Each plug wire lead in a BMW's wire set must have the exact same resistance +/-10% of a specific value which is unique to the ignition system. Since each lead of a wire set has a different length, this can only be achieved by using copper wire (no resistance) with specific value resistorized ends. Our plug wire sets are manufactured to exact O.E. drawings with 19 strands of tinned copper wire and exact resistorized ends. The exact resistance values can not be achieved with Spiro-core wires!

Spiro-Core wire was developed from American and Japanese cars that do not require a specific ignition resistance. Using Spiro-Core wire eliminates the use of expensive resistor type plug connectors, which are used on all European automobiles. The difference is that not all plug wires are equal length. With Spiro-core wire this is why the resistance values of number 1 spark plug wire are much different than the values of cylinder 6. The resistance will vary as much as 1000 ohms per foot of spark plug wire.