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Kurt Kinetic Road Machine Lies!

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Kurt Kinetic Road Machine Lies!

Old 10-11-07, 11:04 AM
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hjeand
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Kurt Kinetic Road Machine Lies!

I usually average around 19 - 20 mph outside on my solo, flat 22 mph loop. This includes slowdowns/stops for traffic crossings. At the gym I usually average 21 mph on the exercise bike. I tried my new KK Road Machine last night, but my wireless computer wouldn't register when I put the sensor on the back wheel so I put the sensor on the floor and made sure it was registering. I couldn't monitor my pace during the ride, but when the egg timer popped I picked up the computer to see that my average was only 17.9 mph. No way I only averaged 17.9! Did I do something wrong, or does the KK need calibrated?
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Old 10-11-07, 11:08 AM
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Go watts or check the other reasons...

1. It's a heavy bike
2. Your position was not very aero
3. Upgrade your tires to reduce rolling resistance
4. The fan created a tailwind
5. A lump under the carpet created a hilly grade
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Old 10-11-07, 11:10 AM
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resistance on a trainer is going to be different from that of a road ride or exercise bike at the gym.
don't try comparing your speed from the road with that of a trainer session. as long as you don't alter the trainer at all, you could compare your rides on it to each other.
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Old 10-11-07, 11:10 AM
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I can always count on egg timers for precise time measurements.
 
Old 10-11-07, 11:13 AM
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"Kurt Kinetic Road Machine Lies!"

A brilliant title to your post.
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Old 10-11-07, 11:14 AM
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Originally Posted by DocRay
I can always count on egg timers for precise time measurements.
Nothing sucks more than burnt cake. I use my egg timers for all my precise time measurement needs. All the pros are doing it!
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Old 10-11-07, 11:20 AM
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On a Cycleops Fluid 2, the same watts result in slower MPH than on the road. My bet is that is also true on a Kurt Kinetic.


What matters is the workload and the time. MPH on a trainer is irrelevant.

So measure your effort by HR, or a power meter, not MPH.

The only way MPH would matter is if you have a power profile for the KK (which I believe is available somewhere) and you're using MPH to extrapolate power from the profile.
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Old 10-11-07, 11:21 AM
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Originally Posted by ratebeer
Go watts or check the other reasons...

1. It's a heavy bike
2. Your position was not very aero
3. Upgrade your tires to reduce rolling resistance
4. The fan created a tailwind
5. A lump under the carpet created a hilly grade
those dam lumps...lol
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Old 10-11-07, 11:22 AM
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KK's are calibrated for power, not speed.

https://www.kurtkinetic.com/documents..._Curves419.pdf
 
Old 10-11-07, 11:29 AM
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^ The assumptions they make for the outdoor power are rather questionable. For example it puts the outdoor power at 419 watts for 25mph.

I can tt at 25 mph, and my FTP is not close to 419.

The power curve is helpful though to estimate your watts by mph on the trainer.
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Old 10-11-07, 12:19 PM
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I don't think their chart is meant to correlate to TT wattage.

To get a realistic comparison to normal outdoor riding, you'd have to tighten the resistance unit just right/compare it to a power meter so that your speed matched their related wattage output on KK's chart. You can get varied results depending on how much you tighten the resistance unit on the Road Machine.

I have the Road Machine Pro with the Rock & Roll frame. It provides a very good simulation of outdoor riding.
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Old 10-11-07, 12:56 PM
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Originally Posted by ratebeer
Go watts or check the other reasons...

1. It's a heavy bike
2. Your position was not very aero
3. Upgrade your tires to reduce rolling resistance
4. The fan created a tailwind
5. A lump under the carpet created a hilly grade
Does the incline of the bike on a trainer affect the wattage required to spin. For example if I use a riser block is it harder then if I didn't? Because I did use a riser.... If so, how? This doesn't make physical sense to me.
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Old 10-11-07, 12:59 PM
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Originally Posted by hjeand
Does the incline of the bike on a trainer affect the wattage required to spin. For example if I use a riser block is it harder then if I didn't? Because I did use a riser.... If so, how? This doesn't make physical sense to me.
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Old 10-11-07, 01:12 PM
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I think I figured it out. My weight. The KK power curve is calibrated for somebody who probably weighs 180 lbs or so. Since I only weight 130 I can go faster outside using the same watts as somebody who weighs 50 lbs more. According to the KK website (https://www.kurtkinetic.com/documents..._Curves419.pdf) By averaging 17.9 mph, I averaged 200 watts during that hour. I then used this (https://www.kreuzotter.de/english/espeed.htm) and verified that if I went 200 watts outside I would go 19.2 mph which is more in line with what I normally do. I'll have to multiply the mph given by the KK by a constant to correctly translate it to what mph would be for me outside then if I want to compare the two (I don't have $1000 to buy a Powertap).
Anybody refute my logic?
Thanks for your help, guys!

PS: the only reason I asked about the risers is I thought I read somewhere that if you stack two risers on top of each other you can simulate climbing. I didn't understand if that made it harder effort or if it simulated it by having you look up.
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Old 10-11-07, 01:15 PM
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Your weight has nothing to do with the computation. And as far as I know the riser only changes what muscles you are using.

Read here: their computer/power curve is only speed sensitive

https://www.kurtkinetic.com/computer_...29995eb70c6517

Last edited by HDWound; 10-11-07 at 01:24 PM.
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Old 10-11-07, 01:35 PM
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If you can't afford a Powermeter, get a cheap heartrate monitor and train based on heart rate. A one hour ride at an average HR of 150 inside and outside would likely have similiar power outputs (but probably quite different speeds).

Better yet (or in addition), buy some Spinervals DVD's for training on your trainer and ignore the speed. I would go crazy on my KK trainer without Spinervals DVD's.
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Old 10-11-07, 01:37 PM
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Originally Posted by ratebeer
I apologize. My sense of humor is not easily communicated by this limiting medium.
Now it all makes sense, that's what those drop handlebar threads were, humor.
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Old 10-11-07, 01:44 PM
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Originally Posted by HDWound
Your weight has nothing to do with the computation. And as far as I know the riser only changes what muscles you are using.

Read here: their computer/power curve is only speed sensitive

https://www.kurtkinetic.com/computer_...29995eb70c6517
Weight has everything to do with it. If you and your riding partner are both going the same constant speed under the same conditions with the same bike, but you weight 50 lbs less then him, you're telling me you're both putting out the same wattage? No way! Since power and speed vary with each person and riding style (wind resistance), KK had to guess at the power curve they tried to mimic. My power vs speed curve in a real environment (i.e. outdoors) will be substantially smaller than the average person. It takes me less power to achieve greater speeds.
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Old 10-11-07, 01:52 PM
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Originally Posted by merlinextraligh
Now it all makes sense, that's what those drop handlebar threads were, humor.
How about that quitting is tantamount to liberalism?
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Old 10-11-07, 01:59 PM
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Originally Posted by hjeand
Weight has everything to do with it. If you and your riding partner are both going the same constant speed under the same conditions with the same bike, but you weight 50 lbs less then him, you're telling me you're both putting out the same wattage? No way! Since power and speed vary with each person and riding style (wind resistance), KK had to guess at the power curve they tried to mimic. My power vs speed curve in a real environment (i.e. outdoors) will be substantially smaller than the average person. It takes me less power to achieve greater speeds.
Your weight only effects acceleration and climbs. Your smaller profile may help with being more aero on flats and the need to produce slightly less power then a bigger person next to you. Other then rolling resistance on the flats your weight isn't much of a deal. I think you would greatly benefit from a physics class before posting more threads though.
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Old 10-11-07, 02:22 PM
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Originally Posted by crydee
Your weight only effects acceleration and climbs. Your smaller profile may help with being more aero on flats and the need to produce slightly less power then a bigger person next to you. Other then rolling resistance on the flats your weight isn't much of a deal. I think you would greatly benefit from a physics class before posting more threads though.
You're talking to a physics major, buddy!
If you want to get technical about it, here's the formula:

P = g * m * VG(K1+S) + K2 * VA^3

Where P is in watts, g is Earth's gravity, Vg is ground speed (m/s), m is bike/rider mass in kg, s is the grade (m/m), and Va is the rider's speed through the air (m/s). K1 is a lumped constant for all frictional losses (tires, bearings, chain), and is generally reported with a value of 0.0053. K2 is a lumped constant for aerodynamic drag and is generally reported with a value of 0.185 kg/m [5].
Note that the power required to overcome friction and gravity is proportional only to rider weight and ground speed. The power required to overcome wind drag is proportional to the cube of the air speed.

So you're looking at about a 10 watt difference at 20mph for a two people 50 lbs apart!
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Old 10-11-07, 02:34 PM
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Um no read the link again. You're on a trainer, not riding outside, your weight has nothing to do with Kurt Kinetic's power curve.

Here's yet another link -- https://www.cyclingforums.com/t294690.html read posts 5-11

Last edited by HDWound; 10-11-07 at 02:45 PM.
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Old 10-11-07, 03:29 PM
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From the Kurt Kinetic website:

"With Tom’s help, we have been able to create an “average” rider assumed to be 165 lbs, riding a 23 lb bike with 170mm crank arms up a 1% grade, at sea level with no wind on rough asphalt... etc. The “outdoor ride” that we reference in the PDF is based on this “average” rider. Tom was then able to calculate how much power it would take for our average rider to maintain a given speed."

The Kurt Kinetic "steals" some of your power to go up the 1% grade. Therefore, for comparable power that you put out on a flat course, you will read as going slower on the Kurt Kinetic, because you are riding up a virtual grade. Weight difference will have a smaller impact.

Last edited by AkAk2000; 10-11-07 at 03:30 PM. Reason: Formatting
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Old 10-11-07, 03:38 PM
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By the way, checked this with Kreuzotter. At 135 lbs, and making some other assumptions (elevation, riding position, etc.), at 225 watts at 0% grade, you'd be going 20 mph. Increase the grade to 1%, and your speed drops down to 17.9 mph.
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Old 10-11-07, 03:47 PM
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Originally Posted by DocRay
I can always count on egg timers for precise time measurements.
I use this -

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