Join Date: Apr 2015
Location: Murrysville, PA, USA. A pleasant, wooded suburb of Pittsburgh.
Tweak, I also follow the RC Forum, where there is constant discussion of tires and performance issues. Many of the RC racers have converted to 140/70 rear tires with great success, and there is a growing consensus that 140/70 is the proper size for the 390's rear rim.
I have been running a Bridgestone EVO S20, 140/70 on my Duke for several months, and I have to say that I am more than delighted with it. It somehow feels more stable and natural on the bike than the (oversized) 150/60 OEM Rosso II. The dry grip is outstanding, and the S20 gives a more comfortable ride than the Rosso II. No chicken strips! The contact patch goes right to the edge. The S20 is a soft sport tire like the Rosso II, and appears to be wearing at about the same rate, so I would expect around 4000 miles of useful life on the very abrasive road surfaces in my area. I think I might try a set of those Michelin Pilot Streets when the time comes for another tire change. Clearly, 140/70 is the sweet spot for the 390's rear tire and I now would not consider using any other size. One small additional benefit is that the 140/70 is slightly taller than the OEM 150/60, so that gives you a bit of additional ground clearance and makes scraping your pegs less likely on turns.
"If you don't know where you're going, you might wind up somewhere else."
2015 390 Duke
1980 Moto Guzzi V50 II cafe racer
1984 Moto Guzzi SP 1000