rake, trail, two cents
one thing to remeber when playing around with offset, rake and trail and such: for a given offset/rake/head angle, changing wheel diameters will have an effect on trail. decreasing wheel diameter will reduce effective trail, while increasing wheel diameter will increase effective trail.
i haven't crunched the numbers on that to verify exactly how much change is effected, but going from a 17 to a 21 front wheel then slapping an offset axle front fork on there actually makes some sense. also explains why certain mx bikes converted to supermoto with no change in fork offset or geometry tend to be a bit squirrely on the brakes...