I'm not sure which are the best, as that can be a bit hard to define, but I changed mine over to NGK Iridium plugs, and felt a change in the way the bike felt. It felt a bit smoother, but the main reason I changed was because mine were hard to get to (being an 05 model) and the iridium plugs should give a longer service life.
I wish I knew also hope you get some more responce to this thread. Of course someome will most likely chime in and say do a search. Well I would not be asking if the search I did FIND NOTHING:thumbup:
I used to be a fan of the Split fire spark plugs but I have been thinking about the Bosch +4's. I haven't changed spark plugs in anything for a long time. More because I haven't had a car last that long then not doing maintenance.
I just installed a set of iridiums that I bought from NGK Spark plug, NGK Spark Plug wire, NGK Platinum Spark plug for High Performance and Racing. for $10 a plug and I am really happy that I did. These are nice plugs. I could tell they work good as soon as I started the engine. the road test was great (wheelies at 8K RPM and a full tank of gas :rockon: ) The engine runs as smooth as silk and I believe the throttle response is better than when the bike was new.
I shant be using the the regular CR9EK anymore.
Now if it would just warm up outside I could go out and really test these things...
I just changed my plugs the bike has almost 7000 miles. The plugs show pretty much no wear, easily could have gone another 7000 miles. I stayed with the CR9EK they are fairly easy to change on my 08 and probably just change them every spring anyway.
I'm at 38,000 miles on my Iridium plugs. I don't think most of you will even ride that much, so for those who installed the Iridium plugs, you probably just performed your very last spark plug change.