Don't know from personal experience about the front tire wear - but would make some sense as the bike with the factory tire - front and rear tires are in alignment, no crabbing whilst going down the road. On the BMW the car tire requires a spacer to offset the rear tire about a 1/4 inch (according to the guy Bob and I talked with at the IBA meet on Thursday). So - if the rear is offset from an aligned front/rear tracking - then the bike will have to crab slightly to keep driving in a straight line - therefore the tire will wear more rapidly.
Now whether or not that is the actual reason - don't know - just looking at it from an engineering point of view.
Double Darksider #847
IBA #54767 BB1500+
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