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Climbing the Marchlyn Mawr Dam Road

Marchlyn Mawr is another one of those semi-closed road hill climbs in North Wales. Similar to Stwlan Dam, the road is closed to cars but bikes can ride it. I’ve climbed it a couple of times now and love it. I believe it’s the highest point in North Wales you can cycle up to (on a road) with a peak elevation of 2,074ft.

Getting to the Marchlyn Mawr Dam Road

I discovered the Marchlyn Mawr cycling road on the Strava segment explore map. It stuck out as a road to nowhere and the elevation profile looked epic. It was instantly added to my North Wales climbs bucket list.

There’s a couple of ways up to Marchlyn Mawr, including the long Electric Mountain climb (Fachwen) which I covered in my favourite North Wales climbs. This route makes the climb 4.9 miles long and 1719ft of ascent.

You can also take the Sling climb up from Tregarth, past Mynydd Llandegai and to the start that way. That extends the climbing to 6.2 miles with 1750ft of ascent.

Marchlyn Mawr Summit

The actual climb

Once you’ve made it through the kissing gate with your bike at the start, you’re on the climb. There’s an initial easy bit but that soon disappears. What follows is half a mile of a double-digit gradient. From the junction which goes off to the surge pool – a climb in itself – the gradient lessens slightly to a more manageable 6-8%.

You can now get a sneak peek of the top of the climb ahead. There’s a little tunnel entrance that goes into the mountain, that’s the finish. If you’re riding with other people, you’ll start to see them riding back and forth up ahead of you. These aren’t the switchbacks of the Stwlan Dam but wide, open loops which make the descent more fun. The gradient also gradually moves back up to closer to 10%. You’ll cross over a cattle grid around this point, careful on the way down as you’ll hit it at over 30mph. The far concrete lip of the grid on the way down can be nasty.

Just before the effort to the top, the gradient backs off again to about 2%, so you get a brief rest. The last 0.2 miles always seem to go by quicker than they should. The climb is doing its last kick up but that tunnel entrance is now fully in view and helps you give everything you have. Most of the segments finish at the CCTV camera. Now at the top, enjoy the views of North Wales and Anglesey.