Gen 2 Hitch plate/recovery point strength
- Thread starter macdrew77
- Start date
What grade are the bolts?
www.boltdepot.com
This isn't something you want to guess on.
The implications of a failed recovery point can be fatal, a fact driven home by the accident in AZ that went viral last week:
l2sfbc.com
Bolt Depot - Bolt Grade Markings and Strength Chart
www.boltdepot.com
This isn't something you want to guess on.
The implications of a failed recovery point can be fatal, a fact driven home by the accident in AZ that went viral last week:
Drop hitch failure leads to death during 4x4 recovery
A death in 4x4 recovery; why you shouldn't use a drop hitch to recovery a 4x4.
l2sfbc.com
billiebob
Well-known member
You are using a product for something it was never designed to do....
Relying on "how much force" from an internet forum is crazy.
Hardware store bolts or Grade 8.... regardless niether is rated for a shock/impact loading.
What is the rating for the hitch, check with the manufacturer, I bet they say zero, not rated for that use.
Relying on "how much force" from an internet forum is crazy.
Hardware store bolts or Grade 8.... regardless niether is rated for a shock/impact loading.
What is the rating for the hitch, check with the manufacturer, I bet they say zero, not rated for that use.
Hitch manufacturer? That is the factory frame crossmember with the pintle hitch pattern. They come with a little tow hook thing from the factory. I'm trying to figure out if it was meant as a recovery point, since it is sold as "Rear Traction Hook MR448317".
I've used it to pull logs and trees out of the ground, but I want to know if it's safe to recover the vehicle using this point.
Also upon further research, the proof load of a single M12x1.25 grade 8.8 bolt is 12,005 pounds force.
I've used it to pull logs and trees out of the ground, but I want to know if it's safe to recover the vehicle using this point.
Also upon further research, the proof load of a single M12x1.25 grade 8.8 bolt is 12,005 pounds force.
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Is anyone curious what kind of kinetic recovery it would take to bust those 4 bolts off? I am, so I learned myself some math.
The minimum ultimate tensile strength of x4 M12x1.25 grade 8.8 bolts is 294,800N. F=m x a. So, to apply 294kN, a 2500kg Montero would need to accelerate at a rate of 118m/s^2.
Now lets apply this to a kinetic rope recovery. Let's take a 6.1 meter long kinetic rope, according to the manufacturer it will stretch 30% of its length or 1.83m. So in a recovery of a completely stuck and immovable object, the rope will decelerate the Montero from starting velocity to 0m/s in a distance of 1.83 meters.
Now we can find what starting velocity will result in an acceleration of 118m/s^2 over a distance of 1.83m
(starting velocity)^2 = (final velocity)^2 x 2(acceleration x distance)
(starting velocity)^2 = (0)^2 x 2(118 x 1.83)
starting velocity = 20.8 m/s or 46mph
TLDR, if you tried to perform a kinetic recovery on a brick wall, you would need to accelerate up to a speed of 46mph to apply 294,800N of force and break your 4 bolts off. This is just theoretical/hypothetical physics, use this information as you will.
The minimum ultimate tensile strength of x4 M12x1.25 grade 8.8 bolts is 294,800N. F=m x a. So, to apply 294kN, a 2500kg Montero would need to accelerate at a rate of 118m/s^2.
Now lets apply this to a kinetic rope recovery. Let's take a 6.1 meter long kinetic rope, according to the manufacturer it will stretch 30% of its length or 1.83m. So in a recovery of a completely stuck and immovable object, the rope will decelerate the Montero from starting velocity to 0m/s in a distance of 1.83 meters.
Now we can find what starting velocity will result in an acceleration of 118m/s^2 over a distance of 1.83m
(starting velocity)^2 = (final velocity)^2 x 2(acceleration x distance)
(starting velocity)^2 = (0)^2 x 2(118 x 1.83)
starting velocity = 20.8 m/s or 46mph
TLDR, if you tried to perform a kinetic recovery on a brick wall, you would need to accelerate up to a speed of 46mph to apply 294,800N of force and break your 4 bolts off. This is just theoretical/hypothetical physics, use this information as you will.
