Henry964

I really have not had the chance to drive my 964 real hard (only around 120 miles/h in the highway) but I have the feeling at that speed as if the tail has a very small left-right movement (more of a sensation that a real thing)
Is this normal in a C2? could this be a tyre pressure/brand issue?

Heirsh

When my tires are in good condition with the proper air, my tail is planted firm and feels solid. In turns pushed hard it has more of a tendency to push than slide (of course you can change that with throttle).

Just my .005

Bull

No, it is not normal. Is the car stock or modified? I would have the alignment checked first.

Henry964

Thank you both for your answers

The car is stock with 17 wheels, except for bilstein shocks all around
I have different brand tyres: 2 new yokohama´s Advan in the rear and 2 used Kumho´s in the front (saving money to buy 2 new yokos for the front)
Also because of a wheel leak (that has been recently repaired) I have 4 lbs more pressure in the rear till I am sure the wheel repair is good (36 f 40 R)

I´m gonna check the alignment

F2 Iceland

Does your spoiler go up????

I've unplugged my spoiler the otherday and tested the car to feel the diffengre,,,, i was suprised how much the little spoiler does on the car,,,

The car was dancing in the back when i was around 160km/h

Henry964

Yes the spoiler goes up

joey bagadonuts

Henry,

Did you notice this movement when decelerating? If you have different grip levels at the rear, you'll notice some yaw (twitching) if you lift off the throttle somewhat abruptly at high revs. If so, then it might simply be caused by an air pressure difference.

If the movement had nothing to do with deceleration, then it's more likely an alignment issue.

Bull

I would eliminate the mis-matched tires and wheel leak ASAP, both to take them out of the picture for this question and to avoid other bad things from happening.

boxsey911

+1

I know good tyres don't come cheap but Henry, you are seriously tempting fate with those tyres on a high performance sports car.

LouZ

++1 on tire brand matching

Also, on 17's, the pressure should be the same all around.

C4Russ

Are you saying you have: an air leak and mis-matched tires with some worn used tires up front yet still drive the car at triple digit speeds?

First, start with a reality check. The car has enough HP to drive it to speed quickly but any suspension deficiency is going to make the car unpredictable at speed. Despite the car's capabilities, Porsche has not yet learned to defy the rules of physics.

Get the car sorted, first. Not by trial and error but with work done on the right parts. Make sure you know it's right before you start doing things like this.

demonfish

I bought my 964, drove it home from sheffield (120 miles) parked it up.

four weeks later, took it out, straight to the ring.

I lapped on Kuhmo Tyres - the previous owner had fitted them, 3k miles on them, so very new.

It was hilarious.

Ice Skating anyone?

Seriously though, cheap tyres are a no no. Your safer closing your eyes and counting to twenty. I know sometimes budget is an issue, if it is, park it up and leave it alone.

I have the same problem, I desperately need an alignment, i also have R888's on, I really want to take the car out. its been 2 months now. but i'd rather wait than die...

On another point, when i had my tyres fitted i ran them at 32psi. when i had a geo baseline he inflated to 36psi, and the difference on the way home was VERY noticable. So i wouldn't be suprised if 40psi is making a very big difference too...

As the others said, eliminate what you can, then alignment.

Stewart H

Kuhmos on a Porsche? I know the US has a huge reputation for being litigious but doesn't culpability come into it somewhere? Porsche AG have a list of recommended tyres and all have a "N" rating to say they have been approved by Porsche. Insurance companies in the UK have been known to refuse claims because of having non "N" rated tyres fitted at the time of the incident. You've got to be completely mad to risk driving a 160 + mph car on tyres not approved by the manufacturer. For the sake of a few hundred £/$ it beggers belief.

I hate to say it but if you can't afford to run your car safely (and I'm not suggesting that this aplies to anybody here) you're not only being a danger to youself.

LouZ

Wow, that explains "1776" Here in the U.S., Kuhmos are one of the most widely used tires on P-cars. (Even though I don't use them...nor any "N" rated tire)

C4Russ

The car can do 160 MPH. I don't however let my ego write checks I can't cash. These cars cannot be driven at their limits on public roads, period. The need for N-rated tires has more to do with manufacturer liabilities and lawyers then with reality. I don't need a tire that can withstand 168 MPH for 24 hours. The few times I see triple digit speeds we are talking seconds, not hours.

Even the guys who track their cars only see triple digit speeds on a few sections of the track. I'd bet the more tame classes may not even see triple digits on every course. The faster cars are also running track tires, not street tires.

I, for one, will continue to run Kumho ECSTA MX's on my Porsche. They are fine for the driving I do and I'll toss a tire that has a worn spot or thump without hesitation. I see plenty of people complain about tire life on their MPSC or other high end tire, I don't care if I only run the Kumho's 1 season. $104...pffft. No big deal.

I'd also wager that most of us can't articulate a difference between the Michelin and the Kumho at street speeds. I have a set of Michelin Pilot Primacys on my C230. They are fine but I'll likely not spend the money on another daily driver. The Kumho's are half the price and perfectly safe for street driving.