Tire Inflation and Lifetime Monitoring via Tread Wear (BFG 37")

[swamp2]

TL/DR: Looks like ideal warm tire inflation pressure is about 32-33 psi for the BFG 37".

I used the chalk test posted here long ago (link) to determine that 35 psi is very good for our rigs.

I'm about 85% street and 15% mixed aggressive off-road. Hoping to up that ratio...

The factory pressure of 38 psi is surely highly driven by EPA/mpg concerns. Wear and comfort (noise not sure) are better lower.

I'm now at about 17.5k miles and here are my tread depths, wear and expected wear:

Conclusions:

1. Need to lower to 33 psi warm (I've been shooting for 35 warm, city). My 35 warm/city will be closer to 38 warm/freeway and I don't typically get that warm unless continuous 75-80 mph for some time on the freeway. I know warm measurements aren't as standard as cold, but they are more meaningful/accurate/useful and super easy to monitor on our rigs.
2. I'm being easy on the tires for a replacement mileage of 50k. Looks like I'll be getting right about 70k out of these.
3. One can see the RR was the most recent tire to get into the 5 tire rotation from being the spare.

Hope there is some useful and actionable data here for others.

(P.S. The mod here put this old (and irrelevant) picture into my thread as a banner, it wasn't me...)

Sponsored

 

[rguest3]

I've been running 34F / 32R psi with 37s on my Broncos. (empty) Not only is the ride much better, but there is even wear across the whole tread of the tire.

 

[Fordified1]

Ignore the warm pressure readings and set it cold and leave alone when hot. Take pressure readings in the shade also. First thing in the morning is best.

Your cold inflation may be closer to 30-31 IDK. But much more consistent readings when cold.

 

[swamp2]

Ignore the warm pressure readings and set it cold and leave alone when hot. Take pressure readings in the shade also. First thing in the morning is best.

Your cold inflation may be closer to 30-31 IDK. But much more consistent readings when cold.

Sorry, nope. Too much variation in morning temperatures (and pressures), esp across seasons.

When you use a tire it has a pretty high power input and lost (dissipated) power obviously warming it up and it is this operating pressure that should be maintained. This operating temperature is also more consistent than cold temperatures as the dissipated power, in part, dominates the ambient temperature of the cold tire.

I'm not saying you can't start with and monitor cold temps, and end up with reasonable results. It's certainly better than ignoring ones tire pressures. It just isn't the real goal nor as accurate.

Why not use the gift of our nice TPMS and nearly real time results right on your instrument cluster?

There is almost always more than one way to "skin the cat" and the way you happen to have been doing it, perhaps for a long time, may not be the best.

 

[Fordified1]

Sorry, nope. Too much variation in morning temperatures (and pressures), esp across seasons.

When you use a tire it has a pretty high power input and lost (dissipated) power obviously warming it up and it is this operating pressure that should be maintained. This operating temperature is also more consistent than cold temperatures as the dissipated power, in part, dominates the ambient temperature of the cold tire.

I'm not saying you can't start with and monitor cold temps, and end up with reasonable results. It's certainly better than ignoring ones tire pressures. It just isn't the real goal nor as accurate.

Why not use the gift of our nice TPMS and nearly real time results right on your instrument cluster?

There is almost always more than one way to "skin the cat" and the way you happen to have been doing it, perhaps for a long time, may not be the best.

Tire manufacturers specify cold pressure for a reason. You’re completely wrong. Sorry. I know this as an absolute fact from maintaining big truck and rv tires. It’s mandatory to use cold temp pressure readings and ignore hot readings except to monitor changes like a tire deflating from a leak.
Remain ignorant on the subject if you choose.
About the only time all 4 tires are exactly the same temperature is first thing in the morning before the sun hits them.

 

[NaMinesClarence]

The only tire that seems to have the correct pressure is the left rear. Or are you content with uneven wear?

 

[swamp2]

The only tire that seems to have the correct pressure is the left rear. Or are you content with uneven wear?

Hmmm, read much?

 

[swamp2]

Tire manufacturers specify cold pressure for a reason. You’re completely wrong. Sorry. I know this as an absolute fact from maintaining big truck and rv tires. It’s mandatory to use cold temp pressure readings and ignore hot readings except to monitor changes like a tire deflating from a leak.
Remain ignorant on the subject if you choose.
About the only time all 4 tires are exactly the same temperature is first thing in the morning before the sun hits them.

Old habits can indeed die hard.

There isn't a black and white wrong here, it's a matter of accuracy and a bit of common sense.

Was this "standard" developed in a time when there was inexpensive, accurate, (near) real time pressure monitoring?

Why do we want an ideal pressure? Many reasons, but for purposes here, even wear. When does a tire wear - under use, at operating temperature, obviously not sitting in a cool (unpredictably cool) morning driveway or garage.

It's very obvious with my pressure monitoring, if one side of the vehicle has warmer tires. I can account for that when adjusting pressures.

I'm not claiming that monitoring pressure under operating conditions is a standard, I'm just claiming it is better.

 

[ed_freeman]

Since we've got so many tire pressure experts here (not being facetious), which tire pressure recommendation should be relied on first... the manufacturers recommendation on the tag inside the drivers door or the recommendation on the tire itself? I guess I can add a 3rd value in as well from the onboard computer and the TPMS readings.

My tires and wheels were upgraded from the stock '23 Black Diamond offering to 315's at the dealership before I purchased it so its a much different tire than original. Always been curious as to which pressure setting to follow.

Many thanks ahead of time

 

[Fordified1]

Since we've got so many tire pressure experts here (not being facetious), which tire pressure recommendation should be relied on first... the manufacturers recommendation on the tag inside the drivers door or the recommendation on the tire itself? I guess I can add a 3rd value in as well from the onboard computer and the TPMS readings.

My tires and wheels were upgraded from the stock '23 Black Diamond offering to 315's at the dealership before I purchased it so its a much different tire than original. Always been curious as to which pressure setting to follow.

Many thanks ahead of time

I believe Swamp2 provided a “chalk test” thread link in the first post.
Almost everyone has concluded that the tire pressure listed on the doors is too high. Ford was going after MPG and protecting themselves from a recurrence of the Explorer tires failures and roll-overs fiasco from the 90’s.
The max pressure stamp on the tires is only for when they are loaded to the max. Swamp2 also explained how he came up with his ideal pressures. The only thing we disagree on is when the readings should be taken.

 

[swamp2]

Since we've got so many tire pressure experts here (not being facetious), which tire pressure recommendation should be relied on first... the manufacturers recommendation on the tag inside the drivers door or the recommendation on the tire itself? I guess I can add a 3rd value in as well from the onboard computer and the TPMS readings.

My tires and wheels were upgraded from the stock '23 Black Diamond offering to 315's at the dealership before I purchased it so its a much different tire than original. Always been curious as to which pressure setting to follow.

Many thanks ahead of time

I'd be willing to bet that all Broncos, regardless of doors, cargo, tires brand and size, will get better wearing and more comfortable tires at 33 psi cold or warm as compared to manufacturer recommended pressures. Similarly, the penalty on mpg will be very slight.

Manufacturer recommendatikns are better than what is printed on the tire as those are maximum limits to be used with heavy loads or towing.

As pointed out above a chalk test or wear monitoring across the tire provide incrementally more accuracy/insight.

 

[jzweedyk]

I assume you have the C range 37" tires right?

 

[swamp2]

I assume you have the C range 37" tires right?

Yes, factory standard.

 

[HertiageMerica]

It is pretty straight forward to just Boyle's Law the whole thing......PV=nRT

P1T1=P2T2 Then you can use figure out what the pressure will be at a given temperature.

you don't need the nR part since it just cancels out on each side and the volume should be about constant.

 

[swamp2]

It is pretty straight forward to just Boyle's Law the whole thing......PV=nRT

P1T1=P2T2 Then you can use figure out what the pressure will be at a given temperature.

you don't need the nR part since it just cancels out on each side and the volume should be about constant.

I guess you meant

P1/T1 = P2/T2 ?

Not sure how much the volume correction matters. If you assume you can air down at constant temperature to maybe 50% of your normal pressure then the resulting volume would be double. Sure we are really only talking about changes within a non airing down scenario, that said the volume change might not be entirely negligible.

Sponsored