Originally Posted by
FastJake
Yep. Because the washer extends the brake out, it effectively gets it further away from the diameter of the tire.
The opposite of this trick is used when your brakes don't quite reach the rims. You make sure to remove any washers behind the caliper for maximum reach to the rim.
Actually, for most forks you have this backward.
The head tube angle and forward rake puts the highest point of the wheel forward of the crown. If you look at a fork from the side, you'll see the rim rises as it moves forward as it leaves the fork. Looking at another way, we can say that the fork crown is behind "top dead center".
Most brakes are behind this highest point, so moving the brake out reduces tire clearance, while mounting closer to the fork increases it. One trick we used to use when using track bikes on the road was to mount the brake behind the fork where there was even more clearance.
This wasn't always possible because of downtube clearance, but where it worked, it worked beautifully.
If all else fails, the OP can try this, but if he has a modern countered bored fork crown, will have to do some finagling with the mounting hardware to make it work.