Firstly, combining them is going to cause problems with there being a few too many topics. In trials chat right now, the oldest reply on the first is only 3 days old, and there's only a couple of them. So the rate of which topics are leaving the first page is pretty fast already.
Seems to me every subject in trials chat and beginners trials chat can be broken up into 2 groups.
1. Topics about parts. (inc whole bikes and clothes).
2. Topics about riding. (physically, technique, things happening on rides etc)
You can literally go down all of trials chat and beginners chat and place every topic into one of these two groups.
About:
48 topics would fit into 1.
10 would fit into 2.
There's also a few stray topics like the tartydays which should really be in Clubs and comps*, not in trials chat, there's also a few topics such as "Did Anyone Hear From Marino Lately?" and "Glossary Of Terms" which aren't really technically in the wrong place, but they won't fit into either of the 2 categories I mentioned.
So my idea would be to base 2 subforums around what I just said, have one subforum relating to physical equipment. Any question/discussion regarding bikes, parts or clothes (protective or regular)
And the other would be for riding technique. The problem is there's a lot more topics about parts than riding tips, so the 2nd subforum would also allow the stray topics to be posted in there too to even the numbers out.
So to sum up:
One subforum solely for bikes, parts, clothing and equipment.
And another for everything else, inc but not limited to riding, hints and tips. Trials politics and general discussion of the sport.
*Sometimes topics like these are purposefully put into trials chat instead of news or member organised rides so they get seen by more people.
Also, while I'm here. I think TF has become big enough now for a subforum solely for the function of TF. Where you'd be able to post topics like this one, people would be able to post their ideas and updates to the site could be posted there too without having everything TF related spread over all the topics (ie. there's a bunch of TF related threads in 'News', this one is in chit-chat, and there's a couple of things in website updates too so it's pretty confusing)