Tire Pressure recommendation (13 Viewers)

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Apologies, but I was confused about some terminology. I was under the impression that you were calculating on gross vehicle weight, and additional weight affected the RCTIP. However, I now see that GVWR is the vehicle itself plus the maximum allowable payload. So additional weight (mods) doesn't come into play so long as I don't go over GVWR.

Correct. The RCTIP is good for all loads up to the GVWR.

This might be a silly question: Does loading 1,000lb swing (6,300 empty rig to 7,300lbs family + mods) affect the amount of force on the tires and change the contact patch with the ground? I the suspension keeps things in proper order?

It's not at all a silly question. Contact patch is not the end all and be all of tire pressure. That is why the infamous "chalk test" for determining proper tire pressure is absolutely worthless. The manufacturer's tire pressure spec for the OEM tires, and the RCTIP I recommend, is a pressure designed to yield the best overall performance and safety over the entire legal weight of the vehicle - all the way from lightly loaded to the GVWR. Under no circumstances is a lower tire pressure advisable, however, under certain conditions a temporary increase in tire pressure may be warranted. Yes, the contact patch will change by varying degrees based on load and speed, but this should not be a cause for concern - the projected variances are factored into the RCTIP.

For example, if I am going on a long highway trip, I will usually increase RCTIP by 2psi to help deal with the added stress on the tire of extended highway speeds. This is not strictly required, but has been suggested by many sources as providing some benefit by reducing tire temperature. It's up to you whether to follow this practice. But at the end of the trip, I go back to the RCTIP.

HTH
 
BFG KO2 LT285/65-18. 125/122R

I can't seem to get into the website you listed to check myself.
 
Hello @gaijin I just bought this wheel and tire set from the person who bought This LC I'm sure there will be a build thread from him soon.

Cooper Discoverer AT3 XLT LT285/65/18 125/122S E4
2014 LX570
Thanks !

Frnt_III_285_65_18.png
 
Hello @gaijin I just bought this wheel and tire set from the person who bought This LC I'm sure there will be a build thread from him soon.

Cooper Discoverer AT3 XLT LT285/65/18 125/122S E4
2014 LX570
Thanks !

View attachment 2318591

I really like those wheels!

The RCTIP for those LT285/65R18 tires on your LX570 is 37psi F/R.

HTH
 
@gaijin I've gone through more pages of this thread than I'd like to admit, going back and forth between your recommendations for people's LC200 psi, and the GVWR / GAWR rating on my 2018 LC door panel badge. I seem to be just slightly off your recommendations based on my GAWR (RR). I keep coming up with about +2 psi needed compared to what I see recommended here. What am I doing wrong? Here are the calculations I'm doing:

GAWR (RR) = 4300 LB / 2 = 2150 LB
LC manual says to adjust tire rating by 1.1x --> 2150 LB x 1.1 = 2365 LB rating needed
Goodyear Wrangler UltraTerrain AT - LT285/65R18/E (125/122Q)

In the tables, I see my LT285/65R18 @ 2365 LB needs something between 40 PSI (2235 LB load) and 45 PSI (2425 LB load).
So I'm basically interpolating between that range and coming up with:
44 PSI (2387 LB load) to support my 2365 LB rating needed from the calculations up above.

Is 44 PSI correct? I'm seeing recommendations for 42 PSI elsewhere in this thread for the same type of tires (LT285/65R18/E).
 
@gaijin I've gone through more pages of this thread than I'd like to admit, going back and forth between your recommendations for people's LC200 psi, and the GVWR / GAWR rating on my 2018 LC door panel badge. I seem to be just slightly off your recommendations based on my GAWR (RR). I keep coming up with about +2 psi needed compared to what I see recommended here. What am I doing wrong? Here are the calculations I'm doing:

GAWR (RR) = 4300 LB / 2 = 2150 LB
LC manual says to adjust tire rating by 1.1x --> 2150 LB x 1.1 = 2365 LB rating needed
Goodyear Wrangler UltraTerrain AT - LT285/65R18/E (125/122Q)

In the tables, I see my LT285/65R18 @ 2365 LB needs something between 40 PSI (2235 LB load) and 45 PSI (2425 LB load).
So I'm basically interpolating between that range and coming up with:
44 PSI (2387 LB load) to support my 2365 LB rating needed from the calculations up above.

Is 44 PSI correct? I'm seeing recommendations for 42 PSI elsewhere in this thread for the same type of tires (LT285/65R18/E).

Here is the complete explanation of what you need to do to calculate RCTIP: Guide to Application of Load and Inflation Tables

You are starting with the wrong numbers - GAWR/GVWR do not factor in the calcs.

Start with the OEM tire size and pressure on your door panel badge: P285/60R18 @ 33psi. Looking in the Load and Inflation Tables, this yields a Load Limit of 2513 LB. It is the same for Front and Rear. This is your starting point.

Since you are replacing P-Metric OEM tires with LT-Metric tires, you need to divide the Load Limit by 1.1, so 2513 / 1.1 = 2285 LB. This is the Load Limit you require for LT-Metric tires. Same for Front and Rear.

Look in the Load and Inflation Tables for LT285/65R18 tires to find the pressure (to the nearest full psi) that yields >2285 LB and you will find 42psi.

So... the RCTIP for LT285/65R18 tires on your LC200 is 42psi F/R.

HTH
 
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Awesome, thanks! I had started doing what you described at first, but somehow I missed where the table's instructions said to divide P-Metric Load Limit by 1.1 (which now makes sense from what I saw in the LC manual), and I was ending up with sky-high PSI values that I knew were wrong. It all makes perfect sense now.
 
@gaijin

As an imposter on this 200 board, I humbly submit for your scrutiny my calculations for a 2006 GX470.
  • GVWR: 6200 lbs
  • OE: P265/65R17 @ 32 psi (door sticker in image)
  • Load Inflation Table = 2260
  • P-Metric to LT-Metric conversion = 2260/1.1 = 2055
  • New Target: LT285/70R17 @ 2055 = psi figure outside of (below) chart range, which starts at 35 psi
  • Note from one of your previous posts: "It is unsafe to run ANY LT-Metric tire on-road at less than 35psi. This can lead to excessive temperature build-up and premature/catastrophic failure."
Vehicle has been modified, however, and I have used a spreadsheet to calculate adds/deletes based on GVWR (e.g., two passengers at 150 lb each instead of eight passengers at 150 lb each, rear seats delete, add accessory weights, and so on). Understanding that this is likely not perfect, my calculations show 602 lbs over 6200 lbs sticker GVWR, so 6802 lbs. (Note: my 'going to Death Valley for eight days' weight is likely to be higher still, but I'm too embarassed to talk about it here.) The currently installed heavy-duty aftermarket suspension is the psychological blanket I am using in place of an official GV upgrade (common in AUS, less in US) to support the rationalization that the overage is acceptable.
  • According to a calculation found in one of your previous posts: 600 lbs / 5 = 120 (common rounding)
  • Add 120 lbs to 2205 lbs/psi = 2175
In the Load Inflation Table, the LT285/70R17 @ 2175 lbs/psi is just above the 35 psi mark.

What is the proper RCTIP? Simply estimating "37 psi" feels too arbitrary after all the math that got us to this point.

My gratitude for your patience and expertise, in advance.

EDIT 1: I did not pay enough attention before leaving the tire shop, and now have about 1,000 miles on these LT tires, when I thought I was getting 'the same' P-version of the tire. Now, I'm working with what I've got...and remembering to pay more attention next time. [head desk]

EDIT 1: Tire type is Falken Wildpeak AT3W LT285/70R17

IMG_20200601_101106.jpg


IMG_20200601_101109.jpg
 
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@gaijin

As an imposter on this 200 board, I humbly submit for your scrutiny my calculations for a 2006 GX470.
  • GVWR: 6200 lbs
  • OE: P265/65R17 @ 32 psi (door sticker in image)
  • Load Inflation Table = 2260
  • P-Metric to LT-Metric conversion = 2260/1.1 = 2055
  • New Target: LT285/70R17 @ 2055 = psi figure outside of (below) chart range, which starts at 35 psi
  • Note from one of your previous posts: "It is unsafe to run ANY LT-Metric tire on-road at less than 35psi. This can lead to excessive temperature build-up and premature/catastrophic failure."
Vehicle has been modified, however, and I have used a spreadsheet to calculate adds/deletes based on GVWR (e.g., two passengers at 150 lb each instead of eight passengers at 150 lb each, rear seats delete, add accessory weights, and so on). Understanding that this is likely not perfect, my calculations show 602 lbs over 6200 lbs sticker GVWR, so 6802 lbs. (Note: my 'going to Death Valley for eight days' weight is likely to be higher still, but I'm too embarassed to talk about it here.) The currently installed heavy-duty aftermarket suspension is the psychological blanket I am using in place of an official GV upgrade (common in AUS, less in US) to support the rationalization that the overage is acceptable.
  • According to a calculation found in one of your previous posts: 600 lbs / 5 = 120 (common rounding)
  • Add 120 lbs to 2205 lbs/psi = 2175
In the Load Inflation Table, the LT285/70R17 @ 2175 lbs/psi is just above the 35 psi mark.

What is the proper RCTIP? Simply estimating "37 psi" feels too arbitrary after all the math that got us to this point.

My gratitude for your patience and expertise, in advance.

EDIT 1: I did not pay enough attention before leaving the tire shop, and now have about 1,000 miles on these LT tires, when I thought I was getting 'the same' P-version of the tire. Now, I'm working with what I've got...and remembering to pay more attention next time. [head desk]

EDIT 1: Tire type is Falken Wildpeak AT3W LT285/70R17

View attachment 2326704

View attachment 2326705

You are pressing me on two points where I currently do not offer advice:

1. I only recommend RCTIP for LC200-series vehicles.

2. I no longer engage in any discussions, no matter how hypothetical, about tire pressures for vehicles that are running over the GVWR.

That said, I must admire your dedication to getting to a solution on your own. I can only guess you used my favorite online Load and Inflation Table Guidelines as a source: Toyo Guide for Load and Inflation Tables

Based on your work, and your correct understanding that no LT-Metric tire should be run lower than 35psi on road, I can agree with your conclusion that if your rig were stock, the RCTIP would be 35psi F/R.

As comments on your work, and in no way to be construed as any kind of recommendation or agreement that it is OK to run any vehicle above its GVWR, I can suggest you might want to look more closely at these two points:

1. Any calculated GVW above the GVWR should be evaluated for its impact on 4 wheels - it appears you are assuming 5 in your calcs. You should be dividing by 4, not 5.

2. GVWR "upgrades" are performed by government licensed shops in Australia. There are no such shops for GX470's in the U.S., so you will see no GVWR upgrades for your vehicle in the U.S. Any shops that do work on other types of vehicles such as heavy trucks, etc. and have a working relationship with the manufacturer of that truck, can apply for and be granted permission to change a vehicle's GVWR - even then, this is almost exclusively done when a vehicle is new and before it is delivered to its first owner.

HTH
 
You are pressing me on two points where I currently do not offer advice:

1. I only recommend RCTIP for LC200-series vehicles.

2. I no longer engage in any discussions, no matter how hypothetical, about tire pressures for vehicles that are running over the GVWR.

That said, I must admire your dedication to getting to a solution on your own. I can only guess you used my favorite online Load and Inflation Table Guidelines as a source: Toyo Guide for Load and Inflation Tables

Based on your work, and your correct understanding that no LT-Metric tire should be run lower than 35psi on road, I can agree with your conclusion that if your rig were stock, the RCTIP would be 35psi F/R.

As comments on your work, and in no way to be construed as any kind of recommendation or agreement that it is OK to run any vehicle above its GVWR, I can suggest you might want to look more closely at these two points:

1. Any calculated GVW above the GVWR should be evaluated for its impact on 4 wheels - it appears you are assuming 5 in your calcs. You should be dividing by 4, not 5.

2. GVWR "upgrades" are performed by government licensed shops in Australia. There are no such shops for GX470's in the U.S., so you will see no GVWR upgrades for your vehicle in the U.S. Any shops that do work on other types of vehicles such as heavy trucks, etc. and have a working relationship with the manufacturer of that truck, can apply for and be granted permission to change a vehicle's GVWR - even then, this is almost exclusively done when a vehicle is new and before it is delivered to its first owner.

HTH

@gaijin

Many thanks for validating the math portion of my inquiry. You have my understanding and respect in regard to where you draw the line with providing advice. My comment on GVWR upgrade is an admittedly wispy security blanket, since the upgrades on this elder GX are nowhere close to what (and when) a proper GVWR upgrade is.

Your engagement with the Mud community, however, is further grounds that this member of the unwashed masses has added to the list he's using to convince himself that an LC200 should have a future in his motor pool.

Thanks again.

EDIT 1: Yes, I used the Toyo Guide you pointed to. This document has become known as the sacred scrolls.

EDIT 2: I misinterpreted the divide-by-five from a previous post; I was getting tired. The post in question showed how to 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. It makes no sense in my application above, I went out and performed a recount on number of tires on the ground, and I have resolved the issue. (there are four) That being said, and without asking for validation or advice on a potentially over-GVWR vehicle, I used the load limit psi step interpolation method to come up with 38.6 psi after applying the method. Thank you, once more.
 
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Thanks in advance. I am both an old LC owner 1996 and a new HE owner. What is the RCIP for Nitto Ridge Grappler LT285/60/18 for a 2020 LC?
 
Thanks in advance. I am both an old LC owner 1996 and a new HE owner. What is the RCIP for Nitto Ridge Grappler LT285/60/18 for a 2020 LC?

The RCTIP for the LT285/60R18 E 122/119Q Nitto Ridge Grappler tires on your 2020 LC200 is 46psi F/R.

HTH
 
Hey Gaijin! It took me ages to figure out how tire sizing works and now i'm out here in the dark googling tire pressures. Head about to explode...

Recommended tire pressure on LT 285/55/20 Geolander G015's? Load index "122", Speed rating "S".... ?

THANK YOU!
 
Hey Gaijin! It took me ages to figure out how tire sizing works and now i'm out here in the dark googling tire pressures. Head about to explode...

Recommended tire pressure on LT 285/55/20 Geolander G015's? Load index "122", Speed rating "S".... ?

THANK YOU!

I'm guessing these aren't going on your Prius, but can you please tell me what vehicle these are going on?
 
Hey Gaijin! It took me ages to figure out how tire sizing works and now i'm out here in the dark googling tire pressures. Head about to explode...

Recommended tire pressure on LT 285/55/20 Geolander G015's? Load index "122", Speed rating "S".... ?

THANK YOU!
lol nah not the Prius! Its the other "eco-friendly save the planet" vehicle.....the 2014 LX570, no trailer being pulled and usually pretty empty inside.

The RCTIP for the LT285/55R20 Geolandars on your 2014 LX570 is 43psi F/R.

HTH
 

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