Roulette wheels are amazing pieces of craftsmanship. Each wheel is made individually, and while every wheel is produced to be a perfect instrument, an instrument that is not tuned regularly will develop flaws and ruin the games expected odds.
On a roulette wheel, those flaws can result in a bias towards a single number or even a group of numbers. Because roulette wheels are designed for constant play, they are manufactured to high standards, and can last for decades. However, there are very few technicians who can clean and refurbish wheels. When a casino neglects a wheel it can develop two distinct problems.
The roulette wheel itself consists of two basic parts: a heavy wooden bowl with an overturned lip or ball track, and a heavy, metal and wood wheelhead that rotates in the bowl. The wheelhead sits on a solid spindle and nearly perfect, effortless spinning is accomplished by bearings. The wheelhead employs a height adjuster and an upper turret to keep the entire wheel steady.
If a wheel becomes unbalanced, the head itself will dip slightly along a section of numbers. The numbers on a roulette wheel are formed above a pocket to hold the ivory ball. As the ball slows down it will often travel across the numbers and drop into a pocket. If the wheel is low in a certain area, the ball is likely to hesitate slightly on the lip of the wheel, causing it to land in the low section more often.
Even a tiny irregularity such as this can make for a biased wheel. In this case, suppose the dip in the wheel is happening along a section of five numbers: 31, 18, 6, 21 and 33. A player betting these numbers will hit them more often than the laws of chance would indicate.
A similar situation arises when the frets, or wooden partitions between the pockets become loose. The spinning ball will often land against a fret and pop back up on the wheel before settling down into another number. However, if a fret is loose, the ball will not bounce back as far. Instead of bouncing up and the wheel spinning past a dozen or more numbers, the ball is more likely to stay in the pocket or drop only a few numbers past the loose fret.
A biased wheel that provides a headache for the casino and a gold mine for the player is one that has two or three consecutive pockets that have loose frets. When this happens, the landing ball is likely to stay in the pocket or drop into a pocket just three or four numbers past, allowing a player to bet on a string of four or five numbers and record winners on a consistent basis.
A wheel with a loose fret between consecutive numbers such as 31 and 18 and also 18 and 6 will offer a very high percentage of the numbers 18, 6, 21, 33 and 16 trapping the ball (assuming the wheel is spun counter-clockwise and the ball is spun clockwise).
Because the roulette wheel is spun in one direction and the ball is spun the opposite direction, frets become loose from the natural punishment of the moving ball dropping against them. The force of the dealer's fingers against them can also damage the frets as the wheel is spun.
Roulette wheels need regular maintenance to avoid these problems. When wheels are neglected, players are likely to find a bias and exploit it. Some roulette systems such as the Six-Pack Plus can be extremely profitable with a biased wheel.