Steering
 

Hey everyone. I'm new to this site. I spend most of my "forum" time on the Ford F-150 site trying to keep my 1995 truck running.
My wife drives a 2010 370Z automatic, and it has 38000 miles. I took it to Discount Tire for new rear tires last Friday, and on the way home noticed that the steering feels "mushy" or "loose" - hard to control. It kinda feels like driving an old car with loose steering. The road surface makes a difference, with rough roads causing more trouble. I checked to be sure that all of the wheels are securely tightened. They had inflated all of the tires to 38lbs, so I let some air out down to 32lbs. That helped some.
We were leaving on a trip so didn't take it back to Discount Tire yet, and it is an hour away, so a pain to take back. My question for all of you is what about replacing the rear tires could cause the steering to change? By the way, replaced the factory Yokohama's with Yokohama YK580 245/45R18's.
Thanks for any ideas.

Far from a tire expert, but just attempting to think about this:

1) These are unidirectional tread pattern tires. Could they have put two left-side tires on for example, or two right-side tires?
2) These are all-season tires. Unsure what the factory Yokohama tires were on the 210 Z, but perhaps summer tires? Thus less traction in the back and more tendency to oversteer?
3) The initial overinflation could have been part of the problem. Had a Ford SUV back in the 1990s that would get positively squirrelly if the rear tires were overinflated a few pounds.
4) Something happened during the tire switch? Accident during the lift operation, etc?
5) Might check alignment.

Sorry, can't be more definitive. Perhaps some of the more knowledgeable guys here can help more.

The new rear tires are a considerable harder compound tire (580 vs. 140) than the stock tires were and therefore less traction. Since you only changed the rears you now have a handling imbalance because of different tire compounds front vs. rear.

Thanks for the quick replies.
The tires seem to be a matched set - mirror images of the tread pattern with "outside" stamped on the outside of each.
The original tires are Yokohama Advan Sports, and I see that the traction is 180 on the old ones and 580 on the new. Would that really cause a noticeable difference in the steering? If so, I guess the only answer is to shell out enough for the front tires also. Probably also a good idea to get the alignment checked after spending that much on tires.
Thanks again for the ideas.

You've thrown off the balance of your car by using two different tires and tire compounds front to back. Yes, it can make that much of a difference. The Z isn't meant to have super soft all-season tires on it, because it is an extremely communicative car with plenty of feedback through the steering wheel.

Soft tires on a rigid car = floppy dynamics.

I have a similar issue. I just bought the Potenza RE760 Sports for just the rear, and am experiencing a similar issue. When I drive faster than 70mph, the car feels floaty, and just not solid as it did with the RE50s all the way around.

My question is this: Will buying a set of RE760 front tires (and having them all the way around) even this out and make the car feel as it did with all RE50s? Or, should I just consider buying RE50s all the way around again. I'm just not sure what to do here. Help me out guys! Thanks.

Quick search on YK580...

Yokohama YK580 Tire - Quiet, Smooth, Grippy and Long-Lasting, But Not Perfect - Yokohama YK580 - Epinions.com

"Despite the fact that the traction in turns, acceleration and braking are excellent, the tires are not very suitable for spirited driving. They are not very responsive: it seems that the initial split second you turn/accelerate/brake nothing happens. Is it the fault of the progressive sidewall that gives you cushy/quiet ride? Maybe. With the YK520 this behavior diminished somewhat as the tread wore, but didn’t go away completely so there must be more to it than just the elasticity of the tread."

You've got tires that should last 3x longer and cost 80% of the RE050s Overall, that's about 1/4 the price on the tire. I would expect a significant drop in performance. Weak sidwalls suck for responsiveness.

Drive carefully!

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Were you able to get this issue resolved by getting some RE760 tires for the front?

I'm in the same exact predicament at the time and could benefit from your insight.

Thanks.