Myths In Cycling

82 replies · 1,776 views

Angstrom
181 posts
#21Jan 28, 2021, 12:57 PM
For pedaling, power = torque x rpm. You can spin a low gear or stomp a high gear and put out the same power.
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stu
646 posts
#22Jan 28, 2021, 2:05 PM
Mark wrote:
I like to use a logic tool called “Dimensional Analysis.” Force has the dimension, pounds (Newtons). Distance has the dimension, foot (meter). Work has the dimension, foot-pound (Newton-meter) because work involves moving a force through a distance. Energy only differs from work because of context— is it available? Power is the rate of work, with the dimension foot-pound per second (= 1.35581795 watts). Here’s the deal— When you get your electric energy bill it is for “kilowatt-hours.”

One possible point of confusion: work and torque have the same units, Newton-meter or foot-pound. The difference is work is a scaler (no direction) while torque is a vector (with direction). The relationship is work = torque ⋅ angle (where angle is in radians, a dimensionless ratio of arc to radius). And power is torque ⋅ angular velocity (radians/second) or in plain English how hard you stomp times how fast you spin.
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stu
646 posts
#23Jan 28, 2021, 2:09 PM
To do a more controlled test of climbing speed vs. weight I'd use the same bike, same tires, same air pressure, same road, same weather, etc. Then compare climbing with no water bottles to climbing with 2 full 16-oz bottles. The only variable would be the weight.

If you're using different bikes then all sorts of differences could affect climbing speed.
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Mark W. Ingalls
62 posts
#24Jan 28, 2021, 2:48 PM
@stu— Sure! And also...

http://en.wikipedia.org/wiki/Energy_flux

🤓
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chas
1,305 posts
#25Jan 28, 2021, 3:29 PM
power=Force x velocity
force=mass x acceleration
velocity=change in position/change in time

Yup. One way I think of it:

I can apply as much torque or force as I want against a wall (or a pedal). But if it doesn't move (0rpm) I have generated zero power. Power needs movement - more movement more power.

Power = torque x RPM. So yeah, the more RPM (at the same torque), the more power.
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chas
1,305 posts
#26Jan 28, 2021, 3:35 PM
ccand51997 wrote:
Do you mind if I ask how you measured the difference? Because 4 pounds is roughly a 4 watt difference when climbing a steep hill which is not really earth shattering. That is why I try to bust that myth; well, not exactly a myth but a gross overestimation of importance. A good tire vs. a poor one can make more of difference than a few pounds on your bike.

I read the articles. Sounds nice - but has GNC done a test??? ;-)

I did a mountain bike vs gravel test once. With low rolling resistant tires on both bikes, they were the same for the first half of the (35 mile) test. At endurance (slower) speeds, aero didn't mean too much. But the mountain bike was probably close to 10lbs heavier and after a couple of hours, I just ran out of energy on the mountain bike. It took a lot of work carrying that weigh around.

Or doing a sprint test. I can get to 25mph a LOT faster on a 16lb bike than a 26 mile bike (rather both ends for the gravel bikes I was looking at).

Or to get more extreme - hill climbing with a loaded touring bike is a LOT of work.

I think there is more to it than the quoted numbers. Thoughts?
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stu
646 posts
#27Jan 28, 2021, 3:38 PM
Mark wrote:http://en.wikipedia.org/wiki/Energy_flux🤓

Hmmm - maybe my bike could use a flux capacitor.
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ljsmith
762 posts
#28Jan 28, 2021, 4:22 PMedited
chas wrote:

I read the articles. Sounds nice - but has GNC done a test??? ;-)

I did a mountain bike vs gravel test once. With low rolling resistant tires on both bikes, they were the same for the first half of the (35 mile) test. At endurance (slower) speeds, aero didn't mean too much. But the mountain bike was probably close to 10lbs heavier and after a couple of hours, I just ran out of energy on the mountain bike. It took a lot of work carrying that weigh around.

Or doing a sprint test. I can get to 25mph a LOT faster on a 16lb bike than a 26 mile bike (rather both ends for the gravel bikes I was looking at).

Or to get more extreme - hill climbing with a loaded touring bike is a LOT of work.

I think there is more to it than the quoted numbers. Thoughts?

First let me say that I love light bikes, and I am pretty close to being a weight weenie. My Salsa Warbird is in the 16.5 pound range. But, I think a lot of the benefit of light weight is psychological, and Jan even says this. When I ride a heavier bike, it really is mentally draining every time I have to stop and get it back up to speed, or climb a big hill. A light bike feels a lot faster and the way it responds to pedaling input just makes you want to ride harder. While a heavy bike feels sluggish and just a chore to pedal. But I think if you were to actually use a power meter and time yourself, the difference would end up being quite small. So if you are racing and every second counts, then it matters a lot. But if you are just out for a long ride with friends, it really doesn't matter. But even knowing that, I also know that I enjoy riding a light bike more, so maybe I am not much faster but I enjoy my rides a lot more.

Now as far as comparing mountain bikes to gravel bikes, mountain bikes almost always have you in a more upright position. This means you are less aerodynamic, but it also means you can not put out as much power. A lower position allows you to get more power from your glutes and hamstrings. So even if you are on a really light mountain bike, you have to use your quads more and they will tire out quicker because of it.
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ccand51997
265 posts
#29Jan 28, 2021, 4:31 PM
chas wrote:

I read the articles. Sounds nice - but has GNC done a test??? ;-)

Or doing a sprint test. I can get to 25mph a LOT faster on a 16lb bike than a 26 mile bike (rather both ends for the gravel bikes I was looking at).

Or to get more extreme - hill climbing with a loaded touring bike is a LOT of work.

I think there is more to it than the quoted numbers. Thoughts?

I usually get flamed for arguing against weight-weenieness but I suppose it is because I obsessed over bikes I could not afford in my youth. I had a Univega that was 27 pounds and the Scwinn Paramount was 22! pounds. I just knew if I had that bike I would win the TdF some day. Now, I know that was beyond me. With my current knowlege I might have been a soiid Cat 2 who could outclimb most people. Those five pounds were not the difference between me and turning pro.

Thanks for the laugh about GNC. Sometimes you have to shake your head at their "tests."

As for your mtb vs. gravel, how hilly was said test? What surfaces were you covering? Was it possible to maintain a consistent wattage throughout? Testing off-road is tricky because taking different lines (at least where I ride) could be vastly different sand/hardpack condiitions. I prefer to find a really rough pavement road and go uphill. In a place that tends to low wind.
I've done some downhill testing too, with my rigid vs. dual suspension gravel bikes. That was pretty enlightening. I made more ground downhill with suspension in 12-15 min of riding than I lost in 45 minutes of climbing. That does not apply on the road, but offroad suspension kills in the races I do.
The 1 second per 250 ft climbed is a rule of thumb I use. That is just based on math. The one race I did on my dual-sus all-road bike was very enlightening to me. First off, I used a 26x42 low so I could spin 70-80 rpm at 190 watts during the first 30 super-steep minutes of the first climb. My bike weighs around 30 pounds, so in theory, I'm giving up 2 1/2 minutes on that climb. However, I suspect the suspension actually helps me climb faster because it smooths everything out when there are washboards and bumps. Then, when I hit the flats, I can ride in the aerobars through almost anything. One part of the race was very telling where I kept chasing this skinny little teenager up a series of rolling hills. I got closer on the flats and then further away uphill. Then on a long, flat section around a lake with lots of washboards I was able to catch him riding aero. As soon as we hit the next hill he left me behind.
On the downhills though, I simply blasted past people like they were standing still. Riding dual-sus with 2.0 and 2.2 tires was just no contest to the dudes on 40mm tires with no suspension.
My point being, I am fairly sure that I am faster on a 30-pound bike with aerobars and dual sus than I would be on a rigid 20 pound bike with 40mm tires. If I had worried about the weight, I would never have done the experiment to try dual suspension. Plus, the difference in how I feel (not taking the pounding) with suspension is huge.
So I encourage people to figure out what works to make them fast, stop relying on 'sensations' or feelings and put numbers to it.
For some races and rides, my 30-pound creation would be an ungainly beast, but for what I do, it rolls.
Mark W. Ingalls
62 posts
#30Jan 28, 2021, 4:57 PM
Back in the day I got so I could sink a 16d with three or four blows of my 22oz framer (two to start and one or two to send). But I used a 12oz hammer for picture framing.

Riding a century on a mtn bike would be tiring. So would riding technical single track on a drop bar bike.
So weight, yeah, and position and gears and steering... The only ‘myth’ is that one hammer can drive all nails the same.
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Mark W. Ingalls
62 posts
#31Jan 28, 2021, 5:09 PM
@ccand51997— Would you please post a photo of you dual sus aero bike?
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stu
646 posts
#32Jan 28, 2021, 5:22 PM
Mark wrote:@ccand51997— Would you please post a photo of you dual sus aero bike?

Only if you post a photo of your 22 oz framer. 🙂
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Mark W. Ingalls
62 posts
#33Jan 28, 2021, 5:26 PM
That was then... This is now...

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Jumbo
123 posts
#34Jan 28, 2021, 5:48 PM
Mark wrote:That was then... This is now...

Fingers crossed for this thread to turn into a debate about e-hammers.
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ccand51997
265 posts
#35Jan 28, 2021, 6:40 PM
Mark wrote:@ccand51997— Would you please post a photo of you dual sus aero bike?

My first iteration was more cobbled together, but this one I just swapped the bars, added the seatpost and swapped the front wheel 29er for a 27.5. Obviously there is a dropped stem, I love the Redshift dual-position seatpost. Once I got the aerobars where I want them, I barely use the drops anymore. Next up is Di2 (I have most everything but the wires and junction boxes) for shifting from the aerobars and some Surly Truck Stop riser bars to keep my aero but bring everything else up.
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Mark W. Ingalls
62 posts
#36Jan 28, 2021, 7:03 PM
Seat post on a dual sus... SHOCKER! 😳
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Volsung
878 posts
#37Jan 29, 2021, 10:34 AM
https://www.bicyclerollingresistance.com/cx-gravel-reviews/rene-herse-steilacoom-tc?fbclid=IwAR0IdcxwGUseiQ5mGkQO11gCzq_tt61RRrbqoyrFCeACuQ5Tj7wRBP3H3Yc

Take this with yet another grain of salt, because Jan made the astute observation that the curvature of the testing drum does not match the curvature of the Earth.
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ljsmith
762 posts
#38Jan 29, 2021, 11:21 AM
Volsung wrote:
https://www.bicyclerollingresistance.com/cx-gravel-reviews/rene-herse-steilacoom-tc?fbclid=IwAR0IdcxwGUseiQ5mGkQO11gCzq_tt61RRrbqoyrFCeACuQ5Tj7wRBP3H3Yc

Take this with yet another grain of salt, because Jan made the astute observation that the curvature of the testing drum does not match the curvature of the Earth.

I'd say the RR looks pretty good when you consider how big those knobs are.
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stu
646 posts
#39Jan 29, 2021, 11:39 AM
Volsung wrote:
https://www.bicyclerollingresistance.com/cx-gravel-reviews/rene-herse-steilacoom-tc?fbclid=IwAR0IdcxwGUseiQ5mGkQO11gCzq_tt61RRrbqoyrFCeACuQ5Tj7wRBP3H3Yc

Take this with yet another grain of salt, because Jan made the astute observation that the curvature of the testing drum does not match the curvature of the Earth.

IMHO Jan's observation applies to absolute results because tire deformation will be different on a flat surface. However I think relative results between one tire and another won't be affected as much. Besides that Rene Herse tires aren't supposed to be optimized for flat surfaces.
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Angstrom
181 posts
#40Jan 29, 2021, 12:00 PM
This is interesting data on the effect of surface roughness on rolling resistance.

https://blog.silca.cc/part-4b-rolling-resistance-and-impedance
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