BajaNomad - Air down tires

Air down tires

bledito - 3-2-2015 at 11:47 AM

What is the reasoning behind air down of tires? Is it to make them softer less prone to punctures and tears? Is it to provide more mass at ground contact for better traction? what is the purpose?

David K - 3-2-2015 at 11:55 AM

Yes.... primarily we air down to not get stuck in sand... usually in the 10-20 psi range depending on what kind of tires and what kind of sand.

The next reason is to prevent flats on Baja chipped rocks roadbeds (graded roads)... usually in the 20-25 psi range to keep the sharp rocks from piercing the tires. This also makes a more comfortable ride.

Another reason is to improve climbing traction off road, also around 15-20 psi. Softer tires can bite much better!

David K - 3-2-2015 at 12:05 PM

Here is a steep beach, sea shells, sand, gravel and wet... my truck is loaded and heavy. See how it is sinking and drifting as I try to drive straight with tires at street pressure (38 psi):

Dry sand is even harder to drive on without deflating.

Now, after dropping the pressure 50% (to 19 psi), the truck floats on top and drives with ease...

I only recently began to deflate for graded dirt roads, and I got lots of flats from sharp rocks by not deflating and being in a hurry (or driving fast because it is fun in a Tacoma).

Barry A. - 3-2-2015 at 12:06 PM

I think that David's "air down" advice is right on target, but essentially for light rigs. On the heavier camper-type rigs be very careful that you have adequate pressure to handle the load you have-------too low and the tires will overheat and fail, or experience rim-cuts when rocks collapse the tire and pinch it between rim and rocks..

Bigger (wide and tall) tires also seem to handle the lower pressures better than narrow tires in my experience.

Bottom line--------with heavy rigs its kinda tricky finding the "right" air pressure, so be careful.

Barry

StuckSucks - 3-2-2015 at 12:34 PM

One more word of caution. When you air down, the sidewall bulge out - just want you want for soft sand. But that bulging sidewall is vulnerable to damage from rocks - be mindful when driving with low tires.

David K - 3-2-2015 at 12:34 PM

Another before and after photo:

Speaking of heavy truck tires... Here is Art's 4WD van/ motorhome on Shell island when he tried front and rear lockers, but not deflating enough air:

Ken Cooke gives a hand!

Once he let out MORE air, Art got floatation, and he was HAPPY!...

On dry soft sand, no problem at 15-20 psi (and 4WD of course):

Even with just 2WD, if you let enough air out, you will float on the sand!

Obviously you don't want to pop off the rim, so 8 psi is likely the absolute bottom range without bead lockers, and don't brake or turn suddenly, don't drive fast but keep up momentum.

dizzyspots - 3-2-2015 at 12:37 PM

Over at www.expeditionportal.com an archived article discussed a more scientific way for airing down....
The suggestion was to load the vehicle as you would normally run it..with the standard hiway tire air pressure.
A) Measure the side wall height ....do the math to get 75% of that height ( ex: 4 inches x 75% is 3 inches)
b) Lower the air pressure just until you reach that sidewall height...make note of that PSI...reinflate to proper PSI
c) That lower psi should be your target PSI for airing down

Make sense?

Air Down

J.P. - 3-2-2015 at 12:39 PM

Airing down tires can sometimes be a Slippery Slope. As if a tire fails because of a Side Wall Break Down it usually Voids the Tire Warranty

ehall - 3-2-2015 at 12:39 PM

It sures smooths out the ride thru rocks when I put the 35" tires on my jeep down to 12 pounds. Alot easier on the body.

dizzyspots - 3-2-2015 at 12:41 PM

and also the sidewall height of the tires that allows for more flotation...a similar article showed graphic examples of taller tires vs wide tires...the extra flotation is a function of an elongated tread..a longer footprint as opposed to simply a wider footprint....so a 265/75-16 when deflated would have better flotation than say a 265/70-16

[Edited on 3-2-2015 by dizzyspots]

David K - 3-2-2015 at 12:49 PM

Been airing down since I was 16 (1974) on all sorts of vehicles and all sorts of tires... never had a sidewall fail. However, if you aren't smart and don't bother to air back up when you leave the beach, that would be dumb! In the old days, we had an air pump that replaced a spark plug while filling. In the 80's we used a cigarette lighter pump... took a while, but no hot parts to remove/ replace... the past few years, a battery connected pump... muy rapido!

My Subaru with little 13" tires floating on Shell Island's sand like a dune buggy in 1978 (I was 20)... 10 psi was the magic pressure for those tires in the sand.

ncampion - 3-2-2015 at 12:51 PM

Here's another question about airing down tires. We often launch an aluminum boat off the beach and a friend is telling me to air down the trailer tires to make it easier to launch/retrieve the trailer. It seems to me that it is not a good idea to air down trailer tires as this gives them more rolling resistance through the sand. I can see having a bigger footprint on drive wheels for traction, but not sure it makes sense on towed wheels. What are the thoughts on that?

David K - 3-2-2015 at 12:53 PM

Surprisingly yes, it does help to also air down non powered tires. Floating on top vs. 'knifing' into the sand...

ncampion - 3-2-2015 at 01:03 PM

OK, I'll try it next time and see what happens.

willardguy - 3-2-2015 at 01:04 PM

Quote: Originally posted by dizzyspots

Over at www.expeditionportal.com an archived article discussed a more scientific way for airing down....
The suggestion was to load the vehicle as you would normally run it..with the standard hiway tire air pressure.
A) Measure the side wall height ....do the math to get 75% of that height ( ex: 4 inches x 75% is 3 inches)
b) Lower the air pressure just until you reach that sidewall height...make note of that PSI...reinflate to proper PSI
c) That lower psi should be your target PSI for airing down

Make sense?

I like it! now were they talking about just sand or all conditions?

elgatoloco - 3-2-2015 at 02:03 PM

Quote: Originally posted by dizzyspots

Science?

Thanks for the link. I will check it out and see how it compares to my personal observations and trail and error. :saint:

bledito - 3-2-2015 at 03:13 PM

so now i am informed, thanks. will start doing this in future off road. what is the suggested maximum speed with them aired down?

willardguy - 3-2-2015 at 03:20 PM

Quote: Originally posted by bledito

so now i am informed, thanks. will start doing this in future off road. what is the suggested maximum speed with them aired down?

hey do yourself a big favor and buy a set of automatic deflaters, set em for the PSI you want, screw em on and crack a cold one. well worth the investment!

David K - 3-2-2015 at 04:16 PM

Quote: Originally posted by bledito

so now i am informed, thanks. will start doing this in future off road. what is the suggested maximum speed with them aired down?

In sand, you will drive what feels comfortable to you, but usually not over 35 mph... in high range 4WD... usually slower as we go along looking for shells and critters to photograph. When deflated, and to keep from getting stuck, you drive in wider arches, no sharp turns... roll to a stop don't hit the brakes. Avoid digging in. If your tires spin when you try to move forward, they have too much air in them. You will need a good dial air gauge that reads below 10 psi for accurately deflating, even if you never go below 15 psi.

The auto deflators Willard mentions are interesting, but I think they are expensive (?), so have always used a small screwdriver or pointy shell to depress the schrader (air) valve in the stem.

Here is one brand for $69: http://www.justforjeeps.com/autide.html?gclid=Cj0KEQiAsdCnBR...

Chalk your tires!

AKgringo - 3-2-2015 at 04:19 PM

This advice is for fairly light vehicles, with oversize tires running on pavement. With your vehicle and/or trailer loaded the way you intend to travel, find a large dry patch of asphalt. Draw a chalk line across each tire and drive in a straight line and observe how the chalk wears off. If the outside edges wears first, increase the pressure. If the center wears faster, drop the pressure.
The chalk will wear off immediately and show you how the rubber will wear in a few thousand miles! You may find that each axle is different, and you might observe uneven wear indicating alignment or worn part issues.
My SUV is light, and camp trailer is even lighter, so I run 26 psi on the car, and 12 on the trailer (same tires all around).
Off road I will go down to half those pressures, and so far have not done any sidewall damage or had a bead leak. I don't drive any farther than I have to aired down, and never at highway speeds. If you have been making good time, get out and put your hand on the sidewalls to see how much heat is being created by the abnormal flexing at low pressures.
Yes to the question of low pressure on the trailer tire, it is the difference between dragging a roller or a spade. But if you have little bitty wheels and tires, you are still going to have problems.

monoloco - 3-2-2015 at 04:27 PM

Except for long road trips, I have kept the pressure of the Yokohama Geolanders on my F-350 at 25 psi since new. They now have 25,000 mi on them and I haven't had one flat or any other problem. The truck does well in sand and rides much smoother on the crappy local roads.

SFandH - 3-2-2015 at 04:33 PM

Any advice for a good 12 VDC compressor to "air-up"?

David K - 3-2-2015 at 04:35 PM

One that clips onto the battery, not plugs into the cigarette lighter...

The MV-50 or MF-50 is one... and inexpensive... http://www.amazon.com/Industries-MV50-SuperFlow-High-Volume-...

The Harbor Freight one is a bit cheaper, but melts the fuse holder...

[Edited on 3-2-2015 by David K]

AKgringo - 3-2-2015 at 04:53 PM

I use a Stanley combination compressor jump starter (sorry, no image), which also has 12v and USB outlets, and an LED light.
I was able to bring all four tires up from 12 to 26 psi (four or five mins/tire), and still have enough juice to jump a Suburban long enough to find out there were problems other than a dead battery.
It is compact, durable, and with the 12v to 110v inverter I carry, it is a hell of a battery for watching movies on my laptop in camp. When I start driving again, the inverter charges up the battery pack. I love it!

dizzyspots - 3-2-2015 at 04:54 PM

Dittoes....have used the MV50..for years...very durable airs up my Tundra tires easy peasy

SFandH - 3-3-2015 at 02:13 AM

The MV50 is now on my Amazon wish list. Thanks for the recommendations.

Floatflyer - 3-3-2015 at 07:28 AM

Anybody appreciate the automatic warning some vehicles(our 2005 Ford Explorer) give you with the GD tire sensors when pressure is reduced? Me either!

David K - 3-3-2015 at 08:59 AM

Quote: Originally posted by Floatflyer

Anybody appreciate the automatic warning some vehicles(our 2005 Ford Explorer) give you with the GD tire sensors when pressure is reduced? Me either!

TPMS (tire pressure monitoring system) is great to warn you when you get a flat before you feel it driving off road... gives you a chance to stop and see/ hear the air rushing out before the tire is totally flat... so you can roll to the best point to use your tire hole plug kit (another reason to have an air pump with you). Of course, when you deflate for sand the light comes on, but you can reset it at the lower pressure if you want to turn it off.

Floatflyer - 3-3-2015 at 09:27 AM

I also hated idiot lights when they became common place. Automatic seatbelts, etc! Dinosaur tendencies, yep!! :biggrin:

David K - 3-3-2015 at 09:35 AM

I hear you... but, technology happens and while I am an old timer in many ways, I love the tech stuff we have now (GPS, A-TRAC, Blue Tooth, etc.).

Look at how flying navigation is changing... compass to VOR to GPS! Man if those satellites ever fail, we are in a world of hurt!! LOL

geoffff - 3-3-2015 at 09:46 PM

Thanks, DavidK, for the sand driving pics & examples!

If it's late & I'm tired after a full day of driving & I just want to get out onto a beach (such as Sand Island) & camp, I'm sometimes lazy and try to drive full PSI in the sand -- and it often works for a while (giving it lots of gas), but if I notice *any* tire spinning, I immediately stop and air down. If I do so before my tires dig in, I can usually just keep going from there without doing any shoveling. 4x4, lockers, and lots of power make it easy to bury all four wheels down deep until your undercarriage is resting on the sand.

Airing down increases the tire contact area. The same vehicle weight spread over twice the rubber area means the ground needs to support only half the weight at any given point.

I drive a large van (just shy of 10,000 lbs). I usually run 50 PSI highway, air down to 35 for Baja washboard dirt (for vastly improved ride quality on the bumps), and air down to 20 PSI for sand. I keep my speed < 50 MPH on dirt and regularly check my tires for overheating from sidewall flex.

My vehicle has an onboard compressor, but it still takes me about 30 minutes to pump up all four tires to full pressure. So I sometimes get lazy about airing down.

-- Geoff

David K - 3-3-2015 at 11:14 PM

You have an awesome Baja rig, geoffff!

redhilltown - 3-3-2015 at 11:56 PM

I think DK briefly touched on it but an accurate tire pressure gauge is REALLY important...many of them are cheap and can be significantly off...I wouldn't trust the ones on the compressors...yeah, they can be accurate but better to double check with a good one.

POPEYE-SCOTT - 3-3-2015 at 11:59 PM

Great read DK... I'm learning a lot. The pump you have looks similar to my craftsman. But the craftsman pump side looks smaller. My dually tires run 80 front and 65 rear. Yesterday I tested my front down to 20 psi.... looks to low for me, I'll test 30 psi when I get to Baja. The pump brought it up to 50-55 in 3 or 4 minutes, that last part to 75 psi was hard pull, pump end getting pretty warm. So when I pump back up I'll limit it to 55 or so, and do full pump back when a large compressor is available. In the meantime I just bought that amazon pump, price is low enough for a back-up and they are small.

David K - 3-4-2015 at 07:51 AM

This one looks like a good one (0-60): http://www.amazon.com/Longacre-50417-0-60-Pressure-Gauge/dp/...

PaulW - 3-4-2015 at 09:20 AM

Gauge
Most of us use a tire deflator the comes with an accurate gauge. Makes it much easier to deflate accurately and quickly. Here is an example, and is the the one I have been using to the last 10 years.
http://www.ebay.com/bhp/tire-deflator
When I go on a Jeep club trip either here in Baja or in Colorado 90% of the rigs use that unit on the link.
For normal tire pressure checking I use and electronic one bought at the local auto store. They all seem to be very accurate regardless of the brand. They eventually die due to dead internal battery and have to be replaced.

For pressurizing I have a CO2 tank in two of my rigs and a VIAIR system in another. Advantages and disadvantages for both. For in my Colorado Jeep I carry the HF as a backup for the CO2 for trips to Moab where we spend 7 days of deflating and inflating and it limits how many uses for the CO2.
Speed wise CO2 beats everything except the air conditioning compressor setups. No electric pump is anywhere close to CO2 speed wise. Really nice when I have to deal with the F350 after stealing the CO2 tank from my Bronco.
For a CO2 setup DIY is the way to go to cut the cost to something reasonable. Lots of how to in the web.
Different setups for different situations.
The HF unit discussed will work fine for seldom use and low cost and I recommend it.
Paul

Nothing to air down

durrelllrobert - 3-4-2015 at 09:20 AM

After WWII my uncle, Jack Terry, who owned Yuma Auto Parts and some of his friends built the original dune buggies to run on the Yuma sand dunes. They used cut down model A's with tractor wheels.

willardguy - 3-4-2015 at 10:19 AM

Quote: Originally posted by PaulW

Gauge
Most of us use a tire deflator the comes with an accurate gauge. Makes it much easier to deflate accurately and quickly. Here is an example, and is the the one I have been using to the last 10 years.
http://www.ebay.com/bhp/tire-deflator
When I go on a Jeep club trip either here in Baja or in Colorado 90% of the rigs use that unit on the link.
For normal tire pressure checking I use and electronic one bought at the local auto store. They all seem to be very accurate regardless of the brand. They eventually die due to dead internal battery and have to be replaced.

For pressurizing I have a CO2 tank in two of my rigs and a VIAIR system in another. Advantages and disadvantages for both. For in my Colorado Jeep I carry the HF as a backup for the CO2 for trips to Moab where we spend 7 days of deflating and inflating and it limits how many uses for the CO2.
Speed wise CO2 beats everything except the air conditioning compressor setups. No electric pump is anywhere close to CO2 speed wise. Really nice when I have to deal with the F350 after stealing the CO2 tank from my Bronco.
For a CO2 setup DIY is the way to go to cut the cost to something reasonable. Lots of how to in the web.
Different setups for different situations.
The HF unit discussed will work fine for seldom use and low cost and I recommend it.
Paul

we use the trailhead deflators, they work great but the military checkpoint kids pull em out of the leather pouch scratch their heads, always sniff em, they're sure its some kind of mota pipe!

chavycha - 3-4-2015 at 11:09 AM

We've been doing a lot of beach launching of our tin boat. Chevy Trailblazer (a heavy 4500# on 245/70/17) towing a 14' boat on 4.80x12 at 40psi, weight about 800lbs.

One thing not mentioned much here is that all sand isn't created equal. Flat Pacific side beach sand is usually well-packed and solid. Dunes are not. Cortez side steep beach sand is marginal. Cortez side about 100 yards from the beach is worst. Dry, loosely packed, yuck.

For beach launching - driving is easier...

Pacific side:
35psi is stuck with 2wd. Fine with 4x4.
28psi and 2wd work on the well-packed beaches, but 4wd most of the time just to be sure.
24psi once on a real soft beach, 4x4 in and out.

Cortez side:
35psi is guaranteed stuck, even with 4x4.
28psi is okay on the beach in front of town with 4x4 hi, unless the sand's soft.
24psi and I don't even have to shift out of 2wd to get the boat to the water. Still have to 4x4 to get it up and out. Doesn't work on the steepest of beaches. Reaching the point of having to air up to go places afterwards.

12psi and 4x4 low has gotten out of everything (so far), including two beaches with some pretty darn dusty/fine sand and a very steep slope. Just barely on one, but just barely is just good enough.

[Edited on 3-4-2015 by chavycha]

MitchMan - 3-4-2015 at 06:54 PM

Don't take this as advice, but, I used to use those cheap hand held tire pressure gauges but I never really felt that they were reliable. Never had a vehicle with beefy off road tires.

Without deflating the tire, it seemed that I would get a wildly different reading depending on fast I stuck that gauge on the tire's valve stem. That is because, if you got it right quickly, that shock of air would push the calibrated stem out really fast...and too far out due to increased momentum due to speed that the stem would be pushed out. You know, speed x weight = momentum.

Also, I always thought the recommended tire pressure was always a bit high as it was probably intended to reflect smooth USA paved freeways and roads as opposed to rough Mexico roads at lower speeds.

So, I use the "thumb test" for a slightly lower than recommended PSI. That means that I quickly press my thumb on the side of a tire at rest to determine if the tire needs air and I can judge the right amount of tire pressure that I prefer pretty accurately. Don't have to kneel at each tire, don't have to unscrew and re-screw the valve stem cap, and it's ten times faster.

Works for me as it's easy to tell which tire is lowest of the four and which is the most pressurized of the four. Also, by looking at the bulge on the side of the tire at rest, it's also easy to guess if the tire pressure is way too low. Furthermore, as mentioned in this thread, lower than recommended PSI provides a smoother ride and rolling over debris and small rocks is less damaging. It's a win win.

When I was a cook, we used to test the doneness of steaks...hundreds of them...by a quick poke of the cooking steak with your index finger. Lots of sensitivity in the fingers. Works on steaks, works on tires.

[Edited on 3-5-2015 by MitchMan]

wessongroup - 3-4-2015 at 07:00 PM

When ya got it down to feel ... the next step is "eyeballing" it ... :biggrin:

Always amazed they used to use horses and wagons ... try letting the air out of one of those wheels ... tough bunch

[Edited on 3-5-2015 by wessongroup]

basautter - 3-4-2015 at 07:15 PM

I recommend 18-22 PSI for riding the sand. Less, and you may get a bead break, more, and you dig in. Adjustable deflators can be purchased at Desert Rat as well as high flow pumps that clamp on your battery. Best of luck!!

SFandH - 3-5-2015 at 07:22 AM

Here are a couple of battery operated digital tire pressure gauges. They are getting good reviews and are only around $12.

Hmmmm

http://www.amazon.com/Accutire-MS-4021B-Digital-Pressure-Gau...

http://www.amazon.com/NorthONE-Pressure-Accurately-Motorcycl...

[Edited on 3-5-2015 by SFandH]

philodog - 3-5-2015 at 08:09 PM

I use the valve caps with a core removal tool built in. Removes the air probably ten times faster than pushing the valve BUT you better not lose that core! Haven`t lost one yet but I always have a pack of spares in the glove box. My tires lose about 1 psi per second with no core so I just count as its airing down. For airing up a scuba tank is faster than any gas station and no 12 volt compressor even comes close. It`s a little less than 1 psi per second for my stock Tundra tires so 15-20 seconds per tire. And for this size tire it takes about 10 psi out of the tank for 1 psi into the tire so a full 3000 psi tank will do MANY refills. I don`t have a SCUBA card and have never been asked for one in Baja.