GMC Terrain, Equinox, and SRX Forum banner

1 - 17 of 17 Posts

·
Registered
Joined
·
7 Posts
Discussion Starter #1
Michelin P235/55 R18

Tire reads max 44lbs
Door Label 35lbs


The car was delivered with 39lbs in each tire. So what is the correct pressure? Thanks in advance for you advice
 

·
Registered
Joined
·
241 Posts
neparon said:
Michelin P235/55 R18

Tire reads max 44lbs
Door Label 35lbs


The car was delivered with 39lbs in each tire. So what is the correct pressure? Thanks in advance for you advice
35 lbs is correct.
 

·
Registered
Joined
·
715 Posts
The number on the tire is the MAXIMUM pressure for that tire.

35 lbs is a compromise for ride harshness.

I run mine at 40 lbs, and a bit higher on a long trip.
 

·
Registered
Joined
·
10,027 Posts
dwendt44 said:
The number on the tire is the MAXIMUM pressure for that tire.

35 lbs is a compromise for ride harshness.

I run mine at 40 lbs, and a bit higher on a long trip.
Won't running a 40+ on a long trip possibly bump against the 45 max pressure once the tires heat up ? Seems risky, to me anyways.
 

·
Registered
Joined
·
113 Posts
I'm in Phoenix and I never get more than 2-3 pounds when the tires heat up on the hottest days.
 

·
Registered
Joined
·
10,027 Posts
inphoenix said:
I'm in Phoenix and I never get more than 2-3 pounds when the tires heat up on the hottest days.
OK, then I'll let you do it !

Yours truly,

The Tire Pressure Police
 

·
Registered
Joined
·
715 Posts
inphoenix said:
I'm in Phoenix and I never get more than 2-3 pounds when the tires heat up on the hottest days.

That's my experience as well. Wisconsin, Illinois trips.

The lower the pressure the greater the difference in pressure between hot and cold.
 

·
Registered
Joined
·
161 Posts
dwendt44 said:
The number on the tire is the MAXIMUM pressure for that tire.

35 lbs is a compromise for ride harshness.

I run mine at 40 lbs, and a bit higher on a long trip.
Do you experience more wear in the center of the tire using those higher pressures, or is that just a myth?
 

·
Registered
Joined
·
52 Posts
I run 35 lbs of air pressure front & rear. I check my air pressure in the morning before i move the nox and add if needed while the tires are cool. I've done this with all my Vehicales over the years with good success.
 

·
Registered
Joined
·
113 Posts
I run 35-36, when they heat up I might get to 38. That's enough for me without maxing the tire. I know they can go over 40, but I don't want to go there. I see way too many tires explode on the roads here.
 

·
Registered
Joined
·
715 Posts
Terrain2011 said:
Do you experience more wear in the center of the tire using those higher pressures, or is that just a myth?
Not sure about the myth; back in the old bias ply days you'd see some truck tires worn down in the middle. Haven't seen much, if any, in recent years.
the last two vehicles I've had, which I ran at higher pressures, didn't seem to show any more wear in the middle then the outer edges.
 

·
Registered
Joined
·
2 Posts
This " pigheaded Dutch selfdeclared tyrepressure-specialist" registered to make you wiser.

The 44psi is the maximum allowed cold pressure, and not that important .
The 35 psi is the reference- pressure( Pr) is the pressure for wich the maxload is calculated for up tot160kmph/99mph , for a standard load personscartyre.
For XL/ reinforced/ extraload Pr is 42 psi.
So 35 psi is no comprymise, as written here, its nnit calculated for the weight on tyre, but couwardly advice, so you can never blame the carmaker.

What I need to calculate a safe pressure to laws of nature is weight on tyres , and max speed you use, and wont go over for even a minute.
From tyres next, and can be read from sidewall.
Maxload or loadindex
Kind of tyre to determine Pr( XL// or not)
Speedcode, to determine speed for wich maxload is given.
 

·
Registered
Joined
·
5,333 Posts
I usually run 36 or 37 PSI in most of our vehicles. And agree, weight of vehicle, size and usual expected load of driver and passenger(s) are a key component to consider.
I found smaller lighter cars usually do better going by the car maker "35 PSI". The reason for this is that, they too will rise from 35 PSI to 38 or even 39 PSI even in 60F to 70F ambient temperatures when driven on the highway for even 20 minutes of so.
Given that the tire patch of a relatively large 17" or 18" tire on a small car is quite a good size in relation to the vehicle size, the 35 PSI cold pressure and 38 to 39 PSI warm tire pressure on a small car rides very firmly at that point. . . even approaching almost too firm for a comfortable ride. But it works out well for MPG and over all handling.

On a vehicle like my truck or SUV. . . I usually go with the 36 to 37 PSI cold and find they may get up to 39 or 40 PSI which still ride ok since the vehicle is heavier than our smaller compact car and often my truck or SUV will be carrying more load.
In winter. . the increase form "cold" to "Warm" tire pressure is not as extreme. So 35 or 36 PSI stays usually within 1 or 2 PSI and seems safe for acceptable tire traction in light snow, rain, etc.
Just my opinion and habit over the years. Of course, there are always caveats concerning specialty tires, sport vehicles, type of use, etc.
 

·
Registered
Joined
·
976 Posts
Won't running a 40+ on a long trip possibly bump against the 45 max pressure once the tires heat up ? Seems risky, to me anyways.
The max is cold tire pressure not the pressure when the tire is hot.
 

·
Registered
Joined
·
2 Posts
The max is cold tire pressure not the pressure when the tire is hot.
Cold pressure is because that is the only reliable way to check. Because you dont know howmuch it has cooled down already , when you measure.
The cold advice is determined to give the tire warm a deflection that wont overheat any part of it,.
Cold advice is determined for 18 degr C/ 65 degr F., some say its 20/68 but not worth discussion because difference in pressure is marginal.
So cold is when inside tire temp is same as outside tire, so ambiënt temp.
So even when outside 100degrF it is called cold pressure when inside tire also 100 degr F.
Within a sertain range of ambiënt temp difference in pressure is marginal, but above 80 degr F , you should calculate te pressure back to that65 degrF.
And with TMPS with internal sensors, temp reading is pretty accurate, so nowadays you could measure warm pressure, and calculate back to 65 degr F. Some TMPS systems do that for you. Its yust a piece of software they have to make for that, using temp and pressure reading.

When 100 degrF cold measured, dont lower to advice, the tire needs that higher pressure to give lesser deflection, so lesser heatproduction a second , because cooling down is also les then , because of lesser temp diferences between rubber and in and outside air.

Reading back, I saw that I reacted on a topic from 2012. Dayly I google for pressure of last 24 hours, so wonder why this old topic came up.
 

·
Registered
Joined
·
976 Posts
And with TMPS with internal sensors, temp reading is pretty accurate, so nowadays you could measure warm pressure, and calculate back to 65 degr F. Some TMPS systems do that for you. Its yust a piece of software they have to make for that, using temp and pressure reading.
Our TPMs did this on our 2011 motorcycles and also on or current 2016 motorcycles.
 
1 - 17 of 17 Posts
Top