Airing down vs bumping
- Thread starter JMT
- Start date
Not really. We wheeled in JV at 7.5 to 8 psi for many years on crappy AR rims. The only reason we went to beadlocks was to stop the tire from spinning on the rim.
Nope, but it was in my driveway when it popped off.
This is a good point to why beadlocks work.
And there is a big difference between a bump and a send.
I've watched 100 different folks try to bump it. Not one of them came even close to getting it right or even close to right the first 20 times and most of them never do. I have no idea of the mechanics behind how their brains work but every single one of them backed up, gave it the correct amount of throttle, held it there perfectly until their back tires touched the bump up. Then they let off the throttle. Every single one.
gasiorv
I'm a new world samurai, and a redneck nonetheless
Supporting Member
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Yep, I see the same thing all the time when I wheel with people I never wheeled with before. I am constantly saying, "do the same thing but stay in it this time".
I have also seen people hammer down to bump, hit and bounce backwards (due to hitting undercut) and they keep doing it over and over and I am like "stop, don't you feel that".
As far as original question, bumping is definitely harder on suspension components and can be harder on axles components "if" you happen to catch traction, but that is really not an issue in the east or south east, more of a West type wheeling issue. Crawling is also not really that hard on stuff in the areas of the country where there is no traction, but when you get into areas of the country where there is traction, crawling can be tough on axle components but probably not as hard as bumping with traction.
No matter where you, or how much air pressure you are at, or what tire or beadlock, etc.... the hardest thing on components is when you get things bound up, either due to undercut or trapped between rocks, or fronts catching traction just on the other side of rock, etc... Anytime you get bound up is when things break. You can feel it bind up, but it takes experience to know to back off and stop and see, unfortunately that experience usually comes with a price and lord knows I have paid it.
I have also seen people hammer down to bump, hit and bounce backwards (due to hitting undercut) and they keep doing it over and over and I am like "stop, don't you feel that".
As far as original question, bumping is definitely harder on suspension components and can be harder on axles components "if" you happen to catch traction, but that is really not an issue in the east or south east, more of a West type wheeling issue. Crawling is also not really that hard on stuff in the areas of the country where there is no traction, but when you get into areas of the country where there is traction, crawling can be tough on axle components but probably not as hard as bumping with traction.
No matter where you, or how much air pressure you are at, or what tire or beadlock, etc.... the hardest thing on components is when you get things bound up, either due to undercut or trapped between rocks, or fronts catching traction just on the other side of rock, etc... Anytime you get bound up is when things break. You can feel it bind up, but it takes experience to know to back off and stop and see, unfortunately that experience usually comes with a price and lord knows I have paid it.
My son ripped a lower control arm mount off the front axle when it was bound up. Instead of backing up like he was told, he went heavy on the throttle in 4 low. The other one that routinely ends up in breakage is bouncing. Seems like in my area people typically double down rather than let off the throttle. I've lost track of how many times u joints have grenaded like this.
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And then there's the bump that goes full send when contact sends you forward putting your gas foot to the floor...
This was supposed to be a bump. I figured it was wet sand and I'd spin the wheels a bit. So I goosed it a touch to get a little momentum. Oops.
-Mac
This was supposed to be a bump. I figured it was wet sand and I'd spin the wheels a bit. So I goosed it a touch to get a little momentum. Oops.
-Mac
Not maintaining momentum is the thing I see a lot. It drives me crazy when people deny that they lift off the pedal after a mild bump.
"Bump" means to hit it with some speed and use momentum to help you over. At one end of the spectrum you carry enough speed to get over while coasting in neutral so there's 0 force on the drivetrain.
At the other end of the spectrum you're using the momentum to "plant" the tire into the obstacle, getting extra traction to propel you up and over. This is where bumping turns into bouncing and absolutely can shock-load the drivetrain when heavy on the throttle.
Airing down not only gives better traction, but in high-traction environments I've noticed that it's easier and smoother getting up and over rocks aired down. Maybe because the tire is shorter, maybe because the tire flex makes the rise less steep. Either way, I can feel that it takes less torque to make the climb, so airing down more is reducing stress on the drivetrain.
But you will have more traction, so if you're bound up you'll have more stress.
You can go a lot lower on soft surfaces like snow and sand than on rocks. I'm on 35x12.5r15s, no beadlocks, and run 8 for rocks and typically 5 for snow. Last time out I was in a rush and aired down by eye, but checked it later and found I was at 2 psi. Probably would have been just fine if it was only snow but I lost a lot of air going over logs (vid here: https://wranglertjforum.com/threads/snow-wheeling-pics-24-25.81835/page-3#post-1646502). Bead came off a couple hours after this.
Nothing wrong with a responsible bump. We bump stuff out here all the time when we have to.
With good grip and just crawling up, the most you can load any component is just how much torque the engine can provide at that rpm multiplied by the gearing between that component and the crankshaft, with an upper limit at the tires slipping point.
Bumping brings dynamic loads into the mix which are basically impossible to accurately calculate, but will be proportional to any difference in vehicle speed vs what the drivetrain wants the vehicle speed to be, squared, and multiplied by the masses of all the components you're asking to suddenly change speeds...additional energy that will have to be transmitted and dissipated into something...and that's added onto the load you would have had just crawling up with good traction.
So yes, without a doubt bumping carries more risk than crawling but what's important is that both of them are VASTLY better options to just spinning the wheels and letting it hop.
I always adopted “When in doubt, throttle out…”
…and if you’ve ever wheeled with me, you know I’m a very doubtful person.
…and if you’ve ever wheeled with me, you know I’m a very doubtful person.
I always adopted “When in doubt, throttle out…”
…and if you’ve ever wheeled with me, you know I’m a very doubtful person.
You throttle so hard the earth rotates and you have to factor in the coriolis effect to get up the obstacle
You throttle so hard the earth rotates and you have to factor in the coriolis effect to get up the obstacle
When I wheel with Victor ( @gasiorv ), he just stares and shakes his head.
You throttle so hard the earth rotates and you have to factor in the coriolis effect to get up the obstacle
When he sits around the house, he sits AROUND the house!
gasiorv
I'm a new world samurai, and a redneck nonetheless
Supporting Member
Ride of the Month Winner
The earth was flat until he dropped that Hemi in the LJ.
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