Tire Pressure recommendation (6 Viewers)

[Sac Cerevisiae]

Maybe this belongs in the SQOD thread. Sorry for the drift. I understand how to get to the recommended pressure for road use based on load limit (ie 43psi for my KO2). And I understand conceptually the benefit of airing down for off road and sand. I’ve seen pics of bead locked tires down to 5 psi. And understand that lower pressure suggests lower speeds.

What I don’t understand is why it’s okay to do so without damaging the side wall. It seems like extended periods of time is spent at low psi when off road. And considerable flexing of the side wall.


Why is it then safe to just air up before hitting the pavement again? Are tires designed to be subject to that flexing as long as they don’t get overheated (with speed)? Or is there some degradation (side wall weakening) and one should expect to replace tires sooner than if they weren’t subject to off road use?

My understanding is that when aired down tires don’t bulge out towards the side but rather longitudinally creating a longer contact patch. There could be additional strain on the sidewalls but not enough to create damage.

A lot of trucks regularly air down and up with no consequences. You’re more likely going to suffer another form of tire damage off-road than sidewall fatigue.

 

[Dan Lee]

Thanks. Yea, I gather that it's common practice. Just out of curiosity, trying to understand why underinflation is bad for street but no consequences when going slow off road. It likely has to do w/ speed but not really quite sure. So, for example: if the recommended pressure based on load is 43psi for my car/tires, why is not okay to drive on the highway with 25psi but perfectly okay off road (driving 30mph) - just conceptual examples? Dumb question, but the cat in me wants to know.

 

[04UZJ100]

Thanks. Yea, I gather that it's common practice. Just out of curiosity, trying to understand why underinflation is bad for street but no consequences when going slow off road. It likely has to do w/ speed but not really quite sure. So, for example: if the recommended pressure based on load is 43psi for my car/tires, why is not okay to drive on the highway with 25psi but perfectly okay off road (driving 30mph) - just conceptual examples? Dumb question, but the cat in me wants to know.

Has to do with speed and the ability of the tire to shed heat that is built up. Each time the sidewall contacts the ground, it compresses. That continual and rapid compression and decompression generates heat which can exceed design parameters when traveling at speed. It will also negatively affect handling and performance.

 

[TeCKis300]

First order concern for inflation pressure is ultimately heat in the tires. Less pressure equals more distortion of the tire sidewall as it goes round creating heat. This is primarily driven by load on the tires and speed.

Second order concerns are stability, tire wear, traction, comfort, etc.

If we can understand inflation pressures in relation to heat. Off-roading can be done with lower pressures as speeds are far lower. Exception is something like Baja running where speeds can be high, and pressures should be adjusted accordingly. A lighter vehicle can run lower pressures.

Understand that the manufacturer recommended inflation pressure on the door jamb has to consider the full envelop of performance, i.e. max payload, gvwr, top speed, hot weather. That establishes a min pressure with margin. Then the pressure is further tailored up for the second order concerns.*

As I don't drive with full payload and gas pedal to the firewall in day to day use, I'm fully comfortable tailoring AT tire pressures for secondary concerns.

*Going back to many of the RCTIPs recommended in this thread. LCs are running unnecessarily high pressures. LX derived RCTIPs are lower, for a heavier vehicle. Which means RCTIPs derived for the LX are fully compatible with at least the payload and speed envelop of the LC as they are both 200-series. Feel free to run the LX lower pressures on account of ride comfort for LCs.

 

[ChowChilla]

2016 land cruiser with BFG KM3 LT275/70/18, what air pressure should I be running for highway

 

[Dan Lee]

Ahhh. Thanks guys. I think I was conceptualizing this wrong. I was thinking in terms of springs and cumulative oscillations. But actually, it seems it's more relevant to think about this as heat sinks. Heat source is oscillation frequency, oscillation range of movement and heat as a function of rotational speed. While at low psi, the tire is able to dissipate the heat build up from oscillation frequency and rotational speed much better than on pavement at highway speeds. So, while the range of movement might be larger, the heat build up is much lower for low psi, low speed than for low psi, high speed. The frequency of oscillation is factor in heat generation and dissipation. It's not the range of movement per se but a combination of factors. I think I'm starting to get it. Thanks!

 

[gaijin]

2016 land cruiser with BFG KM3 LT275/70/18, what air pressure should I be running for highway

The Recommended Cold Tire Inflation Pressure (RCTIP) for those LT275/70R18 KM3 tires on your LC200 is 41psi F/R.

The RCTIP is for onroad/highway use.

HTH

 

[gaijin]

*Going back to many of the RCTIPs recommended in this thread. LCs are running unnecessarily high pressures. LX derived RCTIPs are lower, for a heavier vehicle. Which means RCTIPs derived for the LX are fully compatible with at least the payload and speed envelop of the LC as they are both 200-series. Feel free to run the LX lower pressures on account of ride comfort for LCs.

Tire pressure is a personal choice. However, beware false prophets who advise it is OK to ignore the RCTIP from the auto and tire manufacturers.

What @TeCKis300 is saying, in essence, is if you FEEL your ride at RCTIP feels too harsh, the go ahead and reduce the tire pressure - no problem. If your door jamb recommends 33psi for the stock tires, but you feel the ride is too harsh, then go ahead and reduce pressure to 30psi, or 28psi, or even 25psi - no problem.

This is reckless advice and potentially very dangerous. There is no science behind this advice - just feelings. Do you "feel" like trusting the safety of you and your family to feelings? I hope not.

Further, the LC200 is a 200-series vehicle, but the LX570 is not - it is a 201-series vehicle. These two vehicles, despite sharing a lot of design features, have dramatically different suspension systems. And guess what, tires are part of the suspension system which is tuned by engineers at Toyota for best overall performance. For the 200-series Land Cruiser, the tire component of the system is tuned to support 2,512 pounds of static load. On the other hand, the 201-series LX570 is tuned to support 2,315 pounds of static load. Mix and match these performance requirements based on the feelings of an anonymous internet forum contributor at your own risk.

HTH

 

[04UZJ100]

It’s been a week.

 

[TeCKis300]

Tire pressure is a personal choice. However, beware false prophets who advise it is OK to ignore the RCTIP from the auto and tire manufacturers.

What @TeCKis300 is saying, in essence, is if you FEEL your ride at RCTIP feels too harsh, the go ahead and reduce the tire pressure - no problem. If your door jamb recommends 33psi for the stock tires, but you feel the ride is too harsh, then go ahead and reduce pressure to 30psi, or 28psi, or even 25psi - no problem.

This is reckless advice and potentially very dangerous. There is no science behind this advice - just feelings. Do you "feel" like trusting the safety of you and your family to feelings? I hope not.

Further, the LC200 is a 200-series vehicle, but the LX570 is not - it is a 201-series vehicle. These two vehicles, despite sharing a lot of design features, have dramatically different suspension systems. And guess what, tires are part of the suspension system which is tuned by engineers at Toyota for best overall performance. For the 200-series Land Cruiser, the tire component of the system is tuned to support 2,512 pounds of static load. On the other hand, the 201-series LX570 is tuned to support 2,315 pounds of static load. Mix and match these performance requirements based on the feelings of an anonymous internet forum contributor at your own risk.

HTH

Yes, feelings if you liken it to be that. I prefer engineering judgement. After 20 years in the discipline, and modifying cars as a hobby, I'm comfortable straying outside of the box based on sound logic and interpretation. If you only feel comfortable with your strict interpretations, so be it.

Toyota didn't engineer the LC for any of the tires or suspensions we're putting on. You might as well throw whatever basis you suppose of Toyota engineering out the door.

Modifying tire pressures can be a thing too.

 

[nor_cal_cyclist]

RCTIP for my LC200 running BFG KO2's in 305/65-18, please.

 

[gaijin]

RCTIP for my LC200 running BFG KO2's in 305/65-18, please.

BFG doesn't make an ISO Metric 305/65-18 KO2 tire.

The closest I could find on the BFG web site is LT305/65R18/E 124/121R.

If that is your tire, then the RCTIP for the LT305/65R18/E 124/121R KO2's on your LC200 is 35psi F/R.

HTH

 

[spooltime]

Hi @gaijin - I searched and read the first 17 pages, but didn’t see my exact setup. Hope I’m not asking you to repeat!

Falken Wildpeak ATW3 P285/70R17 117T standard load rock warriors for an LC200 2013

 

[gaijin]

Hi @gaijin - I searched and read the first 17 pages, but didn’t see my exact setup. Hope I’m not asking you to repeat!

Falken Wildpeak ATW3 P285/70R17 117T standard load rock warriors for an LC200 2013

No problem.

The RCTIP for thos Falken Wildpeak A/T3W P285/70R17 SL 117T tires on your 2013 LC200 is 27psi F/R.

HTH

 

[TrekboxX]

Hey @gaijin! What does the master say about 285/75/17's in a Yoko G003 flavor? Thanks!

 

[gaijin]

Hey @gaijin! What does the master say about 285/75/17's in a Yoko G003 flavor? Thanks!

I need more info.

1. Do you mean the LT285/75R17 121/118Q Load Range E Yokohama M/T G003?

2. Are these going on a LC200 or LX570?

 

[TrekboxX]

I need more info.

1. Do you mean the LT285/75R17 121/118Q Load Range E Yokohama M/T G003?

2. Are these going on a LC200 or LX570?

Yes, those are them. On a LC200. Also, do you use a rule of thumb for pressure change with load change? Thanks!!!

 

[gaijin]

Hey @gaijin! What does the master say about 285/75/17's in a Yoko G003 flavor? Thanks!

I need more info.

1. Do you mean the LT285/75R17 121/118Q Load Range E Yokohama M/T G003?

2. Are these going on a LC200 or LX570?

Yes, those are them. On a LC200. Also, do you use a rule of thumb for pressure change with load change? Thanks!!!

The RCTIP for those LT285/75R17 121/118Q tires on your LC200 is 37psi F/R.

No "rule of thumb" for load change - the RCTIP is good for all loads up to the stock GVWR/GAWR of your vehicle. If you load beyond the factory design limits, you are on your own.

HTH

 

[TrekboxX]

The RCTIP for those LT285/75R17 121/118Q tires on your LC200 is 37psi F/R.

No "rule of thumb" for load change - the RCTIP is good for all loads up to the stock GVWR/GAWR of your vehicle. If you load beyond the factory design limits, you are on your own.

HTH

Thanks much!

 

[TTownEP]

@gaijin
I read your post about the source of your RCTIPs and I wanted to take a stab at recalculating mine before I asked you.
2011 LX 570 on P285/50 R20 was stock at 33psi, and I changed to a BFG KO2 in LT275/55 R20 D 115
Using the charts published on Toyo's website, I come up with a RCTIP of 52psi to maintain the 2315lb load rating.
What does the master say?