To lower the gearing, is it better to get a smaller front sprocket or larger rear? Is it 15-39 stock? Also which brand chain and sprockets are best?
Generally I believe it's better to go up on back as its more even chain wear and the front is not such a small pivot for the chain/tighter radius. Also less strain on output shaft I think I read. Costs more and you may need an extra link for +3. 14t front is easier. Look on gearingcommander.com
14/39, works on road and most tracks If you want to know the impact on speed etc for different combinations check here www.gearingcommander.com
I tried 15/40 15/41 and 14/39. 14/39 was the most noticeable improvement (no surprise), and definitely the one I'd recommend.