In normal use, this is a perfectly fine arrangement. Off-road applications are a very different story, however. That is, they deflate their tires with the aim of increasing the size of the contact patch of their tire to the surface. Another bonus is that it can be more comfortable to ride in a vehicle with gummybear-like, aired-down tires, as well. If the pressure goes down low enough, the bead can start to slip against the rim, creating the danger of the bead actually coming off the rim, and inadvertently allowing the tire to slip off the wheel entirely.
This is where beadlock wheels come into play. Those who intend on driving onto terrain requiring serious traction may need to air their tires all the way down to as little as three to six psi, or even lower. There are many different variations of beadlock wheels, but the most common to off roaders which are the ones we refer to in this article are beadlocks with outer-facing rings. The rings face outwards because, generally, if a tire slips off a rim, it usually comes off of the outside bead.
There are models that have rings on both the outside and inside of the wheel, but those can be much heavier, expensive, and more difficult to maintain and mount tires to. The fact is beadlock wheels do exactly what their name says: They lock the tire's bead the part that's designed to be on the rim of the wheel to the wheel. This allows the end user to drop air pressure to a very low level, which increases the size of your tires contact patch, which in turn increases traction, flotation, and more.
With factory wheels you can drop down to about psi depending on the weight of your rig without worrying about the bead of the tire popping off the wheel. Anything below that and you're asking for trouble unless you have beadlocks. We've played with a number of different kinds of beadlocks in lots of different environments, mounting tires on them, using them, abusing them, dismounting them, and so on. Follow along as we go over the parts that make beadlocks beadlocks, what makes them wheels, and how to install tires on them, along with some tips and tricks on how to save time and prevent damage to your new fancy wheels and your rig.
This is the outer clamp that locks the outer bead of the tire to the wheel. On a steel beadlock, this centers the tire, as described on the Inner Beadlock Ring below. This is a machined surface that allows the bead bundle of the tire to center on the wheel and acts as the other side of the clamp that locks the tire's outer bead to the wheel.
Holes with threaded inserts or threads machined into them accept the bolts that clamp the two beadlock rings together, like the pieces of bread in a sandwich, with the tire bead bundle acting as the meat. Some inner beads are machined with a step or knurls to help hold the tire bead in place. Usually these bolts are Grade 8, but they can be Grade 5 on some wheels depending on the design. Most modern wheels have two safety beads about an inch inside the outer rim.
The safety bead keeps the tire's bead bundle from slipping inward on the wheel. That works pretty well until you lower tire pressure below a certain point, depending on the vehicles weight and the forces the tire and wheel are seeing. Generally it's safe to go down to 15 psi, maybe 11 if you're in a lighter rig without beadlocks. Bicycle wheels and those for automobiles have rims. For wheels including beadlocks, the rim is the inner-, or outermost lip that holds the face of the tire's inner bead bundle to the wheel.
Normal wheels have two rims, but beadlocks have one on the inside of the wheel unless the wheels have dual beadlocks. This is the rubber gizmo that does several jobs all at once. Virtually all conventional, DOT rims have a bead bump. As tiny as it looks, the bead bump is what securely locks tires to the rim in conjunction with air pressure.
We can use this concept to calculate air and bead holding force exactly. However, that is really complicated due to the shape of the tire and rim, and lots of unknowns about the tire-to-rim friction. To start with, no engineer or physicist would let me off the hook without first telling you that a vector force always has magnitude and direction.
So why use vector components? All vector forces in the same direction can simply be added together. One is pushing north and the other guy is pushing N. Back on tire pressure, it applies force all the way around the inside of the tire and rim, but …, the vertical components for the top half of the tire above line C are mostly undesirable. So, for my approximation, we will neglect the force on the top half of the tire.
Ever tried to pop a bead off of a rim? As you can see, this is a very conservative guess at the total force. Does the internal beadlock do the same job? This prevents popping tire beads and spinning the rim in the tire. The latter happens with very, very good traction and lots of engine torque like with drag cars and off road rock crawlers. Popped beads also happen at low tire pressure and high side forces as in oval track racing or off road side-hilling. We want to keep the tires firmly on and locked to the rims under all use circumstances.
What my best research tells me is that drag racers were the first to want tires locked to rims. This is still used and there are several special, commercial screw products marketed for drag racers. They are called tire screws, rim screws or wheel screws.
I have yet to see off-roaders use screws. It was primarily for the military. This led to many others offering what we now know as the conventional, mechanical beadlock rim.
Blink your eyes a bit and checkout this beadlock cut away.
0コメント