With an automobile, you can look for the wear bars or measure the tread depth to know when it is ready to replace the tires...

But, with an ATV (in this case, a Bayou 250) with the knobby tires, when should those tires be replaced? There is no wear bar...so any advice will be appreciated...

 

You should be able to tell just by looking at the tires. If they are bald or very little traction is available while out riding, then get some new Meats on there..