Michelin Pilot Sport 4S - Tire pressures

[Casa de Mesa]

Hey all. Just got the following setup in Michelin PS4S:

• Front: 255/40 R18 99Y XL
• Rear: 285/35 R18 101Y XL

I'm looking for suggestions on baseline pressures people are running. I'm aligning and setting up the car this weekend after doing some suspension tweaks, new tires, etc. and looking for a starting point. Once done, I'll monitor the pressures with a pyrometer for temps, etc. but just looking for a starting point on a street car.

Some more info I'm factoring in. Per load index charts, etc. these new tires carry a bit more load per the same psi when compared to the factory spec tires (225/40-19 93Y XL and 255/35-19 96Y XL). Using this link:

https://tiresize.com/pressure-calculator/

...and my door placard showing recommended inflations (33F/35R), I end up with a recommended pressure of 27 F and 29 R.

Three things:

1. I know asking about tire pressures is like asking about motor oil.
2. I know 27F / 29R is low, but that doesn't bother me.
3. I know that a 285 is a meaty thing. I would NOT RECOMMEND this size tire. Compared to the 275s I'm coming from and wanted, it's heavier, has a slightly increased tread width, but a significant bump in section width. I'm running an APEX 18x10 et 25 in the rear and it has been a struggle to clearance the rear fender (quarter panel). A colossal pain in the ass... but they now fit. I hope. 275's were/are on national backorder, I wanted this tire (PS4S) and needed tires sooner.

Thx.

[robgill]

Hey short answer is that 35 cold is completely fine for street driving. Lower pressures on the street aren’t necessary as you are not going to push the tires hard enough to overheat them. Also lower pressures can more easily damage the tire/wheel if you hit a pot hole etc.

On track you would start with lower cold pressures (like 28) so when hot they are around 35.

[Tbonem3]

18s can handle a little less I think than lower profile 19s. I like 32F / 34R or so.

[kermmmit7]

18s and 19s wheels have the same pressure on label 33/35 after conversion this calculator showed 29/33 . You can try it or just stay on original pressure spec.

[Tbonem3]

I was under the impression a lower profile tire requires more PSI i.e., the rears asking for more than the fronts (40 vs 35 profile or 35 vs 30 profile)

[Arith2]

I believe the door card recommends 41psi(not42) front and 48psi for speeds over 100mph. That's what I do.

[Jimbo's M]

I believe the door card recommends 42psi front and 48psi for speeds over 100mph. That's what I do.

No sir. The card states 41 and 48 psi at max vehicle weight, nothing about road speed. At driver only weight, that's gotta be like driving on a washboard.

[Estoril]

I believe the door card recommends 42psi front and 48psi for speeds over 100mph. That's what I do.

Pic of that door card?

[Cubieman]

Pic of that door card?

I'm out in the garge.

[Estoril]

I'm out in the garge.

At 46-50 psi cold - the car should feel like Fred Flintstone's car.

[Arith2]

No sir. The card states 41 and 48 psi at max vehicle weight, nothing about road speed. At driver only weight, that's gotta be like driving on a washboard.

I'll take a picture eventually. The warning is a yellow one above the regular pressure card. It's very common to request higher pressures for high speed. If a Porsche isn't at max load and you exceed a certain speed limit, the dash will scream at you to slow down and put your tires at max load. It's probably to decrease rolling friction and compensate for downforce. A larger contact patch means more heat. The car drives great around town.

[jbfrancis3]

I made the mistake of the following the door card on my ‘05 until Obioban pointed out the change made in the later years of the model run. Addressed here: https://nam3forum.com/forums/forum/m...5-19-275-30-19

[stephen]

I believe the door card recommends 41psi(not42) front and 48psi for speeds over 100mph. That's what I do.

What do your hot tire pressures look like?

[Arith2]

What do your hot tire pressures look like?

2 over maybe. I'm pretty sure all this sort of goes out the window for a track day and it becomes based on whatever set up someone is looking for. This is what I do for the street and that's what the door card is meant for.

[Estoril]

2 over maybe. I'm pretty sure all this sort of goes out the window for a track day and it becomes based on whatever set up someone is looking for. This is what I do for the street and that's what the door card is meant for.

Your hot pressure is only 2 psi over the cold pressure? How is that possible?