The odds aren't worse for splitting numbers the only bet with worse odds then the others is the 5 number bet.

The reason that it might appear to be worse is that since the payoff appears as 17 TO 1 for a split number instead of 18 FOR 1.

If you bet a single number and win you get 35 chips plus you keep the one you bet --- you have 36 chips.

If you bet the split (doubling your chance to win) and win you get 17 chips plus you keep the one you bet --- you have 18 chips (half the single number payoff)

casino advantage remains the same 5.26% (on a double zero wheel).