The car park in question being the one you cycle straight past if doing the 'proper' Wall trail i.e: using the railway cycle path 🙄 Yeah it's a real secret…..
Anyway, you don't have to that long stretch of cycle path along one side of the river and then past the end of the Wall descent.
After doing the first section of singletrack behind the Afan centre, go under the road bridge but don't turn left, turn right and take the steep path down to the river, up the other side and hey presto…you've cut a decent section of boring cycle path out! The remaining cycle path is then a decent warm-up before the climb starts.
Look….