Simply put, you'd need a very large 'chute to be able to stop a wheel that happens to detatch at 200+ km/hour. Or several medium sized ones.
Then there's the problem of where it/they sit(s) when not in use.
In a crash, would the undeployed parachute be ripped off the wheel before it's even left the car fully?
What if a parachute(s) accidentally deployed mid-race for no good reason?
If a wheel does detach, what guarantees the parachute(s) actually deploy(s) properly to do it's job in the first place, and doesn't just flutter in the breeze?
What if the wheel bounces? Chute(s) would become very useless.
Parachutes use some sort of cabling to attach themselves to the thing they are attached to - what if one of those cables happened to catch another car - or worse, a driver?
What if a parachute caught a driver across the face? Now he can't see, and he's got a bloody tire dragging behind him.
Sorry, this idea would cause more problems than it would ever fix.
FIRST POST - Please be gentle?
I've been viewing this side for a while with considerable interest. After the tragic events of last weekend I had an idea & thought I'd join and submit it-
I know it may sound crazy but I'm gonna run with it anyway- crazy ideas often work?!
How about the wheels are fitted with mini parachutes?! It may not have stopped the Senna type disaster which was almost instantaneous, & at close quarters, but with Surtees it may have. And it may be a good "interim" method.
Please consider: Instantly, upon detachment, a wheel sensor "knows" it's detached and, airbag-style, an explosive charge deploys several small chutes instantaneously also. Small chutes would be effective immediately with the airflow. A following driver would have loads more time (a half second is a long time with these guys) and may take avoiding action (a jink). The weight would be minimal as would the cost, relatively. Just a thought.....