I am currently having my R100GS frame strengthened/modified with TAG in Italy. Their strengthening is basically along HPN lines, their mods are more interesting. Their basic package includes changing the rake by 2 degrees, through alteration of the headstock that will require a longer t-clamp stem. They also move the engine position forward within a bandwidth of approx 5-10mm, depending on fork length and rear swing arm used. The way this has been explained to me is that in most "unholy union" mods the front gets jacked up disproportionately to the rear, with the effect that the center of gravity gets moved backwards. The engine relocation is done to mitigate this effect. I will be going for the rake change, but am still considering the engine move. Initially the move felt counter-intuitive for a dirt bike, but I get the argument about rebalancing mass. At this stage I am also put off by the practicalities of the engine relocation on things like exhaust and swing arm. I would assume that there is enough overlap on the exhaust pipe junctures that you can reclaim 10mm overall, the swing arm is a bigger problem. TAG's make their swing arms specifically to deal with this issue, I assume by being +105-110mm. My issue is that I have a shiny new +100mm mono from Moorespeed that I got before focusing on the frame. So my first question is whether there is an obvious way to use my +100mm swing arm for a repositioned engine while keeping shock mounting points where they were intended to be. The two ways I could think of are either at the front or back of the drive shaft: - on the front you could simply put a (10mm) spacer onto the front flange of the drive shaft. This seems easy enough in theory, but problems could arise given extent of movement on this juncture. Also the rotating section behind the flange would be sitting further inside the swing arm and I dont know if this is ok. - alternatively on the rear you could just live with a less deep overlap on the rear coupling. There seems to be approx 5cm of depth there, so would 4cm be sufficient? I would be grateful for any input on this. if its all too much brain damage can live with OEM engine location, but its worth thinking through before ditching idea.