I've read through some previous threads on this, and just went through my own little episode, so thought I'd post my experience and some of the knowledge gained:

I had some new wheels installed on my car last week. Since the rears were gone but fronts still OK, I decided to just put some Hankook V12s on the rear and leave the PZs on the front, and then replace all 4 the next time tires were needed.

So after getting the car back, it took about a 1/2 mile to figure out something was wrong. At first I was worried the center lock nuts weren't torqued enough, but then realized I would feel the wheels shaking violently. It then occurred to me that the new rear tires were the cause.

When I got home I noticed that the tire pressure across the corners was 5-7 lbs high, and I thought (hoped) that might be the problem, so I brought them all back to 'normal' pressure. WRONG...that made it WORSE. More to come on that in a bit.

This morning I was driving on one of the Dallas highways and got to the big left hand turn that's a slight double-radius turn that catches many people off-guard and requires some constant steering input, usually at 70mph+. I swore my car was going to hit a wall. The initial steering input gave me quick response, but then there was a 1/2 second lag when the rear end would start it's weight shift, which led to oversteer, and my car almost facing the wall. It took fair amount of small corrections back and forth to get my car where it felt stable, because this motion caused a rather strong oscillation of movement from left to right.

So that episode led me straight to Boardwalk, and I mean STRAIGHT there.

After talking to John Gladwell (Service Tech extraordinaire), several things became quite clear:

1) The Hankook V12 has a MUCH softer sidewall that the Pirelli's, or other factory tire. It just doesn't take the weight shifts very well. He said that tire is decent for people that are looking for a softer, cruising ride and works ok with 996s due to the reduced power in those cars.
2) The P-Zeros up front have much better grip, so steering input through the front PZ would be sharper than the Hankooks can handle. Given the Hankooks weaker grip & sidewall, they would just amplify the difference in grip and the rear would be relatively 'floaty'. This is one of the most basic reasons as to why the front/rear tires should match: equal grip/sidewall limits.
3) After getting my car back with the new wheels, I noticed the air pressure was 7-8lbs high all around, with the TPMS readout verifying. So, I brought everything back to 'normal' when I reduced the air pressure. It turns out that reducing air pressure makes it worse because that change basically makes the sidewalls that much 'softer'. He said it really doesn't affect the contact patch at all, and has negative impacts on tire wear.
4) I knew my Panamera had 2 TPMS settings for Loads (Full/Half), but didn't realize the 997 also had this. When we changed the TPMS settings in the computer to Full, it now showed my tires as 5-7 lbs LOW. Basically, these two settings affect the warning systems in the car to tell you when to add air. By adding air pressure to the tires, it will 'strengthen' the sidewall for this need.

Next Step: Michelin Pilot Super Sports going on tomorrow/saturday on all 4 corners (as soon as BW receives them). I considered just putting 2 more PZs on the rears, but closer inspection of the fronts told us that they really only have a few 1000 miles left on them, and the PZs are known to degrade quickly when they get close to the end. The MPSS has a better tread wear rating, better grip, makes less road noise and maintains it's tread better over the last 1/4 of tread use than the PZ (per John).

Lessons Learned:
1) The Hankook V12 isn't a bad tire across the board, but not the best for this application (305/30). Of course, Any 305/30 (or similar size) is going to be on a sports car, so not sure why such a size is manufactured if it's not quite appropriate for similar applications.
2) Do NOT mix tire types from front to rear due to the relative difference in grip/sidewall strength. After discussing it with John and thinking it through, the simple logic makes a ton of sense.
3) The higher end of recommended tire pressure will not have negative impact on daily (spirited) driving, but will help reduce tread wear.

 

thx for sharing.

i also had a similar experience and documented it.

https://www.6speedonline.com/forums/...x-ps2-v12.html

its a scary feeling when ur sports car is floating around the turn..

let us know how much u love the MPSS

yes, there are many members who like their Hankook v12s and never had problems.. but the floaty feeling is real (& dangerous..) and usually it seems to be related to mixing other tires with Hankook tires.

BTW, others will suggest a break-in period.. but i did not even want to drive my car the way it was for another mile.. too unstable and dangerous even at grandma speed. lol. so i sold the rear for $100 each (like brand new) and changed it to PS2.. and never looked back.

 

thanks for this information. I was wondering about going from Bridgestone's to Michellin Pilots.

 

Yep, your thread was one of my reference points and good information to start from. Since my car is pretty much a city DD and not tracked, I didn't think it would be a great affect on my drive...but I was found to be wrong.

And I was like you: maybe a break-in period would help, but this setup is just too dangerous to take out on high-speed, busy highways with as many tight turns as we have around here.

 

Thanks for sharing......This could save lives......

 

Good info, thanks.

 

This seems to occur when mixing with Hancooks, also the break-in for hancooks is rated between 500-1000 miles. Every thread I've ever read about going from XYZ tire to Hancook has resulted in similar experience, even more so with mix-match.

I'm in the same boat as you, PZ in the front, but I put Conti DW's in the rear. Didn't experience anything you're describing, just a lot more grip in the rear. Car felt great, since my fronts are still close to 60%, I bought a set of front tires (Conti's) and just have them sitting in the garage. I'll toss them on when I need another set of rears.

Search the forum, you'll find lots of info about the Hankcook, great for city/highway driving and maybe a light spirited burst, but not a high performance tire.

 

No, it happens anytime different compounds are used. You NEVER mix tires. There isn't any manufacturer or tire engineer who would ever suggest otherwise.

 

The same thing happened to me when I put a new set of Hankook's on the rear with the SAME Hankook's on the front (they looked almost new). My PSM would kick in on turns and my back end would break loose. Several trips to the Dealer later and about 1K miles the tires settled in and everything was fine.......MPSS for me going forward!

 

Just did a search on this issue, I wish I had done so before I bought those damn Hankooks! I also live in the Dallas area, just got back from Boardwalk, and John actually brought up your car OP, I had the exact same issue you did on my 996T.

We went and put the front camber to -1.2 and that helped it immensely, but you can still tell the rear is "lagging" the front. I've only had these tires for a couple days and I already hate them.