Tire pressures in snow?
01-14-2009, 05:56 PM
#21
JK Freak
I dont agree with this one bit.
So your trying to tell me that by airing down your tires there really is no measureable difference.
So then why does everyone air down there tires when rock crawling and off roading?
The answer to that question..........
1). Wider foot print
2). Tire will mould around rocks/terrain for better traction.
Just my .02
But what would I know...I own an XK not a JK
So your trying to tell me that by airing down your tires there really is no measureable difference.
So then why does everyone air down there tires when rock crawling and off roading?
The answer to that question..........
1). Wider foot print
2). Tire will mould around rocks/terrain for better traction.
Just my .02
But what would I know...I own an XK not a JK
While on that topic, let me expound some.
When you compress snow, you heat it. This heat tends to break down the crystalline snow flakes, actually melting them. It refreezes almost instantly, but with a crystal structure more like that of hard ice. Tires will conform more to hard ice. That is why "winter" tires have tight tread designs and soft compounds (compounds that remain soft at low temps). You get the best of both worlds. Good traction in snow and improved traction on ice.
You know, man has yet to develop a material that when chilled to the temperature of snow, sticks to snow better than snow does. Snow sticks to snow better than snow sticks to rubber. Especially hard compound rubber used for most hardcore off road tires. Hence, tighter tread blocks that tend to not self-clean work better than large lugs that throw snow all over. It's just the opposite in mud.
That's why the SR-As get a much better bite than the BFG MTs, even siped MTs. Yet, there are additional factors involved.
Science has studied the coefficients of friction for various types of snow acting on a like snow type. Your typical fresh powder has a coefficient of friction around 1.75 give or take a small amount. Refrozen sun heated crust might get up to 0.58 under ideal conditions. This is largely due to it being structured closer to pure ice. A typical soft compound "winter" tire on snow has a coefficient of friction of 0.60, with hard compound rubbers being close to 0.30 on the same dry snow. How much a compound hardens when exposed to cold will determine its specific friction characteristics. This can be tested with a simple pressure durometer tool. The Shore durometer scale is a measurement of hardness (and viscoelastic properties) of rubber by measuring its resistance to indentation.
I'm going to test the compounds of the Goodyear SR-As and the BFG MT KMs. Tomorrow will be damn cold and I have a small durometer tester in the QC lab I can borrow for a bit. One of our employees recently invested $1,200 in five BFG MT KM2s for his ratty Rubi TJ. I'm going to speculate that the Goodyears will be close to 80 on the A scale at 15 degrees, and I'll also guess that the BFGs come in near 20 on the D scale. I'll post the results tomorrow evening. It's supposed to snow tomorrow, so the TJ should be in the parking lot.
My regards,
Widewing
Last edited by Widewing; 01-14-2009 at 05:58 PM.
01-14-2009, 07:24 PM
#22
JK Freak
My regards,
Widewing
01-14-2009, 09:53 PM
#23
JK Enthusiast
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All I know is I went on a run recently and everyone aired down except for a 4-Runner. I have the SR-As on my stock open axle Jeep JK X and his tires looked like a similar type of AT tire. Coming back up the trail, as soon as we hit the ice and snow he was done. Had to hook a Jeep to him and tow him back up to the top of the trail out of the snow. I was aired down to about 20 and never had an issue going up the trail.
01-15-2009, 04:14 AM
#24
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You need to read more of the tread. We're talking about snow. Not rock crawling, not sand, snow. Tires will not conform to snow, snow will conform to the tire.
While on that topic, let me expound some.
When you compress snow, you heat it. This heat tends to break down the crystalline snow flakes, actually melting them. It refreezes almost instantly, but with a crystal structure more like that of hard ice. Tires will conform more to hard ice. That is why "winter" tires have tight tread designs and soft compounds (compounds that remain soft at low temps). You get the best of both worlds. Good traction in snow and improved traction on ice.
You know, man has yet to develop a material that when chilled to the temperature of snow, sticks to snow better than snow does. Snow sticks to snow better than snow sticks to rubber. Especially hard compound rubber used for most hardcore off road tires. Hence, tighter tread blocks that tend to not self-clean work better than large lugs that throw snow all over. It's just the opposite in mud.
That's why the SR-As get a much better bite than the BFG MTs, even siped MTs. Yet, there are additional factors involved.
Science has studied the coefficients of friction for various types of snow acting on a like snow type. Your typical fresh powder has a coefficient of friction around 1.75 give or take a small amount. Refrozen sun heated crust might get up to 0.58 under ideal conditions. This is largely due to it being structured closer to pure ice. A typical soft compound "winter" tire on snow has a coefficient of friction of 0.60, with hard compound rubbers being close to 0.30 on the same dry snow. How much a compound hardens when exposed to cold will determine its specific friction characteristics. This can be tested with a simple pressure durometer tool. The Shore durometer scale is a measurement of hardness (and viscoelastic properties) of rubber by measuring its resistance to indentation.
I'm going to test the compounds of the Goodyear SR-As and the BFG MT KMs. Tomorrow will be damn cold and I have a small durometer tester in the QC lab I can borrow for a bit. One of our employees recently invested $1,200 in five BFG MT KM2s for his ratty Rubi TJ. I'm going to speculate that the Goodyears will be close to 80 on the A scale at 15 degrees, and I'll also guess that the BFGs come in near 20 on the D scale. I'll post the results tomorrow evening. It's supposed to snow tomorrow, so the TJ should be in the parking lot.
My regards,
Widewing
While on that topic, let me expound some.
When you compress snow, you heat it. This heat tends to break down the crystalline snow flakes, actually melting them. It refreezes almost instantly, but with a crystal structure more like that of hard ice. Tires will conform more to hard ice. That is why "winter" tires have tight tread designs and soft compounds (compounds that remain soft at low temps). You get the best of both worlds. Good traction in snow and improved traction on ice.
You know, man has yet to develop a material that when chilled to the temperature of snow, sticks to snow better than snow does. Snow sticks to snow better than snow sticks to rubber. Especially hard compound rubber used for most hardcore off road tires. Hence, tighter tread blocks that tend to not self-clean work better than large lugs that throw snow all over. It's just the opposite in mud.
That's why the SR-As get a much better bite than the BFG MTs, even siped MTs. Yet, there are additional factors involved.
Science has studied the coefficients of friction for various types of snow acting on a like snow type. Your typical fresh powder has a coefficient of friction around 1.75 give or take a small amount. Refrozen sun heated crust might get up to 0.58 under ideal conditions. This is largely due to it being structured closer to pure ice. A typical soft compound "winter" tire on snow has a coefficient of friction of 0.60, with hard compound rubbers being close to 0.30 on the same dry snow. How much a compound hardens when exposed to cold will determine its specific friction characteristics. This can be tested with a simple pressure durometer tool. The Shore durometer scale is a measurement of hardness (and viscoelastic properties) of rubber by measuring its resistance to indentation.
I'm going to test the compounds of the Goodyear SR-As and the BFG MT KMs. Tomorrow will be damn cold and I have a small durometer tester in the QC lab I can borrow for a bit. One of our employees recently invested $1,200 in five BFG MT KM2s for his ratty Rubi TJ. I'm going to speculate that the Goodyears will be close to 80 on the A scale at 15 degrees, and I'll also guess that the BFGs come in near 20 on the D scale. I'll post the results tomorrow evening. It's supposed to snow tomorrow, so the TJ should be in the parking lot.
My regards,
Widewing
01-15-2009, 05:32 AM
#25
JK Freak
Snow shoes Vs running shoes does not equate to airing down, does it?
I air-down for sand (about 18 psi)... I've never aired-down for snow.
Did you note that one person drops to 2 psi. That's virtually flat and is absolutely going to weaken the sidewalls of the tires.
My regards,
Widewing
01-15-2009, 06:17 AM
#26
JK Enthusiast
A few months ago I watched an AEV Project show where they were testing their built Commander and TJ on snow. They were going up a slight incline and the TJ could only go a few feet before its tires started to spin and wouldn't move forward. They were running 9 psi. Then they went down to 4 psi and the TJ went up w/o problems. This was a very convincing test for me.
Also, when you air down it's not the width what makes the big difference but the length of the footprint.
For off-road, I would treat snow like mud. If the mud/snow it's not too deep pizza cutters work best cutting through the snow/mud reaching solid ground.
If it's too deep for that, then airing down for bigger footprint and floatation works better.
Also, when you air down it's not the width what makes the big difference but the length of the footprint.
For off-road, I would treat snow like mud. If the mud/snow it's not too deep pizza cutters work best cutting through the snow/mud reaching solid ground.
If it's too deep for that, then airing down for bigger footprint and floatation works better.
01-15-2009, 09:13 AM
#27
JK Freak
I figured that I would contact B.F. Goodrich and request their opinion on airing-down for trail riding in snow.
From B.F. Goodrich via e-mail received today:
"Thank you for your email.
BF Goodrich does not recommend reducing the inflation pressure on your tires
to drive trails in the snow. You need to still have enough air to handle
the load requirements of the vehicle and that is the air pressures stated on
the placard between your door jams and put there by the vehicle
manufacturer. Driving on any surface or terrain with extreme low linflation pressure
will damage the tires and the possibility of damaging the vehicle and physical injury
be ignored."
My regards,
Widewing
From B.F. Goodrich via e-mail received today:
"Thank you for your email.
BF Goodrich does not recommend reducing the inflation pressure on your tires
to drive trails in the snow. You need to still have enough air to handle
the load requirements of the vehicle and that is the air pressures stated on
the placard between your door jams and put there by the vehicle
manufacturer. Driving on any surface or terrain with extreme low linflation pressure
will damage the tires and the possibility of damaging the vehicle and physical injury
be ignored."
My regards,
Widewing
01-15-2009, 10:07 AM
#28
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I figured that I would contact B.F. Goodrich and request their opinion on airing-down for trail riding in snow.
From B.F. Goodrich via e-mail received today:
"Thank you for your email.
BF Goodrich does not recommend reducing the inflation pressure on your tires
to drive trails in the snow. You need to still have enough air to handle
the load requirements of the vehicle and that is the air pressures stated on
the placard between your door jams and put there by the vehicle
manufacturer. Driving on any surface or terrain with extreme low linflation pressure
will damage the tires and the possibility of damaging the vehicle and physical injury
be ignored."
My regards,
Widewing
From B.F. Goodrich via e-mail received today:
"Thank you for your email.
BF Goodrich does not recommend reducing the inflation pressure on your tires
to drive trails in the snow. You need to still have enough air to handle
the load requirements of the vehicle and that is the air pressures stated on
the placard between your door jams and put there by the vehicle
manufacturer. Driving on any surface or terrain with extreme low linflation pressure
will damage the tires and the possibility of damaging the vehicle and physical injury
be ignored."
My regards,
Widewing
They can't because if they did they are liable for any damages that may occur. We live in a sue happy PC world. As a corporation and manufacture that's a risk they're never going to take. Call Jeep and ask them if it's "safe" to lift a jeep and they're gonna say NO. My first post on this subject was trying to take the scientific approach to the question. And try both ideas! I already know what works and have provided evidence. And was willing to let the OP give both ideas a try and see what works best for there application. But I don't know... "Dirt" is what I do for a living so I don't want to talk below anyones level.
01-15-2009, 10:32 AM
#29
JK Super Freak
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To the OP... It appears that you have two very different answers to the question of what PSI to run off road in the snow. One is to run higher PSI and the other to run a lower PSI. I say try both! Start out the trip running with the +2psi that Widewing has suggested and if that doesn't workout for you... drop down to the 8-15psi range that others have suggested. And please do post what worked out the best for you.
I personally I don't drop PSI unless I need to... Started at 37psi spinning not going anywhere (not pictured) and dropped just to 22.5psi (would have gone lower but not able to air up for the drive home) and achieved this...
I personally I don't drop PSI unless I need to... Started at 37psi spinning not going anywhere (not pictured) and dropped just to 22.5psi (would have gone lower but not able to air up for the drive home) and achieved this...
Wow... I never thought I would stir up such a debate.
I think I am going to start out with my normal 31 psi and see how it goes. If I feel that I need a change, I will try airing down and see how it goes. Definitely going to bring the air compressor with me for the ride home.
In the meantime.....
01-15-2009, 10:44 AM
#30
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Wow... I never thought I would stir up such a debate.
I think I am going to start out with my normal 31 psi and see how it goes. If I feel that I need a change, I will try airing down and see how it goes. Definitely going to bring the air compressor with me for the ride home.
In the meantime.....
I think I am going to start out with my normal 31 psi and see how it goes. If I feel that I need a change, I will try airing down and see how it goes. Definitely going to bring the air compressor with me for the ride home.
In the meantime.....
