The spikes have to get through the grass to be able to stick. On grass tracks (which are still used in some parts of the country and in the caribean) athletes frequently use longer spikes. Also, javelin throwers who have to throw on grass frequently use spikes up to an inch in length. While I don't think you'd want to use spikes that long, I do think something longer than the standard 1/4 inch would be beneficial.
ELITETRACK Founder