August West

So I finally replaced my rear Bridgestone Potenza S-02 tires that were like 8 years old or so (it was my Dad's car) with new Bridgestone RE 970 AS Pole Positions and noticed immediately that the rear end wallows like a Cadillac now. I'm exaggerating but still, I had to pull over just to make sure my tires still had air in them!

Granted the old S-02s were worn to where the belts were gonna get exposed any day now but still I was really surprised by how much the rear end swings now just from the sidewall deflection and tread deflection of the new tires.

Oh, and the only reason I went with the 970s was because I had Bridgestone RE 960 AS Pole Positions on the front and thought I should keep the tires in the same family.

I've since gotten used to the wallow and figure that's what the pendulum effect is like on Porsches but I'm definitely thinking about upgrading to 17 inch rims, lower profile tires and maybe even the 21mm rear sway bar that's recommended for the C4.
I currently have H&R Purps (formerly called Greens) on the car now.

Am I overthinking this? Did I screw the pooch and put the wrong tires on my 964?

Lemass Automotive

I had the exact same issue.
Put new nexan 6000's on the rear. Had 3000's all round previously.
The back end is now all over the shop (C4)
Was going to try another set of wheels with contis for comparison.
Seems its definatly the tyres as everything else seems fine.

Lemass Automotive

Put the new tyres on just over two weeks ago and it's still doing it. Seems to happen at over 60mph first noticed it at over 100 which was a bit clenching

crg53

My first thought is the rolling diameter of your new rear tires compared to your used front tires, if they are not within a certain % (C4), your handling will be off.

Lemass Automotive

Just read this after searching google





seriously exdos is correct its the mould oil and the gear they spray on to stop the rubber going off in storage
this causes major headaches on bikes as you can imagine i normally run the heat torch/burning gear over very lightly this lifts the oil out

or lay some big 11`s up the street

-nick

I would bet on one of two problems-

What pressures are you running?

What sizes are you running?

There shouldn't be any wallow even 100% stock. And new tires can be a little slippery, but sidewall and tread squirm won't ever change. Forget the swaybar, that's fine tuning.

All this said- if you're on original 23 year old shocks, then they absolutely need replaced.

August West

Well, I'm running 44 psi in back and 36 psi up front. I don't think I've got original shocks but even so, with the old S-02s just a few days ago, I could shimmy the steering wheel at 65 mph on the freeway and the car would feel like a go-kart...tight and ready for some slaloming with not much rear-end pendulum swing. With the new tires it's a little disconcerting how the back end moves around so much more.

Bad shocks would have been noticeable with the old S-02s. I just put the H & R Purps on last year and the shocks were deemed good enough not to replace at that time.

The Bridgestones up front are only two seasons old and the tread looks new so I don't think it's a matter of rolling circumference differences between front and back.

I'm running what I presumed to be stock tire sizes. I've got 205/55/R16 91W up front and 225/50/R16 92W on back.

I've since gotten a bit used to it and have figured it into my weight-transfer considerations when setting up for corners. I took the car out a couple of days ago on one of the classic roads around here and gave her a good thrashing and soon felt dialed into the new dynamic.

rstarga

Try 36 front and rear.

Vandit

With the old Pilot Sport PS2s that are currently on my car, the rear becomes a sliding hot mess (at autocross) when the rears start going into the upper 30s. I've got a BFG g-Force Rival set that should be going on in the coming weeks. It'll be interesting if they transform the car.

August West

Seems like if I lower the rear tire pressure from 44 psi to 36 psi, I'll get even more sidewall deflection. I was thinking it'd be a good reason to go to 17 inch rims with lower profile tires to reduce the swinging effect.

This reminds me of Hunter Thompson trying to get his Cadillac El Dorado to handle better by putting 100 psi in the tires...said it handled great after that.

Vandit

I just took a quick glance at tire descriptions for your old tires versus your new tires and, at least per Tirerack's classifications, you took a step down going from a Max Performance category tire to a Ultra High performance category tire. Just looking at the tread pattern, your new tire does look quite a bit more pedestrian than the Potenza S-02. Perhaps this also translates into less stiffness of the sidewall construction.

PV=nRT

August West- I learned about this issue the hard way. I put much better performance tires on my Porsche and immediately noted handling and my ability to precisely control the car degraded. Long story short, nothing wrong with the tires. The better tires simply allowed an existing problem to be more noticeable. In my case that was defective frame welds that had started to crack, within a month they failed completely and my 2012 Porsche broke in two without being wreck. I just had my shoulder reconstructed two days ago to repair it from the injury the defective welds caused.

My stamina is low from the surgery so I can't find the Tire Rack reference that addresses pre-existing problems showing up when better performing tires are put on. Try and find it, it's very helpful. It your still interested in a few days PM me and I'll try to locate it for you.

August West

Brother lay your weary bones! You bring up a good point and I'm gonna take a look underneath tomorrow and have my mechanic look things over next week.

Speedy recovery...

Vandit - you make an excellent point too. The S-02s did seem more like track tires and my current Bridgestones so seem more pedestrian.

I'll see how it goes...I'm so close to pulling the trigger on some 17 inch Zuffenhaus Fuchs Replicas and by doing so I'll mitigate this issue and look great doing it...

evanscott964

Hi guys the tyres that you are having issues with are they N rated? I fitted a set of Falken FK452's on the rear of my winter wheels and took the car out a couple of times and the car was downright dangerous!! Refitted my track wheels and the car was perfect, so I replaced the Falken's with Michelin PS2's and the car was perfect. The construction of a tyre for porsche is a lot different to cope with the weight issue. Hope this helps!!

Lemass Automotive

mine are 265/35/zr18 97Y
says good for 730 kg's per tyre and 186mph ?