I have a 2007 Mini Cooper S with 17" (205/45-17) Web Spoke wheels and Michelin Pilot Sport A/S Plus tires.

About 3 months ago, I purchased 2 new Michelin Pilot Sport A/S Plus tires as my rear tires were heavily worn. The chain tire shop that I went to would not put the new tires on the front (policy to avoid oversteer in wet conditions), but instead put them on the rear. Right away, the car felt sloppy. With the steering wheel straight on a straight road, the car would drift (a few inches) and shift its weight from side to side as if it were windy, when it wasn't. There was a feeling like the car's steering was connected to a rubber band that was stretching and collapsing. It was especially noticeable on the highway at 70+ MPH when driving on a curve. Whenever, I took my foot off of the gas, the car would slide/drift/collapse back to center, sort of like reverse torque steer. This was a very smooth sensation, not jerky, but it definitely shouldn't be there. I felt that I had to constantly be on top of the car and paying attention to the steering as it was wandering in the lane.

Being concerned about this, I had another tire shop put the new tires on the front. This helped reduce the problem somewhat, but it was still there and annoying. I had not experienced anything like this before. This was my second time replacing only two tires, after I installed four new ones a year and half ago, when I bought the car used.

I had been contemplating some suspension upgrades before, and this seemed like the perfect opportunity to install them to try to solve this problem, as I had become convinced after speaking with my SA and friends that the tires were fine. So, I did the following:

- Tire alignment after moving tires to the front. The problem persisted, but to a lesser degree.
- Replaced a loose manual transmission mount. This helped a little, as the car's center of mass was a little tighter, since the transmission wasn't moving around. Still the problem persisted.
- Upgraded to the JCW suspension - fantastic! The car does not lean or dive and applies more rubber to the road. It is stable in almost all circumstances. However, the problem persisted, but to a lesser degree.
- Installed new Madness Motorworks polyurethane front control arm bushings and rear trailing arm bushings. At this point, I was convinced that my bushings were shot, which they were! The original control arm bushings had 80,000 miles on them and looked like it! The car definitely connected to the road better and gripped better on launch. However, the sloppy steering feel and wandering behavior continued. One surprising side effect is that the steering became lighter than before. I can only surmise that the lack of centeredness of the previous worn bushings had worn grooves/pockets into the rubber thus allowing the steering to feel a bit heavier.

At this point, I am completely bewildered as to what the problem is. By the way, I have driven loaners from Mini (a 2010 Cooper and a 2010 JCW convertible) and none of them had this problem. The only thing that I can think of to change that I have not changed is the tires. Is it possible that I have a bad batch of tires? Remember, this problem started 3 months ago, when I added 2 new Michelin Pilot Sport A/S Plus tires to car. Should I replace all of the tires with 4 new ones?

I welcome any and all suggestions.

 

I should add that I could be experiencing heavy to extreme tramlining (groove following) with my tires. Again, could this be a "bad" batch problem or a feature of the Michelin Pilot Sport A/S Plus tires in their current iteration.

 

Find some good smooth pavement and see if the car still does this.

If not, then you would appear to be experiencing tramlining. Different tires, different pressures, and possibly alignment could reduce or eliminate that.

I have heard that tramlining often occurs when the tread pattern of the tire and the grooves in the pavement are too similar; the blocks of tread tend to follow the grooves. I have experienced that tramlining can get worse when you increase the pressure in the tires. I believe that negative camber can also contribute to tramlining, but I am less sure of that.

 

On a smooth road, yes, it does. But this is speed related, meaning it occurs most readily and more often at 50+ MPH. I have tried the factory recommended 38PSI front and rear and as low as 34PSI front and rear. 34PSI was just annoying to me, irrespective of the problem I am experiencing now. I had have 3 alignments in the last 2 months with all of my suspension changes. The chamber is the stock camber from the factory.

 

I had a similar issue in an R53, and after months of screwing around, found out it was a loose rear trailing arm. I'd check both the front and rear arms; make sure the bolts aren't sliding (I couldn't move them by hand, but the mechanic who eventually figured it out saw the marks from the bolts sliding up and down--tightened everything down, and it's been fine since). Don't know if this is the same problem you're having, but it's worth a check--it was the most bizarre control issue I've ever had.

 

How much of a difference in tread depth is there between the older tires and the 2 newer ones?

Reason I ask is because I had a similar problem on my Toyota Solara after only replacing two of the tires. They had the same tread pattern, but the difference in tread depth was making my car uneasy at higher speeds. Just a thought

 

I have a 08 MCS that has a similar issue - rather unstable at times.

stock sized RF's on 16" wheels with 4/32" tread depth on fronts and one new tire on back 10/32" and one 8/32" of another brand. That made things rather funky.

I just installed a set of thoroughly worn out non RF BFG's on 17's with even tread wear - all around 3-4/32" and the problem went away - the car tracks so much better now. Made all the difference in the world.

So different tread depths can cause some funkiness for sure on these cars.

 

I have been meaning to report back for quite a while. The problem was resolved by getting two new tires. I did not inspect the old tires, as the tire shop disposed of them, but they must have had some wear problem at their low (but not extremely low) wear level.

Thanks to everyone for their suggestions and recommendations!