. . . . . . . the towpath in the tunnel between Chirk and Froncysyllte is very narrow (I had to ride it leaning my head over to avoid hitting the roof).
Phil's not wrong about this ^^^; the tunnel is
very narrow and I'm very surprised that he's managed to cycle it - I've run though there a couple times and it is very narrow. (TBH, I wouldn't try to cycle it myself).
If you do cycle through the tunnel, you should have good lights; what Phil didn't mention, is that it is a long tunnel - over 400m long, so you need to focus clearly on the path and take care not to veer off course.
bikes will be hybrids, going north or south of Chirk.
I live just a few miles from Chirk and I know the area very well.
If you are staying in Chirk, it would be
much nicer (IMO) to head west to Glyn Ceiriog, Tregeriog and finish in Llanarmon DC, than to head north to Llangollen or south towards Oswestry.
A trip to Llangollen would be scenic by most standards, but the primary point of interest on that ride would be about halfway at the Pontcysyllte aqueduct - which you'd be well-advised to walk over. As
@Rickshaw Phil has mentioned, there is a road alternative - which has a steep climb to it.
If you cycle west towards Glyn Ceiriog, there's a really nice pub in Dolywern (The Mulberry), a good pub in Glyn Ceiriog (Glyn Valley) and two fine pubs in Llanarmon DC - The West Arms & The Hand. The road is
very scenic - you'd be cycling alongside the river. in the base of a valley, with no difficult or prolonged climbs to worry about. Oh yes, there would be very little traffic to worry about.
IMO, whether you go in a car or by bike, you 'must' take a trip along the Ceiriog Valley to Llanarmon; Llangollen is nice, but if you were to ask a frequent local cyclist such as
@al-fresco which direction he would take, I'm sure that he'd prefer to head west from Chirk.
I look forward to hearing how you get on !