I know Chirag (@Nizhniynovgorod) was up there a couple of weeks back and that the Chichibu side was closed. He said he saw a couple of punctures on the way down, but the road surface has always been crap. Perhaps he'll comment on this thread.
I was up at the lake last night and the diversions for the landslide roadworks were still in place. Not sure whether that means that side of the lake is impassable or not.
I've hardly ridden at all this year but hope to have been up Arima before the month's out.
Morning! Yes, I was there two weeks ago. Hanno side (i.e. side from the lake) is open. I had to take a small diversion to go around the lake, then rejoin the road to the summit (road is also open to cars). From the summit, I had to return the way I came as the Chichibu side was "closed" and I didn't want to chance it. There were many riders going up and down from Hanno, but I saw nobody who coming from/going to Chichibu side.
As for the surface - lots of rocks and I saw a few people with punctures. Thankfully though, I was OK (using Gatorskins).
Went to Arima Toge today (quite unplanned):
1. The road on the north side of the dam/lake is still blocked off for repairs.
2. The road from the peak down to Chichibu Sakura-ko is still blocked off near the top.
3. Road surface is pretty sketchy in places - lots of stones, rocks, branches - but nothing unusually bad for Arima.