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Old 06-01-2012, 12:40 AM   #16
Billtr96sn
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Old 06-01-2012, 02:48 PM   #17
DRONE
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Square4--

I have a rig like yours--1150GS with a DMC car--and I have a car tire pusher. I run less pressure than Mr. Cob and Abenteuerfahrer. I do go on dirt roads fairly frequently usually fully loaded with camping gear on multi-day trips. On my Vredestein Snow+ pusher, I run 26 psi and I think that's fine for both paved and dirt roads. Not only do I like the traction and the ride, but I'm getting pretty even wear. My logic here is that my 4000 lb SUV rides nice on 4 tires at 30 psi--that's 1000 pounds per tire. So why can't my car pusher tire ride nice at 26 psi with a load of about 650 pounds? It's an important distinction that this is a car tire and not a motorcycle tire.

I run with 26 psi in the sidecar tire - Vredestein K60 Scout - not much load on that tire and no reason to make the ride super hard for the monkey.

I run with 30 psi on my Vredestein K60 Scout front tire. This is the trickiest tire. I agree with Mr. Cob that you don't want to go too soft on this tire as you don't want to bend a rim or pop the bead. And it takes a lot of abuse up front there carrying about a 400 pound load and hitting all the rocks and ruts that I hit. But I don't really want to run it higher because I like the steering and braking performance on pavement at 30psi.

I carry a compressor and a tire kit on board, BTW. And Ride-On tire sealant in all 3 tires. Not that either will save my ass every time, but they might save my ass some of the time.
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Old 06-01-2012, 07:20 PM   #18
Abenteuerfahrer
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Quote:
Originally Posted by DRONE View Post
Square4--

I have a rig like yours--1150GS with a DMC car--and I have a car tire pusher. I run less pressure than Mr. Cob and Abenteuerfahrer. I do go on dirt roads fairly frequently usually fully loaded with camping gear on multi-day trips. On my Vredestein Snow+ pusher, I run 26 psi and I think that's fine for both paved and dirt roads. Not only do I like the traction and the ride, but I'm getting pretty even wear. My logic here is that my 4000 lb SUV rides nice on 4 tires at 30 psi--that's 1000 pounds per tire. So why can't my car pusher tire ride nice at 26 psi with a load of about 650 pounds? It's an important distinction that this is a car tire and not a motorcycle tire.

I run with 26 psi in the sidecar tire - Vredestein K60 Scout - not much load on that tire and no reason to make the ride super hard for the monkey.

I run with 30 psi on my Vredestein K60 Scout front tire. This is the trickiest tire. I agree with Mr. Cob that you don't want to go too soft on this tire as you don't want to bend a rim or pop the bead. And it takes a lot of abuse up front there carrying about a 400 pound load and hitting all the rocks and ruts that I hit. But I don't really want to run it higher because I like the steering and braking performance on pavement at 30psi.

I carry a compressor and a tire kit on board, BTW. And Ride-On tire sealant in all 3 tires. Not that either will save my ass every time, but they might save my ass some of the time.
Hola Drone....

Well, me thinks the SUV has 4 tires equally evened out..vehicle weigh distribution pretty even....30 psi each while on a sidecar me thinks 60% is ballasted toward the rear of the pusher tire..thus a bit more psi there !! ? Maybe BMWzenrider can chime in with his scientific analytial thoughts regarding tire loads recommended for the pusher!

Cheers...
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Old 06-01-2012, 08:12 PM   #19
Square4 OP
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Drone; your tire pressures are much lower than what I have been running. For the pusher tire, when I first started running the car tire I put in 32# because it is a typical value for car tires and after a few thousand miles the tire had a very obvious wear pattern with excessive wear on both sides of the tire tread that is typcial for an under inflated tire. I ended up trying some higher settings but when on the asphalt I had to get to 42#s to not have underinflated wear pattern. Part of this may be the tire which was a Federal and perhaps it had soft sidewalls soft tread or a flimsly tread belt that created this wear pattern. When I put on the Arizonian I just put it at the max and only have several thousand miles on it but it is wearing as expected for a pusher tire (slightly higher wear on the right or sidecar side of the tire). Based on your experience, I will try lowering the pressure and track the wear pattern. It would be great to run a lower pressure for smoothing the ride but I do not want to do this if the wear pattern is wrong. I will lower the pressure and measure the tire tread depth across the tire at a marked location and then check on the tread wear. I suspect that I will need to put on 1000 miles in order to see any difference that I can measure accurately. If I do not see any change, then I will lower the pressure and continue the same monitoring process.

What experience have others had regarding tire pressures for both asphalt and fire road travel? How have you determined what is the best tire pressures to run?
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Old 06-11-2012, 08:35 AM   #20
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Square4,
Changing the inflation pressure on your tires can indeed alter the handling and ride.
To give you my personal opinion of what a safe inflation pressure would be for your rig, I would need to know the weight being carried at each wheel, the exact tire size being used there, and your goal. (max safety margin against tire damage, max traction, max wear, etc...)

you have not mentioned exactly what your rig is, or the sizes of the tires.
However, it sounds like you have a R1150GS/DMC rig, yes?
You mentioned part of the size on your pusher tire, but not the profile spec.
I do know that most of the 4valve GS guys are running a 165/80-15 tire, so I will go based upon that assumption.

-----
From my work in the tire industry I know that you can derive a load/inflation table for any tire given some information about the size/construction/etc.
For a typical passenger car radial tire with a profile of 50% or better the equation looks like this:
L=K*P^0.5*Sd^1.39*(Dr+Sd)
There are separate formulas for low profile tires, bias ply, motorcycle, heavy truck, etc...

When a vehicle manufacturers list the recommended inflation pressures for their product, it is arrived by: Taking the max. GVWR, divide by the number of tires supporting the load, and then finding a tire which will safely support that max. load at a chosen inflation pressure.
They then post a single inflation number on the door post or in the manual.

Many cycles have multiple recommended inflation pressures depending upon when ridden solo or with passenger/luggage.
This is because adding passengers/load on a relatively light vehicle like a motorcycle can so dramatically change wheel loading, and the manufacturer and tire maker knows that the grip/wear/handling of a tire can change dramatically if you are over or under inflated for the given wheel loading.

-----
What does this mean for our sidecar rigs?

When you put a car tire on a motorcycle or sidecar, the odds are pretty good that the tire is technically 'overmatched' to the loading of that wheel position.
Even when my heavy rig is fully loaded for a trip (and with my fat ass in the saddle) my pusher tire's static wheel load is only around 650-lbs.
The max load rating of the 165/60R15 car tire that I use in the summer is 900-lbs, or about 28% higher than required.
If you overinflate tires by nearly 30% you WILL notice that they are noticably too hard, don't grip well, and will have classic overinflation wear down the center of the tread in short order.

The 165/80R15 tire size has a typical max load rating of 1,200-lbs!
If your wheel loading is anywhere close to mine, that means leaving that tire at max rated inflation pressure would have it WAY too high for the load on it.

-----
Tire manufacturers actually have complete load/inflation tables available for every tire that they make, so that vehicle designers don't need to go through the labor of picking a tire size, and then going through all the formulas to see if it will support the load and at what pressure.
They just go to the tables for the size tire they are considering and can easily look up whether the tire is suitable, and at what pressure.

However, if you call up Bridgestone, or Kumho, or any tire manufacturer and as a consumer and ask for the load/inflation table for a tire you will get this reply: "XYZ tires always suggests that you consult your vehicle owners manual or contact the vehicle manufacturer for correct inflation pressures."
Their way of covering their butt so they don't get sued.

-----

Luckily, I know both the formulas used by the manufacturers to derive the tables, and the right magic words to usually be able to get the techs at the call center to just read me the load/inflation data from their charts...

And here now for your viewing pleasure....
The load/inflation data for a typical 165/80R15 passenger car radial tire.

Tire: 165/80R15
Pressure .. Load
(psi) ....... (lbs)
---------------
22 .......... 794
23 .......... 833
24 .......... 864
25 .......... 882
26 .......... 926
27 .......... 950
28 .......... 970
29 .......... 1003
30 .......... 1047
31 .......... 1061
32 .......... 1080
....
35 .......... 1199
----------------

Some of you may have already noticed that the load capacity vs. pressure is non-linear. (also that there are a few pressures not listed near the upper end, where the loads are already much higher than most sidecar owners will be at.)

The tire industry usually calulates these published loads with a 10-12% factor of safety, and the numbers generally don't need to be derated for heat/high speed unless you are doing something extrordinarly fringe.
Although part of the reason for this data is to prevent heat build-up in the rubber from cyclitic flexing. So if you are planning on going really fast in the desert, I would run a slightly higher pressure than absolutely needed for your load to reduce sidewall flex, tread squirm, and heating.

As Mr.Cob has pointed out, there IS a practical limit on how low you can go.
Yes, on extremely hard cornering a tire can lose seal with the bead if underinflated too far, but that is pretty uncommon, and takes some serious abuse to acheive.
That is because most wheels designed for radial tires have a "safety bead". It is that hump that makes it harder to break the bead on a tubeless tire than for a tube-type tire/wheel. The safety bead is there to help keep the bead in place in case of a deflation while rolling down the road, so it works pretty well at low pressures as well. But it is not foolproof.
For my 'spirited' riding on some pretty tight twisties I have run my pusher tire as low as 24-26psi(cold) without problems. And we are talking cornering speeds/forces which were making the front tire visibly roll in according to the photo someone took of me. (And it was at max sidewall pressure!)

Another consideration is compressive deflection of the tire when hitting bumps/ruts/etc. The risk of pinching the tire flat against the rim and doing damage to the wheel in extreme cases.
One thing that you have to factor in is that when you compare a typical motorcycle tire to a car tire there is a WHOLE lot more contact patch resisting that compression and there is generally more sidewall to absorb that force as well. The sidewall on a 165/80-15 tire is around 132-135mm tall. The sidewall on the stock GS rear tire (150/70-17) is only around 105-110mm tall. A 1-inch advantage in sidewall height for the car tire, and a whole lot more 'crush space' before you reach the rim as a result.
So the danger of pinching down from lower inflation is usually not as great with an automotive tire as it is on a narrower bike type tire.

Inflation pressure even influences the puncture/cut resistance of a tire.

-----

Probably LOTS more info than you really wanted, but hopefully you and others will find something in there of value.
If not, just remember what it cost you...
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2002 BMW R1150RA
In Memoriam: Harley, 1993-2010 You will be missed.
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Old 06-11-2012, 09:57 AM   #21
Abenteuerfahrer
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BMWzenrider..

I remember now that the tire pressure/weigh ratio was once posted by you somewhere but lost neverthless.

Thanks Karl for posting it again.

So Drone you're basically doing a-OK .....

Cheers...
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Old 06-11-2012, 10:51 AM   #22
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Quote:
Originally Posted by Abenteuerfahrer View Post
Hola Drone....

Well, me thinks the SUV has 4 tires equally evened out..vehicle weigh distribution pretty even....30 psi each while on a sidecar me thinks 60% is ballasted toward the rear of the pusher tire..thus a bit more psi there !! ? Maybe BMWzenrider can chime in with his scientific analytial thoughts regarding tire loads recommended for the pusher!

Cheers...
Static weight distribution on a hack setup is definitely asymetrical, just like everything else about them.

what I have typically gotten with my current rig when I roll it across the scales is a distribution of:
Front wheel: 30-35%
Pusher wheel: 45-50%
Sidecar wheel: 20-30%
(these percentages are with my 'wide load' occupying the driver's station, just like it would be running down the road.)

The percentages move a round a bit based upon loading, driver's position on the bike, and even the position of the camber control.
I have put just one wheel on the scale deck (rear or sidecar) and cycled the camber control from full-left to full-right and can watch the numbers on the scale move, up to 30-40 pounds of weight transfer between the two wheels depending upon load, load height, etc.
Interestingly, I DID try the same thing with just the front wheel on the scale. No change.
Shifting your body around can make a noticable shift in weight distribution at each wheel as well, but it is still harder to influence the load on the front wheel from anywhere on the seat where you can still be in control of the rig.

So while you may get relatively close by just dividing the weight of your rig my three, it won't be as good as getting on a platform truck scale with one wheel at a time.

Not necessarily very 'scientific', but I like gathering data, even if it has limited usefullness.
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Old 06-11-2012, 08:26 PM   #23
DRONE
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Quote:
Originally Posted by Abenteuerfahrer View Post

So Drone you're basically doing a-OK .....

Cheers...
That's what all my girlfriends say too!

My wife . . . not so much.
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Old 06-12-2012, 08:43 PM   #24
Square4 OP
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BMWzenrider;

thanks for all of the information. My rig fits right into what you described. I am running on my 2002 R1150 GSA and the sidecar a 165/80R15 tire. I loaded my sidecar and saddle bags with the loads that I would be taking on a long trip and had the following loading numbers: Sidecar 340#, Front 440#, Pusher Wheel 730# and a total on the scale of 1470#. Now most of the time I do not run that loaded but got these numbers so that I could get shocks that would be capable of handling these loads as needed for long trips. I think that proportionally they come out pretty close to the distribution that you described with 23% on the sidecar wheel, 30% on the front wheel and 47% on the pusher wheel. Now most of the time I do not run with the sidecar loaded to max or the saddle bags with much in them. However, when I was running 32# in the pusher wheel I had a significant under inflation wear pattern on my pusher wheel. This does not seem consistent with the data that you presented regarding the loading capacity at this pressure. At higher pressure the tire wore as expected with both edges of the tire wearing fastest. That was the basis for the original question. If the tire had weak sidewalls would this make it tend to sag on itself and cause wear on both edges of the tire? Is it the tire? Will going to other tires improve this? The original tire was a Federal and it was down to the wear bars in just over 5,000 miles.
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Old 06-12-2012, 10:08 PM   #25
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Quote:
Originally Posted by Square4 View Post
thanks for all of the information. My rig fits right into what you described. I am running on my 2002 R1150 GSA and the sidecar a 165/80R15 tire.
(...)
However, when I was running 32# in the pusher wheel I had a significant under inflation wear pattern on my pusher wheel. This does not seem consistent with the data that you presented regarding the loading capacity at this pressure. At higher pressure the tire wore as expected with both edges of the tire wearing fastest.
Ok, I am a little confused.
Typical overinflation wear is faster wear in the center of the tread.
Underinflation causes the edges to wear faster.


http://blog.tirerack.com/blog/where-...cts-tread-wear

Also, most sidecar setups have the bike leaned out (to the left in the USA), which leads to more wear on the side of the pusher tire that is farthest from the sidecar. And in an earlier post you mentioned that the shoulder closest to the sidecar is wearing faster on your rig.
How is the setup on your rig? Does it pull to the right?

----------

When I had a 165/80-15 tire on my rig I kept it at around 26psi.
From what I remember, that pressure produced even wear on the tire.

My current summer tire is smaller, and I run with the rig unloaded at 26psi for a load rating on the rear wheel of 698-lb. Same result of fairly even wear other than the differential wear caused by the lean-out.

So I don't really know what to say about your rig and the observed tire wear patterns.
Sorry...

----------
If it were my rig, I would opt for a tire pressure that gives enhanced traction and ride before worrying about treadwear. Keeping it in the safe zone, of course.
Even with the 'spirited' riding that I enjoy, I am still getting 15-16,000 miles out of each summer tire (~6,000mi for my winter rubber).
So, once you have the car tire conversion, the cost per mile of the rear tire is pretty low, so I would gladly trade some wear for better grip/handling.

Of course, that is just my opinion. You have to do what makes sense for your situation.
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In Memoriam: Harley, 1993-2010 You will be missed.
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Old 06-13-2012, 07:53 PM   #26
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BMWzenrider;

It was late last night when I was sending my last response and see that I stated something incorrectly. So I want to clarify it.

AT 32 # I got under inflated wear pattern oon the pusjer tire.

At 42# I got what I consider to be more typical wear with slightly more wear on the side of the tire nearest the sidecar. I have a tilt control so it is set up to be adjusted to run in a neutral mode. I have been told that this tire wear pattern is normal because of the effects of the sidecar on the tire during accceleration and braking.

I hope that this clarifies my observations, sorry about the confusion.
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Old 06-14-2012, 09:44 AM   #27
BMWzenrider
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Quote:
Originally Posted by Square4 View Post
BMWzenrider,
It was late last night when I was sending my last response and see that I stated something incorrectly. So I want to clarify it.

AT 32 # I got under inflated wear pattern oon the pusjer tire.

At 42# I got what I consider to be more typical wear with slightly more wear on the side of the tire nearest the sidecar. I have a tilt control so it is set up to be adjusted to run in a neutral mode. I have been told that this tire wear pattern is normal because of the effects of the sidecar on the tire during accceleration and braking.

I hope that this clarifies my observations, sorry about the confusion.
Ahhhh... Drunk posting to ADVrider...
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Old 06-16-2012, 08:03 PM   #28
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Thumb

Actually what happened was that I wrote it and was reviewing it when I got interrupted. When I got back to finish my review I forgot where I was and messed it up. I just went down to the John Day Rally put on by the Oregon BMW club. I tried running 34 #s in the pusher wheel and 32# is the sidecar wheel. It handled nice and I put on 50 miles of forest service roads with lots of puddles, holes, drainage ruts and rocks. It handled well so I am going to do more testing to further evaluate tire pressures. I think I need to find out what works best for some "standard conditions" that I want to use as a gauge for how to set up tire pressures. I need something local for this so that I can run tests and go over and over these conditions at different pressures as well as speeds to understand how they impact handling and then run what I think is the best and see how the tire wears.
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Old 06-17-2012, 09:06 AM   #29
Abenteuerfahrer
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Currently running 32#-front Tourance; 28# pusher; 28# sidecar......good ride on pavement and off road...comfy with the overall Hyperpro shocks on the motorcycle and Progressive 200/350 on sidecar. (carry a pair-just in case).

Now I don't slam-bang the rig through the worst roads....easy does it.. ! Ain't racing a la Moto offroad...always make sure that the pusher is in/on the best lane of travel disregarding the sidecar pretty much .

Cheers...
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Old 06-17-2012, 09:54 AM   #30
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Quote:
Originally Posted by BMWzenrider View Post
Square4,
Changing the inflation pressure on your tires can indeed alter the handling and ride.
To give you my personal opinion of what a safe inflation pressure would be for your rig, I would need to know the weight being carried at each wheel, the exact tire size being used there, and your goal. (max safety margin against tire damage, max traction, max wear, etc...)

you have not mentioned exactly what your rig is, or the sizes of the tires.
However, it sounds like you have a R1150GS/DMC rig, yes?
You mentioned part of the size on your pusher tire, but not the profile spec.
I do know that most of the 4valve GS guys are running a 165/80-15 tire, so I will go based upon that assumption.

-----
From my work in the tire industry I know that you can derive a load/inflation table for any tire given some information about the size/construction/etc.
For a typical passenger car radial tire with a profile of 50% or better the equation looks like this:
L=K*P^0.5*Sd^1.39*(Dr+Sd)
There are separate formulas for low profile tires, bias ply, motorcycle, heavy truck, etc...

When a vehicle manufacturers list the recommended inflation pressures for their product, it is arrived by: Taking the max. GVWR, divide by the number of tires supporting the load, and then finding a tire which will safely support that max. load at a chosen inflation pressure.
They then post a single inflation number on the door post or in the manual.

Many cycles have multiple recommended inflation pressures depending upon when ridden solo or with passenger/luggage.
This is because adding passengers/load on a relatively light vehicle like a motorcycle can so dramatically change wheel loading, and the manufacturer and tire maker knows that the grip/wear/handling of a tire can change dramatically if you are over or under inflated for the given wheel loading.

-----
What does this mean for our sidecar rigs?

When you put a car tire on a motorcycle or sidecar, the odds are pretty good that the tire is technically 'overmatched' to the loading of that wheel position.
Even when my heavy rig is fully loaded for a trip (and with my fat ass in the saddle) my pusher tire's static wheel load is only around 650-lbs.
The max load rating of the 165/60R15 car tire that I use in the summer is 900-lbs, or about 28% higher than required.
If you overinflate tires by nearly 30% you WILL notice that they are noticably too hard, don't grip well, and will have classic overinflation wear down the center of the tread in short order.

The 165/80R15 tire size has a typical max load rating of 1,200-lbs!
If your wheel loading is anywhere close to mine, that means leaving that tire at max rated inflation pressure would have it WAY too high for the load on it.

-----
Tire manufacturers actually have complete load/inflation tables available for every tire that they make, so that vehicle designers don't need to go through the labor of picking a tire size, and then going through all the formulas to see if it will support the load and at what pressure.
They just go to the tables for the size tire they are considering and can easily look up whether the tire is suitable, and at what pressure.

However, if you call up Bridgestone, or Kumho, or any tire manufacturer and as a consumer and ask for the load/inflation table for a tire you will get this reply: "XYZ tires always suggests that you consult your vehicle owners manual or contact the vehicle manufacturer for correct inflation pressures."
Their way of covering their butt so they don't get sued.

-----

Luckily, I know both the formulas used by the manufacturers to derive the tables, and the right magic words to usually be able to get the techs at the call center to just read me the load/inflation data from their charts...

And here now for your viewing pleasure....
The load/inflation data for a typical 165/80R15 passenger car radial tire.

Tire: 165/80R15
Pressure .. Load
(psi) ....... (lbs)
---------------
22 .......... 794
23 .......... 833
24 .......... 864
25 .......... 882
26 .......... 926
27 .......... 950
28 .......... 970
29 .......... 1003
30 .......... 1047
31 .......... 1061
32 .......... 1080
....
35 .......... 1199
----------------
Some of you may have already noticed that the load capacity vs. pressure is non-linear. (also that there are a few pressures not listed near the upper end, where the loads are already much higher than most sidecar owners will be at.)

The tire industry usually calulates these published loads with a 10-12% factor of safety, and the numbers generally don't need to be derated for heat/high speed unless you are doing something extrordinarly fringe.
Although part of the reason for this data is to prevent heat build-up in the rubber from cyclitic flexing. So if you are planning on going really fast in the desert, I would run a slightly higher pressure than absolutely needed for your load to reduce sidewall flex, tread squirm, and heating.

As Mr.Cob has pointed out, there IS a practical limit on how low you can go.
Yes, on extremely hard cornering a tire can lose seal with the bead if underinflated too far, but that is pretty uncommon, and takes some serious abuse to acheive.
That is because most wheels designed for radial tires have a "safety bead". It is that hump that makes it harder to break the bead on a tubeless tire than for a tube-type tire/wheel. The safety bead is there to help keep the bead in place in case of a deflation while rolling down the road, so it works pretty well at low pressures as well. But it is not foolproof.
For my 'spirited' riding on some pretty tight twisties I have run my pusher tire as low as 24-26psi(cold) without problems. And we are talking cornering speeds/forces which were making the front tire visibly roll in according to the photo someone took of me. (And it was at max sidewall pressure!)

Another consideration is compressive deflection of the tire when hitting bumps/ruts/etc. The risk of pinching the tire flat against the rim and doing damage to the wheel in extreme cases.
One thing that you have to factor in is that when you compare a typical motorcycle tire to a car tire there is a WHOLE lot more contact patch resisting that compression and there is generally more sidewall to absorb that force as well. The sidewall on a 165/80-15 tire is around 132-135mm tall. The sidewall on the stock GS rear tire (150/70-17) is only around 105-110mm tall. A 1-inch advantage in sidewall height for the car tire, and a whole lot more 'crush space' before you reach the rim as a result.
So the danger of pinching down from lower inflation is usually not as great with an automotive tire as it is on a narrower bike type tire.

Inflation pressure even influences the puncture/cut resistance of a tire.

-----

Probably LOTS more info than you really wanted, but hopefully you and others will find something in there of value.
If not, just remember what it cost you...
What's your opinion on using a so-called "space saver" tire as a pusher on a rig. It would seam they need to be pretty tough, for what is required of them.
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