Sunday, September 20, 2009

Filbert confronted

Out for a Sunday spin, riding north on Broadway.... oh, the tunnel. Right on Columbus... lots of traffic. Okay, left on Filbert. Better. Oh. There it is. Up ahead...

Flashback to 2006. Frank Chan leads his famous Steepest Hills of San Francisco ride.

The crew from the 2006 Steepest Hills of San Francisco Ride, led by Frank Chan.

It's funny; when I did that ride I was feeling like I should do a real training ride instead. But I put aside the racer self, and embraced the explorer self, and decided to have some pure fun instead. A really relaxed ride, for sure, with the exception of many short brief bursts of pain.

And the worst of it all: Filbert. Filbert from Levensworth to Hyde is listed in John Summerson (The Complete Guide to Climbing by Bike) as the 4th steepest 1/10th of a mile in the United States: 31.5%. There's even a Wikipedia page on the road's steepness. Nasty.

Back to that ride: When the group arrived at the base of Filbert, it was decision time. Go, and the only out is to topple over, or stop. I stopped: unclipped, dismounted, and walked up the hill. The memory has haunted me ever since.

Years later I was telling my girlfriend that riding 18th Street from De Haro to Rhode Island, a shorter and easier climb, was "mostly mental". It's a confidence thing, I'd said. If you think you can't do it, you won't. Yet I said it knowing when the money had been on the table on Frank's ride back in '06, I'd folded. I was hardly one to give such advice. I was a fraud.

So here I was this afternoon, facing down this nemesis from the past. I'd known this confrontation would occur, eventually. Really it was the main reason I hadn't yet swapped the well-worn 34 cog on my Ritchey for a 36, which I generally prefer. And here it was: the time was now.

The view from the bottom (Wikipedia).
A couple walked by. One of them asked me if I was going to climb it. I told them it was one of the two steepest streets in San Francisco, one of the five steepest in the U.S. "No, I probably won't," I said, "It's one-way, after all -- that's my excuse."

But it's not much of an excuse. Sure, it's one-way on this block only, uphill forbidden due to safety concerns, but it's wide enough to support bidirectional traffic. The perpendicularly parked vehicles are a bit pesky. But on this Sunday afternoon, I could easily see nobody was getting into their parked car.

They moved on, and I decided to go. Without thinking too hard about what awaited me, I pushed off, clipped in, and turned into the hill.

There's not much advantage to a fast start. Momentum won't get you far on this beast. I hit it as a slow pace, then confronted the grade. One stroke. Two. Three. Too much! I unclipped, got off and walked back down the hill. Defeated, again. I'd survive the failure. Probably. Eventually.

Then I paused at the side of the road. I thought back to the advice I'd given on 18th Street. I thought back to my friend Janet's advice on climbing steep hills on a mountain bike: keep the body low & forward, chest towards the bars. This keeps the center of mass as far forward as possible, avoiding deweighting the front wheel. And bending the arms avoids pulling on the bars, which would also lift the front wheel. Standard bike geometry is not optimized for 31.5%.

So I banished the negative thoughts from my head, pushed off, clipped in, and confronted Filbert one more time.

One stroke, two, three..... four, five. I was moving. I was steady state. There was no turning back now.

The top was approaching. Two concerns drifted into my mind. One: many steep hills steepen as they approach the end of the block, a consequence of the flattening of the hillside to accomodate the cross-street. Webster approaching Broadway. 22nd approaching Kansas. I had very little margin for this to get steeper.

The other concern was the wind. It was typically gusty today, moderate by San Francisco standards, but still significant. A gust of a headwind as I crested the top would be game over.

I could feel the road steepening ominously under my wheels as the top approached. But I was fully committed. I focused on Janet's advice, and on keeping my legs moving. There it was... so close.... I was there! I'd done it! I'd used every bit of my 34/26 low gear, but I'd achieved my goal.

The guilt of the years lifted from my shoulders. I felt refreshed, free. The ride home from there was fairly effortless. Steiner, normally steep, passed without the slightest insult. Compared to Filbert, trivial.

The first thing I did was to grab my loaded Ritchey Breakaway and stepped on the scale: 69.5 kg. Then I downloaded my PowerTap data.

PowerTap data from Filbert Street

Robert Chung promoted the idea of calculating road grades from power data. It's the opposite of what has typically been done: to estimate power from the route profile. With the Chung method, if you know power, you know speed, you can estimate the wind resistance and rolling resistance, then all that remains is power going into climbing. If you know weight then you can calculate road grade.

So for rolling resistance coefficient I estimated 0.7%. This is on the high side for tires pumped to 115 psi, as I'd done with mine just prior to the ride. But Filbert is rather rough, as roads this steep must be, and cement instead of asphalt. So I viewed 0.7% as a reasonable estimate. There's also the issue of normal force versus total weight on a steep climb. Yadda yadda. Let me simply address that by saying I don't believe rolling resistance drops on steep roads. I used total weight. Feel free to debate this point with me.

For wind resistance, I used the CdA value I'd extracted from repeated climbs of Old La Honda: 0.36 meters squared. I was rather hunched over on the climb, so I viewed this value as probably reasonable. In the absence of a strong wind wind resistance really isn't a big factor on a climb this steep, and I feel the hill mostly sheltered me from the prevailing wind.

The resulting profile is as follows:

Derived profile for Filbert Street

So I get quite close to the published value of 31.5%, although clearly the block falls far short of the promised 1/10th a mile (160 meters). The data confirm what I felt: the climb steepens slightly as it goes on, with a substantial section at 32%. Wow -- 32%. That's steep.


phipps said...

VP needs to work that block into a new Giro di SF course.

Anonymous said...

Way to go! I decided to leave that climb out of the SF Steepest ride I led because of the one-way nature, but then I didn't make it up one of the blocks of Jones. I did get up Duboce though! After Jones and Duboce, Fillmore etc. seemed rather tame.

What is your measurement for the steepest part of Quimby? I think Quimby is steeper in parts than On Orbit. For that matter, Los Trancos at its best seems steeper than On Orbit too.

djconnel said...

I haven't kept track of my "Chung" calculations for most climbs I've done, and for best results I need to weigh myself with my bike soon after doing the ride, so post-hoc isn't too good.

But from 2008 Low-Key Hillclimb profile week 3, the upper portion of Quimby sustains 13%, with steeper sections in the fine detail. On the other hand, On Orbit clearly sustains 18% (again with steeper segments in the details).

The top 10 steepest blocks in SF, according to Wattage:
Top 9 steepest street blocks in San Francisco
1. Filbert between Leavenworth and Hyde (31.5% grade)
2. 22nd Street between Church and Vicksburg (31.5% grade)
3. Jones between Union and Filbert (29% grade)
4. Duboce between Buena Vista and Alpine (27.9% grade)
5. Jones between Green and Union (26% grade)
6. Webster between Vallejo and Broadway (26% grade)
7. Duboce between Alpine and Divisadero (25% grade)
8. Jones between Pine and California (24.8 grade)
9. Fillmore between Vallejo and Broadway (24% grade)