I toppled over a few times, not for a few years now, but I've done it. The grade got too steep for me, so the effort was put into trying to keep upright and pedal, so no time to unclip a foot, and over I toppled. If it is a normal type of steep climb, like a 10% grade, and I am just wanting to stop to rest I can unclip and plant a foot. It is when I am climbing on a road new-to-me, I go around a curve and the road turns into a 20% grade, I can't see the summit, and my legs just give out. When I am climbing in an area new to me, I've learned to eyeball ahead for drives on the right, even if gravel or rutted, because I can turn into a drive and unclip if the grade becomes a long 20%.

It happens every year that I get on to some road with crazy steep grades, unexpected and unplanned. It happened to me within the past few months on a group training ride, there was a road closure on the route and the group leader did his best to reroute us, but I ended up doing a long steep climb with grades up to 18%, curves in the road, kept thinking the summit was close and the grade finally went down to 10% and oh what a relief, and on an ordinary day I think of 10% as steep. I looked at the route in Map later and Map said it was a Cat 2 climb, which I totally believe.

So yes, I understand your fear. If you know the route, you can map it ahead of time in ridewithgps.com, and if you run the cursor over the route line the site will give you a grade, which many cyclists believe to be on the low side, but it is a good estimate if you add a couple of points to be on the safe side, like if Ride says 6% then maybe assume 9%. You can map the route in Map and get more climb data. If you think a hill might be too steep by looking at the route ahead of time, note at what mile it starts, and when you get there make a decision at the bottom whether to try to pedal it or walk it. But if you are on an unknown road for the first time and the grade is too steep for you, look ahead and try to see a drive on the right, and keep going until you reach the drive, turn into the drive and unclip and just sit there for awhile, drinking and eating until you recover. Walk the rest of the hill.