[Anshy21]

Hi all, hope all safe and well

Wondering if anyone can help me diagnose top speed stability issues. I did an autobahn run in Germany and hit the limiter at 164mph indicated on stock size continental sport contact 6s and had no issues with how the car felt at the top end.

Having burnt out my stock rears, I opted to replace them with MPS4S at rear, this left the car feeling very unstable at anything above 50mph and my friends told me it was because I was a) running different brands/makes front to rear, and b) because my fronts were getting close to low (just below 3mm).

So I replaced fronts to MPS4S within a week too. Helped down low but now on basically fresh MPS4S all round in stock sizes and the car feels really unstable after about 130/140mph. Front end goes pretty light and the car starts to squirm/tramline (not on autobahn so tarmac likely a bit worse)

Anyone any ideas? Being honest I've not noticed a vast improvement from the Michelins other than off-line grip which I don't prioritise so may go back to Conti's on next switch. Top end more important to me.

All ideas/advice appreciated

[RoWoX3M]

Originally Posted by Anshy21

Hi all, hope all safe and well

Wondering if anyone can help me diagnose top speed stability issues. I did an autobahn run in Germany and hit the limiter at 164mph indicated on stock size continental sport contact 6s and had no issues with how the car felt at the top end.

Having burnt out my stock rears, I opted to replace them with MPS4S at rear, this left the car feeling very unstable at anything above 50mph and my friends told me it was because I was a) running different brands/makes front to rear, and b) because my fronts were getting close to low (just below 3mm).

So I replaced fronts to MPS4S within a week too. Helped down low but now on basically fresh MPS4S all round in stock sizes and the car feels really unstable after about 130/140mph. Front end goes pretty light and the car starts to squirm/tramline (not on autobahn so tarmac likely a bit worse)

Anyone any ideas? Being honest I've not noticed a vast improvement from the Michelins other than off-line grip which I don't prioritise so may go back to Conti's on next switch. Top end more important to me.

All ideas/advice appreciated

Have you checked tire pressure and alignment? Also, new tires need a few hundred miles to break in. Could be any one of those things.

[Anshy21]

Alignment feels ok and had it recently checked by someone reputable - what pressures do you run? I'll check that first and if it doesn't fix will redo alignment at BMW (trying to not spend a fortune ha!)

[RoWoX3M]

Originally Posted by Anshy21

Alignment feels ok and had it recently checked by someone reputable - what pressures do you run? I'll check that first and if it doesn't fix will redo alignment at BMW (trying to not spend a fortune ha!)

I'm running my winter set up now 35F and 40R. Takes several miles for them to warm up and until they do they can feel a little off.

[Anshy21]

Noted. Thanks for your advice!

[Max Well]

Originally Posted by Anshy21

Alignment feels ok and had it recently checked by someone reputable - what pressures do you run? I'll check that first and if it doesn't fix will redo alignment at BMW (trying to not spend a fortune ha!)

Alignment and balancing also came to mind, as the MPS4S have been amazing tires for us. My wife changed her Contis over to them at 10K miles and has been very pleased (she was considering the MSS springs before that and no longer even mentions it). I've got 12K on my MPS4S and have a new set waiting in the wings but wanted to get another drag strip day in before changing them out.

Hopefully they balanced your new tires as that should be standard, as my wife's required quite a bit of weight modifications when her tires were changed.

Regarding the tire psi, BMW recs from the manual are attached. Note that if M Driver's pkg is present (implying speeds up to ~180mph), they recommend cold psi of 44F/50R for the 21s (if that's what you have).

[Anshy21]

Many thanks! Yeah I have seen a night to day difference on MPS4S on my M140i so thought it was me being crazy to think I preferred the Conti's at high speed. Hopefully pressure fix sorts that out for me. Will post back with updates when I can.

[Influence]

Even at less than 90MPH speeds, I noticed that my MP4S felt a bit "squirrely" at speed and in turns until I broke the 400 mile mark on my car. Then the car felt noticeably more stable.

There are molding compounds that need to wear off and in a car with higher degrees of negative camber, it always seems to take a little bit longer for new tires to "break in" and stabilize the contact patch.

From personal experience, no way would I be taking a set of new tires above 100MPH or even cornering hard until they had at least 400 miles on them.

[spta97]

Originally Posted by Max Well

Alignment and balancing also came to mind, as the MPS4S have been amazing tires for us. My wife changed her Contis over to them at 10K miles and has been very pleased (she was considering the MSS springs before that and no longer even mentions it). I've got 12K on my MPS4S and have a new set waiting in the wings but wanted to get another drag strip day in before changing them out.

Hopefully they balanced your new tires as that should be standard, as my wife's required quite a bit of weight modifications when her tires were changed.

Regarding the tire psi, BMW recs from the manual are attached. Note that if M Driver's pkg is present (implying speeds up to ~180mph), they recommend cold psi of 44F/50R for the 21s (if that's what you have).

I agree with Max - min I would run is the 38/44 for the >100MPH but if you are top ending it, I would go with the 44/50.

Please post back your results as I would be surprised if an all season tire will perform as well at high speeds vs. a summer-only tire.

Note, the higher pressures will result in a rougher ride - for my summers I run the 38/44 but may play with the 44/50.

[car_fan]

Ironically since I upped the PSI to 40/45 on the Conti’s (21’s) the ride appears to be a bit smoother. Still firm, but less harsh on broken pavement and hard bumps. That being said, they still don’t have the ultimate grip of MP4s which I am running on my other car. Once the Continentals need replacement, going to Michelin’s.

[richard in NC]

Originally Posted by car_fan

Ironically since I upped the PSI to 40/45 on the Conti’s (21’s) the ride appears to be a bit smoother. Still firm, but less harsh on broken pavement and hard bumps. That being said, they still don’t have the ultimate grip of MP4s which I am running on my other car. Once the Continentals need replacement, going to Michelin’s.

Ironically, especially on RFTs, increasing pressure can soften the ride. That's because you flatten or put a slight convex curve into the tread surface, allowing some cushioning when it hits bumps. Too low of pressure and you depend on the sidewall for all cushioning. Todays low profile max performance sidewalls are extremely stiff comparatively.

[GrandMasterKhan]

you said you had the alignment "checked". did you mean to say they actually performed an alignment not just "eyeballed it"?

[Anshy21]

Influence noted - I'm going for a high speed run today so and think I will run 42/44 and see how I go. I don't have RFT, just air, and yep it was actually checked on a laser alignment system, not if that classes as eyeballed or not haha.

[sayemthree]

These are all season? If you want the best top speed performance go with a summer tire AS are a jack of all trades, master of none

[spta97]

Originally Posted by sayemthree

These are all season? If you want the best top speed performance go with a summer tire AS are a jack of all trades, master of none

I hear everyone stating that the difference in summer tires is only relevant at the track.

I often question that as I have to believe summer tires would be noticeably better at speeds over 100 MPh. I want to believe there is a non-track advantage to summers to offset the inconvenience of swapping to winters, the harsher ride, and increased wear.

Thoughts?

[Anshy21]

Summers - not all season. Upped pressure to 40F/42R PSI, tyres tested to 165mph in the UK and run like a dream. Cheers all.