Crazy oversteer / wheelspin with Michelin Pilot Super Sport

[wparsons]

Originally Posted by troek

im assuming this wouldnt apply to someone running aggressive camber?

Kinda correct. You can still do the same thing, but what you should see is the line disappearing gradually as you go towards the outside. If you're running lots of camber and too much pressure it'll still balloon in the middle.

[troek]

ahh gotcha.

[7thgear]

with regards to setting pressures




in general, a very good rule of thumb is to have enough air in the tire to support the carcass so that it doesn't roll over.


any more air than that will simply stiffen it up more, and as the pressure increases then absolute grip will begin to decrease as well.


so one way to do it is to chalk your sidewalls and do an autocross. If your sidewalls don't get scrubbed, you can keep dropping pressures.




these are my R1Rs that I've ran for 13 autocross events


as you can see, the wear line hasn't been crossed, just aggressive shoulder wear of the actual compound due to the limited camber





my pressures? 27-28 hot MAX, and i'll usually start the day at 26 psi.


these are 235/40/17 Toyo R1R



always experiment and always be willing to test conventional wisdom when it comes to TIRES, because they all behave differently on different cars and for different applications.


and for god's sake dont' listen to anything ubersuber says. He's a hardcore manual man that doesn't actually drive cars, or drive them at any level worth discussing. Probably has all the wrong inputs, which is why he spins out all the time.

[wparsons]

To add to what Serge (7thgear) said above, he's also running wider tires on a narrow wheel (235's on a 7" wheel) which typically makes them more prone to rolling over, so a less oversized fitment (225's on an 8", etc) could probably run a bit less too.

[Ubersuber]

Originally Posted by reardrv

I have 225/45R17 PSS's on my BRZ and have noticed that do to the much stiffer construction than the stock tires the center on them balloons out at the stock 35PSI tire pressure to the point where the shoulder of the rear tires does not contact the pavement. There was definitely a sway and grip feeling from the rear at 35PSI. Dropping to 34 PSI front and 32 PSI rear cold tire pressure got rid of that feeling. These tires seem to like lower pressures than the stock tires. Even when I autocross I'm at 36 PSI front and 34 PSI rear hot compared to 42 PSI front and 38 PSI rear when I was on stock rubber.

The 225/45 x 17 has significantly more internal air volume than the stock 215/45x17. Subaru has no recommendation for the tire pressure for this size since they don't fit the size to their car. Michelin will. Anyone actually asked Michelin whether they recommend lowering the tire pressures from their recommended cold settings to improve performance? Thought not.

Generally speaking the larger the air volume of the tire for a given vehicle weight the lower the recommended static tire pressure will be.

Autocross requires such completely different suspension tuning considerations that your selected tire pressures would not be useful nor appropriate for the street use of the original poster. Again though, your experience is entirely consistent with the trend the tire manufacturer would recommend I.e. lower static cold pressures for larger section tires of the same wheel diameter.

The objective is to keep the designed contact patch size and shape and seek and maintain the ideal tread compound temperature for best grip and best handling. For street use this means using the tire (or car) manufacturer's recommended settings and you will invariably find that increasing the tire pressure by up to 2psi (assuming recommended cold pressure of 35 psi or so) improves grip and hardens the ride.

Driving on the street you will never get the tires up to optimum temperature unless you are looking to get ticketed.

Also, you might be very surprised to find the effect ambient temperature has on cold tire pressures. One advantage of adding around 2 psi to measured cold tire pressure is that you will more often be riding at the actual recommended pressure when ambient temperatures are lower than in your garage.

[Ubersuber]

Originally Posted by Jrdad

When I first got my MPSS in 225/45 I could turn left at a light in second gear and go wide open throttle half way through the corner on cold tires at 6*C in an attempt to drift, and the car would just stick. I was running 32PSI. Now I've overheated the tires too many times and have spun them shifting to third. All the fun of the primacys without the major difference when it rains now

You should try the Pilot A/S 3 and compare at that temperature. Amazing tires for most street use.

I'm still running mine at 35 psi even though that's the spec for 215/45x17.

[Ubersuber]

Originally Posted by Ferrari

Lowered pressure to 34 in the rear, we'll see if it makes any difference. Thanks for the advice.

And?

[stonenewt]

Originally Posted by Ubersuber

The 225/45 x 17 has significantly more internal air volume than the stock 215/45x17. Subaru has no recommendation for the tire pressure for this size since they don't fit the size to their car. Michelin will. Anyone actually asked Michelin whether they recommend lowering the tire pressures from their recommended cold settings to improve performance? Thought not.

To summarise a lot of very lengthy reply from one tyre manufacture.

We can not & will not give you any recommendations on what tyre pressure to run or adjustments from factory recommended tyre pressures. Our advice is to start at vehicle recommended tyre pressures and change the tyre pressure with signs of abnormal tyre wear or any handling deficit your may experience.

Even with factory fitted tyres your correct tyre pressure will most likely be different from the guidance given with your vehicle! The types of surface you drive on, the exact specification of your car, the sorts of journeys you do, your driving style & the raw materials used in your tyres' batch will all effect the tyre pressure you should run.

My take home from this - tyre pressure is a bit of a black art & the answer needs to be constantly re-evaluated.

[wparsons]

Originally Posted by Ubersuber

The 225/45 x 17 has significantly more internal air volume than the stock 215/45x17.

Define significant. I doubt the difference in volume is as much as you think it is. What about different wheels (same diameter and width, but different barrel shape)? That's likely to have just as big of volume difference as 225/45 to 215/45 will.

Originally Posted by Ubersuber

Generally speaking the larger the air volume of the tire for a given vehicle weight the lower the recommended static tire pressure will be.

Why does volume matter for tire support? You're adding pressure to support the carcass. Sidewall construction would have a greater difference on pressure need than air volume.

[7thgear]

Originally Posted by Ubersuber

Autocross requires such completely different suspension tuning considerations that your selected tire pressures would not be useful nor appropriate for the street use of the original poster.

autocross STOCK class is STOCK


you will see everything at an autocross you would on the road only much more intense


higher g-loads and the requirement to provide MAXIMUM grip right out of the hole for 60 seconds. There are no warmups.


you're actually asking the tire to do far more than you would on the street.


your logic is false, go away.

[Dipstik-sportech]

You beat me to it @7thgear lol

[Jrdad]

Originally Posted by Ubersuber

You should try the Pilot A/S 3 and compare at that temperature. Amazing tires for most street use.

I'm still running mine at 35 psi even though that's the spec for 215/45x17.

When I get them heated up they stick much better, it's just getting to that point. Imho mpss are the best daily driver performance tire. It's just they can't take the heat and I've overheated them too many times. I still love these tires. I'm just not comfortable when pushing these tires.

[Ubersuber]

Originally Posted by 7thgear

autocross STOCK class is STOCK


you will see everything at an autocross you would on the road only much more intense


higher g-loads and the requirement to provide MAXIMUM grip right out of the hole for 60 seconds. There are no warmups.


you're actually asking the tire to do far more than you would on the street.


your logic is false, go away.

http://www.fia.com/championship/euro...s-championship

http://www.casc.on.ca/autoslalom

OK, if you say so.

[Ubersuber]

Originally Posted by stonenewt

Oh look someone doing some measurement & evaluation based setup & finding that lower tyre pressures work better. This also matches my findings with PSS on a completely different car - PSS tyres work better at lower pressures.

Lower pressures than what?

Michelin's numbers?

What are Michelin's numbers for this tire on the BRZ and are you saying Michelin is wrong?

What is the recommended cold tire pressure for the Michelin SS in 215/45 x 17 size on the BRZ?