Reducing overall tyre diameter

[willdew]

I've just bought some rims of ebay for my golf I'm making into a track toy. I'm putting track tyres on them. It occurred to me it might be a good idea to reduce the overall wheel/tyre diameter in order to reduce the gearing and in doing so increase the acceleration.

I appreciate this is all fine in theory - has anyone here done it in practice? And am I missing anything here? Is there a good reason I shouldn't do this?

Thanks, Will