I am going to upgrade to a 520 o-ring chain soon. I got lots of mud on my OEM 428 and it caked up in the front sprocket housing bad! I think it got into the links while I was cleaning it too, and it is making some thunks periodical while I am riding, even though I thoroughly cleaned and lubed it. Maybe I damaged the front sprocket too.
I also want to drop the gearing for a slightly lower 1st ratio. I don't mind losing some speed on the road since I usually just use residential streets for the most part.
So I need to choose sprockets. I made a chart with some commonly available sizes (JT, at least). I made this for my Storm (428H 17/46 OEM) and included the sizes for 520 that I might move to. Then I realized that Hawks are much more ubiquitous so I made one for the Hawk. I hope this is useful for you.
the top line in each chart is presumably your stock sprockets. The additional lines compare the OEM ratio to the chosen front/rear replacements so you can see the raw difference and % change compared to stock.
I sorted these two charts ascending based on ratio, so 428 or 520 ratios go up as you go down the rows.
I haven't looked at the individual gear ratios for 1st -5th inside the engine, but this is just comparing final drive to new choices which works since you already know what you get while riding it. And no one is going to change those internal gears!
Hawk OEM ratio is quite low (0.300), so it isn't surprising that most people want to go higher.
Storm comes with a taller ratio for final drive (0.3696). I will go 12/35 or 12/33, which will drop my final drive ratio by 1.6 or 7.2, respectively. Less than a 2% change is really negligible for off road purposes (or on road, for that matter!), Next time I go riding, I need to really decide if I want to drop 7% before I take the plunge
