Was out there over Christmas.
As you say the humidity is stupifying and it will take you quite a few weeks to acclimatise. I found it best to go out at first light.
My brother in law hooked me up with an ex pat who rides mtb for Team Cannasia and I did a fair bit of mtb riding out at Bukit Timah NR. There’s a Trail centre / Visitor centre with a waymarked mtb circuit – takes around 30 – 40 mins to do the marked loop. This can be varied on subsequent circuits as there are some minor loops diverting off the main path.
Also loads of unmarked / cheeky stuff with some surprisingly technical terrain but you really need someone with local knowledge to show you where. Slighty surreal / initially a bit spooky sharing the trail with the Monkeys, Snakes and Monitor Lizards 😉
Found the road riding pretty dangerous and unenjoyable tbh and there are a very high number of serious accidents involving cars / bikes. You’ll see loads of them streaking through the lights on amber and red. Out there the car is a huge status thing and despite the sophisticated transport network none of it’s been designed with bikes in mind.
Drop in to these guys and I’m sure they can hook you up with local road / mtb rides:
http://cannasia.com/