Back in January I purchased a 2005 MCS that had Bridgestone run-flats on the fronts and Goodyear Eagle RS-As on the rear all in 205/45/17. After purchase I have been running the car pretty hard and enjoying the extremely good handling. I admit that I did not rotate as often as I should have and therefore wore the Bridgestones to a point just before bald and the Goodyears started to show a little wear on the inside shoulder due to the stock camber of the rear. I decided to purchase conventional tires after some extensive reading here. Because of the still very useable Goodyears I had them rotated to the front and placed some Fuzion UHP 215/45/17s on the rear. I have purchased these tires before and have had great experience with them in the past, however the car has now lost all its handling characteristics as the car constantly feels like the rear is wanting to step out on even the slightest corners. I also live in a western state and have to drive a deeply rutted asphalt road to my job and the car absolutely attempts to ensure that I leave the road without heavy steering input and braking. Previously with the run-flats I never had this issue and consistently traveled at 80mph+ on this same road, I am now traveling at 55mph and still on edge if that is safe. I have lost all confidence in the handling of the car. Does anyone have any suggestions or input as to what I'm experiencing?

 

One possibility is that the new tires haven't been driven on enough to wear the somewhat slippery mold release agent off from the treads. That could take 200 or so miles.

If you've already got hundreds of miles on the new tires, it's possible that the two sets of tires aren't very compatible in some other way. Mixing different sets of tires is somewhat of a crap shoot anyway, but you have two different brands from two different tire categories (HP A/S and UHP A/S) with different rubber age and wear. Also, Tire Rack didn't show the Fuzion UHP in size 205/45/17, but did show 215/45/17.

You might try the new tires on the front to see what that does.

Tire Rack Alex may be able to provide a more enlightened explanation.

 

comment redacted by virtue of it's lack of helpful information...I'll move on...

 

Mixing tires is not a good idea...different handling characteristic new vs old...tire pressure is anothing thing to look at...sounds like you're experiencing oversteer, add more pressure to the front or reduce rear...

 

As a general rule you always want the same tires on front and rear when possible so when changing only a pair of tires try to be as close if not identical.

see
http://www.tirerack.com/tires/tirete...urrentpage=180

Runflats should not be mixed with non runflats

Tire size should be the same front and rear

Tire class should be the same front and rear-

From what you wrote-

Your front tires are somewhat worn Goodyear Eagle RSA EMT runflat tires in 205/45-17 High Performance All Season tires

Your rear tires are new Fuzion UHP 215/45-17 Ultra High Performance All Season tires

If you have not done alignment in 6 to 12 months then it might be good to do that whenever you get new tires.

You might also check with Alex@tirerack.com and explain how the handling has changed.

Tire design and wear will affect handling so mixing tires is not always predictable or desireable. Even though both of these tire sizes will fit your OEM 17" wheel they do not have the same sidewall profile or construction so stiffness and handling will be affected. In general runflat sidewalls are much stiffer than non runflat All Season tire sidewalls.

One easy test is to move the Fuzion tires to the front and put the runflats in the back- drive around and see if handling is still not good- if so then suspension and alignment need to be checked. If the handling is much improved then I would suspect that the runflat/non runflat mix or the worn Goodyears on the fronts is not a good combination in which you can buy two Fuzion tires for a total of four.

 

 

Problem solved!!! Mounted a matching set of 215/45/17 Fuzions on the front and the car is back to normal. The softer sidewalls of the conventional tires are still noticeable, but not causing any real issues. Never thought there was such a difference in sidewall rigidity on lateral forces.

 

Good to hear

Here is something to notice

On a runflat if the tire is flat what does it look like?

Answer is it looks fine because the sidewall is so stiff it can run when flat.

On a non runflat if the tire is flat what does it look like?

It looks flat.