ilmthebomb

I recently bought a 2019 c63s and I got new tires for the back because I was having so much fun with it. I ended up getting PS4S for the rears. They are 295 in width. After getting them on I noticed that at highway speeds the car felt floaty. If I made a lane change the steering wasn’t direct like I remembered it being so I checked my psi. Turns out the psi were way too high and I reduced them to the proper number. After wards the problem got slightly better but he car still does not feel stable like it did before the new tires. Any ideas on what the problem could be ?

'1663s

Try letting them wear in for a couple hundred miles. In the past people claimed there was a residue on new tires due to the "release compounds" used to ease the tires out of the moulds. I think this has been largely eliminated but try giving them 150-200 miles running in distance. Also, what pressures are you running? What tire are you coming from?

raphman

What's the stock tire width on the 2019 rears? If you put on a tire that's too wide for the rim, it can cause high speed handling issue since the sidewall is a lot more forgiving and less rigid.

superswiss

So new tires still need about 200-500 miles to wear off the lubricants from the mold, but that shouldn't result in a floaty feel, rather the tires will be a bit slippery at first. As they wear in, they start developing full grip. However, a new tire will have more flex due to the additional tread, but again in my experience that doesn't cause float on the highway. The tire is just not as sharp until it's worn down some more. Performance tires don't develop their full dry performance until they are worn down to about 6-7/32". This is why track oriented tires such as the Cup 2 already start out around 7/32" instead of the more typical 10/32".

As said above, you are clearly not on the stock size. Do you have a coupe or a sedan? Coupe would be close with 285 being stock size, but the sedan has 265 stock size. Also, have you checked your alignment? Since you had fun with the car, it's possible you knocked something out in the suspension.

anerbe

Does you highway have grooves running the direction of the road? If so, your vagueness could be due to a phenomenon called groove wander. This is when the tire ribs interact with the grooves in the highway, which causes small movement / shifts, which feels of instability.

If after a few more miles, you still have it, it could be the design of the particular tire to the design of the highway. Unfortunately, the only want to fix this is to try a different tire spec (size, pattern, etc...).

ilmthebomb

stock rear tire width is 285.

ilmthebomb

I am coming from the stock super sports that are 285 in width.

ilmthebomb

I have a coupe so the stock rear width is 285 and i have moved to a 295

untamedd

on the coupe the rim width in the rear is 10.5" which is perfect for 295s. I myself have 305s in the rear for which a 10.5" rim is also good, although on the lower end of the range. Even wit 305s and stock power, traction issues are still there but car doesnt feel floaty at high speeds though

domjansson

what is the width of the rim you put the 295 on? That may be the issue. Otherwise break them in as everyone has said

Omega4

I’ve had that floaty, unstable feeling when I replaced two rear ps4s tires on a previous car. In my case, the new rear tires mixed with older front tires took a bit to “work together”. Also, if you’ve mixed rear ps4s with front pss, the slightly different tread pattern between fronts and rears may be adding to the feeling. Double check and alter your tire pressures to see if that settles it down any. The installer had my rear pressures at 44psi and I felt like I was bouncing over every slight road deviation.

I just changed to ps4s this past weekend (265/305) and am still getting used to the noticeable extra grip and better overall handling.

superswiss

I would also add to start with making sure your tire pressure is good. What's your cold pressure? But also just to confirm, you just replaced your rear tires with wider PS4S, but you are still on the stock PSS in the front? So in essence you went wider in the rear, but you didn't balance that out with wider tires in the front, too? If you go wider, you should go wider all around and also use the same tires front and back. When I went with the PS4S I did so all around. I'm not going to mix brands or models, but I also stayed with the stock size to not alter the car's dynamics. AMG picked the tire sizes for a reason.

reakwon

did you solve this?

reakwon

did you solve this?

reakwon

whats the exact tires numbers and rim size ?

koifysh

Get an alignment and make sure they use spread toe (spreader bar). Drive for 200 miles to wear in the new tyres.