Pazzo009

Having a Porsche and not driving fast is like being a **** star and hating to have sex. That being said, there is a time and place for everything. In the right environment I feel very secure at that speed and higher, unfortunately not at this time with my new Porsche. Now I'm not saying I felt that I was in any danger, but I just felt like it was not as secure as I am used to in my M5. You're right though, it is a Porsche and it should feel planted at that speed IMO. My theory was if my tire pressure was too high it was affecting something, but whats contrary to that is most manufactures recommend higher pressure for higher speeds. So I guess at this point, it's downforce??? Or alignment like someone suggested.

ny991

I would take a look at the alignment. I had mine up to 140 at Watkins Glen last month and it felt fine. I was in sport and my pressures were about 42. The car does feel a lot lighter if you are not in sport mode.

Pazzo009

Okay thank you. I had it sport plus at the time. I will mention it to my dealer.

chuckbdc

Too much disparity front to rear tire pressure is my bet for the sensation you felt. I use the pressures that you settled on and have never felt any float or lift at the speed you mention, or beyond either.

LexVan

Does the aero kit have an active dynamic rear spoiler? Is it deploying properly?

Pazzo009

No, it is fixed and I would have to assume it actually creates considerable down force.

rpilot

Have your PASM shocks tested out to make sure they are operating nominally, if there is a way Porsche dealers can do that .

GrayBlack

Pazzo009, I know what you mean. I also came from a F10 M5 to a 991 C4S. The M5 felt more planted at higher speeds. I believe a lot of it has to do with the weight of the car. You can definitely throw the 911 around more than the M5 though. Two completely different cars, but both are fantastic.

chuck911

There's your problem. LexVan came closer than anyone with his mold release comment. I seriously doubt it has anything to do with the car, not even much to do with tire pressure. But brand new tires definitely will make a car feel floaty, and it becomes more noticeable at higher speeds. The mold release you can scrub off pretty quick, but it takes a little longer for the tire casings to really settle in. In fact its hard to know for sure but it sounds like you could have been doing this even before the tires had a chance to heat cycle properly. Give those tires several hundred to a thousand miles, I bet your problem goes away.

Pazzo009

I do not have PASM shocks. ( I didn't build the car, I would have gotten them)

Yes the M5 feels more stable at higher speeds. It's also lowered. The steering of the Porsche embarrasses the steering feel of the M5...This is no secret. I still have my M5 and love it as well.

I have never heard of this mold theory but I appreciate you both for teaching me something. Also keep in mind that it was a 63 degree day, car had 150 miles on it, and if it matters, brand new asphalt. It wasn't a feel that made me feel insecure, it just felt a little light. Especially that I'm coming out of a 4300 pound autobahn cruiser.

rpilot

If you have the 991S as you stated, you do have the PASM shocks.. they come standard with the S. I am not sure that is the problem, but like I said earlier... it is worth getting them checked out. Keep us posted.

chuck911

Reading through everything again, I'd put money on it being brand new tires. You can read up on this in detail if you want, but this is a good place to start http://www.tirerack.com/tires/tirete...e.jsp?techid=5
Now there are a couple additional contributing factors (besides the mold release and tread depth factors mentioned at Tire Rack) that will complete the picture: new rubber, new tire shape, new asphalt and PASM.

As tires age the rubber gets harder. Autocross guys all know you will lose time from one year to the next just letting your tires sit in the garage getting harder. The new tread will squish around under load, creating that floaty feeling.

Look at a new tire compared to your older ones. New tires all have a very slight crown or roundness to them compared to worn tires. Soft new rubber combined with the slight crown (and deeper tread) has a lot to do with that great new tire feel of a super smooth ride. It also of course gives a ride that feels less planted.

Now the asphalt comment is really interesting. I missed this first time around because you said "pavement" instead of "asphalt"! New pavement means nothing, new asphalt is a whole 'nother deal. New asphalt has a lot of the same qualities as new rubber. A lot of the petroleum products used to make both are still in there when new. Over time these evaporate off, a big reason both the tire and the asphalt harden over time. Really new asphalt you can even tear up the surface just by driving too hard (cornering, braking) on it. We made the mistake one time of running a DE on asphalt laid down the day before and within an hour had ruined 3A. It looked okay but was not cured enough. What happens is that as you drive across it the surface asphalt binds to the tire more strongly than to the asphalt below. Depending on load it may not tear up, it may just squish around a little. That's why it was interesting to me that you noticed this on new asphalt.

One more piece of the puzzle: PASM.

You're used to a car that has been set up with a single-setting suspension. (If I'm wrong let me know.) Unlike PASM that constantly makes real-time adjustments based on load and driver input, yourM5 is stiff all the time. You could be cruising straight down the road, its stiff as always and giving you that feeling. All the time. Your 991 on the other hand, if you're just cruising along it lets the shocks soften up appropriate to speed and road surface. I'm guessing that new asphalt was pretty darn smooth. So you're feeling, at that precise moment, your suspension being about as soft as Porsche has deemed appropriate for the speed you're at. This to you, being used to single-setting firm response, well it doesn't surprise me you think of it as floaty. Especially combined with everything else.

The beauty of PASM is that it gives you this comfy ride whenever you don't really need it to be racer-responsive, and yet at the same time it is always ready and gives you as crisp a response as you need the instant you need it. (Even in Sport there is enough overlap that the softest Sport ride is nearly as compliant as the normal PASM setting and will feel softer than the ride of a non-PASM 991, that's how much latitude it gives you.) This can be a little disconcerting to one used to the old single-setting feeling, but you will quickly get used to it. By the time you get 500-1000 miles on it, the tires settled in and you're more used to PASM you will no doubt find yourself one day doing 140 and wondering how it suddenly became far more stable than your M5...

Oh, and Thank God you're not doing that "just the tip" break-in BS!

meine911

Keep us posted. I've only hit 120 so far and it was glued to the pavement.

lbahoshy

It might be that you're just not used to how a 911 feels. Certainly the weight distribution is totally different than an M5.

My first test drive in a 911 (997) I had a similar sensation of the very light front end and it may also be described as the car feeling "floaty" at the front and I was used to driving a Boxster at the time.

I wonder if it's just that; you're perception of "floatiness" because of the much lighter front end. The grip is there, but the car is a lightweight compared to the tank like M5. Just something to consider. This feeling will certainly go away as you get used to the car.

I'm also curious where you can do 140 mph in New York? I've done that in my old Boxster S but I was younger then. If I do that now and get caught by the cops, it's bye bye license for a while and car gets impounded for a week.

chuck911

How much road do you need to do 140? Quarter mile rolling? Half mile standing?