Clueless here. What kinds of bikes do most trials rider ride? I guess I'm talking more on the lines of what I've seen on TV and Youtube of around town and small boulder type riding as opposed to in the woods competition. I know there are very specialized trials bikes often with no seat and what appears to be 1:1 gearing. It looks like fun and a good way to get some exercise, but do I need to spend the buck on a new specailized bike?

Google "Inspired Bikes"

Yep If you want to ride trials then you need a trials bike. I grew up riding trials on motorcycles and am now getting back into it up here in maine. Nothing like it. Am looking into trials bicycles too. Just a little old to fall on tar and cement. Scottish six day trials. Google it. Or GAS GAS, Sherco, Montessa, tons of fun.

Trials bike designs look like they came from modified BMX bikes. Can I reasonably start on a BMX? What braking setup do I need? Are trials bikes freewheel or fixed?

They can be both fixed and free. I think most ride a free though. Big diff between a bmx and a trials. A tiny rigid frame mtb would work ok. I see trials bikes on CL every now and then.

Anything with 29 in wheels....

There's "stock" trials, done on a fairly standard 26" hardtail MTB frame, and there's "modified" trials, done on a specialty 20/22/24" wheeled frame.

Brakes have gone to hydro disc on the high end, but even center pull cantilevers can be used when set up properly for low modulation.

Did you eat paint chips containing lead as a child?

https://www.pinkbike.com/news/Random-...bike-2011.html

MacAskill has a signature bike now.

i can turn my old mountain bike to a trials bike by converting it into a single speed?

https://www.observedtrials.net/vb/