Tire Pressure recommendation (5 Viewers)

[gaijin]

@gaijin - I'm trying to understand the charts you posted earlier (you know, feed a fish, teach to fish . . .). So the math is find P size weight (per the psi on the door tag) in the P table. Multiply x .9 (as the manufacturer uprated the p size by 1.1), and use that weight on the LT chart?

And many thanks!

That's about it. The LX570 comes stock with P285/50R20 tires which have a Recommended Cold Tire Inflation Pressure of 33psi. On the tables, this is a Load Limit of 2315 lbs.

Divide 2315 by 1.1 and you get the adjusted Load Limit for LT-Metric tires (2315 / 1.1 = 2105 lbs).

Now all you have to do is look in the tables for your LT-Metric size and find the pressure that yields >2105 lbs.

Since the Load Limit / Pressure tables are in 5psi increments, one can interpolate the intermediate Load Limits by subtracting a Load Limit at the pressure below the target value from the next pressure above the target value and dividing by 5 - this will give you the Load Limit increment for each 1psi between the published values.

Clear as mud, right?

HTH

 

[grinchy]

Absolutely clear, yep. I didn't do any scaling, so was in the wrong column on the LT charts. Glad to understand it better Thanks!

 

[SWUtah]

I'm still listening. I like to know how things actually work.

No need to " sense" anything. I can tell you I am far from being finished with this topic. Otherwise, I'd be in my " little bit of the universe by myself" instead of engaged in a discussion on this forum.

When you state that by running my tires at 35 psi, at highway speeds, that my tires would overheat and self-destruct that's not been my experience in over 50k miles with these tires. And in all honesty and without the slightest hint of sarcasm, I wonder why not?

I have 180k miles on my LC - over 100k of those I put on in the past 2.5 years. The majority of that time I've been loaded up, and running at 33 psi. And in the past year, I've spent a lot of time in the Mojave and Death Valley areas, at speeds of up to 105mph on pavement and up to 60mph off road. At times it was over 115 degrees outside. I wonder why I didn't experience tire failure under these conditions. I would be less puzzled if I just cruised around town. It seems unlikely that I just got lucky for thousands of miles. That is why I'm skeptical of the 46 psi number.

I would like to know how these load limit numbers are calculated in the first place. Example: what calculations or experiments were conducted to conclude the load limits at a given psi?

I'd like to be able to check the work of the TRA. I see no reason not to question any claim made by any organization or individual, no matter how established or revered. Especially when I'm getting dramatically different results in over 50k miles of testing in the field- specifically:

1- tread wear pattern doesn't match that of an under-inflated tire
2-no excessive heat build up- psi doesn't increase by more than 4psi from cold starting pressure
3-no blowouts

My hunch is that IF you could take away the risk of lawsuits, the persons that actually came up with these industry standard numbers would tell us that within a certain range, it doesn't really matter what psi you run. I also wonder how low you'd have to go and for how long you'd have to drive before you did actually see excessive heat build up and eventually a blow out. I wonder if that number for my tires is more like 15psi rather than 33psi.

If I could find the science behind the load inflation tables perhaps I could work that out for myself. Or perhaps I'll just have to go run them at 15psi and at high speeds out in the desert until one of them blows. I'd prefer the former.

I believe the max load on the door placard is significantly higher than you quoted, but I'm going to wait and check tomorrow. The LC is parked about 1/4 mile away.

In the meantime, any ideas as to the science behind the load limit tables?

Excellent post any input

 

[SWUtah]

I'm still listening. I like to know how things actually work.

No need to " sense" anything. I can tell you I am far from being finished with this topic. Otherwise, I'd be in my " little bit of the universe by myself" instead of engaged in a discussion on this forum.

When you state that by running my tires at 35 psi, at highway speeds, that my tires would overheat and self-destruct that's not been my experience in over 50k miles with these tires. And in all honesty and without the slightest hint of sarcasm, I wonder why not?

I have 180k miles on my LC - over 100k of those I put on in the past 2.5 years. The majority of that time I've been loaded up, and running at 33 psi. And in the past year, I've spent a lot of time in the Mojave and Death Valley areas, at speeds of up to 105mph on pavement and up to 60mph off road. At times it was over 115 degrees outside. I wonder why I didn't experience tire failure under these conditions. I would be less puzzled if I just cruised around town. It seems unlikely that I just got lucky for thousands of miles. That is why I'm skeptical of the 46 psi number.

I would like to know how these load limit numbers are calculated in the first place. Example: what calculations or experiments were conducted to conclude the load limits at a given psi?

I'd like to be able to check the work of the TRA. I see no reason not to question any claim made by any organization or individual, no matter how established or revered. Especially when I'm getting dramatically different results in over 50k miles of testing in the field- specifically:

1- tread wear pattern doesn't match that of an under-inflated tire
2-no excessive heat build up- psi doesn't increase by more than 4psi from cold starting pressure
3-no blowouts

My hunch is that IF you could take away the risk of lawsuits, the persons that actually came up with these industry standard numbers would tell us that within a certain range, it doesn't really matter what psi you run. I also wonder how low you'd have to go and for how long you'd have to drive before you did actually see excessive heat build up and eventually a blow out. I wonder if that number for my tires is more like 15psi rather than 33psi.

If I could find the science behind the load inflation tables perhaps I could work that out for myself. Or perhaps I'll just have to go run them at 15psi and at high speeds out in the desert until one of them blows. I'd prefer the former.

I believe the max load on the door placard is significantly higher than you quoted, but I'm going to wait and check tomorrow. The LC is parked about 1/4 mile away.

In the meantime, any ideas as to the science behind the load limit tables?

Starting I think most of this is about Lawyer’s and company’s versus real world performance and based on members experience. I ran KOs on my 100 series for 40,000 miles 33 PSI no problem?

 

[SWUtah]

I'm still listening. I like to know how things actually work.

No need to " sense" anything. I can tell you I am far from being finished with this topic. Otherwise, I'd be in my " little bit of the universe by myself" instead of engaged in a discussion on this forum.

When you state that by running my tires at 35 psi, at highway speeds, that my tires would overheat and self-destruct that's not been my experience in over 50k miles with these tires. And in all honesty and without the slightest hint of sarcasm, I wonder why not?

I have 180k miles on my LC - over 100k of those I put on in the past 2.5 years. The majority of that time I've been loaded up, and running at 33 psi. And in the past year, I've spent a lot of time in the Mojave and Death Valley areas, at speeds of up to 105mph on pavement and up to 60mph off road. At times it was over 115 degrees outside. I wonder why I didn't experience tire failure under these conditions. I would be less puzzled if I just cruised around town. It seems unlikely that I just got lucky for thousands of miles. That is why I'm skeptical of the 46 psi number.

I would like to know how these load limit numbers are calculated in the first place. Example: what calculations or experiments were conducted to conclude the load limits at a given psi?

I'd like to be able to check the work of the TRA. I see no reason not to question any claim made by any organization or individual, no matter how established or revered. Especially when I'm getting dramatically different results in over 50k miles of testing in the field- specifically:

1- tread wear pattern doesn't match that of an under-inflated tire
2-no excessive heat build up- psi doesn't increase by more than 4psi from cold starting pressure
3-no blowouts

My hunch is that IF you could take away the risk of lawsuits, the persons that actually came up with these industry standard numbers would tell us that within a certain range, it doesn't really matter what psi you run. I also wonder how low you'd have to go and for how long you'd have to drive before you did actually see excessive heat build up and eventually a blow out. I wonder if that number for my tires is more like 15psi rather than 33psi.

If I could find the science behind the load inflation tables perhaps I could work that out for myself. Or perhaps I'll just have to go run them at 15psi and at high speeds out in the desert until one of them blows. I'd prefer the former.

I believe the max load on the door placard is significantly higher than you quoted, but I'm going to wait and check tomorrow. The LC is parked about 1/4 mile away.

In the meantime, any ideas as to the science behind the load limit tables?

Starting I think most of this is about Lawyer’s and company’s versus real world performance and based on members experience. I ran KOs on my 100 series for 40,000 miles 33 PSI no problem?

 

[gaijin]

Starting I think most of this is about Lawyer’s and company’s versus real world performance and based on members experience. I ran KOs on my 100 series for 40,000 miles 33 PSI no problem?

Certainly lawyers (and lawsuits) and company design criteria have had an irrefutable effect on recommended tire pressures, but all of that has to meet a baseline of safety performance that is based on science/experience.

I have read a lot about tires and recommended pressures and have posted my opinions and recommendations based on current state of the technology as published by the Tire and Rim Association. I would point you to two links which highlight the importance of correct tire pressure and what can happen if tires are incorrectly inflated:

- The first is a Wikipedia summary of the Firestone Tire / Ford Explorer controversy: Firestone and Ford tire controversy - Wikipedia. The key takeaway in the context of this discussion is that Ford's recommended tire pressure of 26psi (too low and later increased) was a key contributing factor to increased tire temperature leading to catastrophic tire failure. There's a lot more in the link - good reading.

- The second is a succinct summary on tire use and maintenance published by Kenda Tire: Automotive Tires, Passenger Car Tires, Light Truck Tires, UHP Tires | Automotive | Kenda Tires | Automotive Tires 101. Key points from that are:

Proper Tire Pressure: Why it Matters
Driving on underinflated or overinflated tires compromises any or all of the following.

Stopping distance: Properly inflated tires maximize tread contact with the pavement, and traction along with it. Stopping with improperly inflated tires takes more distance to stop the vehicle in an emergency situation.

Ride and handling: When the tires have too much air, they're overly rigid, which means they don't absorb as much impact, so the car rides rougher and suspension components wear faster. An overinflated tire's tread may crown, allowing only the center portion to contact the pavement, which decreases traction. When the pressure is too low, the ride might be softer, but the tread may not meet the road uniformly.

Fuel economy: Underinflated tires greatly reduce fuel economy.

Treadwear: Along with the traction decrease that comes with overinflation, it also causes the tread to wear more quickly in the center. Underinflation causes wear closer to the sides and allows more heat buildup, speeding wear.

Load bearing: Each tire is rated to carry a maximum amount of weight at a prescribed tire pressure. Some cars specify a higher pressure for greater loads. At best, a tire that's underinflated for the load at hand will suffer the problems detailed above. Extra heat generated in the tire can cause it to fail even if it had held up under a lighter load.

My point is that tire pressures and tire Load Limits are not arrived at capriciously by either vehicle manufacturers or tire manufacturers. Anyone wo chooses to operate at tire pressures different from those recommended by the vehicle manufacturer do so at their own risk - and it is a real risk.

HTH

 

[Dan Lee]

I get your point. And I would tend to agree that Toyota arrived at some PSI through some intelligent balancing of competing vectors; it may be weighted toward a particular vector (one that we don't prefer) but it wasn't a random choice.

That being said, it was likely based on some assumptions. Those assumptions may change as we change tires (different sidewall, different tread, different materials and friction, etc).

How do we decide what's optimal?

 

[linuxgod]

I get your point. And I would tend to agree that Toyota arrived at some PSI through some intelligent balancing of competing vectors; it may be weighted toward a particular vector (one that we don't prefer) but it wasn't a random choice.

That being said, it was likely based on some assumptions. Those assumptions may change as we change tires (different sidewall, different tread, different materials and friction, etc).

How do we decide what's optimal?

There are certain minimum requirements that you need to meet. i.e. for load capacity you need a minimum PSI for the weight each tire carries. Outside of those use some scientific methods (i.e. chalk test to determine maximum contact area, record your fuel economy over multiple tanks, etc) and trust the guy with the PSI tables.

 

[SWUtah]

The seasons make a big difference also I was running 43 this Summer and now they’re all down to like 40 cold heading into winter. But I will say that when I drive the vehicle and the tires get completely warmed up the tire pressure maintains at 43. Next oil and filter change and tire rotation in a couple months I’ll have them all put back to 43 cold. I have only about 10,000 miles on these BFG KO2’s but they are wearing perfectly even actually don’t look like they’re wearing at all I’m sure correct tire pressure plays a role in that.

 

[MTKID]

I saw a close tire back in the thread but not the NOKIAN HAKKAPPELIITTA LT2 LT275/65R20 126/123Q max 80psi cold, which is now on our 08’ LX.

Thanks in advance!

 

[gaijin]

I saw a close tire back in the thread but not the NOKIAN HAKKAPPELIITTA LT2 LT275/65R20 126/123Q max 80psi cold, which is now on our 08’ LX.

Thanks in advance!

The Recommended Cold Tire Inflation Pressure for those LT275/65R20 tires on your '08 LX570 is 36psi F/R.

HTH

 

[gaijin]

The seasons make a big difference also I was running 43 this Summer and now they’re all down to like 40 cold heading into winter. But I will say that when I drive the vehicle and the tires get completely warmed up the tire pressure maintains at 43. Next oil and filter change and tire rotation in a couple months I’ll have them all put back to 43 cold. I have only about 10,000 miles on these BFG KO2’s but they are wearing perfectly even actually don’t look like they’re wearing at all I’m sure correct tire pressure plays a role in that.

Why not just correct your cold tire pressure now? It makes no difference what pressure the tires "warm up" to, the specified pressure should be measured while the tires are cold; i.e. at ambient temperature.

All I can do is lead a horse to water ....

HTH

 

[SWUtah]

Why not just correct your cold tire pressure now? It makes no difference what pressure the tires "warm up" to, the specified pressure should be measured while the tires are cold; i.e. at ambient temperature.

All I can do is lead a horse to water ....

HTH

Because I’m lazy and only drive 5 miles to the gym and 5 miles home and maybe another couple miles a day on nice roads and when I take it in the Lexus dealer for 5000 mile service along with an oil filter change and rotate the tires, I’ll probably have them put 45 in all around so that when they cool down I can adjust them all the same. Last time even though I told them to put 45 pounds and Instead they put 32 pounds then and I had to make them redo it before I left because I checked them I kind ofhave fun screwing with them. I have the extended CPO maintenance for two years so I have about another year of free maintenance so I figure I might as well make them do their job. I could also take them to discount tire and get them rotated for free because that’s where I bought them. But then When I took it in to Lexus for a service that’s free and told them not to touch my tires they would rotate them anyway so I would have all the tires back where they were before I took it to discount tire.

 

[gaijin]

fair enough

 

[MTKID]

The Recommended Cold Tire Inflation Pressure for those LT275/65R20 tires on your '08 LX570 is 36psi F/R.

HTH

That should make for a nice ride improvement from the 47-49 the installing tire shop put in!

 

[gaijin]

That should make for a nice ride improvement from the 47-49 the installing tire shop put in!

It certainly will! I'll never understand why shops that make their living with tires won't spend the extra 10 minutes it takes to research the correct tire pressures

 

[MTKID]

Well, I might as well ask about my summer tires too. Cooper Discoverer AT3 XLT LT285/75R17 121/118S E BSW on the same 08’ LX. Not sure if this would be the same as the non-XLT version.

TIA

 

[Markuson]

That should make for a nice ride improvement from the 47-49 the installing tire shop put in!

Yep. A shop once installed KOs on my 100 series and I thought my suspension must be screwy.

-Turned our the idiot shop had put the MAXIMUM pressure listed on the sidewalk (which was somewhere between 60-80lbs!!! Can’t remember exact number...but it felt like the Flintstone a mobile with stone wheels!

Sometimes the monkey wrench itself...really is the smartest “tool” in the shed...

 

[gaijin]

Well, I might as well ask about my summer tires too. Cooper Discoverer AT3 XLT LT285/75R17 121/118S E BSW on the same 08’ LX. Not sure if this would be the same as the non-XLT version.

TIA

The Recommended Cold Tire Inflation Pressure for LT285/75R17 tires on your LX570 is 35psi F/R.

HTH

 

[ga12r1]

How about Cooper Discover AT3 XLT LT285/60R20
125/122S E BSW on a 2010 LX570?

TIA