FTP on hills vs flat - why different?

Discuss light weight issues concerning road bikes & parts.
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Gearjunkie
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Joined: Tue Feb 19, 2008 5:17 am
Location: NZ

by Gearjunkie

Hi

I don't currently have a power meter but when I did, I noticed that when doing 20 minute FTP tests it was MUCH harder to sustain high power on the flat rather than climbing.

Then I read this the other day:

https://www.bikeradar.com/road/gear/art ... -it-48624/

Including:


"Moninger recommends finding a road grade of anywhere between 2 and 4 percent if possible, as this will engage more of your glutes and back muscles and result in the best possible power.
“I see differences of between five and 15 watts, depending on the person,” Moninger says. “It’s the same with a trainer, and it’s the same reason power on a time-trial bike is lower, even for the best TT riders in the world.”"


So that got me wondering, is that really the reason for the difference? Or is there another reason? Could it perhaps be due to lower cadence when climbing, with higher toque (for same actual power) being wrongly stated as a higher power output? Maybe power meters are (wrongly) calibrated to or just interprete a high torque (at lower cadence) for the same amount of work as greater power? In other words, could it be that power meters are overstating power at lower cadences?

Or maybe it's to do with dead spots in a pedal stroke - when climbing (particularly standing at low cadence) riders tend to mash rather than spin more smoothly, resulting in higher peak torque (and so causing overstated power?) at certain points in each revolution?

I don't know.

But would like to know.

Thoughts?

AJS914
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Joined: Tue Jan 28, 2014 6:52 pm

by AJS914

I don't know the answer but I wonder if there is a difference between fighting gravity (uphill) versus fighting wind resistance (flat). I would assume that riders will go faster on flat ground.

by Weenie


vanillaflyweight
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Joined: Thu Aug 10, 2017 5:54 am

by vanillaflyweight

Assuming a constant uphill grade it is much easier to have consistent power and wind is not as critical. At speed on the flat even small deviations in wind direction/speed will greatly affect your power. Possibly in a velodrome the power difference would be reduced??

TobinHatesYou
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Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

There's many factors involved. You have to be very disciplined on flat ground to maintain power. You also engage different muscle groups while climbing as your lack of momentum elongates your power phases. I don't think power meters are incorrectly measuring torque or cadence for the most part...that's a red herring.

Jere
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Joined: Sun Aug 07, 2011 5:35 am
Location: York Pa

by Jere

Hi

This may help with your questions
https://cyclingtips.com/2013/09/climbin ... -affected/
JB

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Gearjunkie
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Location: NZ

by Gearjunkie

Thanks, that's a very interesting read.

Rings true to my own experience.

petromyzon
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Joined: Mon Apr 05, 2010 4:14 pm

by petromyzon

The majority of power meter designs (particularly those that use magnets to report cadence) assume that the angular velocity of the cranks during one revolution is constant. This is why Q rings and Osymmetrics cause an artificial inflation of power measurement; the cranks turn at different rates depending on the position because the effective gear ratio is different.
However, if you are pedalling evenly throughout the rotation there is nothing about low vs. high cadence that needs calibration. The power is simply the product of torque and angular velocity.
In theory some systems with accelerometer-based cadence could provide higher resolution and therefore be less vulnerable to the errors from non-round rings. However, I think they suffer with other forms of error (i.e. vibration from road bumps). It's not something I've really seen discussed by power meter manufacturers as there is no accepted standard for PM accuracy and precision anyway so they don't really want to get in to the nitty gritty of what causes problems with measurement.

I think it is fairly widely accepted that differences in body position, muscle recruitment and inertial load have the largest contribution to power production. Certainly if you want to be good at climbing you should train on climbs and if you want to be fast on the flat you should train this skill as well. It's definitely not just due to measurement error. Specificity!

RocketRacing
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Joined: Thu May 10, 2018 2:43 am

by RocketRacing

I have increased my ftp significantly this winter (not due to weight loss) via an indoor direct driver trainer (the power stingy tacx neo 2). Makes me want to do my next run up the alps de zwift with my bike set at a fixed 8.5% incline. A kickr and kickr climb would be interesting also. Conpare ftp (powet) efforts on different angles.

Muscle recruitment factors in the different powers on flat vs hill. Rider to bb position changes also, so leverage changes. Aero vs weight explains why light is right for climbs, and aero is king for flats.

But it is what you train. Suddenly recruit the extra muscle/power without the cardio to match, and you are in trouble, and ftp could drop. As noted, i have trained on a static flat trainer for virtual climbs... but i am very curious to see my numbers setting the bike at an incline. I suspect my numbers will drop a bit.

While i think about it... on my last ~1 hr sustained climb i reduced saddle tenderness to zero by climbing out of saddle intermittantly, for the toughest inclines. My average ftp went up. It could be natural increases, but i also feel that out of saddle work allowed me to distribute the workload to more muscle groups (vs sitting the entire climb). My average heart rate went up about 10 points, but so did power when i stood.

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IrrelevantD
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by IrrelevantD

RocketRacing wrote:
Sat Mar 23, 2019 5:15 pm
While i think about it... on my last ~1 hr sustained climb i reduced saddle tenderness to zero by climbing out of saddle intermittantly, for the toughest inclines. My average ftp went up. It could be natural increases, but i also feel that out of saddle work allowed me to distribute the workload to more muscle groups (vs sitting the entire climb). My average heart rate went up about 10 points, but so did power when i stood.
That all makes sense. You're engaging more muscle groups when you're out of the saddle (upper body), which will increase your HR. Power will go up as you're putting more leverage into the pedals (higher torque). The trade off is because you're engaging more muscle groups, you won't be able to sustain it as long. It's all a matter of how fast you can recover from the out of saddle efforts and at what % of FTP. If you for example do 3min at 150% and are able to recover in 3min at 80%, you're averaging 15% more power than if you did the same 6min at 100%.

That cyclingtips article Jere posted is a pretty good read as well. Makes me think back to some discussions I've had with a friend of mine that's a sprinter. He asked me why I run 53/39 rings when 50T at 110rpm would get me well over 35mph (where we live is fairly flat). It's because I can't hold 110rpm. He can sprint out +1100W at 160rpm no problem, but my power starts to drop significantly at anything over about 100 and I don't think I could even spin above 120. I'm perfectly happy grinding out 80~90rpm on at 53T ring and don't start wishing I had lower than a 39 small ring until the road turns up above 10%, which is rare arorund here. I do all of my FTP tests on Elite smart rollers, so I honestly have no clue how my power would differ being able to get out of the saddle. We don't have any significant climbs out here longer than about 5min, so it'd be imposible to test without driving an hour or two.
* There is a 70% chance that what you have just read has a peppering of cynicism or sarcasm and generally should not be taken seriously.
I'll leave it up to you to figure out the other 30%. If you are in any way offended, that's on you.

Stitchking
Posts: 153
Joined: Fri May 25, 2018 7:30 am

by Stitchking

Just want to chuck it in here that the equation for power is literally torque x cadence. Your pm isn't measuring power, just torque.
Its why sprinters like cav are still fast. He's not that strong (relatively speaking) but he has the leg speed to smash out a super high rpm at a respectable torque, leading to a high power output

Sent from my SM-G935F using Tapatalk


TobinHatesYou
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Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

Semantics I guess. If you consider the PM to be just the strain gauges, then it is just measuring torque. If you consider the PM to be the strain gauges + AV sensor + other electronics, it is calculating power based of formulae.

Perhaps power meters should be called power calculators.

Stitchking
Posts: 153
Joined: Fri May 25, 2018 7:30 am

by Stitchking

I think my point is that the power equation at its simplest is not affected by low cadence-high torque vs. High cadence-high torque. I think we can all agree that most powermeters are power calculators.

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RocketRacing
Posts: 455
Joined: Thu May 10, 2018 2:43 am

by RocketRacing

Thanks, i had not read that article prior, and it makes sense from my experience. I strugle to make power on the flats vs the climbs... and of interest, that is on zwift with only virtual grade changes. The only difference was a reduction in resistance. I overcame it by shifting into a smaller gear than i felt was required and forcing the effort. Gradient, power, and cadence were the same.
IrrelevantD wrote:
Sat Mar 23, 2019 7:13 pm
RocketRacing wrote:
Sat Mar 23, 2019 5:15 pm
While i think about it... on my last ~1 hr sustained climb i reduced saddle tenderness to zero by climbing out of saddle intermittantly, for the toughest inclines. My average ftp went up. It could be natural increases, but i also feel that out of saddle work allowed me to distribute the workload to more muscle groups (vs sitting the entire climb). My average heart rate went up about 10 points, but so did power when i stood.
That all makes sense. You're engaging more muscle groups when you're out of the saddle (upper body), which will increase your HR. Power will go up as you're putting more leverage into the pedals (higher torque). The trade off is because you're engaging more muscle groups, you won't be able to sustain it as long. It's all a matter of how fast you can recover from the out of saddle efforts and at what % of FTP. If you for example do 3min at 150% and are able to recover in 3min at 80%, you're averaging 15% more power than if you did the same 6min at 100%.

That cyclingtips article Jere posted is a pretty good read as well. Makes me think back to some discussions I've had with a friend of mine that's a sprinter. He asked me why I run 53/39 rings when 50T at 110rpm would get me well over 35mph (where we live is fairly flat). It's because I can't hold 110rpm. He can sprint out +1100W at 160rpm no problem, but my power starts to drop significantly at anything over about 100 and I don't think I could even spin above 120. I'm perfectly happy grinding out 80~90rpm on at 53T ring and don't start wishing I had lower than a 39 small ring until the road turns up above 10%, which is rare arorund here. I do all of my FTP tests on Elite smart rollers, so I honestly have no clue how my power would differ being able to get out of the saddle. We don't have any significant climbs out here longer than about 5min, so it'd be imposible to test without driving an hour or two.
Last edited by RocketRacing on Mon Mar 25, 2019 12:45 am, edited 1 time in total.

TobinHatesYou
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Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

Most trainers don’t have large enough flywheels to feel like you’re properly pedaling on flat ground. The Neo definitely doesn’t with its virtual flywheel and even older KICKRs with 13lb flywheels don’t feel great. With such little kinetic energy being stored, everything basically feels a little bit like climbing when indoor training. The closest I’ve gotten to replicating outdoor riding is with the CycleOps Hammer’s 20lb flywheel.

by Weenie


bm0p700f
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by bm0p700f

My best ever power for 50minutes was on a flat windy airfield circuit. Long hills have me producing less. I don't ride long hills often though.

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