I certainly hope you wouldn't shoot someone for stealing a bike.
I wouldn't shoot them for standing up in a truck and driving off. That is circumstantial evidence. If my bike was in the truck, whole different story. I live in Texas, I have had my CHL a while and I'm well-versed in Texas law.
To wit:
PC 9.42 Deadly Force to Protect Property. A person is justified in using deadly force against another to protect land or tangible, movable property:
(1) if he would be justified in using force against the other under Section 9.41
(I can type that one out, too, if need be. It basically states that the BG must be taking something that does not belong to him); and
(2) when and to the degree he reasonably believes the deadly force to be immediately necessary:
(A) to prevent the other's
imminent commision of arson, burglary, robbery, aggravated robery,
theft during the night-time from escaping with the property, and
(3) he reasonably believes that:
(A) the land or property cannot be protected or recovered by any other means, and
(B) the use of force other than deadly force would expose the actor or another to a substantial risk or death or serious bodily injury.
In other words, theft at night and fleeing, if you have a reasonable belief that there may be no other way to retrieve your property, you have a defense to prosecution, and it is very likely you will not be charged in the first place.
The Joe Horn case was right on the edge, but he prevailed. Several others have made (or not made) the news in the last two years. Each time, the homeowner/business owner has prevailed, usually not even charged.
Not sure I'd go that far, but this ain't New Yawk. Texas law is based loosely on old-time law, where stealing a man's property (horse) could leave him in dire straights, perhaps unable to survive. If you want to B&E or commit theft/burglary/robbery (and yes, I know the definition of each), especially after dark, you are taking a calculated risk.
As it should be...
The key is to
know the law and remain within it.
Oh, and OP...get a few cable and disc locks. Make it a little tougher for the thieves.