The above tablle is speed in (km/h) at 3 different big rings 34/36/39 using 100RPM.
The table is for 23-32 on the back.

Here is the same table calculated at 40RPM

I just used http://sheldonbrown.com/gears/" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false; to caclulate it

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Parlee Z5 ML

The point i was trying to make was how the TV camera's never make it look that steep or hard.

TV or photograph neither will reveal true gradient. The fact that it looks easy it's the rider doing that.
Since the TV cameras almost always focus on the head of the race they don't show you what the sprinters are doing on a HC climb

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I was some 20%+ stuff at the weekends but was training rather than having just done 150km at high pace. 34 x 25 fine for me for anything I've come across.

I climb all the time on my big ring 53t X 11/26 . I have climbed a lot of the tour climbs but there not 20%
I climb once a year in scotland which does have some 20% gradients but they are only for at most a few hundred yards maybe half a km at a stretch but any further and I would have to get on the small ring . I don't look stylish I can tell you once it gets that steep for that long. If I get a chance I will go and do some Giro climbs and have to start using a small front ring [ just don't feel right ] Just tend to go to the usual places i.e. tour de france climbs . I think I really should start using the small ring but My crazy ego won't let me . My friend finished the etape, the mountain stage from this year. 10.000 started only 3000 finished . It took him 12 hours or something crazy and he went past sh%tloads of riders ,they were sweeping them up in the broom wagon like trash on the road. He Rides a 50/34 at the front and he went 28 at the back and it worked.

I moved from UK to Switzerland earlier this year and it does not surprise me that pros are using low gears. In UK 34x25 was fine and even I could get up UK hills on 39x25 without much bother. Fact is that UK hills are not all that tough.

In CH the climbs are longer, with steep 5-10km climbs all over the place. This means that you either end up riding at 50rpm and ripping up your legs and potentially damaging knees, or riding at 65rpm and doing a threshold workout just to get up the hill, which just stops being possible at some point. Or if you run out of food, get lost or just choose your hills unwisely you're toast. Thus I'm not proud to say that I recently walked up a hill for the first time in about 20 years and have had some other 'character building' experiences recently.

Obviously the answer is not to get lower gears but to sell the Colnago and get a Ducati. Or perhaps try one of those newfangled electric bikes, since they can produce up to 250W. Now that would help me ride like Cancellara.

While I agree UK hills are mere bumps, the idea that a 34 is even necessary in the South East is a complete anathema to me, despite having 2 plates, 10 pins & no cartilage in my right ankle!

for something completely different, i gotta ask you: how do you fight the desire to gear down when riding more compact setup?

i never take anything different into the hills ( maybe not 20% but some 10-15% few-km climbs) than my standard 39x23, sometimes 25, because every time i tried compact cranks or 25+ cogs i couldnt help myself to use them in the critical situations = go slower. i know it may not look as charming, but it sure does work for me training-wise

I rode the Punta Veleno on 36 x 25 this year, at the end of a very long ride.

Probably would have struggled to make it up there on 39 x 25.

Saw that Pozzovivo used a 34 x 29 to win up there in Giro del Trentino, I definitely would have been faster with that set up!

Tymon: I'd say that fighting the desire to use your lower gears may be the problem. If you change down early and use a higher cadence throughout, you'll reap the benefits. If you mash until you can mash no more and then change down you'll find it extremely difficult to get your legs spinning again.

Changing from 39x25 to 34x25 this summer (and getting a garmin) has had an immense impact on my riding style and made me faster. Even though the hills are mostly significantly easier here in Dorset than where I was training in Dartmoor with the 39.

If you have a powermeter: you know how much power you can generate for a given amount of time, so you just do that (follow your training plan...), no matter what gear.

Otherwise: for hills I rode before, I know how fast I can go, so I do that. If I don't know the hill I base my effort on HR and how well/bad I feel.

This is a bit of a mystery to me also.
On a steep climb, I almost always end up just gearing down until I am in my lowest gear and struggle up with that at about 40 rpm.

But by time, power, and comparison with other (better) climbers it is clear that staying in a higher gear is better, even though I will end up slogging at 40 rpm in that gear also.

It is probably a matter of training, but I try mightily to train to go to higher powers while spinning a lower gear, but it hasn't had any beneficial effect. So I limit my low gear by simply estimating what I must push to get up the hill at a decent rate, and then don't take any bigger cassette sprockets with me on the ride. In other words, I have no bailout gear and not even a low gear that I think I can really "handle". But the times come out faster.

This is for a race only. I often take lower gears to train on. (34-28)

For a long climb I am faster if I use a reasonable rpm (75-90). I can get up climbs at a lower rpm but I do not put out as much power on the power meter and my legs tire more quickly. That's important when you're doing 10,000 or 15,000 feet of climbing in a day.

Watch the pros on a climb. Most of them spin a fairly high rpm.

If you are struggling at 40 rpm in your lowest gear, you need lower gearing. As pointed out earlier even the pros are running 34x30 or lower when they need it.

If it doesn't hurt enough, shift to a smaller cog.

+1

Many experiments on club runs to see who could get up Cheddar Gorge on the highest gear proved conclusively that a) 52x17 is for weaklings b) non participants in the pissing contest would usually get to the top of the steep bit faster using the inner chainring and the 21 sprocket.

I would recommend riding some reps of a challenging hill at a few different rpms and similar levels of perceived effort to see what gets you there fastest. Obviously riding until your eyes pop out by turning a bigger gear at the same rpm will be faster.

from the looks on tv
i would say most riders ride around 80 rpm up the hills and riders such as contador ride around the same but they can spin for longer periods of time to throw attacks, but most of the time it looks like most riders climbigs stay at 80rpm.
the question of why do i climb faster with taller gearing, i think has to do with attrision once you are really tired your cadence will drop to a low sustainable number like 40-50 and it will not matter what gear you are in (it will but not that much) your body will always try to at least manage that number. kind of i can spin up to 150 my 53/15 and my 53/16 at 180 but that is the most i could spin any gear even if am on a downhill with tail wind i would not be able to spin any faster with out looking and felling uncofortable on the bike.