When to air down and to what PSI?

[G.I.G.]

I just received my MV50 air compressor that I ordered last week and it works like a champ! Now that I have an air compressor to bring with me when I go 4-wheel'n, I was wondering when I should air down and to how much? I am running stock SE wheels and Bridgestone Revo A/T tires. I am not planning on doing any crazy rock crawling or anything over my head. I'm wondering what conditions warrant airing down and with my current setup, how low could I drop the PSI in my tires?

 

[PaulSula]

I just received my MV50 air compressor that I ordered last week and it works like a champ! Now that I have an air compressor to bring with me when I go 4-wheel'n, I was wondering when I should air down and to how much? I am running stock SE wheels and Bridgestone Revo A/T tires. I am not planning on doing any crazy rock crawling or anything over my head. I'm wondering what conditions warrant airing down and with my current setup, how low could I drop the PSI in my tires?

Just read about this in a 4wheelparts.com magazine. They advise, 25% drop from street pressure. So for me that would be 24psi. (32psi is my street pressure)

My question to add on to yours is, what are you guys/gals using to air down? Staun deflators, the back of a pressure gauge, your keys?

Hope that helps! Happy Easter!

 

[G.I.G.]

Just read about this in a 4wheelparts.com magazine. They advise, 25% drop from street pressure. So for me that would be 24psi. (32psi is my street pressure)

My question to add on to yours is, what are you guys/gals using to air down? Staun deflators, the back of a pressure gauge, your keys?

Hope that helps! Happy Easter!

Cool, thanks for the info. I'll try to look up that article.

I notice in your sig you're running M/T's. Can M/T's withstand lower tire pressure than A/T's?

I bought a tire pressure gauge with a built in release valve at Checker Auto parts for about $5. It's seems to be pretty accurate and easy to read (more so than a traditional pen type tire pressure gauge). It provides a great way to lower the tire pressure while being able to monitor what PSI you're at.

 

[PaulSula]

I don't know if MT's can be lowered more than AT's. But if someone does, please pipe in. I will be using the pen style pressure gauge to deflate mine once I get a compressor. Too cheap to buy the staun deflators.

 

[createbmx]

so the other day I went offroading which a bunch of other guys. It involved mud puddles up to the hood in depth, and small rock climbing, hills and water crossings. They all stopped to air up before we were to head home, and I realized that I went the entire day with street pressure.

I didn't notice a difference.

 

[PaulSula]

CreateBMX- I totally agree. I was able to find a digital copy of the article which I have linked below. The author advises against airing down unless you can air back up when you leave the trail. I have never aired down when off-roading simply because I don't have a compressor.

In reguard to helping off-road, the reduced pressure can be used, "if nothing else, to smooth the ride".

The full article is online at
http://www.myvirtualpaper.com/doc/Offroad-Adventures-Magazine/april_final/2009032601/22.html

 

[techno]

LAI1n
Lowering tire pressure from highway psi can do more to improve traction off-road than almost anything else you can do. Your tread can then envelope rocks and trail irregularities that your tires previously only touched the top of. Lowered psi won't balloon out your sidewalls much bu it will allow them to conform more easily to trail side rocks instead of resisting to the point of puncture.
Dropping pressure from 30psi down to 10psi will yield at least three times the trail grabbing footprint, but at a loss of 2/3 of the contact pressure. Usually that loss in contact pressure can be gained back with the added weight of off road recovery gear and other stuff that you take when out in the sticks. Also, the static tire radius is reduced which means more torque to the ground.
The down side of lower psi is it costs you ground clearance. My 32s give me better than stock clearance so I can afford a small loss sometimes. The bigger your tires the less the problem.

Whether or not you need the performance benefit is totally up to your own experience and judgment. If your doing just fine traction wise at highway psi then there's no real reason to go lower other than ease of driving and puncture resistance, depending on the conditions. Personally I like to drop my mud tires down to around 22psi for moderately difficult trails. I like the added suspension benefit and don't have to use as much right foot to clear obstacles. I go lower still in sand, usually about 15.
I use a Pro-Comp tire gauge and Staun deflators set at 22. In the early days of wheeling before I got all the gear I would often just lower the pressure for an even amount of time per tire, 45 seconds each for example, and go from there.

 

[G.I.G.]

Great info, techno. Thank you!

I run my tires at 36psi on the street which is probably on the high side for off-roading. As you had mentioned, if the conditions don't necessarily warrant airing down and you have enough traction, why go too crazy. The improved ride quality and making the tire less prone to puncture make it worth while to air down now that I have a compressor. I was also concerned about ground clearance so for most situations, I don't see myself going below 25 or 28psi. It's great to at least have the option to air down now that I have a compressor.

 

[Thai]

Lowering tire pressure from highway psi can do more to improve traction off-road than almost anything else you can do. Your tread can then envelope rocks and trail irregularities that your tires previously only touched the top of. Lowered psi won't balloon out your sidewalls much bu it will allow them to conform more easily to trail side rocks instead of resisting to the point of puncture.
Dropping pressure from 30psi down to 10psi will yield at least three times the trail grabbing footprint, but at a loss of 2/3 of the contact pressure. Usually that loss in contact pressure can be gained back with the added weight of off road recovery gear and other stuff that you take when out in the sticks. Also, the static tire radius is reduced which means more torque to the ground.
The down side of lower psi is it costs you ground clearance. My 32s give me better than stock clearance so I can afford a small loss sometimes. The bigger your tires the less the problem.

Whether or not you need the performance benefit is totally up to your own experience and judgment. If your doing just fine traction wise at highway psi then there's no real reason to go lower other than ease of driving and puncture resistance, depending on the conditions. Personally I like to drop my mud tires down to around 22psi for moderately difficult trails. I like the added suspension benefit and don't have to use as much right foot to clear obstacles. I go lower still in sand, usually about 15.
I use a Pro-Comp tire gauge and Staun deflators set at 22. In the early days of wheeling before I got all the gear I would often just lower the pressure for an even amount of time per tire, 45 seconds each for example, and go from there.

x2. For me, i use Staun deflators too. I set them at 18 psi. I run 35 psi on-road. And i do air up at the end of the day. I have BFG AT KO.

IMHO, airing down is one of the best thing to do off-road. I always air down as soon as i hit the trail/park. And since you guys have A-TRAC (and not lockers), losing traction on a tire is a problem, which could mean losing momentum. Therefore, i think that airing down is a must for 4runner owners who take their 4runner off-road.

An off-road instructor once told me...when going up a hill (e.g. rockledge), you would want to air down the front tires MORE than the rear tires to give more traction to the front tires. On a hill, all your weight is to the rear axle...therefore, your traction capability is mostly on your rear axle. So, by airing down the front tires more than the rear tires, you distribute some of that weight to the front axle, thus giving more effective traction to the front axle...aka leveling out the rear bias on an incline. I have never tried this, but this makes sense to me!

 

[RonMAIDEN]

Depends on the trail too since I've run a few trails 3-4 times and I've aired down to 25psi a couple times on my Nittos and other times I've left them at 35psi and on a couple of trails it made no noticeable diff so sometimes airing down hasn't been worth the trouble.

If it's a real rocky trail and on the more difficult side I'd air down and use recomendations from the rest of the group if they've been on the trail before.

Airing down isn't always a need to do thing.

 

[Thai]

Airing down isn't always a need to do thing.

You just don't know what is around the corner or mudpit or rockedge....

 

[techno]

An off-road instructor once told me...when going up a hill (e.g. rockledge), you would want to air down the front tires MORE than the rear tires to give more traction to the front tires. On a hill, all your weight is to the rear axle...therefore, your traction capability is mostly on your rear axle. So, by airing down the front tires more than the rear tires, you distribute some of that weight to the front axle, thus giving more effective traction to the front axle...aka leveling out the rear bias on an incline. I have never tried this, but this makes sense to me!

Thats an interesting thought and it does make sense. I think I would only do this as a last resort for a hill I was having lots of trouble with. I would start to worry about the negative effects as a result of essentially having different diameter tires front to rear.

A friend of mine built a fully sealed roll bar and fitted it with air valves. He would pressurize it to a 100psi or so and had enough volume to air up four tires after a day of wheeling. Another friend had a special A/C compressor with an airline fitting so he could use that to pump the tires tires up. That system (Endless Air I think it was called) was really fast, it could air up to 35 psi from flat in under a minute easily.

 

[Thai]

I would start to worry about the negative effects as a result of essentially having different diameter tires front to rear.

What negative effects?

 

[techno]

Drivetrain wind up and tire scrub.

The front will want to travel a shorter distance than the rear from the same amount of input from the drivetrain. Or am I still thinking in terms of static radius? Hmmm... I might have to think about this a bit more...

 

[Thai]

Drivetrain wind up and tire scrub.

The front will want to travel a shorter distance than the rear from the same amount of input from the drivetrain. Or am I still thinking in terms of static radius? Hmmm... I might have to think about this a bit more...

I guess that you are right...the locked center differential would bind????

 

[G.I.G.]

IMHO, airing down is one of the best thing to do off-road. I always air down as soon as i hit the trail/park. And since you guys have A-TRAC (and not lockers), losing traction on a tire is a problem, which could mean losing momentum. Therefore, i think that airing down is a must for 4runner owners who take their 4runner off-road.

Hey Thai, how would airing down affect 4R owners any differently, lockers or no lockers? Or for that matter, whether you have a LS diff or A-TRAC or not. Wouldn't the same advantages/disadvantages apply with or without lockers?

 

[Thai]

Hey Thai, how would airing down affect 4R owners any differently, lockers or no lockers? Or for that matter, whether you have a LS diff or A-TRAC or not. Wouldn't the same advantages/disadvantages apply with or without lockers?

With ATRAC, you want maximum traction on all wheels...and leave ATRAC as the last resort. The problem with ATRAC is that in a few situation (slow speed rock climbing, mudhill), the transfer of power from wheel to wheel lags (it is a reactive system...it has to sense slippage before working)...thereby, you lose momentum.

With a locker, you have constant power delivery...so, it is a PRO-active system (as long as you lock it before going up the hill)...therefore, if one wheel loses traction, the other wheel still has constant power going to it...no lost of momentum.

When you air down, you maximize your traction to mother Earth. Less chance of you losing traction than if you did not air down.

My thoughts....

 

[G.I.G.]

Gotcha, that makes sense.

Not to change the subject, but I remember hearing an interview or reading an article somewhere that A-TRAC could actually be more advantageous than lockers in certain instances due to increased wheel articulation and steering response. That might be a stretch as lockers are a great off-road commodity, but something to think about none the less.

 

[Thai]

Gotcha, that makes sense.

Not to change the subject, but I remember hearing an interview or reading an article somewhere that A-TRAC could actually be more advantageous than lockers in certain instances due to increased wheel articulation and steering response. That might be a stretch as lockers are a great off-road commodity, but something to think about none the less.

I don't think that ATRAC nor lockers help wheel articulation. With lockers, you do NOT depend on wheel articulation as much because the other wheel (on the same axle) ALWAYS gets power (when the axle is locked). (A fully locked vehicle will have 100% of power at any one wheel at any time.)

As for steering, it is true...but it mainly applies to ATRAC vs. front locker argument. When you lock the front axle, steering is compromise if you decide to turn the steering wheel at large angles. Lockers like to go straight. With ATRAC, you can make large radius turns without a problem...less stress on the differential. This is why i think that the 2009 4runner Trail Edition (and FJ Cruiser) has a great system (rear locker + front ATRAC)...this combo should be good for most people. Of course, for older 4runners, the addition of ARB locker is equally cool. For hardcore off-roader, a fully locked vehicle is still ideal.

 

[G.I.G.]

I don't think that ATRAC nor lockers help wheel articulation. With lockers, you do NOT depend on wheel articulation as much because the other wheel (on the same axle) ALWAYS gets power (when the axle is locked). (A fully locked vehicle will have 100% of power at any one wheel at any time.)

As for steering, it is true...but it mainly applies to ATRAC vs. front locker argument. When you lock the front axle, steering is compromise if you decide to turn the steering wheel at large angles. Lockers like to go straight. With ATRAC, you can make large radius turns without a problem...less stress on the differential. This is why i think that the 2009 4runner Trail Edition (and FJ Cruiser) have a great system (rear locker + front ATRAC)...this combo should be good for most people. Of course, for older 4runners, the addition of ARB locker is equally cool. For hardcore off-roader, a fully locked vehicle is still ideal.

Cool, thanks for the clarification Thai. Now that you mention it, I think I read about that in the IFS + Front Locker sticky. I see how a rear locker plus A-TRAC would be ideal for most 4R owners. I certainly understand how a fully locked vehicle is still ideal for hard-core off-roaders, and hense, having a solid front axle. I remember the Jeep purists freaking out about the IFS on the Liberty and then on the Grand Cherokee. Not to mention the Patriot and Compass....