A common change for the 848 seems to be to change the front sprocket from 15 to 14 teeth. After having a look on ebay.de I found a German seller, drift1978, who sells 14 tooth front sprockets for the Ducati with the 525 sized chain at about €20.
The reason that I wanted to change it was to give the bike a better low speed performance for town driving and to enable me to get into top (6th) gear at a speed less than 130 kmh (80 mph). I suspect that the low speed issue is also affected by the flapper valve in the exhaust, but that is the topic for a further post.
The Ducati workshop manual (available as a .pdf download on the internet) tells me that you need to split the chain to remove the front sprocket, but I have no tools for dealing with chains due to my BMW background. I removed the sprocket cover to see how tight the space is in that area, it is tight! Next step was to loosen the two 10mm allen bolts that lock the rear chain adjuster in place and, using a large C spanner, loosen the chain. There is enough slack to take the chain off the rear sprocket and give plenty of space on the front. The locking plate can then be removed from the 32mm nut. The clutch slave cylinder must be removed at this stage other wise the chain will not allow the sprocket to be taken off the shaft.
The refitting of the 14 tooth sprocket is easier as it is slightly smaller. After tightening up the nut the lock washer can be reused up to three times. The chain is then refitted to the rear sprocket and then re-tensioned. Torque the two 10mm allen pinch bolts to 35 Nm and then spend 2 hours trying to clean the grime off your hands!
The test drive showed it to be a very worthwhile job, the 500 metres of track through the woods to the road was much easier to negotiate in first gear. On the road there is no difference at normal speeds, but it will pull top gear at around 120 kmh. Riding through town is much nicer.
The whole job should take about an hour including cleaning the bike.