Crazy oversteer / wheelspin with Michelin Pilot Super Sport

[Ubersuber]

It is very easy to see in what way Subaru changed the 2015 models from the descriptions of the handling.

As for comparing handling characteristics of heavier awd cars to the rwd BRZ by comparing spring rates that is just absurd.

[wparsons]

Originally Posted by Ubersuber

As for comparing handling characteristics of heavier awd cars to the rwd BRZ by comparing spring rates that is just absurd.

Funny, you're the one that brought it up. Many times over. Let me refresh your memory:

Originally Posted by Ubersuber

Of course the Impreza is awd so can tolerate more rear roll stiffness under power. Lift off tuck in will be more assertive with higher rear roll stiffness on an awd car but that is generally a benign or even useful effect. The BRZ does not have the front drive forces which reduce the front grip in corners. Subaru seems to have overlooked the need to adjust the rear roll stiffness to compensate for the increased front grip resulting from no drive to the front axle.

[stonenewt]

Originally Posted by Ubersuber

My point was only that you don't fix handling problems with tire pressures. You fix handling problems first and then optimize tire pressures.

It all begins with the shape and temperature of the contact patch. You optimize your suspension to keep the contact patch the correct shape and pressure on the road and only then do you adjust tire pressures to fine tune those aspects of the tire. For road use the recommended tire pressure is the minimum pressure you should use. Generally speaking you can increase grip by increasing tire pressure from that recommended setting.

...

One thing we disagree on: running even a couple of psi low can seriously overheat a street tire especially when running at high speeds or with heavy loads. It is flat out dangerous which is the motivation behind the misguided TPMS regulations (misguided as currently implemented. The idea is sound and the technology is there to properly implement TPMS it just isn't being used properly).

Strange because I have two car manuals on my desk. One of which recommends a higher 3psi pressure when fully loaded. But in the paragraph underneath says that tyre pressures up to 0.3 bar (4.5psi) lower or 0.1 bar (1.5psi) are fine but may cause excessive or uneven wear of the tyre. The other doesn't even give a recommended tyre pressure but rather tells me to keep the tyre pressure between 23 and 35psi on the front and 25 to 37psi on the rear. The latter has several pages of information on choosing and adjusting the tyre pressures, a lot of that is talking about how to tune handling to your preferred feel & balance. Or in your terms 'fix'.

Two interesting points here, first of the manufacture with the narrower tyre pressure range seems to be far more concerned with over pressure than under pressure. Secondly 11-12psi is a huge pressure range if a couple of PSI really will cause overheating issues!

Originally Posted by Ubersuber

Carcass construction does indeed affect the recommended pressure as does tire section. However, higher performance tires have less sidewall support than lesser tires and lower profile tires with smaller air volumes require higher tire pressures than lesser tires. This is in general, there may be exceptions.

Actually they're all over the place! Let's take my 120d's 225/40R18 tyres. I can go from economy/touring tyres to high performance sports/fast road tyres. As a general rule er well.. it's all up in the air really! AD08s & Sottozeros like the same high pressure. The PSS like lower pressures. P7 Blue like high pressures about half way between & P7 work at the same sort of pressures as the PSS.

[EAGLE5]

Don't feed the troll. Use the ignore feature.

[unsurety]

Originally Posted by jsimon7777

Don't feed the troll. Use the ignore feature.

I was gonna say just that. On the bright side, a lot of people post insightful responses to him, so it's not all for nothing.

[Ubersuber]

Originally Posted by unsurety

I was gonna say just that. On the bright side, a lot of people post insightful responses to him, so it's not all for nothing.

Interesting viewpoint. Occasionally, those responses are useful but often they are full of misinformation. Lots of experts on this forum.

[Dipstik-sportech]

Originally Posted by Ubersuber

Interesting viewpoint. Occasionally, those responses are useful but often they are full of misinformation. Lots of experts on this forum.

There are also people who think they're experts and just spew nothing but misinformation, such as a certain suberman.

[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.

[wparsons]

Originally Posted by Ubersuber

Interesting viewpoint. Occasionally, those responses are useful but often they are full of misinformation. Lots of experts on this forum.

Like when you claimed you should NEVER run less than 35psi in any tire on this car because it's not safe?

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.

Useful real world experience that should help the OP!

[stonenewt]

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.

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.

[Ferrari]

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

[wparsons]

Put a strip of chalk all the way across the thread on all four wheels and drive it like 100 feet straight at slow speed. See where the line is worn off. If it's just in the center, keep dropping the pressure until it's even across the tread.

If it's not wearing off at all, drive further. Just make sure it's straight, going around a corner will alter the contact patch.

[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

[troek]

Originally Posted by wparsons

Put a strip of chalk all the way across the thread on all four wheels and drive it like 100 feet straight at slow speed. See where the line is worn off. If it's just in the center, keep dropping the pressure until it's even across the tread.

If it's not wearing off at all, drive further. Just make sure it's straight, going around a corner will alter the contact patch.

im assuming this wouldnt apply to someone running aggressive camber?