Bear

Depends on what you want: faster acceleration or more top end, which will obviously depend on the sort of track you are at. Can't remember what the standard figures are, but normally people go for up to one lower on the front and three higher on the back for faster acceleration, which will easily pick up the front wheel. I dunno about going for more top end at the cost of acceleration because for road use I never had to go faster than 130 without wanting to get there quickly! If you drop a tooth on the front it's equivalent to adding 3 to the back I think.

Someone did a table a while back with figures for the different settings I think, but I can't be bothered to look for it. Search under gearing, sprocket size or summat like that and you may strike gold.