The mountain road is steeper than any of the other places mentioned. I used Oziexplorer to log points every 10 m, and found that the GPS accuracy was variable due to trees obscuring sats at various points. Nevertheless, the graph below shows the elevation profile, starting from 2 Bunya Cres, taking Bowen Mt Rd down to Grose Vale Rd, then coming back up the same roads to Bunya Cres and on to 1 Lieut. Bowen Rd (the highest point) - then back down via Bellbird Cres and Wattle St.
The graph includes 1 in 8 slope lines as a guide to the slope, and shows both the gradient over 10 m and averaged over 90 m.
The climb is murderous averaging 1 in 16 (6.25%) over 5 km The worst part is around 20 to 34 Wattle, where it reaches around 1 in 7 (or 15%) and has a couple of 10 m stretches near 18%.
After a bit of googling, I found a number of rural councils have road standards that require slopes to be no more than 12.5%. Up to 15% is allowed on private driveways - but the indication is that anything over 12.5% is considered a big safety risk for public thoroughfares.
Estimating based on angle of vertical poles is obviously not very accurate. I expect that all the other examples I cited will turn out to be somewhere between 10 and 12.5% slopes. Still way outside my capability - I cheated by carting my GPS up Bowen Mountain in my car
RobS wrote:My cousin lives in that area. Is it actually safe to cycle on that road, the road is quite narrow and there's some blind corners. That whole section around Serpentine Ln and Wattle St looks fairly evil. So Wattle st is even worse?
By sight Wattle St seemed worst, and the GPS agreed. However, I did only one pass on Wattle St, and elsewhere there was considerable variation in elevation and gradient readings on successive runs (in opposite directions). It's plausible that the gradient is more like 12.5% rather than the 15% values I sampled. See this Google Earth Route for a full log of what my GPS saw - if you'd like to study the GPS samples closer and see how erratic they get.
Bowen Mt Road is quite narrow, has no shoulders, so it is pretty evil, and traffic was surprisingly unsparse for such an end-of-the-road township. I'd take my hat off to anyone attempting it - particularly if they ride all the way up from Richmond - it's pretty much a constant uphill climb.
Edited: 30/08 - added KMZ file.