# Do Power meters have torque Limits?



## A.Z.KOETSIER (23 Oct 2015)

So as many of us know a power meter actually measures torque and then calculates power using a cadence sensor.

I am confused as to why so many power meters have a *wattage limits*, surely this means there is either a torque or cadence limit? I have seen cadence limits specified from a minimum of 30rpm to a maximum of 200rpm

Does this mean it can measure up to 2000w at 30rpm all the way to 200rpm?

This would mean a Power meter could read up to *atmospheric quite God like* maximum torque of 637Nm, if one would want to produce 2000w at 30rpm! & _Only_ 95.49Nm would be needed to produce 2000w at 200rpm.

*Why does any of this matter?*

Well lets say there was a torque limit of say '150Nm' this would mean only riders able to spin their cranks up to 127rpm while maintaining this max force would hit 2000w.

In my case I would never hit the wattage limit as I produce max wattage between 90-115rpm range. Even if i was producing 2000w the '150Nm' power meter would never register more than 1810w @ 115rpm

Am I missing something simple here? Are there Torque limits, are these variable based on rpm? Because if not a power meter that can read up to 637Nm (deduced from limits above) and 200rpm it would read up to 13340w !


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## Profpointy (23 Oct 2015)

presumably it's in case some buffoon uses them for, say, a motorcycle, or to measure the power of ab electric deill, they can't then moan to the maker


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## A.Z.KOETSIER (26 Oct 2015)

Would appreciate any comments & thoughts cyclechat guys & girls....?

While we on the topic do WATTBIKES have resistance limits (torque limits) 

I noticed that they have cadence vs wattage tables based on which setting you use.

Does this mean the only way to achieve a FTP of 300w, you would have to spin over 100rpm on a wattbike *Trainer*?

Or to achieve a max 5sec wattage over 1045w on a wattbike *PRO* you would need to spin over 130rpm?

Seem a bit strange that. What about riders that produce power lower down the rpm range? would they have to change their riding style just to achieve the power goals?


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## Citius (26 Oct 2015)

I'm not really sure what the issue is. You will only ever generate maximum force (or torque) at zero or very low RPM. Nobody is going to break a power meter whilst underway unless they are able to generate super-natural levels of torque and/or cadence.

The fact that you do not hear of many power meters or wattbikes being broken in this way suggests how serious the problem is.


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## A.Z.KOETSIER (26 Oct 2015)

Im not concerned over breaking power meters with torque.

My curiosity came about when trying a wattbike out at an expo. Me and some friends tried to push some big wattage seeing who the alpha male and ruler of the universe was! 

I got on with a pair of sandals (it was summer in south africa) and prepared to go super saiyan. The Wattbike guy put the resistance to maximum and I went for it.

To my surprise it felt as if i was pedaling with the chain dropped off (ok not that bad, but close). The wattage was quite low.

My friend then got on but stayed seated and pushed the same numbers at the same rpm.

Its important to note he weighs 30kg less than me, and on the road I out sprint him. But we had the same power ?

so is the only way to achieve big wattage on a wattbike by having higher rpm? is this the same for some power meters?


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## Citius (26 Oct 2015)

A.Z.KOETSIER said:


> so is the only way to achieve big wattage on a wattbike by having higher rpm? is this the same for some power meters?



A Wattbike _is_ a powermeter. High wattage is achieved through high pedal forces and/or high cadences, regardless of what you are riding and how the power is being recorded.


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## A.Z.KOETSIER (26 Oct 2015)

Ok cool. so if i understand correctly.

The wattbike trainer has a max resistance of 300w at 100rpm (according to the table shown before,supplied by wattibike)

100rpm is above a cadence I can hold for an hour (FTP) 

Would I be able to get produce a FTP higher than 300w below 100rpm on a Wattbike Trainer?


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## Citius (26 Oct 2015)

I think you are confusing calibration settings with power output/measurement. The Wattbike can obviously measure power outputs greater than 300w. It wouldn't be much use as a training aid if it didn't.


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## A.Z.KOETSIER (26 Oct 2015)

I am aware you can measure over 300w on a wattbike. Please refer to the tables I have attached previously. It states that on *Level 10* the highest setting , A rider will produce 300w at 100rpm.

My question, which I think you are misunderstanding , ' Would I be able to produce a FTP higher than 300w* BELOW* 100rpm on a Wattbike Trainer? '

Or would I have to spin higher than 100rpm, and thus having to change my riding style to achieve the power goal?

On the road I am able to produce over 300w below 90rpm as there is enough opportunity for resistance (gears, gradient)


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## zigzag (22 Nov 2015)

there is a wattbike pro, which provides much more resistance (i've only come across the pro version in several different venues and gyms). i was able to max over 1800w at level 7 and 120rpms. you can certainly achieve 300w below 100rpm on wattbike pro.


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## A.Z.KOETSIER (23 Nov 2015)

zigzag said:


> there is a wattbike pro, which provides much more resistance (i've only come across the pro version in several different venues and gyms). i was able to max over 1800w at level 7 and 120rpms. you can certainly achieve 300w below 100rpm on wattbike pro.



Yes, I have attached the wattbike Pro resistance tables in a earlier post. 

Interesting that you mention 1800w @ 120rpm, the tables show 120rpm @ level 7 = 695w. I assume the wattbike must add instantaneous resistance as the drive train builds momentum?

This wont help for FTP tests thou.


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