Kurt Kinetic Power Curve

Discussion:

ekn ewers

2007-02-14 14:39:12 UTC

Hi all,

I produced one of these a few years back (when I still had a PM), but I can
not seem to locate it.

I am searching for a Speed vs. Power curve for the Kurt Kinetic road machine
trainer. I need this to train with estimated power while I am without the
SRM.

Thanks to anyone that can help.

Ken

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Chris Clarke

2007-02-14 16:19:43 UTC

Permalink

It's on the Kurt Kinetic webpage:

http://www.kurtkinetic.com/pdfs/Power_Curves419.pdf

Who would have guessed?

Post by ekn ewers
Hi all,
I produced one of these a few years back (when I still had a PM), but I can
not seem to locate it.
I am searching for a Speed vs. Power curve for the Kurt Kinetic road machine
trainer. I need this to train with estimated power while I am without the
SRM.
Thanks to anyone that can help.
Ken

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ekn ewers

2007-02-14 17:10:24 UTC

Permalink

yeah, I did a little search and found a Speedometer that does the
computation for you and displays power for 50 bucks...not a bad toy to have
for those that can not afford power. I assumed that they would not be so
kind to give up the formula to DIY (to boost sales of the computer). What a
great company!

They also give the formula (somewhere). Someone sent it to me off list.

Thanks

Post by Chris Clarke
http://www.kurtkinetic.com/pdfs/Power_Curves419.pdf
Who would have guessed?

Post by ekn ewers
Hi all,
I produced one of these a few years back (when I still had a PM), but I

can

Post by ekn ewers
not seem to locate it.
I am searching for a Speed vs. Power curve for the Kurt Kinetic road

machine

Post by ekn ewers
trainer. I need this to train with estimated power while I am without

the

Post by ekn ewers
SRM.
Thanks to anyone that can help.
Ken

andy kruse

2007-02-14 17:35:45 UTC

Permalink

I heard from a secondhand source that Kurt provides power curves for
several popular trainers. I also helped a friend (who has a really old
trainer for which a power curve is not provided) by setting up my PT
on his trainer, riding several different speeds/effort levels and he
was able to calibrate the computer accordingly.

Incidentally (as I'm sure most of you are aware of), with an actual
power meter, it's pretty easy to see how bad the power curves are on
some cheap trainers. My friends' trainer jumped something like 125w in
between 34 and 36 kph... (less than 1 mph speed difference).

Post by ekn ewers
yeah, I did a little search and found a Speedometer that does the
computation for you and displays power for 50 bucks...not a bad toy to have
for those that can not afford power. I assumed that they would not be so
kind to give up the formula to DIY (to boost sales of the computer). What a
great company!
They also give the formula (somewhere). Someone sent it to me off list.
Thanks

Post by Chris Clarke
http://www.kurtkinetic.com/pdfs/Power_Curves419.pdf
Who would have guessed?

Post by ekn ewers
Hi all,
I produced one of these a few years back (when I still had a PM), but I

can

Post by ekn ewers
not seem to locate it.
I am searching for a Speed vs. Power curve for the Kurt Kinetic road

machine

Post by ekn ewers
trainer. I need this to train with estimated power while I am without

the

Post by ekn ewers
SRM.
Thanks to anyone that can help.
Ken

ekn ewers

2007-02-14 17:44:14 UTC

Permalink

Yes and the curve is very sensitive to tire pressure, pressure of roller
against tire, etc, etc. But if you have nothing else, it gives you a place
to start.

I constructed my own curves in the past, and they were pretty similar to the
data presented on the website. As long as you are ok with a certain amount
of error.....I dont plan to do any serious analysis, its basically trivial.

Some trainers are much better than others in terms of consistent power
curve/real world road riding curve. Kurt has worked very diligently to this
end.

Post by andy kruse
I heard from a secondhand source that Kurt provides power curves for
several popular trainers. I also helped a friend (who has a really old
trainer for which a power curve is not provided) by setting up my PT
on his trainer, riding several different speeds/effort levels and he
was able to calibrate the computer accordingly.
Incidentally (as I'm sure most of you are aware of), with an actual
power meter, it's pretty easy to see how bad the power curves are on
some cheap trainers. My friends' trainer jumped something like 125w in
between 34 and 36 kph... (less than 1 mph speed difference).

Post by ekn ewers
yeah, I did a little search and found a Speedometer that does the
computation for you and displays power for 50 bucks...not a bad toy to

have

Post by ekn ewers
for those that can not afford power. I assumed that they would not be

Post by ekn ewers
kind to give up the formula to DIY (to boost sales of the

computer). What a

Post by ekn ewers
great company!
They also give the formula (somewhere). Someone sent it to me off list.
Thanks

Post by Chris Clarke
http://www.kurtkinetic.com/pdfs/Power_Curves419.pdf
Who would have guessed?

Post by ekn ewers
Hi all,
I produced one of these a few years back (when I still had a PM),

but I

Post by ekn ewers

Post by Chris Clarke
can

Post by ekn ewers
not seem to locate it.
I am searching for a Speed vs. Power curve for the Kurt Kinetic road

machine

Post by ekn ewers
trainer. I need this to train with estimated power while I am

without

Post by ekn ewers

Post by Chris Clarke
the

Post by ekn ewers
SRM.
Thanks to anyone that can help.
Ken

Ergoman

2007-02-15 00:30:33 UTC

Permalink

In my limited experience the Kurt Kinetic power curve is accurate only
so long as the resistance unit is operating at or near room
temperature. Once you've ridden at any pace for more than a few
minutes the unit warms up, fluid viscosity decreases, and then power
calculated by speed or by the Kurt Kinetic meter which uses speed will
be high by something like 8 to 10%. Has anyone else observed this
phenomena?

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Jordan Whiley

2007-02-15 12:47:53 UTC

Permalink

I've noticed I can pedal at a slightly faster speed given the same
power output (measured via PT) once the unit is warmed up, but not on
the order of 8-10%. It's been more like 2-3% (about 0.4-0.6 mph faster
@ 22 mph).

Post by Ergoman
In my limited experience the Kurt Kinetic power curve is accurate only
so long as the resistance unit is operating at or near room
temperature. Once you've ridden at any pace for more than a few
minutes the unit warms up, fluid viscosity decreases, and then power
calculated by speed or by the Kurt Kinetic meter which uses speed will
be high by something like 8 to 10%. Has anyone else observed this
phenomena?

Ergoman

2007-02-15 13:34:44 UTC

Permalink

2-3% speed is equivalent (or close to equivalent) to 8-10% power at
the speeds and power most of us train. Has anyone ever seen any
documentation on the Kurt Kinetic that suggests how and what operating
temperatures the power curve was determined?

Post by Jordan Whiley
I've noticed I can pedal at a slightly faster speed given the same
power output (measured via PT) once the unit is warmed up, but not on
the order of 8-10%. It's been more like 2-3% (about 0.4-0.6 mph faster
@ 22 mph).

andy kruse

2007-02-15 14:08:49 UTC

Permalink

No idea, but I would postulate that if they're calibrating the
computer's power curve to a "cold" trainer, it isn't much use, since
warming those trainers up takes only 10-15 minutes of riding most of
the time.

I'm no track sprinter, so I can't say for sure.... but I'd guess that
most of us ride our trainers for more than 15 minutes at a clip. :)

This does, however, reinforce the notion that the Kurt power computer
isn't a substitute for a "real" power meter - it's just a gadget that
will show "ballpark" power outputs and probably shouldn't really be
used for serious power training, or compared with output readings from
a "real" PM. (But it still should be useful referencing against
itself).

Post by Ergoman
2-3% speed is equivalent (or close to equivalent) to 8-10% power at
the speeds and power most of us train. Has anyone ever seen any
documentation on the Kurt Kinetic that suggests how and what operating
temperatures the power curve was determined?

a***@gmail.com

2007-02-15 18:37:37 UTC

Permalink

Post by andy kruse
No idea, but I would postulate that if they're calibrating the
computer's power curve to a "cold" trainer, it isn't much use, since
warming those trainers up takes only 10-15 minutes of riding most of
the time.

I think they're using a "hot" trainer for the curves. I have the
Performance trainer they tested, and I compared their curve to what I
saw using a PT. Their curve is WAY too high (~20%) when the trainer
is cold, but is within about 2% once it's warm. I've seen power
curves posted for the KK trainer on the cyclingforums power board, and
again the KK equation matches up better with the hot trainer than the
cold.

It's great of KK to provide their equations to the public. I turned
them into a web utility, if anyone is interested. It generates speed/
power charts to use while on the trainer, and if you record your speed
with a Polar or iBike, it will modify the ride file to add in the
missing power data. It's at http://curveship.dyndns.org/
trainerpower/ .
-- Adam

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Dan Connelly

2007-02-15 17:59:15 UTC

Permalink

http://www.kurtkinetic.com/powercurve.php

Kinetic Road Machine:
P = (5.244820) * S + (0.01968) * S3

S: mph
P: watts

simplify: P = 5.2 S + 0.02 S3
dP / P = (5.2 + 0.06 S2) / (5.2 + 0.02 S2) (dS/S)

= (1 + 0.012 S2) / (1 + 0.004 S2) (dS/S)

So if you're riding 20 mph, (dP/P)/(dS/S) = 2.23

In other words, a 2-3% change in speed = a 4.5% to 6.7% change in
power.

Dan

Robert Chung

2007-02-15 18:30:09 UTC

Permalink

Post by Dan Connelly
http://www.kurtkinetic.com/powercurve.php
P = (5.244820) * S + (0.01968) * S3

Notice the inconsistency in coeffs with this:
http://www.kurtkinetic.com/calibration_chart.php

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