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  #1  
Old 16th April 2010
fisherman fisherman is offline
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Default Car unstable with new tires!

Hi,
I have a 2004 93 Aero.
I recently changed my Michelin Pilot Primacy tires for Bridgestone Potenza RE050A. Front and rear.
Although these tires are more comfortable, less noisier and gripier than the Primacy’s the car is unstable at high speed with an edgy/loose behavior.

Where I previously could drive at very high speeds I just don’t dare it now. It just don’t gives me confidence.
The car just doesn’t feel planted and super stable as before. And the steering feels lighter too.

The Potenza’s allegedly are better than the Primacy’s. Well, in every other aspect they are, except on this one.

I just don’t know what to do. I already change the fronts to the rear and vice-versa, calibrate and aligned the wheels two times, checked tire pressure, my Saab dealer checked and rechecked the suspension, arms, shocks… everything. Next step is to fit another set of tires.

This is frustrating!
Does this happened to any of you?
I appreciate to hear your thoughts.

Thanks in advance.
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  #2  
Old 16th April 2010
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brock1 brock1 is offline
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Quote:
Originally Posted by fisherman View Post
Hi,
I have a 2004 93 Aero.
I recently changed my Michelin Pilot Primacy tires for Bridgestone Potenza RE050A. Front and rear.
Although these tires are more comfortable, less noisier and gripier than the Primacy’s the car is unstable at high speed with an edgy/loose behavior.

Where I previously could drive at very high speeds I just don’t dare it now. It just don’t gives me confidence.
The car just doesn’t feel planted and super stable as before. And the steering feels lighter too.

The Potenza’s allegedly are better than the Primacy’s. Well, in every other aspect they are, except on this one.

I just don’t know what to do. I already change the fronts to the rear and vice-versa, calibrate and aligned the wheels two times, checked tire pressure, my Saab dealer checked and rechecked the suspension, arms, shocks… everything. Next step is to fit another set of tires.

This is frustrating!
Does this happened to any of you?
I appreciate to hear your thoughts.

Thanks in advance.
I too had the same problem with some continental tires and wish I had just gone back to the OEM tire (pirelli). The continentals have gotten better with time but, the pirelli's gave me alot more confidence (just very noisy). Good luck. If you can somehow go back to the old tire, I would recommend it as I wish I had!!
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  #3  
Old 16th April 2010
fisherman fisherman is offline
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Thanks brock1,
At first I though I was getting insane, but then the dealer felt it to. And now you.
I tried to get back my old tires (they still have some life in them) from the tire shop but it was too late.
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  #4  
Old 16th April 2010
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Have you experimented with the tire pressure? I'm not sure which direction to go, but maybe going to the other end of the range might help, and costs nothing to try.
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  #5  
Old 16th April 2010
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It is not unusual to notice a softer, lighter feel after installing new tires. The reason for this is the thickness of the tread on the new tires compared to the old, worn tires. New tires have more rubber and therefore will flex and give more than the thin rubber of the old tire.

The Potenza is a very grippy tire with a relatively low tread life, this means the rubber is softer than many other all season tires. Give the tire time to break in and wear a bit. We recommend to clients that they don't leave the shop and go crazy on new tires before having some time to break in and remove any residual oils from the factory.
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  #6  
Old 16th April 2010
fisherman fisherman is offline
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To JMarkert. I usually set the maximum tire pressure recomended, but I already experimented a couple different tire pressures. It realy don´t change much.

To BadBrains. I understand what you're saying.
As we speak the tires have aprox. 2000km on them. When you say "time to break in and wear a bit", are 2k km enough to the tire to "settle"?

Thanks to all.
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  #7  
Old 16th April 2010
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I replaced my Pirelli P6 OEM tires with BFGoodrich SuperSport (Yokohama ADVAN's were my second choice) tires last July. New tires seem to handle alot better that those P6s but they are noisier by quite a margin. I was thinking about replacing them with Potenzas when the time comes. Id be interested in hearing what is causing your issues.

zippy
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  #8  
Old 17th April 2010
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just a couple of thoughts. Have you looked at the tires being unbalanced? Typically unbalanced tires will sound bad at higher speeds. This happened to my fiancées car. I had a pain rotating her tires on her toyota and inadvertently unbalanced her tires.

Second thought, unlikely though, but could they have wrapped a rim? That would cause it too.
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  #9  
Old 17th April 2010
fisherman fisherman is offline
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Hi zippyluvssaab. A friend of mine runs Pirelli Pzero in his 2003 Aero (I think it was the OEM tire at the time). They're not as grippy as the Potenza's but they're stable at high speed.

Bear in mind that my problem with the Potenza's only arises at high speeds.
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  #10  
Old 17th April 2010
fisherman fisherman is offline
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Quote:
Originally Posted by furgs View Post
just a couple of thoughts. Have you looked at the tires being unbalanced? Typically unbalanced tires will sound bad at higher speeds. This happened to my fiancées car. I had a pain rotating her tires on her toyota and inadvertently unbalanced her tires.

Second thought, unlikely though, but could they have wrapped a rim? That would cause it too.
Do you mean wheels/tires unbalanced? Where you attach weight to the rim? Yes, twice .
The rims were checked too, they're ok..

Thanks
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  #11  
Old 17th April 2010
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I adjusted my tire pressure from 40 psi to 35 front and 32 rear and they are a little more stable like this. My saab mechanic (dealer) that has worked on my car from day one always told me to run 40 in the pirelli's, which is why i ran 40 in the continentals.
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  #12  
Old 17th April 2010
shaker-93 shaker-93 is offline
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I'm assuming your new tires are the exact same size too right??

I bought a set of Potenza RE760's and they are great - very grippy and quiet. The car feels a lot more solid with these on (at high speeds) than my winters anyways
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  #13  
Old 17th April 2010
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Experienced that problem when I went from stock size tires to a 235/40 17. Went back to original size and changed to michelin a/s plus. Love this tire. Quiet and stable and in the rain they're confidence inspiring, no hydroplaning at all. Best tire I've had thus far.
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  #14  
Old 17th April 2010
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Have you checked the load rating on the tire compared to Saab's recommended load rating?

When I was looking to replace tires on my 2005 Aero, 225 45/17 I noticed many of them were not rated 94 or above as recommended in my owner's manual. A lower load rating may mean a weaker sidewall which may tend to flex more at higher speeds.

I recently had a flat on my 2004 Aero, 225 45/17, and the tire store replaced it with a 90 load rated tire, I could feel the squirm on the first corner. I am currently waiting for them to get in a 94 load rated tire to switch out.
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Old 17th April 2010
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Quote:
Originally Posted by fisherman View Post
To JMarkert. I usually set the maximum tire pressure recomended, but I already experimented a couple different tire pressures. It realy don´t change much.

To BadBrains. I understand what you're saying.
As we speak the tires have aprox. 2000km on them. When you say "time to break in and wear a bit", are 2k km enough to the tire to "settle"?

Thanks to all.
I would think that 2000km would be enough for the tire to 'settle' and break in. I suppose it is possible that this model of tire just doesn't agree with your vehicle.

I have seen the same type of thing with a 2009 Lexus IS250 AWD and BF Goodrich tires. The car pulled and wandered even after we aligned it twice. The client was never comfortable with the tires and ended up buying a new set of Michelins - problem solved. It is rare, but it happens.
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Old 17th April 2010
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Quote:
Originally Posted by DPSCOTT View Post
Have you checked the load rating on the tire compared to Saab's recommended load rating?

When I was looking to replace tires on my 2005 Aero, 225 45/17 I noticed many of them were not rated 94 or above as recommended in my owner's manual. A lower load rating may mean a weaker sidewall which may tend to flex more at higher speeds.

I recently had a flat on my 2004 Aero, 225 45/17, and the tire store replaced it with a 90 load rated tire, I could feel the squirm on the first corner. I am currently waiting for them to get in a 94 load rated tire to switch out.
Very good point. Load rating is often overlooked.
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  #17  
Old 17th April 2010
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Very good point on the load rating......Something I had not even considered. Thanks. You gotta love this site---Always something to learn.
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  #18  
Old 18th April 2010
fisherman fisherman is offline
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Quote:
Originally Posted by DPSCOTT View Post
Have you checked the load rating on the tire compared to Saab's recommended load rating?

When I was looking to replace tires on my 2005 Aero, 225 45/17 I noticed many of them were not rated 94 or above as recommended in my owner's manual. A lower load rating may mean a weaker sidewall which may tend to flex more at higher speeds.

I recently had a flat on my 2004 Aero, 225 45/17, and the tire store replaced it with a 90 load rated tire, I could feel the squirm on the first corner. I am currently waiting for them to get in a 94 load rated tire to switch out.
The load rating is 94 front and 91 at the back.
I couldn't find all 4 tires with 94 rating.
All have Y speed rating.
Already put 91 front and 94 back. No difference at all.
My Saab dealer says they have some cars running with 91 without problems.


Thanks.
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  #19  
Old 16th May 2010
fisherman fisherman is offline
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Default Update

Some update on this.

My dealer was kind enough to lend me a set of 4 tires.
Now I have a set of Pilot Sports at front and Potenzas at the rear.
The car handles great and is rock solid at high speeds.

Everything points to a faulty tire. Now I need to pinpoint the culprit.
I'll keep you posted.
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  #20  
Old 16th May 2010
TunnanXWD TunnanXWD is offline
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For lack of true technical jargon, but to get the idea across ..

How is the "break" in the edge of the tires .. would the corner/edge of one tire be a bit more rounded than a hard edge or " square" .. ??

One car I had came with Goodyear Eagle run flats ... high performance tires that had a very squirmy or skittish feel. Like when you watch the F-1 drivers warm the tires and they go side to side.

Changed on the advice of a few other owners and got Kumho's with a bit more rounded edge and I can finally relax and drive the car. You could argue that I gave a bit up when it came to the high speed stuff ... but there is a point that it's academic.

I'll try to keep that in mind at speeds over 150.
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