jaholmes

I have a set of Pirelli Scorpion tires with the pressure set at what the door says. I'm wondering if I can drop a few lbs. They don't seem to be as grippy as they should. F-n snow!

k722070

I tried a few different levels, the 51 rear was too high for me.
I'm using 38 front, 40 rear, very grippy and handles well. obviously not as firm a ride as the 51 rear from door.
but my snow is much different than chicago. usually deep and very dry out here and not as much ice as just hard pack snow surface.

tirerack recommended 38-42, start there, get a compressor and try different levels.

Slow Guy

May I ask where you came up with 51 for the rear?

k722070

sorry, 50.
I was trying to remember what the manual listed, I should have looked first. fully loaded reads 39-50 for the 21 inch, which was how they were mounted. there is no listing for 21 inch winters.
local porsche dealer only gave door panel pressure, 39-49. they had no recommendation for 21 inch winters.
tire rack gave the 38-42 so I lowered to that and went from there.

jaholmes

I am not running the fully load PS, just the normal. In Chicago we have way more ice and I feel like the tires are off. I was expecting them to stick more.

ltc

Question #1: what does the sidewall state?
Question #2: what is specified on the manufacturer's website for the tire?

ltc

AFAIK, the door label only applies to the specified homologated tire at time of assembly and delivery, which is probably NOT the winter tire in question.

pdxjim

39 F 43 R

Slow Guy

I'm not a tire expert but I have mounted more than my share of tires so, as to Q#1: The only thing I recall seeing on a tire sidewall other than the Max Tire Pressure and Max Load Rating is (maybe) the Max Bead Seating Pressure which, for those that don't know, is the max pressure the tire mounting tech should use to get the tire to seat on the rim, and this would be a VERY short term pressure, about 30 sec. max.

Q#2: I would only consider the tire mfgr's website info accurate if they included the car make/model in the listing. Just because that tire size fit a Jeep doesn't mean that's the pressure you want on your Cayenne. I would pretty much bet dollars to donuts they're going to refer you to the vehicle mfgr. for tire pressure recommendation. (think Ford Explorer and Firestone) Just my .02

Personally I wouldn't run the max pressure rating indicated on the door unless the vehicle was actually at or near max load. Towing a heavy trailer is one time I would run max pressure.

jaholmes

I called the dealer and they said

37F 44R

So just a pound or so less.

jaholmes

I called the dealer and they said

37F 44R

So just a pound or so less.

There is no info on the side wall.

ltc

If the tire has been homologated by PAG, then they will have the inflation pressures listed/available.
If not, then it still should have a max inflation/load spec on the sidewall (in addition to the aforementioned mounting pressure/beading spec)

In the absense of any data, then simply drive the car around and do a 3 point pyrometer reading across the tires...... a bit overkill for the pig, I admit.

As for max inflation/beading pressure.....ignore it. 100psi makes mounting/beading go a LOT faster
Hey, it works for kart tires.....sounds like a cannon when one of those things explode....or so I've heard.

Slow Guy

I have never seen a tire with no info on the sidewall, that doesn't mean there isn't a tire without info, I just haven't seen it. I suspect there is a DOT requirement that the info be there.

ljugete

I have a set of 18" Snow & Ice tires on dedicated OEM CT wheels. I believe that you would have optimal performance from smaller tires (17" is best size). 21" snow tires will not perform as well (good for dedicated summer tires).

OEM recommended PSI for my 18" winter tires are 38 front and 41 rear (for my 20" summer tires pressures are 38 front, 44 rear).

egr58

Agree with above. I have 08 CS that came with 18 inch Michelins. Just made the switch to 20 inch Pirelli Ice and Snows, started at 44 R 38F - too squirrelly. Like 40R 38F in actual snow (lower speeds), very good grip. Lately our weather here has been in the twenties (Fahrenheit). On dry road and higher speeds tires naturally build more heat and psi increases, so they are not mushy. Seems to work for me - so far. Like a lot of things, can be very subjective. Just be careful not to go outside the manufacturers' window of recommendations.