Think about income/loss from racing just like gambling income/loss..
The IRS monitors the expense write-offs and will come down hard on one who just has expenses and no winnings..
Similar to the guy that claims the home office expenses for his computer hardware/software but no income.. The IRS is not stupid, without an ongoing DBA and income stream, if one claims the expenses they will get caught either now or later..

Just my $0.02..