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-   -   Point of lowering tire pressure (http://www.wranglerforum.com/f282/point-of-lowering-tire-pressure-112785.html)

thor989 09-14-2011 12:05 PM

Point of lowering tire pressure
 
I hear everyone talk about lowering their tire pressure, but i have no idea why? Can someone please explain it to me? :hide:

Gkbassn4 09-14-2011 12:07 PM

The tires will handle certain terrains (trails, mointains, beaches, etc) better and smoother and not as rough. The con is bad fuel economy in return.

kfdjason7620 09-14-2011 12:08 PM

Lowering tire pressure allows the tread to conform more to the terrain and have more grip

SirGeorgeKillian 09-14-2011 12:09 PM

Because with less psi in the tire, the surface area is added. Think of a O versus a D with the flatter part being on the bottom. It also gives the tires a little ability to conform to obsticals, once again adding to traction.

On road, this is a bad thing. Bad MPG, and tires heating up due to friction and blowing out or wearing out prematurely will happen.

thor989 09-14-2011 12:10 PM

Quote:

Originally Posted by Gkbassn4 (Post 1569435)
The tires will handle certain terrains (trails, mointains, beaches, etc) better and smoother and not as rough. The con is bad fuel economy in return.

Is that why people buy on board air compressors?

UnlimitedLJ04 09-14-2011 12:10 PM

lower air pressure = more flexible tire = more conformity to terrain = more traction

http://image.fourwheeler.com/f/techa...in_conform.jpg

lower pressure on the left, higher pressure on the right.
http://www.aircti.com/pics/2%20tire%...%20patches.JPG

Quote:

Originally Posted by thor989 (Post 1569444)
Is that why people buy on board air compressors?

yes...without an air source of some type, how are you going to pump the tires back up after trail riding?

running tires with too low a pressure on the street at speed will destroy the tire.

kfdjason7620 09-14-2011 12:11 PM

Quote:

Originally Posted by thor989

Is that why people buy on board air compressors?

That, and some people put air lockers in there differentials

NC10735285 09-14-2011 12:12 PM

Ok - so lowering = more grip in sand, mud - - however too low a pressure makes the side wall vulnerable - and actually decreases the grip on the street.

So if you lower the pressure to go offroading - -be sure to bring it back up when you get back on teh street.

thor989 09-14-2011 12:14 PM

ohhhh ok, awesome thanks guys!

kfdjason7620 09-14-2011 12:16 PM

1 Attachment(s)
Too low?? :doh:

Sherpa 09-14-2011 01:06 PM

Quote:

Originally Posted by Gkbassn4 (Post 1569435)
The tires will handle certain terrains (trails, mointains, beaches, etc) better and smoother and not as rough.

I finally splurged and bought an air compressor (SuperFlow MV50) a few weeks ago. I wanted it specifically so I could air down on the trail, then air up for the drive home. Last Thursday, I took a few friends and headed up in to the local canyon to run the Forest Lake trail. During the "high speed" portion of this run (~20 MPH), there are miles of washboard surfaces that typically rattle you to death at my street pressure of 26 psi. Now that I have a compressor, I aired down to 14 psi.

Oh. My. Gosh.

It was a revelation. I knew it would be an improvement; nevertheless, I was amazed at how much more comfortable I was. The lower pressure also helped me get better grip once I was at the rocky portion of the ride. Once the ride was over, it only took a few minutes to air back up and enjoy the drive home.

I will never again go 'wheeling without that air compressor.

Imped 09-14-2011 01:31 PM

Footprint & deformation.

TJe0454 09-14-2011 01:34 PM

Quote:

Originally Posted by kfdjason7620 (Post 1569462)
Too low?? :doh:

more like too much torque :thumb:

Bubba68CS 09-14-2011 01:38 PM

Quote:

Originally Posted by kfdjason7620 (Post 1569462)
Too low?? :doh:

Those are designed specifically to do that:

Mega Slow Motion (MegaMo) 1000 frames per sec. Dragsters - YouTube

:thumb:

IslandTJ 09-14-2011 02:15 PM

Quote:

Originally Posted by Sherpa (Post 1569563)
I finally splurged and bought an air compressor (SuperFlow MV50) a few weeks ago. I wanted it specifically so I could air down on the trail, then air up for the drive home. Last Thursday, I took a few friends and headed up in to the local canyon to run the Forest Lake trail. During the "high speed" portion of this run (~20 MPH), there are miles of washboard surfaces that typically rattle you to death at my street pressure of 26 psi. Now that I have a compressor, I aired down to 14 psi.

Oh. My. Gosh.

It was a revelation. I knew it would be an improvement; nevertheless, I was amazed at how much more comfortable I was. The lower pressure also helped me get better grip once I was at the rocky portion of the ride. Once the ride was over, it only took a few minutes to air back up and enjoy the drive home.

I will never again go 'wheeling without that air compressor.

Nice :).

jskinn27 09-14-2011 02:19 PM

the quick response would be, for better traction. it adds more surface area between the tire and the surface, which results in better grip and better conforms to the trail.

freeskier 09-14-2011 02:25 PM

Quote:

Originally Posted by NC10735285 (Post 1569456)
Ok - so lowering = more grip in sand, mud - - however too low a pressure makes the side wall vulnerable - and actually decreases the grip on the street.

So if you lower the pressure to go offroading - -be sure to bring it back up when you get back on teh street.

Actually with sand and mud it's not for grip. As already stated lowering the pressure increases the surface area of the tire touching the ground. When you increase the amount of surface area touching the ground, less weight is being pushed down on say 1 square inch of tread. It's the same principle as a snow shoe. Instead of sinking/digging into the mud or sand you can "float" on top of it.

Now mud gets further complicated as people will tell you you want thin tires to cut down through the mud and find hard ground, but if the mud is just to deep that won't work, you need to be able to float on it.

DevilDogDoc 09-14-2011 04:06 PM

Quote:

Originally Posted by kfdjason7620 (Post 1569462)
Too low?? :doh:

Ah wrinklewalls..... Good memories there!

surferbob 02-22-2012 05:24 AM

I realize this thread is pretty old. I constantly read these threads about tire pressure. I've got 31x10.5xR15 pirelli scorpions on my Tj jeep. The shop I bought them from say the tire pressure should be about 32 psi. I ride them at 26 psi after reading these a bunch of posts.
On the beach I lower down to about 20 psi but the jeep heats up very quickly. Is 15 psi too low for these tired on the beach? What is the max speed when they're down that low? (when I hit the hard sand)

4Jeepn 02-22-2012 05:49 AM

Quote:

Originally Posted by surferbob (Post 2060571)
I realize this thread is pretty old. I constantly read these threads about tire pressure. I've got 31x10.5xR15 pirelli scorpions on my Tj jeep. The shop I bought them from say the tire pressure should be about 32 psi. I ride them at 26 psi after reading these a bunch of posts.
On the beach I lower down to about 20 psi but the jeep heats up very quickly. Is 15 psi too low for these tired on the beach? What is the max speed when they're down that low? (when I hit the hard sand)

As for heats up does it over heat? How far above 215ish is it reading? 15 psi should be fine.. I would make sure you have an air source near by though. as for driving on hard packed sand at that psi.. I think any legal speed limit for the beach you should be fine with. I have gone 55mph on drive payment with 15-20 psi if that helps.

surferbob 02-22-2012 06:10 AM

Quote:

Originally Posted by 4Jeepn

As for heats up does it over heat? How far above 215ish is it reading? 15 psi should be fine.. I would make sure you have an air source near by though. as for driving on hard packed sand at that psi.. I think any legal speed limit for the beach you should be fine with. I have gone 55mph on drive payment with 15-20 psi if that helps.

It's fine when I'm on the hard sand at low tide. However, if I drive a mile or 2 in the soft sand the jeep starts to head towards the 250 mark quite quickly and I get gurgling when I stop the engine. It normally runs at about 210 during everyday use.
I've changed the water pump to a flowkooler 1750 and the thermostat robertshaw high flow. Haven't had a chance to it out on the beach yet. I stress about overheating on the beach because I don't want to lose my jeep to the incoming tide of the ocean.

s14sh3r 02-22-2012 08:03 AM

Quote:

Originally Posted by surferbob (Post 2060624)
It's fine when I'm on the hard sand at low tide. However, if I drive a mile or 2 in the soft sand the jeep starts to head towards the 250 mark quite quickly and I get gurgling when I stop the engine. It normally runs at about 210 during everyday use.
I've changed the water pump to a flowkooler 1750 and the thermostat robertshaw high flow. Haven't had a chance to it out on the beach yet. I stress about overheating on the beach because I don't want to lose my jeep to the incoming tide of the ocean.

It takes a lot more power to drive through soft sand. Are you keeping it in a low gear and keeping the rpm's up?

SirGeorgeKillian 02-22-2012 11:12 AM

Changing the thermastat and water pump without adding a better radiator might be causing more harm than good. The reason your stock setup flows at the rate it does is because it takes time to cool the coolant. If your radiator cant handle it, you are just circulating more hot coolant...

Dextreme 02-22-2012 12:26 PM

On sand, drop your psi down on your 31's to 10-12psi. Your tires will float over the sand instead of dig. You engine will not have to work near as hard (run cooler). I have tried 15 psi and it wasn't low enough...12psi worked great on wet sand, 10psi worked better on dry sand.

surferbob 02-22-2012 01:51 PM

Quote:

Originally Posted by s14sh3r

It takes a lot more power to drive through soft sand. Are you keeping it in a low gear and keeping the rpm's up?

That's exactly what I'm doing. The revs are too low for third but are too high for 2nd (staying at the 2 mark in 2nd and the 1 mark in 3rd). I'll try lowering the tires more.

Jerry Bransford 02-22-2012 02:01 PM

I'm not sure what you mean by saying you stay at the 2 mark in 2nd and 1 mark in 3rd but if you mean the marks on the tachometer, those are 1K RPM indicator marks and those are too low. Don't be afraid of higher RPMs for such situations, your engine is perfectly happy at significantly higher RPMs.

surferbob 02-22-2012 03:14 PM

Quote:

Originally Posted by Jerry Bransford
I'm not sure what you mean by saying you stay at the 2 mark in 2nd and 1 mark in 3rd but if you mean the marks on the tachometer, those are 1K RPM indicator marks and those are too low. Don't be afraid of higher RPMs for such situations, your engine is perfectly happy at significantly higher RPMs.

Yeah that's exactly what I mean. Just got lazy to express the whole thing. (2000 rpms and 1000 rpms). I'm just really worried about overheating, the tide coming in and losing my baby(jeep). Not to mention ending up on the wall of shame at the local gas station lol. Was even thinking of removing the air con system (especially the condenser) to create more airflow. The next time I use the air con will be the first. I'd rather just take the doors out and enjoy the breeze.

Crown King 02-22-2012 04:31 PM

Quote:

Originally Posted by surferbob (Post 2060571)
I realize this thread is pretty old. I constantly read these threads about tire pressure. I've got 31x10.5xR15 pirelli scorpions on my Tj jeep. The shop I bought them from say the tire pressure should be about 32 psi. I ride them at 26 psi after reading these a bunch of posts.
On the beach I lower down to about 20 psi but the jeep heats up very quickly. Is 15 psi too low for these tired on the beach? What is the max speed when they're down that low? (when I hit the hard sand)

Surfer Bob, I run mine at 8 or 9 at Glamis dunes...NO issues, goes everywhere!

Jerry Bransford 02-22-2012 04:35 PM

Quote:

Originally Posted by surferbob (Post 2062290)
Yeah that's exactly what I mean. Just got lazy to express the whole thing. (2000 rpms and 1000 rpms). I'm just really worried about overheating...

When wheeling, the engine is actually more prone to overheating at lower RPMS than higher RPMs. :)

surferbob 02-22-2012 07:15 PM

Cheers guys. The info really helps


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