Since upgrading my tires [from 195/55 on OEM wheels to 205/50 on 7" wide wheels] on my car I've noticed something that a Vehicle Dynamics guy told me, but I couldn't figure out the physics: The car now tends to oversteer more with the wider rubber. I've got the JDM rear strut brace on the car, but it makes little difference on the road and I'd imagine that the differences on a road course would be small. I've removed it and played around and sure enough the car rotates much more than with the OEM wheels/tires.

Has anyone else noticed this? Any theories as to why this may be?

 

Your new rubber may not be as sticky.

When I went with wider wheels/rubber all the way around, I had to go up on springrate to get the car to rotate how it once did. This is why people run a 225 on the front and 205 on the rear for autox because 225 all the way around causes the car to push.

 

She's not pushing. She's rotating noticeably more than before.

 

The best explanation I can think of at the current moment is that your old tires were worn badly in the front, causing the front to break loose sooner(push), and when you switched to new tires, you had more traction in the front which resulted in less understeer.

 

.....I believe RATEDR was experiencing something similar to this recently.

He seemed to think removing the jdm rear tower bar brought it back neutral.....

 

I doubt it's rotating so much as turning more, because the fronts have more grip.

Warren