Car feels unstable at high speed

[michaelalex17]

My 2015 M3 with active suspension feels unstable above 100mph (tested in Mexico). I am recently coming from an e92 335i and that car felt very planted all the way to 155. When I am going 100+ on a perfectly flat and straight high way in the m3 I have to make a lot of steering corrections just to keep it straight and it doesn't feel as planned. The sensation is almost like is a gust of wind were blowing the car from side to side. I have tried all the different steering and suspension modes, but the second I go over 100mph the car starts to feel twitchy and not planted. The tires are filled to 33psi all around (door insert recommended tire pressure) which honestly seems low to me would think it should be around 38 front 40 rear. I also thought it could be an alignment issue but the car tracks perfectly straight if I let go of the wheel. Any thoughts on this issue would be greatly appreciated. Thank you

[Masheen]

Have You mounted spacers on your car ? If so, that might be the reason.

[STR8-6IX]

Originally Posted by michaelalex17

My 2015 M3 with active suspension feels unstable above 100mph (tested in Mexico). I am recently coming from an e92 335i and that car felt very planted all the way to 155. When I am going 100+ on a perfectly flat and straight high way in the m3 I have to make a lot of steering corrections just to keep it straight and it doesn't feel as planned. The sensation is almost like is a gust of wind were blowing the car from side to side. I have tried all the different steering and suspension modes, but the second I go over 100mph the car starts to feel twitchy and not planted. The tires are filled to 33psi all around (door insert recommended tire pressure) which honestly seems low to me would think it should be around 38 front 40 rear. I also thought it could be an alignment issue but the car tracks perfectly straight if I let go of the wheel. Any thoughts on this issue would be greatly appreciated. Thank you

try inflating to 37 psi all around. play around with the PSI's, even 1 psi would be somewhat noticeable.

I am suspecting that the tires are under inflated for such a speed.

[Aaaaaaaaa]

You know what happens when one tire is off by 1/2 PSI

[michaelalex17]

Originally Posted by STR8-6IX

try inflating to 37 psi all around. play around with the PSI's, even 1 psi would be somewhat noticeable.

I am suspecting that the tires are under inflated for such a speed.

That was really my thought as well, but figured that might not be the problem since it is the recommended tire pressure

[michaelalex17]

Originally Posted by Masheen

Have You mounted spacers on your car ? If so, that might be the reason.

Nope, completely stock

[RickFLM4]

Road condition?

(Presumably summer) tire condition?

[STR8-6IX]

Originally Posted by michaelalex17

That was really my thought as well, but figured that might not be the problem since it is the recommended tire pressure

I recommend you inflate the tires to 37 PSI and try again - report back if you can.

the faster you go, the more air you need in your tires.

[gatorfast]

Strange. Maybe try sport or sport + steering?

[dkhm3]

No issues here, went 109 the other day and solid.

[nicknaz]

Check the alignment

[Alpine300zhp]

Originally Posted by STR8-6IX

try inflating to 37 psi all around. play around with the PSI's, even 1 psi would be somewhat noticeable.

I am suspecting that the tires are under inflated for such a speed.

This is exactly correct. Over or under inflation in this car will result in instability. I run 33-34 psi cold on MPSS tires. This is the best pressure based on my couple of years driving this car.

[antych]

Originally Posted by michaelalex17

That was really my thought as well, but figured that might not be the problem since it is the recommended tire pressure

I did 167mph on autobahn with this tyre pressure. That's not the problem, the cars was completely stable.

[SD ///M4]

On our Euro Delivery in May last year, my wife and I both top-ended my M4 at 271 km/h (168 MPH) on the German Autobahn and both times the car felt absolutely solid as a rock. The car was brand new and bone stock.

If you're unstable at 100+, you definitely have something going on with your car.

[SD ///M4]

Originally Posted by STR8-6IX

the faster you go, the more air you need in your tires.

Not exactly true. If you check the sticker in the driver door jamb or your Owner's Manual, depending on which wheels and tires you have, BMW recommends one tire pressure (31 psi front and back for my M4 with 19" wheels) for speeds up to 100 MPH, and a higher tire pressure (34 front and 37 rear) for speeds 100+.

[F83]

Bad road? These cars can get pretty bad tramlining given 255s on the front.

[horsepower_and_hounds]

I have a small vibration that comes and goes but this is the most stable car I have ever owned. The faster you go the better it feels. I have been adapting it with the JB4 and E85 doing 4:30 am early morning 4ht and 5th gear pulls....60 to 120 and 140. That thing just glides...even with the vibration

[M4Now!]

+1 on tramlining

Cheers

[michaelalex17]

Originally Posted by M4Now!

+1 on tramlining

Cheers

Should have clarified I am running the stock MPSS tires with about 2,000 miles on them. I think the issue might be tramlining, since I did about 110ish on a different road in Mexico today and the car felt very stable. The original road I was on seemed very smooth so I don't know why that would have happened. Is everyone running 33psi on the pilot super sports? That just seems really low to me

[Draper]

Originally Posted by michaelalex17

Should have clarified I am running the stock MPSS tires with about 2,000 miles on them. I think the issue might be tramlining, since I did about 110ish on a different road in Mexico today and the car felt very stable. The original road I was on seemed very smooth so I don't know why that would have happened. Is everyone running 33psi on the pilot super sports? That just seems really low to me

Wider tires will cause smaller contours to feel more noticeable. That's probably why you are seeing a difference from your 335.

32-33 cold PSI is the sweet spot. My dealer had mine up to 36 when I picked up the car, and the handling was terrible until I dropped them down.

[michaelalex17]

Originally Posted by Draper

Wider tires will cause smaller contours to feel more noticeable. That's probably why you are seeing a difference from your 335.

32-33 cold PSI is the sweet spot. My dealer had mine up to 36 when I picked up the car, and the handling was terrible until I dropped them down.

That makes sense about the wider tires, I had 235's up front on the 335. That's really interesting about the tire pressure, I have had several sports cars and this is the lowest tire pressure recommended on the inside of the door sill I have seen

[azn_fcuk]

Check the weights on your wheels to see if any have fallen off perhaps they need to be balanced again.