The R is for resistor. The plugs incorporate a 5k ohm resistor internal. The plug caps also incorporate a resistor.
The US models had a 10k ohm resistor in the plug caps.
I don't know what the Canadian plug cap values were.
But, it seems NGK has discontinued the 10k caps, expecting everyone to switch to resistor plugs and then use the 5 k caps now offered, to acheive the 10k value. I think most vehicle manufacturers have swtched to using resistor plugs.
Using spark path resistance has multiple benefits.
It slows the rise time of the spark pulse (nanoseconds or microseconds) as well as limits the current outflow from the coils. As the coils only store a fixed amount of energy, slowing the outflow results in a longer spark event, which is good for our bikes both for more thorough combustion and a bit longer life of the spark plug electrodes.
Slowing the rise time in such small amounts has no effect on engine run factors. But, as the ignition wires are unshielded, fast edges generate RFI that overwhelms radio receiver inputs. The faster the rise time, the more high frequency components that fast edge emits.
I speculate that Canadian import restrictions mandated the resistor plugs primarily for improved radio interference reduction. Aircraft bands are susceptible, particularly with long range reception.
Cheers,
