Tomasz Pietryszek/Photodisc/Getty Images
Split rim wheels are a good idea, in theory. This wheel design uses a locking ring on the outer bead to hold the tire in place, as opposed to the fixed bead on one-piece rims. A split-rim allows any average mechanic to replace a big truck's tire tube on the side of the road with little more than hand tools and a jack. While very popular in the rural areas of Central and South America, India and China, these rims are also dangerous when misused or badly maintained.
Under the typical 60 psi inflation pressure of a large truck tire, there's about 12 tons of force attempting to push the locking ring off the rim at all times. Any minor defect or crack in the locking ring can create a weak spot, giving those tons of pressure a place to express. If the locking ring cracks, the rim will explode like a bomb, seriously injuring or killing anyone in the path of the lock ring shrapnel.
The first rule of working on any split rim is to completely deflate the tire tube before attempting to remove the ring. Once the pry bars edge the ring loose, even a few pounds of pressure in the tire can turn the locking ring into a projectile. Many manufacturers and safety administration bodies recommend removing the valve stem entirely before touching the lock ring.
If the tire drops below 80 per cent of its recommended inflation pressure you must deflate it completely, reset the ring and refill. An underinflated tire can allow the ring to shift around and out of its groove. Upon refilling, the unseated ring responds to the additional pressure by dangerously flying off the rim. You must the maintain the tire within 20 per cent of its maximum inflation pressure at all times.
Using matching components sounds like an obvious requirement, but this can be a tall order when you break down 200 miles from the nearest mechanic and you need to use whatever is lying around. Rural people can be ingenious when it comes to repairing a vehicle in the bush, but using lock rings designed for a different wheel isn't like buttressing a steering end-link with duct tape. The duct tape is dubious but might get you to a mechanic if you're careful. Nonetheless, mismatching components remain a dangerous option.
- Tomasz Pietryszek/Photodisc/Getty Images