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David K
Honored Nomad
Posts: 64855
Registered: 8-30-2002
Location: San Diego County
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Mood: Have Baja Fever
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Physics is doing the chalk test... Guessing is the other method.
The recommended tire pressure in the door jam is great UNTIL you install different brand or type of tires.
Did you even look at the photos... I was close with 37 psi, but thinner chalk in the center proved I was slightly over-inflated.
The tires have a 44 psi max pressure. When I first installed them and set them to the door jam pressure (which was 29 ft/32 rr, for BFG Rugged Trail
TA tires) they felt 'squishy'.
In any case , I have run them at 34-35 psi for the past 10 years and they have felt and lasted great.
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JZ
Select Nomad
Posts: 10565
Registered: 10-3-2003
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My rough numbers
75-80 when towing
65-70 normal driving
33-35 dirt
20 sand
15 deep sand
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mtgoat666
Select Nomad
Posts: 18389
Registered: 9-16-2006
Location: San Diego
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Mood: Hot n spicy
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The chalk test performed by you attempts to measure contact area in cold tires at very low speed. Does the chalk test have any relation to contact
area at speed when tire is hot and is rotating at 800 rpm? Is low-speed contact area the only important variable for tire performance?
Tire and auto mfgs develop tire pressure recommendations based on performance, longevity, safety, load carrying capacity, fuel economy, performance
under turning forces, and a number of other factors.
The load inflation tables are the best way to convert your stock tire pressure recommendations to alternate tire pressure when running non-stock
tires.
How does your chalk test tire pressure compare to what load inflation tables say is correct pressure?
Who you gonna trust for tire performance recommendations to survive a high speed panic stop at high speed on the highway or an unexpected sharp turn
at high speed?
Did you see that one of the factors in Firestone/Ford explorer legal case was ford recommending 26 psi, and Firestone recommending 30 psi. Did
following the at 4 psi lower tire pressure recommendation explain all the excess deaths driving explorers?
Wouldn’t a chalk-head person compare the chalk test result to the load inflation table results? Ask yourself, Do you feel safe driving 80 mph with
your tires at substantially lower or higher pressure than the load inflation tables recommend?
[Edited on 10-23-2022 by mtgoat666]
Woke!
“...ask not what your country can do for you – ask what you can do for your country.” “My fellow citizens of the world: ask not what America
will do for you, but what together we can do for the freedom of man.”
Prefered gender pronoun: the royal we
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David K
Honored Nomad
Posts: 64855
Registered: 8-30-2002
Location: San Diego County
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Mood: Have Baja Fever
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It is not "my" chalk test. It is a the scientific way easily to determin idea tire pressure. You have got to be smart enough to perform it under the
average conditions you are driving (load and temperature). Most Nomads already know that tire pressure changes when they are warmed up. I guess I
neglected to consider your special needs in this post?
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mtgoat666
Select Nomad
Posts: 18389
Registered: 9-16-2006
Location: San Diego
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Mood: Hot n spicy
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Quote: Originally posted by David K  | | It is not "my" chalk test. It is a the scientific way easily to determin idea tire pressure. You have got to be smart enough to perform it under the
average conditions you are driving (load and temperature). Most Nomads already know that tire pressure changes when they are warmed up. I guess I
neglected to consider your special needs in this post? |
Scientific!
You are funny, DK! 
Woke!
“...ask not what your country can do for you – ask what you can do for your country.” “My fellow citizens of the world: ask not what America
will do for you, but what together we can do for the freedom of man.”
Prefered gender pronoun: the royal we
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John Harper
Super Nomad
Posts: 2289
Registered: 3-9-2017
Location: SoCal
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I have a couple questions.
How many overall miles do you usually get out of off road tires? I don't see them mileage rated on some tire sites.
How many miles do you drive annually? How many miles of dirt roads do you drive annually?
I put about 10K on my truck a year, maybe 500 dirt miles per year in Wyoming and Baja the last 4 or 5 years. Street tires, no off road flats, run
20psi on dirt, 34 street. Only flat so far is from a street nail. 70K mileage rated as well.
I'm probably just the average dirt road explorer like most of us. More than some, less than others.
John
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JZ
Select Nomad
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Registered: 10-3-2003
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Get about 20-25K miles out of my tires.
Only had two flats in years of offroading in Baja. Both on the same trail. One cut the side wall. The other was just a slow leak.
Now dirt bikes are a much different story. Flats are pretty common.
[Edited on 10-24-2022 by JZ]
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David K
Honored Nomad
Posts: 64855
Registered: 8-30-2002
Location: San Diego County
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Mood: Have Baja Fever
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I don't typically drive as long as the tires are 'safe' (for highways)... I replace them when the 'meat' gets thin! A 40,000 mile rated tire is good
to me for about 30,000 miles. I think 35k is the most I have put on any tires.. and that was the very meaty (and noisy) Cooper Discoverer STT tires...
They did good in mud! Here they are after crossing the (less-than-dry) Laguna Salada, getting to Guadalupe Canyon in Sept. 2006:
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John Harper
Super Nomad
Posts: 2289
Registered: 3-9-2017
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| Quote: Originally posted by JZ | Get about 20-25K miles out of my tires.
Only add two off flats in years of offroading in Baja. Both on the same trail. One cut the side wall. The other was just a slow leak.
Now dirt bikes are a much different story. Flats are pretty common.
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How many off road miles out of that? 20-25K is what if kind of figured, not that great IMO. I think that's about what those little 50 series street
tires get as well.
My buddy regularly brings his dirt bikes over for me to pull the wheels due to flats. He got a piece of metal about 1/4" x 3" long in a rear tire a
few weeks ago, weird.
[Edited on 10-24-2022 by John Harper]
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mjs
Nomad
Posts: 309
Registered: 2-20-2013
Location: Off grid in San Felipe
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The manufactures placard is the correct pressure for stock tires. However if you change to oversized tires you can easily figure the correct pressure.
No chalk required.
The best method is to weigh your vehicle for front and rear axle weight with a normal load. Once you have the axle weights you can look up the correct
tire pressure in the The Tire and Rim Association Load Inflation Table. Download link at https://www.toyotires.com/media/pxcjubjs/application_of_load...
Or you can use the calculator at to quickly calculate the correct pressure. https://tiresize.com/pressure-calculator/
You should also determine correct pressure when fully load especially for a pick up or SUV.
BWOE, my Dodge has OEM 265/70R17 with max load rear pressure of 70 psi. I have oversized 37x13.50R17 tires. The correct pressure for max load with my
current tires is 43 psi. This provides longest tire life and smoothest ride. The tire load capacity still exceeds the weight rating of the axle.
The biggest problem I have is whenever the truck is serviced by a dealer or quick lube place they automatically inflate the tires to the OEM 70 psi.
Even though I give them the correct pressure on the work order and they don't even seem to be aware that they just exceeded the tire mfg's 65 psi
maximum.
Re the OP's original question, I've run BFGs, Nitto and various others. Last set I bit the bullet and bought Toyo RTs. Best by far. Quiet, smooth and
wearing great so far.
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John Harper
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Location: SoCal
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Same here. I've never understood spending so much money on low mileage rated off road tires, try to go with most mileage per dollar. I do keep my
suspension and braking in top condition and check inflation regularly.
OTOH, I have no problem buying high performance street tires for my Harley. Along with upgraded brakes and suspension. It's all you got on a bike.
I got 4 Kumho 235/75/15 with 70K mileage rating for $470 OTD a couple years ago. After 20K now, they still look like new, plenty of tread left and
only one street nail. Probably 1K on FS and Baja roads. Mostly dry roads, no mud or deep sand as yet.
How many of us drive over 300 off road miles a year?
John
[Edited on 10-24-2022 by John Harper]
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mtgoat666
Select Nomad
Posts: 18389
Registered: 9-16-2006
Location: San Diego
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Mood: Hot n spicy
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| Quote: Originally posted by John Harper |
Same here. I've never understood spending so much money on low mileage rated off road tires, try to go with most mileage per dollar. I do keep my
suspension and braking in top condition and check inflation regularly.
OTOH, I have no problem buying high performance street tires for my Harley. Along with upgraded brakes and suspension. It's all you got on a bike.
I got 4 Kumho 235/75/15 with 70K mileage rating for $470 OTD a couple years ago. After 20K now, they still look like new, plenty of tread left and
only one street nail. Probably 1K on FS and Baja roads. Mostly dry roads, no mud or deep sand as yet.
How many of us drive over 300 off road miles a year?
John
[Edited on 10-24-2022 by John Harper] |
For rock cuts/punctures, I tend to get the most flats when the tread life is almost gone; for nails/screws, tread wear doesn’t seem to matter.
My lt tires seem to be tougher than p tires and more capable for towing, but I prefer p metric for ride quality.
Woke!
“...ask not what your country can do for you – ask what you can do for your country.” “My fellow citizens of the world: ask not what America
will do for you, but what together we can do for the freedom of man.”
Prefered gender pronoun: the royal we
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PaulW
Ultra Nomad
Posts: 3075
Registered: 5-21-2013
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The validity of the chalk validity has been greatly reduced with the belted radial tire.
Having worn-out many sets of various tires I have proven using the pressure/load will provide excellent results for wear and handling for highway use.
Bottom line is the chalk method has become an exercise for fun, but does not provide and meaningful technical validity.
For off highway driving I use Harald's method or 1/2 or 1/3 of normal as my best guide. Lately for easy gravel roads I have been using 2/3 to shorten
up the air up time. Helps the ride quality vs highway pressure.
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David K
Honored Nomad
Posts: 64855
Registered: 8-30-2002
Location: San Diego County
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Mood: Have Baja Fever
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For sure, deflating for off-road has lot's of variables... The chalk test was to find optimal highway (paved road) pressure and has NOTHING to do with
off-road driving.
Since we are now comparing deflating pressures, mine go something like this: Deflate as much as needed! LOL
OK, too vague, I guess?
For my current tire brand (Hankook Dynapro "all terrain/mud" ATm) on my 4-door Tacoma 4x4:
Street: 34 psi
Dirt roads: 20-24 psi
Deep beach sand: 15-18 psi (these tires are the best sand tires I have run on my Tacomas, perhaps why I like them so much?)
With stiffer (3-ply) sidewalls, like BFG All Terrains or my Cooper STTs, it was necessary to deflate to at least 10 psi to achieve floatation, on deep
beach sand. I believe harald automatically drops to 10 psi on all dirt roads for his G-Wagon on BFGs. Harald (4x4abc.com) is the true expert!
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PaulW
Ultra Nomad
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The Cooper you mention has stiffer sidewalls than the BFG KM2 tire and work better with fewer psi off-road.
To corelate to the Harald recommendations:
your 34psi hwy pressure results
20psi=59%
24psi=71%
15psi=44%
18psi=53%
For what it is worth. Comment - Your off road pressures seem a bit high.
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elgatoloco
Ultra Nomad
Posts: 4332
Registered: 11-19-2002
Location: Yes
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I have a 1999 F-250 with 382,000 miles and many of those in Baja and other places with a camper. The first 40k I had the factory tires and since then
have run BFG AT and 50k is target. Still waiting to have a tire failure of any kind off road. Have picked up some metal a few times NOB and Discount
tire has either repaired or in one instance replaced at prorated cost. When in Baja or on any dirt I run the front at 30 PSI and the rear at 35 PSI.
Makes for a smooth ride on any surface and I have never had a concern about tires.
YMMV
MAGA
Making Attorneys Get Attorneys
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David K
Honored Nomad
Posts: 64855
Registered: 8-30-2002
Location: San Diego County
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Mood: Have Baja Fever
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Maybe, but as I said, deflate as much as needed.
I still have a fear of sidewall puncture, if deflated too much on rocky roads... ??
I resisted deflating on dirt roads until just a few years ago. I only deflated for sand, as that was needed.
On dirt roads, I could drive fine without deflating... However, I learned from reading Nomads that deflating on graded roads reduces tire puntures
from the little sharp rocks. I got lots of such flats going to Gonzaga and Chapala, or south of L.A. Bay on the easy-to-drive graded roads of the time
(2001-2011)... I was a slow learner, LOL! Shari (in 2007) even said I should lower the street pressure to smoothe out the washboard when we all went
to San Roque.
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JZ
Select Nomad
Posts: 10565
Registered: 10-3-2003
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| Quote: Originally posted by elgatoloco | I have a 1999 F-250 with 382,000 miles and many of those in Baja and other places with a camper. The first 40k I had the factory tires and since then
have run BFG AT and 50k is target. Still waiting to have a tire failure of any kind off road. Have picked up some metal a few times NOB and Discount
tire has either repaired or in one instance replaced at prorated cost. When in Baja or on any dirt I run the front at 30 PSI and the rear at 35 PSI.
Makes for a smooth ride on any surface and I have never had a concern about tires.
YMMV |
What psi on the pavement?
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eguillermo
Nomad
Posts: 113
Registered: 10-10-2008
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If there's still any patience out there for my level of tire naiveté, I have another question . . . 
My main reasons to get a new set of tires are basically a) it seems like the KOs haven't been very durable, and, more importantly, b) I'm worried that
tires that have been patched -- at least 2 of them on the edges where only the local mom & pop shop was even willing to patch them -- are likely
to be even LESS durable.
Fragile tires aren't what anyone wants in Baja, especially off-road. But is that correct thinking, to assume that patched tires are less durable?
Otherwise, they still have a trip's worth of wear in the tread for sure.
Seems like conventional wisdom, but one hates to assume!
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Maderita
Senior Nomad
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When you say "patched", that is rather vague. Patched on the inside, plugged from the outside, or plugged and patched? Are the holes from
nails/screws, or was it a gaping hole from a forklift running into it?
I'm comfortable with nails/screws in the tread area being patched either way. Haven't had failures of plugs. But I also carry a plug kit and 12v air
compressor if a plug were to fail.
With bigger holes, I buy new tires. The old tires are given to rancher friends who use them mostly on dirt roads. The same giveaway for tires with
less than 35% tread life remaining.
My 4x4 vehicles find BFG KO and KO2 tires to be very durable offroad. For wear mileage, I never drive enough highway miles to find out.
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