1) has the cat been neutered recently - they sometimes continue spraying for a week or two after the op.
2) Phone the vet and ask their advice (try to ignore the laughter at the other ond of the phone
)
3) Buy some of the pepper that is used to put on gardens to prevent cats messing and dust the tyres with it
4) You can now buy ultra-sonic devices that keeps cats off gardens - attach one of these to the bike. Added benefit - it keeps bats away as well
Trying to be helpful, but probably failing
