I have put brand new Sport Cups on the rear of my car with an end result being fishtailing under accelleration at speeds above 125 MPH. The tires were, of course, aligned and balanced by a qualified shop as were the front PS2's.

I run 345/30R19 and 275/35R18. This is something new to my car. I have played with my Pfadt CO settings, tire pressures (have been increased all the way up to 35-36 hot).

I have tried any tires in the past including OEM, INVO's, and NT05's. The combo I now have provide a very smooth ride (The best its ever been).

The problem is fish tailing while under acceleration at the track (straight-aways) at 125 MPH ++++.

I will bring the car back to be realigned and balanced. Any other ideas??
I am at my witts end. The combo handles very well around corners and traction is excellent.

The car is a 2008 Z06 with 700 RWHP and 625 FT#.

Also have Pfadt sways.

HELP!!!!!!!

 

Were you putting down 700 with the other tires?

It might be time for some sort of rear spoiler to push the rear down (reduce the amount of lift) at those speeds.

See what LG has to offer.

 

Good idea but I have the GM performance full length spoiler. I assume this would suffice?

 

I think that's mostly for show

 

What front tires? Mis-match front/rear can cause instability. That would be the first thing I'd check.

Too stiff of a rear sway bar or shock/spring setting can cause the rear end to be loose as well. Adding a rear wing without front aero to make up for it (more than a 'street' splitter) will fix the loose condition but will give you a high speed understeer.

 

was it only you that was fishtailing?

those tires can't hook that power. get some r comp tires at the least! if your on the strip get some dr's

 

Actually - I hook about 90% in 1st and 100% in 2nd. I have Sport Cups on the rear not PS2's. SC's are 80 TW.

 

I am running PS2 Front and Sport Cups rears - you think that may be it. I will call Michelin on Tuesday. I thought it would be ok. We will see..................

Secondly, I have never had this problem before. I have the CO's set at 7 or 8 front and rear. I could try tightening that up a bit to see if it helps.

 

It's possible, there were some posts a while back of weird dartyness with runflats front, replacement tires of a non-runflat rear, granted that's a more extreme case in stiffness difference. Also another thought MPSC tires are softer, yes, but don't get grip until they are hot (i.e. road course), possibly they could just be cold and slick on these runs? (not that anyone would be doing this one the street, right???)

Took a car with Hoosier R6's for a ride on the street on a cold day (50 degrees), it was scary w/o temp in them.

 

This happened all of a sudden - I think it is attributed to the tires or suspension. I was at 650 with no problems at all.

 

I will call Michelein and Pfadt in the morning.

 

Just to clariify. You hook 90% first and 100% 2nd so that means you have full traction and then you break loose all of a sudden at 125 after you had traction? I really hope you get it figured out because I am getting ready to buy the sport cups or Pirelli Corsa

 

Hooking 100% in second (up to 70mph?) and then ists fine until 125 in 4th? gear and it breaks loose then? That makes no sense. Is it breaking loose on the release of the clutch or just when you hit 125? Can you elaborate? Is it during a turn? Was it displaced at 125? I dont see how you can have full traction in 2nd which cant be at 125mph and then not have traction at a higher gear.

A mismatch in tires front to rear is not what the issue is. Maybe you simply need to go with a better rear tire like an 18" rim with a MT 345, and yes the MT is light years ahead of the PSC tires you have in the rear.

 

Problem is you cant corner with those. What about the Pirelli Corsa? I definatley dont think its the mis matched tires!

 

I don't understand either, could it be the taller than stock rear tire causing the engine drag message to appear or is the back end really moving around in a straight line at 125+?

 

I am not breaking loose. It is a slow sway back and forth like something is out of wack.

I start out 1st, 2nd, 3rd, 4th applying the throttle very consistent, even. Slow (well maybe fast but defintately not spinning) but steady increase and then all of a sudden when I hit 125-135 i get a slow sway back and forth. The tires are not spinning - something is not aligned.

1. I will talk to Pfadt.
2. I will talk to Michelin.

Running things through my mind I have had the:

1. The Brake pads changed recently.
2. I am always playing with the Pfadt CO's.
3. I have changed tire pressure.

I have in the past few months:
1. Changed the tires to PS2/SC Combo.
2. Had the car aligned and balanced.
3. Increased my HP (By decreasing the pulley size).
4. Added coolers - Maybe my foglight opening coolers (Just kidding).
5. Changed gears - 4.10 to 3.73

 

If you think you can have both at 700rwhp, you would be the first.

The tire he has or the hoosier R6/A6 would be the only other choices.

Traction isnt only a function of tire width. A 275/17 MT ET street would outperform his 19" 345 corsa in the straightaways. The 18" aspect is what would give him the traction. An R6 or A6 on an 18 would best the 19" in all areas. 19" is a bling wheel and no race car uses them for traction or for handling. For a bit more than the silly price of the rear tire he has he could have almost bought an 18" with the taller sidewall 345 R6. An 18" with 345's will far outperform an 19" 345 in handling as well as traction.

People can resist it all they want and when they finally waste about 2k on tires, they will realize an 18" is nearly mandatory at this power level.

Traction is a priceless add on. No other mod made my car even half as improved as the 18" rim did. $10k in power output will never do anything when spinning. I cant understand it when people will spend anything for power and then try to avoid the smallest of things. Heck, call a CNC place and pay for 2 rims to be made with the Z06 design or send out two front Z06 wheels to get widened to 12.5".

No insult but the time alone the OP put into rallying Toyo to make a 19" race tire was unreal. It doesnt have the sidewall to work right.

 

That hurt Spin - I was trying to do everyone right and gasping for (traction). The SC's do hook up the problem is as described in my previous post.

 

what PSI is the tire runing? add some PSI to the rear and see if it helps. sounds like when someone runs radial and bias ply tires together.

 

I did say no insult. As I was typing the original version of that, I said to myself, this guy is going to take this as a personal shot so I re-typed in 2 more times to sugar coat it. I guess people dont like hearing "it cant be done with your (19") rim." I knew you would react like that by the amount of time and energy you put into trying to get the tire world to make a 19" race tire. It doesnt work but you would have personally paid for a 19" race tire for the existing rim thinking it would be as good as an 18 or smaller diameter. Its not a new question you ask and its not a different answer.

The C5r and C6r use 18" and no drag car uses a 19".

The info you are being given is that your 19" rim is the reason its happening. An 18 at the drag track or on the street with 26-28psi will have more room for irregularities.

Relax, its not an attack.

Countless threads on this same issue always say the same thing: Ditch the 19. I bet if you swapped to a 345/18 of the pilot sport cup, that would be a vast improvement all around handling and traction. None of the guys with the info bother posting this info because of this type of response. They know about the smaller side wall and how it hurts things but they dont want to bother with something that doesnt help them. It doesnt do anything for me to help out on threads such as this but I do to help and have done as much for corvette traction as any other member. I dont sell tires, rims, nor am I making any money telling you the reason your issue is there is from the 19.

DISCLAIMER: No insult or hurt is intended. I respect you and want you to find what your looking for.