"Mall Crawler vs. Rock Crawler"
02-04-2013, 04:39 AM
#31
With a small contact patch, you get more pounds of pressure per square inch of contact. With a big contact patch you get less pressure per square inch. That's why narrow tires work better in snow, and why they present a lot of grip on rock. With less pressure per inch, a wide tire offers flotation for better performance in loose dirt, mud, and sand.
In narrow grooves (road tire) there isn't enough packed snow area for traction.
Wide grooves, such as in mud tires, are too wide for the snow to keep packed – it falls out.
Mud tires cab be effective in some types of snow, for another reason: The large & deep rubber cubes are stuck in the snow and act like paddles which push back.
The groove width of winter (or AT) tires, is wide enough to create friction area, and narrow enough to keep the snow in the grooves.
Wider winter (or AT) tires offer more groove area = more snow-on-snow friction.
Airing down offers yet more friction area.
(This is how it generally works, but it also depends on the snow type, as snow flakes can be dry or wet & heavier.)
The only case where narrower tires give better grip on snow is when the snow is shallow enough to allow the tire to sink through and touch the asphalt or ground (It's the same with shallow mud).
A wider tire might not penetrate all the way through, and not touch the ground.
I drove on a deep snow covered narrow mountainous road near Jerusalem with 245 tread tires. At a certain point it was impossible to continue and I turned back. A few weeks ago I drove on the same road, similar snow, with 315 tread tires, and went all the way through.
The only difference was that, this time, I had nearly 30% more traction area.
Larger diameter also helps, as it creates a smaller "wake" pile in front of the tire.
As for rocks, why, then, rock crawlers have wide tires rather than narrow ones? Would have they really increased traction by using narrower tires?
Obviously, a wider tire gives more friction area, and better complies with the shape of the obstacle it is on.
Take the 'BEAST' for instance. Dave (CALIJK) made one of the most capable rock crawlers. He sure knows a thing or two about rock crawling and offroad driving... his tires are 14.5" wide.
My tires are 315 (~12.5"), and grip better on everything, vs the 245 I had before.
The contact patch also gets bigger (longer, not wider) with low tire pressure, and smaller (shorter) at higher pressure.
So, unless the tire is picked for looks only, a wide tire is not automatically the better tire. It depends on how/where the Jeep will get driven.
Where the 245 used to spin, the 315 spin much less and grab more.
(Part of the improvement comes from the increased diameter, but that's the smaller contributor to the improved traction.)
Over the vast majority of terrain type, the wider tire has more traction, while a narrower tire will have an edge only on a narrow range of depth/type of snow or mud.
Last edited by GJeep; 02-04-2013 at 07:28 AM.
02-04-2013, 12:50 PM
#32
JK Super Freak
I'd think a 4wd conversion would be more important out of the gate before lift etc..
Jeep pre-runner?Here in New England I have never seen, or even 'heard' of any 2wd Jeeps.
02-04-2013, 09:00 PM
#33
JK Freak
Hey jeepgirl , you didn't put up pink stick on angels on the windows as your first mod ? Ha HA ! So , tell us the truth ,you don't own three jeeps all to your self right ? One belongs to your boyfriend , or husband , one is your dads , or brother , and maybe one belongs to you ? I don't even know of any guys that personnaly own three jeeps , more or less a girl . I'm just sayin ...
02-04-2013, 10:13 PM
#34
JK Super Freak
On snow, as you probably know, most of the friction/traction doesn't come from the rubber, which has low friction with snow. Most of the traction is between the snow which is packed in the tire grooves and the snow on the ground.
In narrow grooves (road tire) there isn't enough packed snow area for traction.
Wide grooves, such as in mud tires, are too wide for the snow to keep packed – it falls out.
Mud tires cab be effective in some types of snow, for another reason: The large & deep rubber cubes are stuck in the snow and act like paddles which push back.
The groove width of winter (or AT) tires, is wide enough to create friction area, and narrow enough to keep the snow in the grooves.
Wider winter (or AT) tires offer more groove area = more snow-on-snow friction.
Airing down offers yet more friction area.
(This is how it generally works, but it also depends on the snow type, as snow flakes can be dry or wet & heavier.)
The only case where narrower tires give better grip on snow is when the snow is shallow enough to allow the tire to sink through and touch the asphalt or ground (It's the same with shallow mud).
A wider tire might not penetrate all the way through, and not touch the ground.
I drove on a deep snow covered narrow mountainous road near Jerusalem with 245 tread tires. At a certain point it was impossible to continue and I turned back. A few weeks ago I drove on the same road, similar snow, with 315 tread tires, and went all the way through.
The only difference was that, this time, I had nearly 30% more traction area.
Larger diameter also helps, as it creates a smaller "wake" pile in front of the tire.
As for rocks, why, then, rock crawlers have wide tires rather than narrow ones? Would have they really increased traction by using narrower tires?
Obviously, a wider tire gives more friction area, and better complies with the shape of the obstacle it is on.
Take the 'BEAST' for instance. Dave (CALIJK) made one of the most capable rock crawlers. He sure knows a thing or two about rock crawling and offroad driving... his tires are 14.5" wide.
My tires are 315 (~12.5"), and grip better on everything, vs the 245 I had before.
You agree that airing down is beneficial because (among other things) it increases the contact area with the ground. How can you object to a wider tire, which does the same - increases contact area ?
Be it on hard soil, gravel, mud, sand, rocks, steps, snow or steep inclines/declines, I constantly get better traction from the 315 All Terrain tires, than I did from 245 All Terrain.
Where the 245 used to spin, the 315 spin much less and grab more.
(Part of the improvement comes from the increased diameter, but that's the smaller contributor to the improved traction.)
Over the vast majority of terrain type, the wider tire has more traction, while a narrower tire will have an edge only on a narrow range of depth/type of snow or mud.
In narrow grooves (road tire) there isn't enough packed snow area for traction.
Wide grooves, such as in mud tires, are too wide for the snow to keep packed – it falls out.
Mud tires cab be effective in some types of snow, for another reason: The large & deep rubber cubes are stuck in the snow and act like paddles which push back.
The groove width of winter (or AT) tires, is wide enough to create friction area, and narrow enough to keep the snow in the grooves.
Wider winter (or AT) tires offer more groove area = more snow-on-snow friction.
Airing down offers yet more friction area.
(This is how it generally works, but it also depends on the snow type, as snow flakes can be dry or wet & heavier.)
The only case where narrower tires give better grip on snow is when the snow is shallow enough to allow the tire to sink through and touch the asphalt or ground (It's the same with shallow mud).
A wider tire might not penetrate all the way through, and not touch the ground.
I drove on a deep snow covered narrow mountainous road near Jerusalem with 245 tread tires. At a certain point it was impossible to continue and I turned back. A few weeks ago I drove on the same road, similar snow, with 315 tread tires, and went all the way through.
The only difference was that, this time, I had nearly 30% more traction area.
Larger diameter also helps, as it creates a smaller "wake" pile in front of the tire.
As for rocks, why, then, rock crawlers have wide tires rather than narrow ones? Would have they really increased traction by using narrower tires?
Obviously, a wider tire gives more friction area, and better complies with the shape of the obstacle it is on.
Take the 'BEAST' for instance. Dave (CALIJK) made one of the most capable rock crawlers. He sure knows a thing or two about rock crawling and offroad driving... his tires are 14.5" wide.
My tires are 315 (~12.5"), and grip better on everything, vs the 245 I had before.
You agree that airing down is beneficial because (among other things) it increases the contact area with the ground. How can you object to a wider tire, which does the same - increases contact area ?
Be it on hard soil, gravel, mud, sand, rocks, steps, snow or steep inclines/declines, I constantly get better traction from the 315 All Terrain tires, than I did from 245 All Terrain.
Where the 245 used to spin, the 315 spin much less and grab more.
(Part of the improvement comes from the increased diameter, but that's the smaller contributor to the improved traction.)
Over the vast majority of terrain type, the wider tire has more traction, while a narrower tire will have an edge only on a narrow range of depth/type of snow or mud.
I lived a few years in a British Columbia, Canada, mountain logging town. Most of the 4x4 crew trucks ran Michelin 215/80 tires with block tread. These logger guys made good bucks and could buy any tire they wanted. Other residents also ran skinny tires in winter. This skinny tire habit came out of several generations of loggers getting in and out of the bush in an area where it snows 13 feet annually. Sometimes the roads stayed white for months. The driving ranged from running 40-50 MPH on snow-packed highways to crawling deep snow on side roads and logging trails. You didn't hear about folks getting stuck much.
I totally agree with the points about tread styles. The tread should clear easily at highway speed, and hold some snow when crawling. If the spacing is too narrow or wide it doesn't work.
In snow at anything faster than crawling speed, the tire should act a bit like a sled runner for better directional stability - that's why the right skinny tire works. On a wide tire the contact patch is typically wider than its length. Airing down helps by squaring up the contact patch, but a contact patch that is longer than it is wide gives the best stability in snow. If a skinny tire is aired down the contact patch gets bigger by becoming longer and the tire holds its line much better.
The bottom line is that if two tires have the same contact patch area, the tire with a longer and narrower contact patch will get farther in the snow than one with a short and wide patch - given that everything else is equal (which it seldom is).
No doubt that width helps a lot in sand, mud, and other stuff where some flotation works. I'll stay away from the rock crawling question for now. I have many years and many thousands of miles of experience in snow, but I'm still figuring things out on the rock pile.
Its great that the 315s are working. Whether they are better because of width, tread pattern, tread compound, diameter, or all of those - the thing that matters is they get the job done for you.
Last edited by Freewill; 02-04-2013 at 10:24 PM. Reason: Typo
02-05-2013, 04:15 AM
#35
by Freewill
Good reply and worthy discussion points. . .
I lived a few years in a British Columbia, Canada, mountain logging town.
Most of the 4x4 crew trucks ran Michelin 215/80 tires with block tread. These logger guys made good bucks and could buy any tire they wanted. Other residents also ran skinny tires in winter.
This skinny tire habit came out of several generations of loggers getting in and out of the bush in an area where it snows 13 feet annually. Sometimes the roads stayed white for months. The driving ranged from running 40-50 MPH on snow-packed highways to crawling deep snow on side roads and logging trails. You didn't hear about folks getting stuck much.
Hmm... You introduce something I didn't refer to – "40-50 MPH on snow-packed highways". Good reply and worthy discussion points. . .
I lived a few years in a British Columbia, Canada, mountain logging town.
Most of the 4x4 crew trucks ran Michelin 215/80 tires with block tread. These logger guys made good bucks and could buy any tire they wanted. Other residents also ran skinny tires in winter.
This skinny tire habit came out of several generations of loggers getting in and out of the bush in an area where it snows 13 feet annually. Sometimes the roads stayed white for months. The driving ranged from running 40-50 MPH on snow-packed highways to crawling deep snow on side roads and logging trails. You didn't hear about folks getting stuck much.
The snow we have here is different. The flakes are wetter and stick together once they're on the ground (the temp' drops to just a bit under freezing point).
No way I could drive at 50 MPH on this kind of snow with my AT tires, and stay on the road, even if it was straight & wide.
What I described was at a much lower speed, on a narrow, snaky mountain road, with tight up or down sloping turns.
On that road and that kind of snow, narrow tires get stuck, or make you slide into a creek.
I totally agree with the points about tread styles. The tread should clear easily at highway speed, and hold some snow when crawling. If the spacing is too narrow or wide it doesn't work.
In snow at anything faster than crawling speed, the tire should act a bit like a sled runner for better directional stability - that's why the right skinny tire works.
On a wide tire the contact patch is typically wider than its length. Airing down helps by squaring up the contact patch, but a contact patch that is longer than it is wide gives the best stability in snow.
If a skinny tire is aired down the contact patch gets bigger by becoming longer and the tire holds its line much better.
The bottom line is that if two tires have the same contact patch area, the tire with a longer and narrower contact patch will get farther in the snow than one with a short and wide patch - given that everything else is equal (which it seldom is).
We were obviously referring to two very different snow conditions, and what you're saying sounds very reasonable and convincing.In snow at anything faster than crawling speed, the tire should act a bit like a sled runner for better directional stability - that's why the right skinny tire works.
On a wide tire the contact patch is typically wider than its length. Airing down helps by squaring up the contact patch, but a contact patch that is longer than it is wide gives the best stability in snow.
If a skinny tire is aired down the contact patch gets bigger by becoming longer and the tire holds its line much better.
The bottom line is that if two tires have the same contact patch area, the tire with a longer and narrower contact patch will get farther in the snow than one with a short and wide patch - given that everything else is equal (which it seldom is).
I presume that this – "You didn't hear about folks getting stuck much", also involves drivers' skill.
No doubt that width helps a lot in sand, mud, and other stuff where some flotation works. I'll stay away from the rock crawling question for now. I have many years and many thousands of miles of experience in snow, but I'm still figuring things out on the rock pile.
Its great that the 315s are working. Whether they are better because of width, tread pattern, tread compound, diameter, or all of those - the thing that matters is they get the job done for you.
I agree, it's probably due to all of those, that the 315 (315/70/17 Mickey Thompson MTZ, Load D) works for me on both roads and diverse kinds of terrain.Its great that the 315s are working. Whether they are better because of width, tread pattern, tread compound, diameter, or all of those - the thing that matters is they get the job done for you.
Yes, the 315 are good. For offroading, 40"X15.50 would have been even better...
For a DD, which is quite capable offroad, I find the (so called…) 35"s and a 4" lift to be a well balanced compromise.
For a Jeep which is expected to cope with a different set of demands, the compromise between road & off road may be different.
I'm glad we had this exchange, as I've learned something new from you, about conditions I'm not familiar with.
Last edited by GJeep; 02-05-2013 at 04:40 AM.
02-05-2013, 04:45 AM
#36
JK Super Freak
In 07 that was my plan. Then after while I realized the stock Rubi suspension and tires would handle anything I had the guts to tackle around here. And then the Jeep grew on me as a daily driver and has withstood a lot of abuse in (almost) stock form.
But I admit that I envy the looks of a lifted big tire Jeep when I see them.
But I admit that I envy the looks of a lifted big tire Jeep when I see them.
02-05-2013, 05:49 AM
#37
In 07 that was my plan. Then after while I realized the stock Rubi suspension and tires would handle anything I had the guts to tackle around here. And then the Jeep grew on me as a daily driver and has withstood a lot of abuse in (almost) stock form.
But I admit that I envy the looks of a lifted big tire Jeep when I see them.
But I admit that I envy the looks of a lifted big tire Jeep when I see them.
The Sport I had before, was quite capable too, while it lasted it's stock "era"...
02-05-2013, 05:59 AM
#38
JK Super Freak
Another stock suspension'er here too. I fooled around with budget boosts, - even 1/2" spacers just for stance, but I love the stock ride for what it is.
It doesnt take much to throw the handling off on these things. The half-inch spacers up front were noticeable, as were 1" lowering blocks for the rear swaybar mounts (which were left on after a BB removal).
It doesnt take much to throw the handling off on these things. The half-inch spacers up front were noticeable, as were 1" lowering blocks for the rear swaybar mounts (which were left on after a BB removal).
02-05-2013, 06:56 AM
#39
JK Junkie
id like to keep mine stock but
just got a ps bumper that's 125 lbs up front do you guys think I should change my springs from 14s to 17s or 18s or spacer I don't want to change the factory rake or anything realy but bumpers do weight
02-05-2013, 07:03 PM
#40
JK Super Freak
Join Date: Apr 2012
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Not to hijack this thread but I'll answer this random question. I think higher rated springs would be better suited for a heavier bumper and provide a better ride than your soft/short 14's. I think you could find a set of 17's or 18's cheaper than spacers too, I know I've got a set of 16/58's that I've been trying to give away since Christmas!