil argument... all I can say is I do it this way because it entertains me... seriously.

Peace
Bruce in Philly (now Atlanta)

MrIncredible

You said you bought new tires recently... I replaced my rears not long ago and ever since, I'm nervous to really give it the beans going around a corner. It just doesn't feel planted to me and I thought maybe it's because my car is lowered and the tires haven't "worn into the alignment" yet. If that makes any sense.

Wayne Smith

New tires come complete with a layer of mold release that is slippery. A friend had his new tires throwing PSM codes on his dash as we headed into the mountain passes. It can take up to 500 miles to wear this off.

And new tires can have defects. I put a major brand's tires on my car, and it threw me around a bit. Everything looked good until at around 5K miles, one of the rears developed a bubble on the sidewall. The factory treated me right on warranty, and the replacement tires have been fine.

But there's a lot that is not necessarily obvious that can screw up handling.

Petza914

Aside from all the good prior advice, tire pressures can make a huge difference in dartiness, especially with the narrow sidewall from a 20" wheel. Try setting your tire pressures at 30 F / 35 R if they're currently higher than that and see if things improve.

Your 245 & 305 widths are just fine as long as the aspect ratios are appropriate to not have more than 2% difference in diameter / rolling circumference front to rear as that will throw off the PSM and ABS systems and if an AWD car can damage the transfer case as it tries to rotate them at the same speed. Yours is a C2S so not AWD and no transfer case concern.
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M3Cavalry

Interesting point. The tires are set to the OE recommendations, which seem high. A lower pressure would in theory give a bit more grip, I would think. My butt dyno may be feeling the car skipping a bit on a rough road surface, as opposed to the tire having good purchase and still sliding. I think I’ll try your recommended pressures.

I would never have put 20s on the car myself, but I’m interested in seeing whether I can live with them before spending more. With high pressure and minimal sidewall perhaps the tires are just not flexing enough to accommodate imperfect surfaces. Will test and report back.

Bruce In Philly

Grip and ride are two different characteristics. Back when I used to go to the track, I learned very quickly that handling characteristics can change quite a bit by just 1-2 pounds in the tires, and 1-2 pound differences front to rear resulting over vs under steering. I used factory alignment specs back then. Tire temps also come into play here. For my current car and non-track use, I set my tire pressures based on sweeper performance... I can not describe in words how to diagnose and change, you must do your own experimenting... it is pretty easy to tell if you improved or reduced performance and or comfort. In short, there is a optimization curve with each tire and suspension configuration specific for your car... to low and you loose grip... too high and you loose grip. You just have to experiment.

Back when I was tracking my 2000 Boxster S with Michelins, I was impressed the guys at the track knew exactly what to set my tires. Factory alignment? Michelins? Therefore pressures should be xx, yy. Boy were they right... I ran some tests over my first two-day event these guys were spot on. You have customized suspension, non-standard tires, and an unknown alignment... you will have to do your own experimenting to dial in the correct pressures.

I just had new rear Michelins put on a month or so ago... I never told the tire shop what pressures to use as I knew I would check and redo them anyway when I got the car home. Driving home, I could tell the pressures were way too high even with the mold release on the tires. The ride was hard and car moved all over the place. I forget what the shop set them at but it was so high, I wondered what the heck they were thinking. Doesn't matter, I know what pressures are good for me and my alignment.

Peace
Bruce in Philly (now Atlanta)

preelude

Like Bruce suggested, start with alignment. Incorrect toe or track specs can make the car very nervous.

PV997

You should check your control arm bushings while you are at it, particularly at 110k miles. Damaged control arm bushings will screw up alignment as the wheels don't hold the same positions when exposed to dynamic road forces that were used during alignment. With bad bushings the car will tend to go toe out due to road forces, which makes a car very darty. Provided both front wheels have good grip, the car heads as intended as they cancel each other out. But if one wheel loses grip (like from a bump), the car darts in the direction of the wheel that still has grip.

I just went through this on my Saab DD with 160k miles. New front control arm bushings made it drive like a new car, it had gradually worsened over time and it wasn't obvious until it got terrible.

Petza914

This for sure. My upper and lower control arms on one of my 928s were loose, so loose that it was toed out all the time, which was very stable, but as soon as the alignment shop set the toe in correctly, I left the shop went to get on the highway and the load made the wheel toe out and almost put me into the concrete wall.

da Vinci Dan

Higher miles with aftermarket Wheels, tires, and likely worn suspension components will certainly all contribute to handling issues. I would do a thorough inspection of all components. If you're committed to the wheel tire combo, then you may need to just get it as good as you can. If you want the traditonal more factory handling, I would go back to stock or at least Porsche spec.