Automotive vs Backyard Engineers & Tire Pressure

[RidingOnRailz]

Automotive vs 'Backyard Engineers' & Tire Pressure

Yes, another tire pressure thread, but more psychological in nature. Now I have been perusing tire pressure threads and conversations in dozens of auto forums on the VerticalScope platform, and a common gene seems to run through a lot of these conversations:

That the individuals who own, drive, and/or work on the vehicles those forums are dedicated to, think they know more about the tire pressures for their specific vehicles than the people who designed and built the things.

When their assertions as to how high or low their tire pressures "should be" are challenged, either by folks like myself or Barry, more knowledgeable about tires and wheels than average, they take often grave offense. Almost a presidential-politics-level of "who are you to tell me how much air should go in my tires" offense.

My question: Why do they think they know better than their car's manufacturer about tire pressures for their car, and the above information, is designed to delve into the psychology behind these uninformed/ misinformed attitudes.

[RidingOnRailz]

IE:

The cocky attitudes displayed from post #11 on, in this thread:

https://www.insightcentral.net/threa...ng-with.15081/

[Blue Bowtie]

For a specific TPC on a specific vehicle, there is a pretty darned good chance that the engineering performed by the factory to determine correct tire pressures for a given position (front/rear) are about as close as it will get to being right.

Start changing the TPC (tire design), wheel width, and possibly the vehicle loading, and all of that becomes merely a guideline to correct pressures.

As an example, I have a 2003 S10 4X4 with Z85 suspension. Tire options were the "standard" Goodyear LT/M&S 4/2 ply radials rated for 1,609 lbs. at 35 PSI (TPC 105S), or optional Goodyear AT/M&S 6/4 ply radials rated for 1,984 lbs. (TPC 104Q). That latter set was also capable of off-roading at 18 PSI inflation or "normal" use at 50 PSI.

If another brand or TPS (or load index) tire is mounted to that, all bets are off, regardless of the 235/75-R15 size match to the originals.

I think you are probably correct that the factory had their numbers right for those original designations.

[RidingOnRailz]

Originally Posted by Blue Bowtie

For a specific TPC on a specific vehicle, there is a pretty darned good chance that the engineering performed
by the factory to determine correct tire pressures for a given position (front/rear) are about as close as it will
get to being right.

Start changing the TPC (tire design), wheel width, and possibly the vehicle loading, and all of that becomes
merely a guideline to correct pressures.

As an example, I have a 2003 S10 4X4 with Z85 suspension. Tire options were the "standard" Goodyear LT/M&S
4/2 ply radials rated for 1,609 lbs. at 35 PSI (TPC 105S), or optional Goodyear AT/M&S 6/4 ply radials rated for
1,984 lbs. (TPC 104Q). That latter set was also capable of off-roading at 18 PSI inflation or "normal" use at 50 PSI.

If another brand or TPS (or load index) tire is mounted to that, all bets are off, regardless of the 235/75-R15 size
match to the originals.

I think you are probably correct that the factory had their numbers right for those original designations.

TPC,TPS? Grrrr... acronyms make me itch!

But seriously, yeah, most of the 'backyard engineers' I hear complain about:

Factory tire pressures leave a 'bulge'(in the part of the tire touching the pavement).

Factory tire pressures feel 'mushy'.

.... are "underinflation!"

"When I add 5psi to what's listed on the door, the handling "improves", as does gas mileage"

etc...

[CapriRacer]

Part of the problem here is that the placard tire pressure spec is the result of a particular goal the OEM had. You can't have everything, so the pressure spec is a compromise.

Many people have different goals - and since tire pressure is an easy thing to change.......

The net effect is that some people think that the placard pressure is totally wrong - or at least only applies to the original tires.

[RidingOnRailz]

Originally Posted by CapriRacer

Part of the problem here is that the placard tire pressure spec is the
result of a particular goal the OEM had. You can't have everything, so the pressure
spec is a compromise.

Many people have different goals - and since tire pressure is an easy thing
to change.......

The net effect is that some people think that the placard pressure is totally wrong -
or at least only applies to the original tires.

And, as you stated before in an adjacent thread, the cold pressure(s) arrived at are often chosen to work with specific spring rates and suspension compliances, and deviating too much from them could have implications.