Gearing vs Weight

[Dave]

Originally Posted by tomato coupe

It's meaningless to state the difference is 60 W, because that is only true for one particular rate of ascent.

If you run a calculation for your own use, you get to pick the speed, body weight, bike weight, gradient and wind. My example was merely to point out that the difference isn't huge, like twice as much. The actual values were 334 and 281.

For a 10% grade, no wind, same bike weight, 8 mph speed the difference was 53 watts.

Here's another calculator that everyone can try.

https://wattscalculator.com/

[paredown]

Originally Posted by Mark McM

As a practical example:

Say there are two identical twins who each weigh 162 lb. and can both produce the same power output for a sustained effort. One is riding a 38 lb. Schwinn Varsity (200 lb. total) with a 34/33 low gear, and the other is riding a modern 18 lb. bike (180 lb. total with a 34/30 low gear. The rider on the modern bike has 10% lower total weight, and a 10% higher gear. At the same power, the rider on the modern bike will be going 10% faster, and since his gearing is 10% higher, he will be pedaling at the same cadence as the rider on the Varsity. So at any given point along the climb, both riders will be riding at the same effort level (power and cadence).

But here's the difference: Because the rider on the lighter modern bike is going faster, he/she will finish the climb sooner, and therefore expend 10% less total energy. Maybe for a short climb this won't matter, but for a long climb (or a long ride with many climbs), the energy savings can add up

This seems intuitively right to me. My (old) personal example--on our first loaded tour (when the occasional mastodon could be found) my brother and friend had both acquired "good" bikes, and I was still riding a gas pipe bike boom special--easily 6 or 8 pounds heavier. We were all young and pretty fit, and there was probably only about a 20 pound body weight spread between us.

I was young, so recovery was not a problem, so i would start every day fresh and optimistic, but after another 100 mile day, I would be completely knackered, while they would both still be capable of riding longer if they had too, and would still be able to go up that last climb (isn't there always one more hill before the campsite?) at a decent pace. Duration -- as an explanation for the advantages conferred by a lighter bike, it stuck in my mind...

[weisan]

We can talk about numbers all day long and numbers are important, don't hear what I am not saying but there's always a gap between what's on paper and what transpired in reality, why is that?

Simply because we are humans, we are not machines.

[prototoast]

Originally Posted by weisan

We can talk about numbers all day long and numbers are important, don't hear what I am not saying but there's always a gap between what's on paper and what transpired in reality, why is that?

Simply because we are humans, we are not machines.

There is a very direct relationship between gearing, speed, power, and weight while climbing.

The stuff that's hard to quantify is what goes into that power number. But if you take power as fixed for the purposes of the discussion, which I think is appropriate given the original question, there's not much mystery to it.

[Clean39T]

Originally Posted by weisan

Simply because we are humans, we are not machines.

The taller the gear,
Faster, faster, faster - fly!
Legs giving out now.

[FastCanon]

I don't feel like it's linear when it comes to climbing hills. I produce much more power than my wife and she has wider gearings and lighter. When we climb a hill, I would try and ride up the hill as fast as I could and then turn around to where she was at only to find I wasn't that far ahead. On flat, I seem to go much farther.

[Hilltopperny]

Losing actual body weight is hands down the best way to improve climbing. I got sick a little over a week ago and lost around 20lbs. I was amazed at how much more efficient my climbing was even without regaining my strength.

I didn't over exert my self on the two rides that followed, but the fact that I could push a 30lb full suspension up some steep terrain without any issue after being bed ridden for four days a few days prior was enlightening to me.

I went to the local xc trails the next day on my 25lb full suspension and rode for two hours and the results were the same. Climbing has become significantly easier with less effort. I felt like a new man! I plan on getting out on my road bike some time this week and testing that out as well. I tend to not ride well in the heat and we are in the mid 80's for the next 3 days, but I bet that 20lb weight loss will increase my ability to exercise in the heat as well.

[Likes2ridefar]

Seems simple in my view. It’s all about w/kg. What gears you use doesn’t matter if they provide the cadence/range needed to keep the pedals moving at a certain watt output. Greater w/kg, everything else equal, will always predict the winner up a climb. We of course know there are many variables that can impact that outcome…flat tire, sick, over trained, a really crappy bike, etc..

[Dave]

When my 10-36 arrives, I'm looking for 8 mph using my 46/36 at 80 rpm, up a 13% grade. Beats going 4-5 mph in a 30/44. The watts calculator says 384 watts required for a 13% grade. I'll be be setup to get 200 watts of assist, maximum.

[Mark McM]

Originally Posted by FastCanon

I don't feel like it's linear when it comes to climbing hills. I produce much more power than my wife and she has wider gearings and lighter. When we climb a hill, I would try and ride up the hill as fast as I could and then turn around to where she was at only to find I wasn't that far ahead. On flat, I seem to go much farther.

Comparing relative speed on hills vs. relative speed on the flats is a bit apples and oranges. Speed on hills primarily comes down to Power/Weight ratio, whereas speed on the flats primarily comes down to Power/Aero-drag ratio. Smaller riders tend to have higher Power/Weight ratios, so they tend to do better on the hills than larger riders. Larger riders tend to have higher Power/Aero-drag ratios than smaller riders, so they tend to do better on the flats than smaller riders. If you are larger than your wife, that could be a contributor to your relative differences on hills vs. flats.

As far as linearity - the steeper the road, the more gravity drag dominates, and the flatter the road, the more aero drag dominates. Gravity drag is quite linear, so speed on steep hills will be nearly proportional with Power/Weight ratio. Aero drag is non-linear, so speed will not be proportional to the Power/Aero-drag ratio. In fact, while gravity drag power varies in direct proportion to speed, aero drag power increases with the cube of speed. So the power to overcome aero drag at 30 mph won't be just twice as the power to overcome aero drag at 15 mph - the aero drag at 30 mph will actually be 8 times as high as at 15 mph.

[FastCanon]

I'm shorter than my wife but heavier. Maybe when I'm pushing up the hill, she was pacing with me and then when I slow down, she's slowing down just to mess with me.

Originally Posted by Mark McM

Comparing relative speed on hills vs. relative speed on the flats is a bit apples and oranges. Speed on hills primarily comes down to Power/Weight ratio, whereas speed on the flats primarily comes down to Power/Aero-drag ratio. Smaller riders tend to have higher Power/Weight ratios, so they tend to do better on the hills than larger riders. Larger riders tend to have higher Power/Aero-drag ratios than smaller riders, so they tend to do better on the flats than smaller riders. If you are larger than your wife, that could be a contributor to your relative differences on hills vs. flats.

As far as linearity - the steeper the road, the more gravity drag dominates, and the flatter the road, the more aero drag dominates. Gravity drag is quite linear, so speed on steep hills will be nearly proportional with Power/Weight ratio. Aero drag is non-linear, so speed will not be proportional to the Power/Aero-drag ratio. In fact, while gravity drag power varies in direct proportion to speed, aero drag power increases with the cube of speed. So the power to overcome aero drag at 30 mph won't be just twice as the power to overcome aero drag at 15 mph - the aero drag at 30 mph will actually be 8 times as high as at 15 mph.

[martl]

Originally Posted by FastCanon

I don't feel like it's linear when it comes to climbing hills. I produce much more power than my wife and she has wider gearings and lighter. When we climb a hill, I would try and ride up the hill as fast as I could and then turn around to where she was at only to find I wasn't that far ahead. On flat, I seem to go much farther.

The physics are known about this. At the bottom of it, it comes down to the Power (Watts) which is Energy (Joule) per time (seconds). One Watt is One Joule per second.

Applied to cycling (or any sort of vehicle), this Power is used to overcome resistance. A bike always has an inernal resistance due to friction on anything that moves - tires versus the road, internal friction in the drive train etc; and aerodynamic drag.

None of these are constant or linear (although some are nearly linear). Especially the aero drag is relative to speed, the formula is c(w)*A*speed², with A being the projection of the frontal area and c(w) a factor determined by how "aero" the system (=rider sitting on the bike) is.
It shows that speed is squared, which applied to the real life means it is the major factor above speeds around 15km/h / 10mph.

On a flat, these are all the factors, hence more power = more speed.

When climbing, another factor comes in, which is lifting work. You lift the weight of the system a certain amount of meters, which also requires Work/Energy. This can easily be calculated by the "potential Energy" formula Ep = m (mass) * g (gravitational constant 9,81m/s²) * h (height difference).

To elevate mass a kg a height difference of b meters, Energy x is required. This simply adds to the rest.

This is why at a climb, power to weight ratio is the determining factor, even more so the steeper the climb is, because the speed will be lower, making the part of areo drag small to neglectible.

I rode a few hill climb competitions where the height difference was well known and i was timed precisely, using an SRM power meter. comparing the wattage measured by the SRM to wattage calculated by these formulas (m*g*h), they are pretty accurate. There is an error which comes from not calculating the areo and rolling resistance, but on climbs averaging speeds between 10-15km/h, these were constant respectively the difference was negligible.

Originally Posted by weisan

We can talk about numbers all day long and numbers are important, don't hear what I am not saying but there's always a gap between what's on paper and what transpired in reality, why is that?

Simply because we are humans, we are not machines.

Mostly, because we usually don't measure all the factors mentioned above


And if you've read this far you may ask, where does the gear ratio come into play? Well, it doesn't. not until you scratch on the boundaries of personal skills like bike handling etc. There is a lowest (and highest) cadence where you can still ride, and there is a maximum gradient where you can still control the bike and stay on it If you *would* have enough power to propel the bike, but cant stay on it or cant torn the crank that slow, a lower gear ratio may help extend that margin. What it absolutely doesn't, is make you go faster; because the Watt you can generate for a given time stay the same.

A different gear ratio doesnt make you faster or slower. Different weight doesnt make you faster or slower on a flat. It does on a climb.

There is a school that claims there is a sweet spot ("Efficient pedalling") - which is where all those inventions like oval chainrings or other devices that claim to use your power more "efficient" are coming from, but this has not seen any confirmation in any reliable study i know about.

[Dave]

I try to keep my cadence in the 75-90 range, with 90 being rare on steep climbs. If I needed to only pedal at 65, the gear ratio is too big and too much torque is required. In that respect, gear ratio selection is certainly relevant. I've got bikes now equipped with 30/44 low gears that produce just over 4 mph at 80 rpm. I wouldn't want any lower.

Even with an ebike, the needed torque can't exceed the combination of rider input and the 50-80 Nm that the motor might add.

[morrisond]

Can your muscles that are Fast Twitch muscles produce more power at high RPM than slow twitch muscles at low rpm?

Also when going up a hill due to the angle does that engage more of the slow twitch muscles?

The reason I'm asking is that recently I was going up a climb standing and noticed that if dropped my Torso towards the bars it got a lot easier to pedal.

[benb]

For the amount of body weight we are talking about I would conjecture your aerodynamics improves as well.

20-30lbs is a lot. Your body is noticeably smaller but you also probably adjust your position along the way which will stack up additional savings.

Again maybe going from 50-60lbs overweight to 20-30lbs overweight doesn't do this, but 20-30lbs overweight to race weight it's gotta be a factor.