Can rear tires affect steering feel?

[7Andrei7]

Hi everyone!
My car (2.0T GTL RWD) came with 19" staggered Continental ContriSport 5 tires. After 2 summers, my rear tires were almost completely done while the fronts still had about 5mm left (of 8mm). So I decided to only buy a rear set and keep the fronts for one more summer.
Since I was pretty unhappy with the noise and inability to properly balance the Continentals I decided to buy a set of Nokian Powerproofs for the rear. They have very similar style thread and I got the exact same specs: 255 35 R19 96Y XL.
Driving on the highway feels no different (except the lower tire noise coming from the hatch) but driving on side roads is very different. The steering feels more nervous and bumps in the road or a gust of wind launches the car sideways. I feel like I need to fight with the steering more while at the same time having less feel when I push it hard. It's very weird as it feels to both understeer and oversteer at the same time.
How can this happen? I've checked the alignment and balance when I installed them and all is perfect. There is no vibration. Just steering feels lighter and disconnected.
Could it be because the rear tires have much more grip? Or because they are softer or worse? The "handling" reviews are pretty similar for the Contis and the Nokians. However, Nokians are better at pretty much everything else. I never could have imagined that the rears would influence the handling so much.
I'm trying to figure out if I need to also replace the fronts or if the rears are really bad and I need a completely new set.
Thank you!!

 

[Ulikefishsticks]

How many miles are on those tires? I had bought new tires a while back and it felt squirly in the rear end. It could be many factors, in my case it was wearing down the tread enough to get a good contact with the ground. PSI of tires or balance issue. It's also not recommended to have different tires on the car. That may play a role. My guess is you need to get it worn down a bit to get a good contact patch. Also just a sanity check for wheels torqued and if those tires are directional, make sure it's the correct direction.

 

[NS_Stinger]

Well running mismatched tires especially with a staggered setup is a big no-no so I'd expect weird handling characteristics from that for sure, but yours do sound more extreme. If the rears are directional I'd ensure they were mounted on the correct side otherwise this is basically what happens when you do exactly what you shouldn't and mix/match tires.

 

[7Andrei7]

@Ulikefishsticks I just installed them yesterday and did a 500km drive today. Balance, pressure and alignment are all fine. Your experience gives me hope!

@NS_Stinger Why do you say that? I've checked before and even tire manufacturers say it's fine to mix tyre brands or wear depth as long as tires with the same specs/thread are on a specific axle (front/rear). Are you recommending that cars with staggered setup should always get new tires all around or that rears and fronts should be the same brand&model?

I will check tomorrow to make sure they did not install them the wrong way but that would be very surprising indeed.

 

[Ulikefishsticks]

Experienced drvers are usually hyper aware of the car characteristics. It could just be the tire feels different to you. Sidewall strength, compound used, tread pattern. Just take it easy on them and see if it smooths out.

 

[Snowwhite]

adjust the rear tire pressure and try again. go up a couple of psi, if that doesn't make it better, go below the original setting. My cars have felt less jittery with more pressure in the rear tires than the fronts, but your experience may vary.

 

[NS_Stinger]

@Ulikefishsticks I just installed them yesterday and did a 500km drive today. Balance, pressure and alignment are all fine. Your experience gives me hope!

@NS_Stinger Why do you say that? I've checked before and even tire manufacturers say it's fine to mix tyre brands or wear depth as long as tires with the same specs/thread are on a specific axle (front/rear). Are you recommending that cars with staggered setup should always get new tires all around or that rears and fronts should be the same brand&model?

I will check tomorrow to make sure they did not install them the wrong way but that would be very surprising indeed.

I'm saying that I'd only use the same tires all around and replace at the very least in pairs as needed. What would concern me most is the difference in the level of dry/wet grip each tire has, for example having a really grippy tire in the back in the wet versus a terrible wet tire up front. Yes tire sizing is priority one for sure but mixing and matching tire types would concern me, mostly at the limit but still even normal driving could feel more unpredictable depending on what mix you're running.

 

[7Andrei7]

Normally I would have also tried to buy the exact same brand and model but the Conties are just not that good.
When it comes to grip, there are so many factors from front to rear axle (wear, weight, traction, size of tire) that even on identical tires each axle will respond slightly different.
This is my first car with a staggered setup so it’s the first time I need to buy new tires for just one axle. My research might be completely wrong..

 

[Hilleagle]

Bear in mind brand new tyres need to run in. The tyre has a coating to help remove if from the mould when manufactured, so your first few miles will always feel odd.

Another factor can be the tyre shoulder. used tyres settle and cornering and normal driving will affect and wear the shoulder and this can affect the feel, which you don't notice over time, but becomes apparent when you replace, even with the same tyre from the same manufacturer.

In my experience, I would always recommend buying tyres in pairs, just as you would always change any parts across an axle ( brakes / suspension), however, I don't see an issue with changing just rears because it is a staggered set up and I have no concerns you went for an alternate brand. If you had got budget on one axle and premium on the other you would expect differences.

I would be concerned about the marked difference to the feel of the car with just new rears on though.

You say the tracking and alignment was checked and ok. Was it adjusted in that process?

The only other factor I can think of is the condition of your front tyres. I know you say they have plenty of tread, but to have 5mm left on fronts after the same mileage has seen you replace the rears, is a marked difference, unless you changed the rears at 3mm and not below.

Hope you get a solution and please update us.

 

[MerlintheMad]

Replacing in pairs is a current event with me. In August of 2019 I replaced my OE PS4 rears at c. 14-15K miles. I put 4K miles on them then replaced the fronts. Now, over 19K miles later (some 4K are on the Nitto Motivos, though), I'm replacing the rears again: the fronts have c. 4K less and I'm keeping them on. I'll pay more attention to any "feel" changes this time: last time I was oblivious.

 

[7Andrei7]

So, just to come back with an update after another 400km.
Firstly I checked and all tires are installed correctly.
Alignment was only checked and confirmed to be ok (saw the machine myself).
Before replacing the rears I had done about 2k km with the summers (old rears) and so that’s what I’m comparing to. The old rears were replaced at about 3mm of thread left.
Now, driving today I could push a little more and I can now understand the behavior.
At low speeds (below 90km/h) there is not much difference to the old setup.
At higher speeds though, when I start to turn, the steering feels lighter and car starts to turn in very fast (as you would expect to get some oversteer) but then it suddenly feels like the rear doesn’t want to follow immediately. There is a delay that kind of changes the weight of the steering and makes it feel like it’s about to understeer which makes me apply more steering and then suddenly the rear grips and the car turns too much.
So basically the balance feels way off.
I had all tires to the 2,5 bar standard pressure. In the last 50km I inflated the rears +0,1 to the fronts and it felt a little better. Will add some more tomorrow.
Thank you all for the feedback! I hope to figure out if I need new fronts or if these new rears are shit and I need to get a new brand.

 

[MerlintheMad]

I hope to figure out if I need new fronts or if thee new rears are shit and I need to get a new brand.

I've been reading about your rear tire, and it can't be "shit"; it gets generally high reviews. So, adjust while you have old front tires, or get matching new front tires.

 

[RogueIV]

If the rear is lacking a bit in traction you might need to drop the pressure slightly, but really just play with it a bit. Didd they give you a spec sheet when they checked the alignment?

 

[7Andrei7]

@RogueIV they did not print out the sheet but showed it to me on the screen and everything was in the green. No adjustment required. Also, previous tires were the same spec. and all felt well so I have no reason to suspect alignment. I did play a little with the pressure today and I now believe it's all because the difference in grip and age between rears and fronts. Nothing more I can do with this setup.

@MerlintheMad After today I'm fairly sure it's not the rears to blame but the fronts that are just too worn at this point to keep up.
Since I was doing a road trip in the past few days I could do a lot of "testing". My conclusion at the end of today after driving back home on roads I know well, is that the rears grip very very well and are definitely not to blame. It's the fronts that can't keep up with the transfer of masses and make the whole car feel unstable.
I've decided to order a new set of Nokians for the front as well and hope the car will go back to the feel I know and love.
I'm afraid of doing any more mixing and matching at this point, at least with any Continentals. A lot of learning from this experience.

 

[7Andrei7]

Just in case anyone was wondering, I had the new front tyres installed (Nokian Powerproof 225 40 r19) and the car behaviour returned to normal. Super stable and predictable again. The Nokians are definitely quieter and more comfortable than the Continentals but there is also slightly less feel in the steering in confort mode. Might change over time.

I'm still confused by this experience. The old front tyres are about 50% worn (4,5-5mm of 8mm of thread left) so I'm very very surprised the car behaved so badly with new rear tyres. Pics below.
But, I'm at least happy that it's all back to normal.

Would be very interested if others changed their rear tyres and kept the older fronts. Did you feel any significant change?

 

[RogueIV]

I think the issue may have been lessened if you ended up with the same brand/model tire in the rear. Different tread compounds front and rear might have been part of your issue.

Also, FWIW, The Contis have a mediocre rating and age only lessens the grip a tire has.

 

[MerlintheMad]

Would be very interested if others changed their rear tyres and kept the older fronts. Did you feel any significant change?

Yes: I noticed immediately that the "thrum" noise that was starting to become obvious went away the instant I drove on the freeway with brand new Michelin PS4S in the rear: the fronts are c. 4K miles behind the replaced rears and are still performing well: car is quiet and handling/grip is very good. We have to take into account the comparison between RWD and AWD here.

 

[NS_Stinger]

Yes: I noticed immediately that the "thrum" noise that was starting to become obvious went away the instant I drove on the freeway with brand new Michelin PS4S in the rear: the fronts are c. 4K miles behind the replaced rears and are still performing well: car is quiet and handling/grip is very good. We have to take into account the comparison between RWD and AWD here.

I ended up in the same boat. My front PS4 tires are still in great shape but my rears are toast, so I decided to just replace the rears. The PS4 are either discontinued or impossible to find so the shop is going to install PS4S tires in the rear. The tread pattern on these two tires is very similar so I'm crossing my fingers...

 

[MerlintheMad]

I ended up in the same boat. My front PS4 tires are still in great shape but my rears are toast, so I decided to just replace the rears. The PS4 are either discontinued or impossible to find so the shop is going to install PS4S tires in the rear. The tread pattern on these two tires is very similar so I'm crossing my fingers...

Like I said, I ran PS4S brand new on the rear while using up the last 4K miles of my OE PS4 on the front: I drove The Dragon that way and didn't experience any white knuckle moments or any road noise harmonics either.

 

[RM7]

Well running mismatched tires especially with a staggered setup is a big no-no so I'd expect weird handling characteristics from that for sure, but yours do sound more extreme. If the rears are directional I'd ensure they were mounted on the correct side otherwise this is basically what happens when you do exactly what you shouldn't and mix/match tires.

Says who? People who sell tires?

Running staggered tires already means that your front and rear tires will handle differently, but Kia also sets up the car square from the factory too. Those are going to be two widely different handling setups. All that BS about having to "match front and rear tires" is just BS on an RWD setup or staggered AWD setup, as long as you have the same diameters. Now, I'm not saying put winter tires on the front and summer tires on the rear, but with like-type of tires with similar tread-wear ratings, this is just not a thing.

Hell, on the AWD cars Kia allows you to choose between 20/80 or 50/50 torque split, so again, the front end of the car may behave quite differently from the rear, using different front and rear tires may help you. It's not some big evil thing. There are reasons why it might be good and reasons why it might not, like inability to rotate tires. As long as the type of tire/use/treadwear/size is pretty much the same, go for it. I did it on my old camaro with 275s out back and 255s up front when I got a nail in one of the front tire sidewalls about 2 weeks after I took ownership. I sure as hell wasn't going to buy 4 tires, no point.