BajaNomad - Tire pressure when off-roading

Tire pressure when off-roading

bajalou - 4-21-2009 at 08:52 AM

Rather than hi-jack Bajacat's thread about San Felipe trip, I figure I'd start a new one about tire pressures.

This is taken from Extreme 4X4 Trails and Ecological 4-wheeling Adventures.

I've followed this advice and believe it's great advice for getting through tough places with the least trouble. It points out things that I never thought of and when I follow them - it works

Extreme 4X4 Trails

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Letting the Hot Air Out of Tire Talk
Tire Pressures for 4-Wheeling

by Harry Lewellyn
Experiences Playing in the Sand

I guess I should cut those reluctant to lower their tires down to sand pressure a little slack. My first time onto the beach in San Felipe, Baja, I did the air pressure trick, with a little unwillingness, and wasn’t sure it was really necessary. Then, over the next three or four years, I would first tackle the mellow white stuff at full street pressure and when all my power, skill and finesse failed, I would let ‘em down and move ‘em out. Me, low range and low gear, would struggle along at a whole five MPH. Deflation they defied resistance as I sailed along in high range, OD, at whatever speed I chose! Time and again, year after year, I tested the softies with the same undeniable results. Low tire pressure just plain works in the sand!
What Affects Optimum Sand Tire Pressure

Optimum sand tire pressure is a combination of many things, of which old husband's tales are least productive. However, your tires, their construction methods and materials, what your car weighs, how it is loaded, and wheel width all play into the sand-pressure tire formula with predictable results. For this article, I will neglect tire temperature which I suppose could be critical if you test below freezing and play at +80°. Why low pressure works and how to determine your best sand pressure follows.
Why Low Pressure Works

It’s a simple fact, which some diehards still deny, the bigger the footprint, the softer the stuff you can travel. Mother Nature knows it. Take a look at the feet of camels, polar bears and marsh birds. They are big and spread out to distribute their weight over a larger surface area. For those who say skinny, hard tires are better for snow, mud or whatever, please tell me why they don’t use ten-speed bicycle-type tires on snowmobiles? Sand rail people and mud boggers know big feet work better too! With that out of the way, lets take a look at tire pressure and footprints.
Tire Pressure and Footprints

Right next to your wheel, on the tire, find the small black print that specifies maximum load pressure. For example, my BFGoodrich Radial All-Terrain T/A 30x9.50R15LTs state 1990 pounds at 50 pounds per square inch (PSI) cold. Most folks, generally including those who install tires, run them up close to this, and neglect the actual term, "MAX. LOAD" pressure. The street pressure, TREAD FOOTPRINT figure below represents Coyote assessed over inflation.

Do you really need maximum load pressure?

Consider that standing flat and level (static), loaded the way you normally run is one thing. Now further consider you lose full tread width contact as the 4X cruises at higher and higher speeds. Centrifugal force tries to increase the diameter of the tread. You only have to look at dragster tires when they light 'em up to convince yourself of this tire reality. The sidewalls tend to hold the outer edges closer to their static diameter than the center of the tread and hence the center of the tread spins into an ever increasing diameter with increased speed. In other words, while moving at highway speeds, the tire is trying to run more on the center of the tread than the edge. That’s why I feel my full width, static contact test (described below) is conservative. My tire life and wear pattern prove putting more rubber on the ground increases longevity.
Full tread width contact, street pressure

Since this article deals with sand tire pressure, see a back issue of Ecological 4-Wheeling for full details on how to safely determine your exact, full tread width contact, street pressure. Summarizing Tire Pressure, April, 1990 4-Wheeling, you don’t want to overheat the tire and should only be able to slip a business card under the outside and inside edges of the tread less than 1/4 inch. Reprints of past 4-Wheeling articles available for $4.00 each.

Follow along with some arithmetic that scopes in the same results. Four tires times 2000 pounds each (1990 MAX. LOAD rounded up to simplify math) equals 8000 pounds total (tire) load capacity. My Explorer weighs 4000 (3800 rounded up), or half the maximum capacity of all four tires combined. That roughly says half the pressure should yield ample load capacity.

As a result of both methods above, I run 26 PSI, night and day, seven days a week, and typically get 60,000 to 80,000 miles out of a set of BFG T/As, including sand runs at much lower pressure. I trust this information will add practicality to determining your street pressure and encourage you to accept overall lower tire pressure. No figure is shown for the increase in street pressure footprint, but it should approach full tread width.
Optimum Sand Pressure

To determine your optimum sand pressure, perform the following test on a flat, level and smooth surface, fully loaded as you would be for a sand run (gas tank and passengers included). Measure the vertical height to the bottom of the wheel (rim) from the ground. This is your 100%, street pressure, wheel height. Now reduce this height by 25%. In other words, let out air until your wheel is 75% of the street height. Measure and record this pressure and depending on your vehicle and loading scheme, front and rear tires may differ.

This is your optimum sand pressure. As the TREAD FOOTPRINT figure shows, this typically results in more than a 250% increase. That is like having ten tires where you only had four. This pressure is only valid for exactly what you tested. Change vehicle, tires, wheels or load and you have to retest.

It’s obvious a vehicle change would dictate retesting. Tires differ in number and stiffness of sidewall plys and rubber compounds, hence the need to retest with a tire change, and in actuality, tire age/wear too. Wider or narrower wheels influence how the sidewalls bulge, so this too requires doing the deed anew.

How did I measure the 250% increase? I measured the pressure, painted the tread, let the tire down onto a piece of paper and “printed” the footprint for various air pressures. I could see the edge begin to make contact and footprint increase with ever-decreasing pressure.

The results are dramatic, but carefully observe the PRESSURE-HEIGHT CURVE, and understand this is not a universally applicable curve. It is specific to my 4X, tires, wheels and load. Wheel height and footprint are obviously related. Putting the curve into words, the footprint really starts to increase (wheel height decrease) with the last few drops in PSI. Note I measured no height change from 50 to 37 PSI. From 50 to 20 PSI resulted in only 3/8 inch drop in height. The drop from 20 to 12 PSI was about 1/2 inch and the drop from 12 to 7 PSI yielded more than 3/4 inch drop in height. These last few pounds are where the real effect takes place. Give them pudgy cheeks!

I’ve had people tell me the low pressure trick does not work. "I went down to 16 or 18 PSI and still had trouble in the sand," so the claim goes. It should be apparent from the curve, the last few pounds really count! A good indicator other than ease of movement comes by watching your engine temperature gauge. If you are heating up, your pressure is still too high or you’re really in some tough stuff!

So does this mean flat tires are best? I believe not. Again the 75% rule is somewhat tire and wheel dependent, but at too low tire pressure, the center of the footprint begins to well up, reducing the footprint and creating a small “traveling hill” in the center of the footprint. This hill offers increased resistance to vehicle movement.

For my combination of 4X, tires, etcetera, my optimum sand pressure is six to seven PSI and I typically get by with eight to ten.
Tire Gages
The Great American Big Numbers Misconception

Before we move on, let's talk pressure measurement - tire gauges. I’ll leave the type - stick, dial or digital - up to you and a future article in 4-Wheeling. What I’m primarily addressing is the Great American Big Numbers Misconception; the bigger the number, the better it is.

As a kid, I remember one of my first automotive questions was, "What does the speedometer go up to?" Not how fast does the car go, but how big is the number at the end. This end number on both speedometers and pressure gauges has little, and sometimes a negative bearing, on gauge usefulness.

Actually, I have quite a few tire gauges. Several fell prey to the Great Numbers Misconception. I carry and use two. One for everyday street use and another for low pressure. My street pressure gauge goes to 50 PSI and my low pressure gauge goes to 20. It’s pretty hard to measure 10 PSI on a gauge that starts at 20 PSI. Most 120 to 200 PSI gauges don’t even start until 20 or more. These are useless for sand pressure measurements. Don’t waste your money on high pressure gauges! Consider having two and perform the above tests and field air-down measurements with the same low pressure gauge. The exact accuracy of the reading or value is not as important as repeatability.

And something to plan for is the eventuality of no gauge or a failure. This is easily handled by knowing how long it takes to air down from street to sand pressure. I use the one-thousand-one, one-thousand-two, second counting method. I can let 50 seconds worth of air out of my tires before I need to take a reading. It’s usually another ten more seconds before I reach my optimum. Given a gauge failure, I will still stand a fair chance at "bringing ‘em back alive" - me, the car and the tires.
Four Affects of Low Tire Pressure

Low tire pressure changes four things: footprint; ground clearance; rolling radius and what I call Obstacle Rolling Resistance. Footprint was covered above. Common sense and the TREAD FOOTPRINT figure shows the center of the axle is lowered by the decrease in wheel height. This results in lower ground clearance and consider the softer tires also flex and give more resulting in compression loss of ground clearance too. But on the other hand, ground clearance is not that important in the sand.

Rolling radius is part of the equation which contributes to your net moving force; your overall gear ratio; your "stump pullin’ power". See December 1988, Ecological 4-Wheeling, for a complete treatment of net moving force. Think of it this way: you know how bigger tires eat up low gearing and smaller tires effectively give you lower gears? Flatter tires act like smaller tires and increase your pulling (moving) power.
OBSTACLE ROLLING RESISTANCE

Move on to the OBSTACLE ROLLING RESISTANCE figure below to learn how significant this sleeper is! Several years back, I was convinced a tire’s ability to conform to obstacles played a big part in ease of movement, but I had no idea how significant it was until I measured it. Here’s my experiment.

Face-off two 4Xs some 30 feet apart, on a flat, smooth surface. Take the winch of one and connect it to the other, with a dynamometer (a big fish scale) in the cable. Put a pair of 2X4 wood blocks in front of the pulled vehicle and measure the force (pull) required for different towed vehicle tire pressures.

A simple, lowly 2X4 offers more of a climb angle (hill) than you might initially think. It is roughly 25° to 30°. Knowing this, it’s now easy to see why not so big rocks require the thrash and bash technique to climb with hard tires.

The 2X4 tests showed a 40% difference between street and sand pressure! And it may be worse than that because the initial burst of pull required to get the street pressure tires started up over the obstacles (the 2X4s) was not precisely recordable with my crude equipment and test methods. With the sand tire-pressure, it was obvious the dynamometer saw a gradual buildup in force as the tires smoothly conformed and crawled over the obstacles. What this 40% difference means is you now have roughly six tires where you only had four. Add this to the "ten tires" of the pressure drop and you now have 16 where you had four. Any more questions about the effectiveness of lowering tire pressure?

There is a lot more to making this test perfect and I would be most happy to redo it using proper equipment and controls. Anyone have access to strain gauge cells and strip chart recorders?
Rock Crawling

Actually, I suspect this is also why lower tire pressure is very effective for rock crawling. The Obstacle Rolling Resistance factor, as I call it, plays an even more crucial role when rolling through the rocks.
Caution!

Now comes the soap box. Use Caution! Caution! Caution! with low tire pressure. The Obstacle Rolling Resistance factor works against you with speed and in the rocks! Soft tires easily bend and break wheels. Drive with caution when back on hard ground or the rocks! And you obviously need some way to reinflate the tires back to street pressure when you hit the black stuff.
Even in 2WD

You 2-wheelers take note as well, for this trick works equally well in 2WD. But remember, you must still deflate all four tires even though you are only putting power to two. Your hard front tires create hills that your rears must continually try to climb.
Treading Lightly

I also feel lower pressure is more ecologically compatible. With better traction you don’t have to spin the tires and hence leave Mother Nature unscathed.

You’ll be doing yourself and Mother Nature a favor when you lower your tire pressure the next time you hit the soft stuff.

© Harry Lewellyn

Ecological 4-Wheeling Adventures
P.O. Box 12137
Costa Mesa, CA 92627
voice: (949) 645-7733
fax: (949) 645-7738
email: info@eco4wd.com

BigWooo - 4-21-2009 at 03:25 PM

Long article, but good info. I never knew there was a formula, I just let air out until it "looks good". We usually drop the pressure to smooth out washboard though. That's more of a balance between smoothing the ride and not overexposing too much of the sidewall to the loose/sharp rocks.

bajalou - 4-21-2009 at 03:38 PM

Just remember, If you've dug a hole deep enough that your differential is on the ground, you have to dig it out before deflating.

Airing down works best before getting stuck, but if you do get stuck, stop immediately and air down.

elgatoloco - 4-21-2009 at 03:45 PM

Quote:

Originally posted by bajalou

................, but if you do get stuck, stop immediately and air down.

Worked for me a few weeks ago at Playa San Rafael. :saint:

Phil C - 4-21-2009 at 04:27 PM

18 to 20 lbs front, 20 to 24 ,depending on load, rear. Multipal Chevy Suburbans 10,000 Mi. off road in Baja. You do present the sidewall to the terrain. I've used BFGs Ats. Not many problems. If you're realy off road everyone gets flats... Carry two spares.....

[Edited on 4-21-2009 by Phil C]

woody with a view - 4-21-2009 at 04:42 PM

Quote:

Carry two spares.....

what he said. the small amount of bed space required to carry a second spare is minimal. the satisfaction of knowing you can get 3 flats before you're stuck is incalculable......

David K - 4-21-2009 at 04:57 PM

Harry has a great book for four wheeling... He was a guest at Viva Baja 3...

My sand driving tips (beaches, arroyos, desert, dunes)

A 'easy' place to start your ideal sand pressure is drop to 50% of your normal street pressure... 30 psi street to 15 psi sand. I can get through the sand/ crushed shell beach at 15 psi in my Toyota, but it does float better at 10 psi. What you want to do is create a buldge in the sidewalls that acts like a life preserver or inner tube on water, in that it will cause the tire to 'float' on the sand and not spin and dig in. What will sink into sand more: your pointed finger, or the palm of your hand?

Next is have some momentum to cruise over the dry deep sand and arrive at the wet, low tide part of the beach (provided there is any!)... This is like driving on pavement compared to the dry sand, the tracks get erased by the next high tide, and you vehicle will run cooler !

Do not brake suddenly or turn sharply in the sand. When you come to a stop, do so slowly and have your vehicle pointed straigh... and downhill if possible. That will make getting going again much less a problem.

Pacific Sand vs. Gulf Sand: BIG DIFFERENCE!

The Pacific beaches are mostly flat, small grain sand and if much easier to drive... even without lowering air pressure... Try it first at normal pressure (4WD) . If your rig struggles or tires spin... STOP and deflate!

Gulf beaches are typically steep and have large grain sand and crushed shell or pummice mixed in... This is like quicksand, even to a 4WD! Don't even try without deflating 50% or more of your air pressure.

With enough air out of the tires, even 2WD vehicles can drive in sand (not just dune buggies or rear engine VWs, but regular cars, vans, & motorhomes! Just don't turn suddenly and pop the tire off the rim (usually could only happen below 8 psi).

Have a good dial gauge the reads below 10 psi!

Remember, do not beach drive in populated areas or in sea turtle nests (in season)... A properly deflated tire will not go as deep as a human footprint, in the sand, so they aren't the danger as some would have you think!

NOTE: Like driving Hwy. 1 in the desert ,over 50 mph (80 kph), beach driving is also 'illegal'!

[Edited on 4-22-2009 by David K]

BajaWarrior - 4-21-2009 at 05:01 PM

Quote:

Originally posted by woody in ob

Quote:

Carry two spares.....

what he said. the small amount of bed space required to carry a second spare is minimal. the satisfaction of knowing you can get 3 flats before you're stuck is incalculable......

SpareSpare.

Got lucky found this identical spare to my spare on CraigsList, even in my own community!

$35.

I thought they guy was nuts to get rid of it, it's brand new! First to be used, second spare riding comfortably underneath.

r.SpareSpare.JPG - 40kB

boe4fun - 4-22-2009 at 07:45 AM

What's the rule for towing a small boat trailer? I'll be towing a 13 1/2' Gregor down next time (Sept-October) and plan on going to Gonzaga via Coco's Corner, Agua Verde, and San Roque on the return leg. Any hints on how much to air down? Thanks in advance, Paul Boe

bajalou - 4-22-2009 at 09:34 AM

Take a look at the track the trailer makes in the sand. If it's cutting into the sand for any depth 2-3 inches, then airing down would probably help.

mtgoat666 - 4-22-2009 at 11:19 AM

Quote:

Originally posted by David K

Pacific Sand vs. Gulf Sand: BIG DIFFERENCE!

A properly deflated tire will not go as deep as a human footprint, in the sand, so they aren't the danger as some would have you think!

NOTE: Like driving Hwy. 1 in the desert ,over 50 mph (80 kph), beach driving is also 'illegal'!

You are always good for a laugh, DK :lol:

using your tire/footprint logic, it seems you would rather someone drive over your foot than step on your foot. this sounds like a good study to conduct next time you visit shell island and have drunk 10 shots of tequila

BFG All Terrains

Curt63 - 4-22-2009 at 07:33 PM

Thanks for the informative post. I am surprised that you run 26 lbs on road. My local Community College Auto Shop teacher suggested I run max. pressure on the road.

There is a great reason why so many of us run All Terrains for on road and offroad - TRIPLE LAYER SIDEWALLS!!!!!!

If you are going to air down and/or rock crawl your tire sidewalls bulge and become far more vulnerable. Shredding the sidewall becomes a real possibility and can't be fixed. Triple layer protection is huge.

And they run quiet on the road!

Saludos

bajalou - 4-22-2009 at 08:26 PM

Quote:

Originally posted by Curt63
Shredding the sidewall becomes a real possibility and can't be fixed.

Saludos

I have a tire man in San Felipe that will vulcanize to repair sidewall punctures.

Curt63 - 4-22-2009 at 09:22 PM

Is there anything those Mexicans can't fix?

David K - 4-23-2009 at 08:02 AM

The sidewalls on BFGs aren't as bulletproof as they make them sound... I have experienced a sidewall cut/ leak on a sandy road on new T/As (must have been a rock somewhere)... I have seen many T/As with blown out sidewalls... I have had 3 ply sidewalls (Cooper tires) and 2 ply sidewalls... never a cut/ leak in any. However, 3 ply sidewalls are much more difficult to drive in sand and require letting more air out to get them to 'buldge'.

Also, more aggressive mud tires do poorly in sand, where as street treads or smooth tires do great.

Curt63 - 4-23-2009 at 03:34 PM

Yeah yeah yeah, BUT how many of those tires say "Baja Champion" on them.

That's kind of cool!

Seriously, if you are aware of a better on road, offroad combo tire, I'd love to know the make and model.

Saludos

Thanks, Guys...

Mulegena - 4-23-2009 at 04:25 PM

This is a really interesting thread. I'm not an off-roader like you but it seems I've done my share of adventuring, and I've got a couple of questions to throw out to you all :

1. I've heard that lowering your street psi makes for a better ride, but wonder if there is a formula for figuring it, just as the sand formula was presented here; how low can you go on pavement for efficient everyday driving? How does a lower psi figure in miles per gallon?

2. I'm in the market for another car and am asking for suggestions. Here's the wishlist: In the interests of ecology and economy I'd like one that would give good mpg and have a low carbon-footprint. It'd be my daily driver but I'd like it to be sturdy and have clearance to go some of the rugged roads in Baja (like run over the hills from Mulege to San Juanico for instance), 4x4 standard/automatic optional.

Thanks, Mulegena

Curt63 - 4-23-2009 at 04:51 PM

Get a Taco (Toyota Tacoma) or a 4 Cyl Toyota Four runner (avoid the 3.0 liter V6). I love my Tundra, but its a gas hog.

Ask Ironman Ivan Stewart, Toyotas do OK in Baja.

David K - 4-23-2009 at 05:00 PM

Toyota Tacoma is numero uno in Baja... If you want to be more 'green', then might I suggest a Subaru AWD or older 4WD Wagon... You will not have the ground clearance to get to Mision Santa Maria, but with careful placement of the tires, most everywhere else should be reachable!

Mulegena - 4-23-2009 at 05:22 PM

Quote:

Originally posted by David K
Toyota Tacoma is numero uno in Baja... If you want to be more 'green', then might I suggest a Subaru AWD or older 4WD Wagon... You will not have the ground clearance to get to Mision Santa Maria, but with careful placement of the tires, most everywhere else should be reachable!

Ok, how 'bout a Tracker or Samurai or even VW bus?
and do you recommend a 4x4 or would 2x2 do?

Thanks un tiempo mas, Mulegena

David K - 4-23-2009 at 05:28 PM

Sure... they would do... I just happen to have personal experience with Subaru (1977-1993) owning 3 4WD wagons each with over 100,000 mostly Baja miles on them!

4WD, always...

Thanks, David!

Mulegena - 4-23-2009 at 05:32 PM

You get a gold star... or taco with all the trimmings!

Mil Gracias, Mulegena

David K - 4-23-2009 at 05:39 PM

Quote:

Originally posted by Mulegena
You get a gold star... or taco with all the trimmings!

Mil Gracias, Mulegena

Oh boy! Thank you!!! :cool:

Taco with all the trimmings

Curt63 - 4-23-2009 at 07:58 PM

This website shows amazing Tacos and stunning photography. One of my favorites

http://www.bajataco.com

David K - 4-24-2009 at 07:47 AM

Quote:

Originally posted by Curt63
This website shows amazing Tacos and stunning photography. One of my favorites

http://www.bajataco.com

'bajataco' is a Baja Nomad... and we got to meet him at Viva Baja #3 (he and his esposa flew to Oceanside with Capt. Mike, from Arizona to attend):

Sharon and Chris 'Baja Taco', flew into Oceanside with Capt. Mike and Janeen,
from Arizona! See their Baja photos:
http://www.bajataco.com/Baja/bajamap.html

Hot Air

John M - 4-24-2009 at 05:58 PM

This thread is starting to inflate itself.

Harry Lewellyn is really a research/test/fanatic! The book shown is well worth it, even for us "older guys" like AridNeal.

His advice is right on the money, real world experience, and I'd follow it without a doubt.

You think the article that started this thread is pretty long? You ought to read the one Harry did on whether or not to drain water from an ice chest while off-roading! It's a doozy!
(or is that doozey?) or...

BFG ALL TERRAINS RULE! We've plugged a sidewall or two and the tires are still floating along.

John M

David K - 4-24-2009 at 06:18 PM

Ice Chest Water? Drain man, drain! :lol:

Unless it is only containing cans of beer!! :coolup:

comitan - 4-24-2009 at 06:47 PM

DK, What if your vehicle overheats or you are stranded out in the middle of nowhere and no water.

Drain, man, drain?

John M - 4-24-2009 at 07:17 PM

Comitan - you got that right!

But the article didn't consider that issue.

Hey David K, no fair condensing four pages into three words!

But it isn't quite that simple in all cases. Wish I had the skills to type it our here, but it would take me way too long.

No need to hijack this air talk with ice talk

John M

TMW - 4-25-2009 at 10:30 AM

I remember helping Mike Doherty in a SF250 race a few years ago and he broke an axle in his class 8 truck. He got stuck several times before we lowered the tire pressure down to 4lbs in his BFG 37 inch project tires. He made it up and down the three washes and almost got out of Matomi but came upon a stuck buggie where he too got stuck and timed out of the race. It was a one wheel drive truck that was a handfull to handle because it was always wanting to turn.

David K - 4-26-2009 at 09:46 AM

Quote:

Originally posted by comitan

DK, What if your vehicle overheats or you are stranded out in the middle of nowhere and no water.

Well C, as a desert camper all my life I am never low on water and I don't include the ice chest water in the calculation. I have a 6 gallon water jug for general purpose needs and lot's of drinking water... in addition to the fine Mexican beer.

Besides, I drive a Toyota... and it never breaks down! :lol:

tires and tire pressure

4x4abc - 4-26-2009 at 06:29 PM

here is my take on tires and tire pressure for off-pavement driving :

know the (manufacturer recommended) street pressure for your stock tire size (see sticker inside gas filler door - its not the max pressure on your tire side wall!)
for all dirt roads, rough trails and hard packed beaches deflate to 2/3 of street pressure
for all soft sand beaches deflate to 1/3 of street pressure
http://www.4x4abc.com/jeep101/soft-sand-deflate.html

softer tires will also create a smoother ride on washboard
softer tires will less likely have tread punctures
side wall cuts by larger surface rocks can only be avoided by driving very carefully - more tire pressure will not really save you
http://www.4x4abc.com/jeep101/rocks.html

If you are done driving on dirt you can still drive safely with 2/3 pressure on pavement - you don't have to immediately pump up your tires to street pressure. Only if you plan on driving above 50 mph for the next 5 hours, street pressure is recommended. It'll make the tire live longer and will save you gas (2/3 pressure on pavement will drop your mpg by about 2).
1/3 pressure (beach) should be brought up immediately if you like to drive fast on washboard (if you don't drive faster than 30 mph, you can keep 1/3 for a while). Pavement will definitely demand more than 1/3.
Safest tool to re-inflate the tires is a $10 upright bicycle pump. Forget plug in compressors - when you need them they are dead (and they are painfully slow).
http://www.4x4abc.com/jeep101/plugnplay.html

The best tire for Baja is BFGoodrich - either as AT or MT.

If you drive on Baja dirt a lot, you should consider tires with more air volume (wider, taller tires). Larger tires with more air volume are stronger and safer than stock size tires. They can also be driven at lower psi than stock tires and that makes for a much better ride on washboard.

When I started exploring Baja I had so many flat tires that I eventually carried 2 spares. After I had larger tires installed I never had a flat again (last 20 years).

saludos
Harald

35" tires

BFS - 4-26-2009 at 06:38 PM

quick question:
i somehow now am driving around on 35" tires. They are huuuuge! But not sure what is the best tire pressure for these things. I usually have 18 to 20 psi for driving around the very poor roads around BCS and drop down to 12 when i need get across lots of sand, but this was on stock or slightly oversized tires. Should I go so low with these big guys?
thanks
Aq

BajaWarrior - 4-26-2009 at 06:52 PM

Quote:

Originally posted by aqbluegreen
quick question:
i somehow now am driving around on 35" tires. They are huuuuge! But not sure what is the best tire pressure for these things. I usually have 18 to 20 psi for driving around the very poor roads around BCS and drop down to 12 when i need get across lots of sand, but this was on stock or slightly oversized tires. Should I go so low with these big guys?
thanks
Aq

What type of truck do you have and what is it's weight?

I have 35" BFG tires on an '88 Toyota 4x4 and I run 4 pounds for beach and 6 pounds for desert. At 6 pounds they do not look flat...

I purchased tis truck new and ran the same size tires back then and inflating the tires to only 18 P.S.I. on the highway and got 60k out of a set of BFG's.

4x4abc - 4-26-2009 at 07:49 PM

Quote:

Originally posted by aqbluegreen
quick question:
i somehow now am driving around on 35" tires. .... Should I go so low with these big guys?
thanks
Aq

aqbluegreen,

since your 35's were most likely not stock you can follow this method to find out the correct street pressure (and then follow the 1/3 and 2/3 rule for sand and dirt):

Make a chalk line all the way across the tire thread, and drive a few yards. If the chalk line rubs off in the center your pressure is too high - air down more. If the edges of the chalk line rub off first, try adding some air. Your goal is that the line rubs off from shoulder to shoulder.
For long freeway trips add 20% to improve mpg.

bajalou - 4-26-2009 at 08:31 PM

Thanks 4X4ABC for chiming in on this - great stuff on your links also.

mtgoat666 - 4-26-2009 at 10:52 PM

Quote:

Originally posted by 4x4abc

Quote:

Originally posted by aqbluegreen
quick question:
i somehow now am driving around on 35" tires. .... Should I go so low with these big guys?
thanks
Aq

actually, that's a fools way to roll dice with tire pressures. if running stock tires, your minimum pressure for street and highway driving should same as written on your door frame. if running non-stock tires, go to a tire store and ask them to look up pressure and load ratings for your tire / vehicle weight. really, when you are running 70 MPH on a hot day, you want to stay above minimum pressure. low pressure tires at high speed lead to blow outs, don't roll dice with hokey chalk lines and voodoo.

TMW - 4-27-2009 at 07:26 AM

Quote:

Originally posted by 4x4abc

Quote:

Originally posted by aqbluegreen
quick question:
i somehow now am driving around on 35" tires. .... Should I go so low with these big guys?
thanks
Aq

Also make sure your rims are wide enough that they are not bowing the tire. Larger tires on stock rims for example will not allow you to take advantage of the full footprint except at low tire pressures.

salvavida - 4-27-2009 at 08:28 AM

AQ
Consdering the over all weght of your rig I would say 20 lbs will be good for wash board and normal sand. Any lower and you'll get a lot of side to side roll and side wall bulge. There's probably some similar rigs around your area, see what their doing.

BFS - 4-27-2009 at 04:13 PM

Gracias!

Aq

TMW - 4-29-2009 at 05:51 PM

Intersting info on the door of my 2004 GMC Z71. It came with P265/75R16 tires. 35lbs FT and 35Lbs Rear. I haven checked the owners manual but the sticker doesn't say if the rear is 35Lbs loaded or unloaded. I am assuming it is unloaded since that is how it would normally be driven. It's a mute point since I switched to LT285/75R16 tires. I run 40Lbs FT and 30 Rear unloaded and 40Lbs loaded for Baja.

Neal Johns - 4-30-2009 at 10:12 PM

TW, for liability reasons, the recommended pressure on the door jam is at maximum specified gross (Loaded).

TMW - 5-1-2009 at 07:30 AM

Thanks Neal

Ken Cooke - 5-11-2009 at 09:55 PM

Interco's TrXus MTs have performed flawlessly.

BFG ATs and MTs - sidewall failures in Baja -- NO BUENO!

Not sure how the new BFG MTs will handle Baja, but your sidewall is a very important upgrade to consider when 4WDing in Baja.

Cuidate, amigo. :!:

Interco TrXus MT