# Can speed on a trainer be used as substitute for power?



## Jetmugg (Sep 22, 2010)

I do some interval training on a Cyclops 2 fluid trainer. I have a Garmin 305 Edge computer with speed, cadence, and HR. I do not have or use a power meter.

I have been training with HR, but obviously, there are problems with HR as an indicator. Time lag is a big one. Also, I have found that at times, my HR can be high, but my perceived power output is lower (maybe also due to lag).

This brings me to my question - as long as I use the same trainer every time (I only have 1, so that isn't a problem), shouldn't I be able to use the indicated speed (taken from a rear wheel sensor) as a substitute for power?

I'm thinking that speed on the trainer might be a more effective measurement than HR for these trainer-based workouts. Speed will update much more quickly than HR, and I think it may be a better all-around measurement of how strong I am.

Thoughts?

SteveM.


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## rbart4506 (Aug 4, 2004)

Yup you can do that..

I did that a few years back with my KK Road Machine...KK has a power curve that relates speed to power...

The thing to remember is that tire pressure will affect the resistance and therefore speed....Tire slippage...But it's still a good way to go if you don't have a power meter...


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## spade2you (May 12, 2009)

For a while, I used hr, and cadence+gearing to figure out where I was. With tire pressure consistent, it'll get the job done.


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## rbart4506 (Aug 4, 2004)

spade2you said:


> For a while, I used hr, and cadence+gearing to figure out where I was. With tire pressure consistent, it'll get the job done.


It's funny that you mention cadence. Even now, when I am on the trainer and using a power meter, I watch my cadence when doing longer intervals.

I know that when I am in a certain gear I need to maintain a cadence of 'X' to achieve my power goal of 'Y'


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## spade2you (May 12, 2009)

rbart4506 said:


> It's funny that you mention cadence. Even now, when I am on the trainer and using a power meter, I watch my cadence when doing longer intervals.
> 
> I know that when I am in a certain gear I need to maintain a cadence of 'X' to achieve my power goal of 'Y'


I still like doing it this way. Theoretically, I could do without the power meter on the trainer and rollers and just go by cadence and gearing on the trainer/rollers if I wanted. I mostly picked up the power meter to better pace myself in time trials, which paid off nicely. Fortunately, the power meter provides you info when you're on the road. 

To the OP, I'd still recommend getting a power meter when you can. Sooner is better. I'm not complaining about my fitness, but I kinda wish I knew what kind of shape I was in the years before I had it.


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## Jetmugg (Sep 22, 2010)

Thanks, guys. I couldn't figure any reason why speed or cadence/gearing on a trainer wouldn't work for power comparisons. Of course, that technique is only usable on the trainer, and not on the road during a time trial. Even as a back-of-the pack Cat4, I still like to have some data about whether or not I'm improving.

I'm putting a power meter at the top of my wish list. I'm thinking that a wireless power tap is the direction I'll eventually go. They seem to be a good compromise between cost and versatility, and are pretty popular. 

Now I have a new topic to research. I currently have a Garmin 305 head unit, but I'm 99.5% sure that it cannot accommodate power input. That means I'll be needing a new head unit also. I like the Garmin stuff, so I need to understand the compatibility of the Garmin units with powertap hubs.

As always, any advice is appreciated.

Steve.


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## rbart4506 (Aug 4, 2004)

Garmin 500 or 800...

Go 500 unless you want maps...Then it's the 800...


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## spade2you (May 12, 2009)

I use a 500, which seems to be standard on most bikes these days. I have GPS on my phone, so that's not much of an issue. The only time I've had a small need for GPS on my computer was at a race in AR where I really didn't know the course very well. Otherwise, super happy with my 500.


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## PissedOffCil (Jan 3, 2008)

There's actually software for this exact purpose : http://www.zonefivesoftware.com/sporttracks/plugins/?p=trainer-power-track

Some trainers behave better than others with the speed to power curve. Long rides are especially a problem since the trainer warms up and then the curve doesn't match anymore. The KK trainers do a good job at being steady so you are left with finding the proper tire & pressure combo to match the curve.

Anyways, once you got that you can use the excel spreadsheet I did and plug the numbers to get your power zones from speed. Check it out here.


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## PDex (Mar 23, 2004)

+1 on this. The SportTracks software and the available plugins are a good addition. The trainer plug in has numerous trainers and rollers in the database. My Junior-racing son is still too young (and his old man is too cheap) for a power-meter, but this is a good compromise during the winter training periods.









PissedOffCil said:


> There's actually software for this exact purpose : http://www.zonefivesoftware.com/sporttracks/plugins/?p=trainer-power-track
> 
> Some trainers behave better than others with the speed to power curve. Long rides are especially a problem since the trainer warms up and then the curve doesn't match anymore. The KK trainers do a good job at being steady so you are left with finding the proper tire & pressure combo to match the curve.
> 
> Anyways, once you got that you can use the excel spreadsheet I did and plug the numbers to get your power zones from speed. Check it out here.


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## Jetmugg (Sep 22, 2010)

This looks like an excellent application of computing power. I'm going TT'ing tomorrow night, but I'm already looking forward to my next trainer workout.

Thanks again,

Steve.


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## claphands (Apr 24, 2009)

I use this. 
http://thebikegeek.blogspot.com/2009/12/while-we-wait-for-better-and-better.html
Quick,easy and in the ball park.

This is not my work. I'm just a user of somebody elses hard work.


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## Jetmugg (Sep 22, 2010)

Good stuff here. I think I'm going to re-do the Carmichel LT test using speed instead of HR on my Fluid 2 after a 20 minute warmup.


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## Alex_Simmons/RST (Jan 12, 2008)

I think the main thing is repeatability of the resistance on the trainer and how to know if resistance has varied. It only takes a small partial turn of the knob on back of a Computrainer for instance to throw the power readings out by quite a bit. In fact the reading can vary 20-30W simply due to tyre warming up, which is why you do roll down calibrations after a good warm up.


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## Jetmugg (Sep 22, 2010)

Good point Alex. I am "hopeful" that a fluid trainer like my Cycleops Fluid 2, which doesn't have any kind of adjustable resistance, will provide a usable level of consistency, especially if subjected to a pre-set warmup routine. I try to keep the tire pressure and roller-to-tire engagement at the same level each time. I realize that it won't be as accurate as a true strain-based power meter, but I do think it will be a better metric than HR, which is what I have been using. In the meantime, I'll be saving my pennies for a Powertap setup.

For example, when using HR as my indicator, and trying to do a 3-minute SEPI, I think that I am actually doing more of a "Peak and Fade" interval, as I push harder during the first minute, trying to get my HR into the prescribed range. Then during the next 2 minutes, I end up backing off the speed/power, in order to maintain my HR in the desired range. 

Can you share any more information about roll-down calibrations?

Steve.


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## Alex_Simmons/RST (Jan 12, 2008)

Jetmugg said:


> For example, when using HR as my indicator, and trying to do a 3-minute SEPI, I think that I am actually doing more of a "Peak and Fade" interval, as I push harder during the first minute, trying to get my HR into the prescribed range. Then during the next 2 minutes, I end up backing off the speed/power, in order to maintain my HR in the desired range.


If the intervals are short & hard, you might be better off using wheel speed as your guide. PE and HR have a lag that makes them less useful for hard intervals of less than 5-minutes.



Jetmugg said:


> Can you share any more information about roll-down calibrations?


This is computrainer specific. 

I'm not sure you can measure the roll down accurately enough on a regular trainer to provide similar adjustment factor for the speed - power relationship for any given trainer. 

The CT does it electronically and can measure roll down time from speed A to speed B in hundredths of a second.


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## maxxevv (Jan 18, 2009)

If you're using Android smartphones, there are a few possibilities when it comes to getting a powermeter without too much hassle. 

The Sony Ericsson Xperia X8, X10, Arc and soon to be released Xperia Active all have ANT+ protocol. There's a free App on the Android market called "My Tracks" that allows the phone to connect with ANT+ compatible devices such as the Quarg powermeters. Even heartrate straps that are either ANT+ or Bluetooth compatible. 

It has all the functions of the Garmin 800 and more, with full Google Maps and automatic way points, uploading of data , etc, etc ... 

Best part, you have a phone already and it serves double duty. Of course, the battery part may be an issue if you're on extended half day rides ... 

Something well worth exploring if you're already using such a device.


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