Need help with handling issue

[RarlyL8]

I recently changed out my rear tires/wheels to get a better aspect ratio look. After the swap I noticed the car drove a bit differently but expected that as the new tires are 1" taller than the old ones. All was good until I met up with a blacked out Z car on the highway yesterday and did an off ramp run with him. When exiting the off ramp I quickly got well into the 3 digit mph, then felt the handling get pretty unsettled. Once out of the curve and on a staight line all was good. I cannot describe well the feeling other than the car did not feel tight and planted like it used to, but rather squirmy or soft.
What can cause this?
The tires are now 1" taller which throws off the front/rear bias.
The tires have a shorter sidewall which should tighten it up.
The tires are Nitto drag radials on rear, Fusion performance street on front. Chose the Nitto because the tread pattern looks very similar to the Fusion. The 15's were Pirelli P-Zeros.

Here is before and after:

[IMR-Merlin]

same compound tires?

[gumba]

I would at the very least check the rear camber & toe. I wouldn't be surprised if the front changed also. Maybe it's just the angle you did the photo, but the back appears to have positive camber.

[RarlyL8]

No suspension changes were made so camber didn't change (probably the picture).
Yes the compound on the Nitto rears are very soft as they are drag radials, could this be the problem?

[turbo owner]

Lower the rear and corner balance to see if that will fix it.

[mreid]

Drag radials are made for straight line performance. What you were probably feeling was the relatively soft side wall allowing the tread to shift side to side.

[ChrisD87]

Sorry for the off topic but those wheels and tires look so mean! Are you running 15x9-11's?

[RarlyL8]

Lower the rear and corner balance to see if that will fix it.

I may do that. Really didn't want to have to lower the rear as it looks good as-is.

What you were probably feeling was the relatively soft side wall allowing the tread to shift side to side.

If that is true these tires must go! I hit the corners hard when running the mountains as I know my car well, I need good feedback from the tires.

Are you running 15x9-11's?

First set of wheels/tires was 15x8 and 15x12 running 225/50 and 345/35 Pirellis.
Swapped out the 15x8/225s for 16x9 245/45-16. That combo worked very well but looked odd (to me).
Second set of wheels/tires are 17x12.5 running 315/35-17

Anyone else running Nitto's having the same issue?
Anyone else running 16's up front and 17's out back having an issue?

[motorracer]

Mine did the same. All is good now that they are worn down a little. Back to go kart like.

[JFairman]

Lowering it won't reduce the drag radial side wall flex and it's a lot of work if you have to re index the spring plates and then do a 4 wheel alignment.
Those tires aren't made for cornering.

Call the tire maker or place you bought them and see if they have any suggestions like maybe running higher pressure in them.
I think you need to get new summer tires made for handling and high speed cornering,

[turbo owner]

Brian, see if the car will wiggle while pushing side to side in the back. If NO stick with suspension changes. Up a little in the front and down and in the back.

T-bar suspension can be finicky if not right.

[Craig 930 RS]

Holy crap man, your tires could not be more different front to rear! Definitely the cause

[wayner]

Are they brand new?
Mold release agent is slippery unit it wears off.

Was it could out?
Tires may heat up at different temperatures.

[IMR-Merlin]

Originally Posted by JFairman

Call the tire maker or place you bought them and see if they have any suggestions like maybe running higher pressure in them.

This will change the contact patch too, it's best to do some tire temps to see what the pest PSI to run is. Pyrometers are cheap these days and after a short spirited run, you can get some baseline temps.

If you need some input on what to do once you get baseline temps, let me know.

[Craig 930 RS]

Doing over 100 with so so street tires and a soft sidewall drag tire ... case closed, right?

[wayner]

The diameter difference was a way that the teams in the old days got more tire on the ground, skirting the rules that limited width, instead going with larger diameter.

[seebobgo]

Drag tires are not for exit ramps. The side walls are to soft.
I never mix match tires.

[RarlyL8]

Yes good idea to play with the pressures. When I first started running huge rear tires 20+ years ago I noticed that I needed to run similar pressures front and rear rather than the factory bias.

The tire diameter front/rear bias is the same now as it was when I ran the 15" wheels, I don't think that is the problem. I ran a 1" bias on the Red Rocket as well.

I went out this afternoon (70°F) and hit the mountains hard to really try to better feel what is going on. What I am seeing/feeling is the tires stick - they do not slide like the 345's did, and they just don't feel the same. After rounding a few of my favorite corners I started cranking up the throttle and the tires simply do not slip. I think this may be it, by not slipping and giving me that feedback they are working the suspension harder and I'm not used to that. The unsettled feeling I get could be because I don't know what is going to happen when it does slip. Also tires are brand new which may be at least part of the problem. I'll wait a bit and see if they get better. Got to say I don't like it that these tires don't slip, and I don't know what it would take to get them to do so. There is an abandoned air strip close by where we used to do auto-x, I think that is where I need to go next.

[RarlyL8]

Rods(RSR) - I'm pretty sure I saw a picture of your gray beast with these Nitto tires out back. If so how are they doing for you?

[Craig 930 RS]

What are we missing here? The two extremely different kinds of tires are definitely the cause!!