New Rear Tires= Scary Handling

[ben parrish]

My rear tires were getting pretty thin so I went on the search for a less expensive alternative. I've ran Bridgestone Potenzas' for the last ten years on this car but I needed to save a few pennies and thought I would try something different.
I've had great luck for the past few years with Hancook tires on my wifes car and the Jetta so I decided to try them on the 911. I went with the Ventus V12 K110....had great reviews....as good or better than the Bridgestone's
I still have the Potenza RE750's on the front.
The handling is very unstable; it feels like the rear end is swaying..like the sidewall is flexing a LOT. I have never been so unnerved driving this car. Braking in a curve caused a big "pucker" moment.
Could this simply be because the tires are mismatched or have I made a big mistake switching brands? I have read that you shouldn't mix different tread patterns on the same car. Could this be causing a perfectly planted car to go squirrely on me?

[Vandit]

How many miles do you have on the tires? New tires are usually greasy for the first few hundred miles.

[Jack Olsen]

Did you check the pressures of the rears relative to the fronts?

Some new tires have a layer of molding compound that has to be scrubbed off.

[crustychief]

Originally Posted by Jack Olsen

Did you check the pressures of the rears relative to the fronts?

Some new tires have a layer of molding compound that has to be scrubbed off.

+1. Especially noticeable on a motorcycle!

[ben parrish]

I put about 50 miles on them yesterday. Seriously, the handling is scary....I have never experienced anything like it. I didn't verify the pressures (stupid) but this shop has done a lot of tire work for me without ever missing a beat. I had to break in a curve yesterday and it scared the crap out of me. It felt like the rear wanted to break loose...this has never happend in all the years I've owned this car...13 and counting.

[brads911sc]

FWIW... I ran Potenza's for years and they are a very stiff tire compared to many... even the P-Zeros I run now feel softer... So it might be that your new tire is significantly softer with more flex... +1 on running them a few hundred miles. maybe take a nice 3-4 hour road trip with some higher speeds... break them in good before making a decision...

[rusnak]

Just for giggles, check the speed rating and see if they match front to rear.

And push your knee against the rear bumper sideways while looking at the rear wheel. See if the rim moves relative to the fender or body. If the rim is moving, then that is what is causing the squirelly handling.

[911Jarle]

Originally Posted by ben parrish

My rear tires were getting pretty thin so I went on the search for a less expensive alternative. I've ran Bridgestone Potenzas' for the last ten years on this car but I needed to save a few pennies and thought I would try something different.
I've had great luck for the past few years with Hancook tires on my wifes car and the Jetta so I decided to try them on the 911. I went with the Ventus V12 K110....had great reviews....as good or better than the Bridgestone's
I still have the Potenza RE750's on the front.
The handling is very unstable; it feels like the rear end is swaying..like the sidewall is flexing a LOT. I have never been so unnerved driving this car. Braking in a curve caused a big "pucker" moment.
Could this simply be because the tires are mismatched or have I made a big mistake switching brands? I have read that you shouldn't mix different tread patterns on the same car. Could this be causing a perfectly planted car to go squirrely on me?

I used these tires on my BMW 850, and they where fantastic.
I've never tried them on my Porsche, but on my 850 they where far better than the prior Toyo tires.

I'm inclined to believe that your front and rear tires are missmatched. Also, check pressure like mentioned.

Cheers, Jarle

[jason2guy]

i tried the same thing and that happened to me as well. and the new ones were the same brand and model. everything was back to normal as soon as i got new front tires

[trond]

Intersting discussion. I am struggling to understand why my 1980 SC handles to poorly. It really gets out of shape in fast bumpy corners when the tires are squealing, and when braking in corners (which I mostly don't do at speed anyway). It really is unsettling. It is the first car I've had ever with such nasty behaviour on the limit. I have new Bilstein HDs and new Michelin Pilots front and rear. I believe the problem is in the front which is not settled at all.

Maybe I need to try different tires and see what that does as this thread suggest...

[85 911C]

I had the exact same problem as you described, so I took my car over to Jeff Gamroth at Rothsport Racing (Portland, Oregon) as I was upgrading my suspension at the time. I told them the issue I was having and it was because of the mismatch tires. After matching all the tires up the problem went away immediately. (Note this was before anything was done to the suspension.)

I will tell you I will never make that mistake again as the car felt outright scary to drive especially at speed.

[DanielDudley]

Mismatched tires.

[GH85Carrera]

I recently put a new set of Toyo Proxies on my car. The first 100 miles was scary. It was like driving a mid 1970s Lincoln Continental. I could move the steering wheel a lot and nothing would happen for a long time. It was a very greasy feeling. Now I have 2,000 miles on the tires it is getting better.

[Jim Richards]

did you get an alignment when you had your tires replaced?

[Wavey]

Originally Posted by GH85Carrera

I recently put a new set of Toyo Proxies on my car. The first 100 miles was scary. It was like driving a mid 1970s Lincoln Continental. I could move the steering wheel a lot and nothing would happen for a long time. It was a very greasy feeling. Now I have 2,000 miles on the tires it is getting better.

Ditto, same here. Same tires, but the first DE did a good job of breaking them in.

Ben, I'd confirm that they are mounted correctly (they're directional), the pressures are correct, then give them 500 miles or so. But if they don't match the fronts, they'll never be right. These cars seem to be very sensitive to that.

[naparsei]

Check the pressures first, and possibly bump up the rears for a quick test drive. Obviously if you can't resolve it quickly, I would match the tires.

[mikesride]

I had a very reputable shop put my directionals back on the wrong side once! Wow even going in a straight line over 80mph it was scarey!!!

[Zeke]

Where does this braking in the corner come from? I thought we knew better.

[89911]

I'd say you just have tire squirm from new tires. The first 100 miles or so, the handling it going to be unpredictable from the compounds on the tire. Combine this with treads that are brand new and most likely double the depth of your front one and you will get some unpredictable behavior. Some tires are better then others but generally you will never get a high performance tire with a treadwear rating much above 200. You can't have increased performance with big thick treads. This is why they shave the track tires to begin with. You will notice the performance gets better as you wear them out.

[Steve@Rennsport]

Hi Ben,

This has been an issue on these cars for a very long time. The "Cardinal Rule" for 911's has been to replace all four tires at the same time, even though the fronts may have some time left on them.

You did two things: mixed tires of different brands and contruction as well as rear tires only.

I'd suggest replacing the fronts to match your new rears to aleviate your handling issue.