This route starts in Kiambu with a pretty nice 20 km to Limuru town, mostly climbing with an average gradient of 2,2%, some sectors hit up to 8%, including a 4 km climb in the third category. The road passes through mostly tea and some coffee fields, the tarmac is good but rough, so be prepared for the constant vibration in your wrists. Once you reach Limuru town and make the turn in direction Raini the fun part begins; you now have an 11 km descent on smooth, like glass tarmac. From Raini you have the option to take a parallel road back to Limuru for another 14 km with some additional elevation gain; sugarcane fields predominate all around.  Back in Limuru you can either enjoy once again the fast descent to Raini or take the detour to Kiambu and end your route there.

Tips

During the weekend and especially in the earlier hours, the traffic is relatively low, so if you are more adventurous, you can cycle from and back to Nairobi on your own. Personally, for transportation to and from this cycling route, I use Bolt or Uber, only during the weekends do I return on my own to Nairobi.

Attention must be paid to every vehicle and especially to the motorcyclist; most of them do not obey the road rules in any form; Do not underestimate the pedestrians either. Back-up red lights, a gilet, or a jacket in alarming colors are recommended. 

Something else to watch out for are the speed bumps and speed humps situated around schools, markets, and pedestrian crosswalks; some of them are pretty cruel - 4 parallel asphalt humps.

The route starts in Ruiru (Kenyatta Road) and is almost flat for 10 km. The road is just renovated with brand new tarmac to Gatundu town, where the hilly part begins. Ascending all the way, the route offers many ups and downs, some of them (I counted four) with gradients of 10–11% and one with up to 13%. The road passes through countryside with some small villages and coffee and tea fields. Reaching the top and Mundoro town after 35 km and 670 m elevation gain, the descent to Ruiru begins, offering ideal road conditions and surprising down and up (the segment name is Drop Moja Wazimu, 1,5 km, noted with a grade of -6,5% and a vertical ascent of 98m). The road snakes down through small villages and fields; please pay attention to the speed humps and bumps.

There are strong and numerous cycling groups riding the same route every day. They usually leave shortly after 5 a.m. from the Independence Monument, taking NR6 in the direction of the north until Preaek Ta Meak Bridge and then back.

Here I’ll put some notes on this route with several possible returns back to the city.

Taking NR6 in north direction is great way to enjoy the cycling in its pure form. Perfect tarmac, almost no traffic lights after Chroy Changvar Bridge, wide traffic lanes, low intense traffic in the early hours (5:30-7:00 am). Once you reach Preaek Ta Meak Bridge after 22 km full gas you can return back on the same road or you can take road 380 parallel to the other side of Mekong river. The road pass through villages and has more countryside feel, the road is covered with good tarmac/ concrete with some short exceptions. In June 2023 begun reconstruction on this road, so need to be checked before undertake ride with your road bike there. 

Crossing the river back to Phnom Penh is possible on several points depends whether you want to go through the city or skip the heavy traffic straight back to Independence Monument. I took usually the ferry between Areiksart Ferry Port and Kampong Chamlong. The ferry ride takes 10 minutes and costs 500 riels (25 cents).

Second option for return route is to take NR8 (from Preaek Ta Meak Bridge) and then NR7 heading until the same ferry service. Its picturesque countryside road through some waterlily ponds.

Third, you can include in your ride the Mekong islands. Take the ferry to the Silk island and cross the iron bridge to the Koh Dach island after that. There is a nice road around the Koh Dach island, better on the west side.

Besides the roads everywhere are numerous markets to buy water, fruits, coconuts or some food. 

And least but not last: the area is flat as a pancake, do not expect any major climbs except the bridges.

Starting from Naga Ferry clockwise you have 88 km for the full round. There are some things to be taken into consideration: they haven't finished putting up all the street lights on the ring road yet, and there are not many places to buy water or coconuts on the south-west part of the ring.

Chisor Mountain Temple is situated some 50 km south of Phnom Penh. The route follows the main NR1 and NR2, characterized by a heavy traffic immediately after the city which gets much tolerable as the route progresses south. The temple itself is situated on a "mountain" at the foot of which 400 steps await you. At the top, before entering, you have to pay a small entrance fee (8000 reals or 2 $). A forgot to take money with me so I went back downstairs to pick them and I climbed the stares again.
Note: take your sneakers in a backpack.

To get there just follow NR5 until you reach the retour to Oudong. On my way back to Phnm Penh I took the roads thought the villages, less traffic, charming countrysite atmosphere, a lot of places to drink coconuts and have a meal.