joecitizennn

I just switched from 16s to 17s on a 951 of mine and it corners worse. The tires that came off were bridgestone potenza zr rated on phone dials, 225 50 16 and 205 55 16. The tires that went on were hankook ventus vr4 zr rated in 255 40 17 and 215 45 17. In fact the problem is bad enough the car is a little unsettling to drive. I have not had this problem before, i have 5 944 type porsches currently running a mix of bridgestone, yoko, mastercraft, nexen and even one with kelly springfield on 15 through 18" rims. They all behave the same, you go into a corned at speed and the rear of the car tilts slightly to a hunched position and sits there like a rock till you are out of the curve, but this 951 on 17" boxter rims with hankook is downright scary in a curve. First the *** wiggles around at the slightest movement of the steering wheel, it feels like it wants to walk all over the road. Second, when you enter a curve you cant find that confortable solid spot, the car just seems to want to keep leaning more and more and if you dont hold the wheel rock steady the car seems to want to wobble... like driving a stinking pontiac or something. I have tried various tire pressures between 35 and 45 psi all with the same general results. With the bridgestone tires that were on the car I had no hesitation at plowing through curves at full throttle with the tires singing, so I dont feel that the car is at fault. Any thoughts on why this is happening?

zerMATT951

I looked at Ventus V4's but settled on Ventus V12's because V4's are a all-season high-mileage tire that seemed to sacrifice handling based on Tire Rack reviews. I haven't driven on either, but the V12's are being installed on Friday. This will be my first try with Hankook's, but I know a couple other local V12 users who have been really happy with them.

bonus12

Are the wheels balanced? Have the tires been used for at least 500 miles?

daveo90s4

Since you have 5 944's why not swap these wheels for those on a car that handles fine and see if the problem stays with this 951 or migrates with the tyres and wheels?

joecitizennn

As I stated the car does really good on the potenzas. It is a solid car in the corners. I may put these rims and tires on my 89 and see if it corners poorly.

The tires are balanced and have 250 miles on them.

Van

Did you do anything else? Sounds like your toe-in might be off.

racerxrick

hmm...Ventus V12's here and very predictable

schip43

+1 check the camber and toe settings!

zerMATT951

Got my V12's mounted today, they feel good so far, but I think they may need a little more air for my taste. I'll break them in a bit over the next couple of days in prep for a fun run on Sunday with Rick (and hopefully some others)... but there is a good chance of rain in in the direction we are headed, so there may be a change of plans. Will let you know how I like the 17" V12's after the weekend .

racerxrick

lowered from 40% to 30%

ZR8ED

Well differing tire brands/compounds aside as they are near impossible to compare unless they are on the same car in the same rim/tire size combo, in the same driving conditions. Is it getting colder where you are? Some tires just don't cut it in the cold. I recall a set of A008 Yokohamas. Great in the summer, and total hockey pucks in the fall.

Changing the tire size (16's to 17's) affect your car as much as changing your spring/shock etc suspension setup, as well as changing your unsprung weight (they are now likely heavier). You may need to deal with some suspension setup changes to dial in this new tire/wheel package.

Good luck, and be careful!

pnbell

Sounds like your Rear Shocks might be failing... Push on the rear bumper and compare the resistance to the front.

Also your 21545R17 are slightly smaller than your 25540R17 both in Total Circumference and Sidewall height; 22545R17 would have been a better matched size.... However i don't think this would make a huge handling difference on a street car.

My advise is 'Check your rear Shocks '

racerxrick

I was just wondering the same thing...for instance the 18" rim/tire combo I chose matches the the height of a stock "S" wheel/tire combo.

joecitizennn

These rims and tires are not going to be on the car for long, I have a set of 993 turbo twists in 18" that are painted alpine white to match the car that will be running 285 30 18 and 225 40 18 tires. I just need the tires. I know my shocks are pretty newish and the car feels stiff on all corners, so the 18s will be an interesting test.

joecitizennn

The following is a quote from 1010 tire reviews that i found interesting. There were several others like it.

Tires are being replaced in the near future. Tires are dangerous. If driving on a grooved road. Causes the car to follow the grooves. The car will wag from left to right. If not careful, end up in other lane. Not impressed. Noisy on the road