I read somewhere else here about not being able to get a factory Ducati 41t sprocket anymore. I bought mine when I bought my GT in April last year; it's a Ducati part, but sorry- I don't know what the part number was. It's silver, with the same factory markings as the stock 39t.
**edit**...Doh! I should read my signature line every now and again- I put a 42t on the rear of the GT...Jeez...
I am interested in this as well. I hate the fact that at 35-40 mph, my bike's RPMs are too high in 2nd gear but too low in 3rd. Also hate that at 70 mph, the RPMs in 5th are a little too high and 6th a little too low.
I'm assuming the 14/41 sprockets and 520 chain alleviate this problem?
There are different opinions on what works best, but 15/42 works pretty well. For reference, the stock 15/39 made 70 mph (indicated, not actual) about 3750/3800 rpm. 15/42 raises the rpm maybe 300, so 70 mph is around 4000/4100.
I like it for town riding, as first gear is much lower. It makes the gears closer together though, so you're shifting more. Next time I'll do some math and split the difference between stock and what I have now.
525 or 520 chain size has nothing to do with gearing...
DP doesnt make their sprocket anymore. Also, your only option for a rear silver sprocket is going with a AFAM hard aluminum or Vortex. I tried sourcing an Esjot or Sunstar but couldnt find a supplier.
I purchased a 42T Supersprox which is gold and black. I like it a lot but all the gold is getting old. I will probably be switching to a 520 setup with Drive System sprockets (black) They are the old distributors for the AFAM silver steel sprocket which is no longer imported to the US. http://www.sprocketcenter.com