This article is very interesting - http://www.slotforum.com/forums/blog/356sp...p?showentry=943 - but take a look through the forum and type "gears" in the search engine. If you play with a few variations on your cars you'll get an idea about whether you want acceleration or top speed. Or maybe you want to fit a faster motor? Or if you're still using a standard controller - the Scaley type, for example - then upgrading to something better, eg. Parma, Slot.it, Prof Motor, will probably get better results than changing gear ratios.