proper tire pressure
Thread Starter
Racer
Joined: Mar 2022
Posts: 354
Likes: 193
proper tire pressure
I am running 245/35/ZR19 front
and
305/30ZR/20 rear
some people say i should have higher pressure since they are larger than OE tires. Some say lower pressure to ensure the larger tread has proper contact.
i hope there is someone out there that can supply the correct answer based on math/science/experience.
i do NOT track the vehicle. i do drive aggressively at times.
also
which is more accurate. TPMS in the dash or my handheld digital gauge?
thank you all
and
305/30ZR/20 rear
some people say i should have higher pressure since they are larger than OE tires. Some say lower pressure to ensure the larger tread has proper contact.
i hope there is someone out there that can supply the correct answer based on math/science/experience.
i do NOT track the vehicle. i do drive aggressively at times.
also
which is more accurate. TPMS in the dash or my handheld digital gauge?
thank you all
Team Owner
Joined: Sep 2000
Posts: 24,983
Likes: 2,691
From: Far NW 'burbs of Chicago
St. Jude Donor '13
A handheld digital gauge is usually quite accurate, I have three from different makers 2-10 years old, they all read identically most times and max difference ever is .5 lb
The handheld digital should be more accurate, the TPMS is just a rough number to tell you if something is wrong.
If no one comes up with a better method of determining what pressure is best for YOUR tires on YOUR car, get an alignment done and use 30 psi to start. Every 2k miles use a tread depth gauge and measure each groove on each tire and write the numbers down. Quicker wear in the middle of the tread means over inflation, quicker wear on the edges means under inflation, wear on just one edge means alignment is off.
The handheld digital should be more accurate, the TPMS is just a rough number to tell you if something is wrong.
If no one comes up with a better method of determining what pressure is best for YOUR tires on YOUR car, get an alignment done and use 30 psi to start. Every 2k miles use a tread depth gauge and measure each groove on each tire and write the numbers down. Quicker wear in the middle of the tread means over inflation, quicker wear on the edges means under inflation, wear on just one edge means alignment is off.
Drifting
Joined: Aug 2017
Posts: 1,832
Likes: 337
From: Dayton, OH
Here is a link to the calculator I use. It considers differance in size as well as differance of load range.
https://tiresize.com/pressure-calculator/
I was quite pleased with the results.
https://tiresize.com/pressure-calculator/
I was quite pleased with the results.
Le Mans Master
Joined: Jun 2019
Posts: 5,395
Likes: 2,127
From: Loveland
YES. I agree. The OEM pressure is sometimes based on standards to improve fuel economy. Other pressures are based on performance. Just like you said, check the wear over time. This will be the best pressure to make your tires last the longest. This isn't best for racing, or even comfort, but will make your tires last longet.
Drifting
Joined: Aug 2017
Posts: 1,832
Likes: 337
From: Dayton, OH
If you go to larger tires the contact patch is different but the weight of the car is the same. Pounds per square inch. Same pounds of car, more square inches of contact patch, the whole tire actually. The amount of force per square inch the tire sees will be less and the tire will not have the proper shape.
I went to larger tires and used the placard pressure setting. Even though the tires were larger I didn't seem to have more grip, less actually, and it didn't feel like the tires were, for lack of a better description, 'happy'.
I used the 1010 calculater which indicated a significantly lower pressure. When I lowered the pressure (All four tires.) I could feel an improvement in cornering and ride quality. The front felt more settled.
Stick Shift Enthusiast
Joined: Oct 2005
Posts: 7,469
Likes: 2,657
From: Troy & Dearborn, Michigan
I'm sure it does and as long as you are using tires that are the same size and the same load range the setting in the manual is good.
If you go to larger tires the contact patch is different but the weight of the car is the same. Pounds per square inch. Same pounds of car, more square inches of contact patch, the whole tire actually. The amount of force per square inch the tire sees will be less and the tire will not have the proper shape.
I went to larger tires and used the placard pressure setting. Even though the tires were larger I didn't seem to have more grip, less actually, and it didn't feel like the tires were, for lack of a better description, 'happy'.
I used the 1010 calculater which indicated a significantly lower pressure. When I lowered the pressure (All four tires.) I could feel an improvement in cornering and ride quality. The front felt more settled.
If you go to larger tires the contact patch is different but the weight of the car is the same. Pounds per square inch. Same pounds of car, more square inches of contact patch, the whole tire actually. The amount of force per square inch the tire sees will be less and the tire will not have the proper shape.
I went to larger tires and used the placard pressure setting. Even though the tires were larger I didn't seem to have more grip, less actually, and it didn't feel like the tires were, for lack of a better description, 'happy'.
I used the 1010 calculater which indicated a significantly lower pressure. When I lowered the pressure (All four tires.) I could feel an improvement in cornering and ride quality. The front felt more settled.
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Cruising
Joined: Apr 2024
Posts: 11
Likes: 0
The most accurate/easiest I find is using the chalk method, since you see what actually makes contact (great if you don't have a temp probe or anything else). Basically draw a straight line of chalk across the tread, then drive in a straight line a couple hundred feet, then see if the outer, inner, or across the tire chalk is getting scrubbed off more. Then inflate/deflate as appropriate until the chalk wears off consistently and you've got the right PSI.