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If you haven't tested your FTP - ouside
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What good are FTP numbers gleaned from an indoor trainer.......to someone who hasn't tested, outside?

First, how would one discern accuracy?
Second, what good would an FTP # derived at from an indoor trainer be to someone who didn't train/race (outside) with a PM?

If you train (indoors and out) with power, what are some reasons for power discrepancies (between indoors and out)? If there's a discrepancy between your indoor and outdoor FTP, which is higher? Why?
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Re: If you haven't tested your FTP - ouside [nc452010] [ In reply to ]
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nc452010 wrote:
What good are FTP numbers gleaned from an indoor trainer.......to someone who hasn't tested, outside?

First, how would one discern accuracy?


Some people ride better indoors than they do outdoors. Some people ride better outdoors than they do indoors. Some people ride about the same.

Further, some people lose power when transitioning from road bike to TT bike. The amount of power loss varies on how much you ride a TT bike. So if you tested on a road bike indoors but riding a TT bike outdoors, that's another thing to consider.

Accuracy would depend on the device you're using to measure. I have an understanding that my indoor FTP is different than my outdoor FTP so I don't assume they are the same.

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Second, what good would an FTP # derived at from an indoor trainer be to someone who didn't train/race (outside) with a PM?


Well, it would help you with your indoor training. It might help you get a better understanding of your RPE which can in turn assist with outside training/racing. A lot of people don't really obsess over power in a race (or they shouldnt, anyway), so it's not much of a loss there but would be a loss for the outside training.



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If you train (indoors and out) with power, what are some reasons for power discrepancies (between indoors and out)? If there's a discrepancy between your indoor and outdoor FTP, which is higher? Why?


I mentioned some people get differences from what type of bike they're riding. It also depends on how much they ride each bike. A lot of new people to indoor training vastly underestimate what kind of fan you need to keep you cool, that can impact your numbers.


What are you trying to learn or hope to make a decision on? These seem like broad questions trying to figure out if you should be buying a indoor smart trainer vs an on-bike power meter? Or something else?
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Re: If you haven't tested your FTP - ouside [nc452010] [ In reply to ]
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For me the main thing has been being able to do a repeatable test and learning how those numbers relate to your race numbers. One thing that I would also keep constant is test on your race bike and race PM in a race position.

This year i have not found need to test FTP since i get such a good idea about race numbers from simply doing my intervals and knowing were my cycling is in relation to past yrs from my interval numbers.

2024: Bevoman, Galveston, Alcatraz, Marble Falls, Santa Cruz
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Re: If you haven't tested your FTP - ouside [racehd] [ In reply to ]
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I have a PM on my tri bike. I've been training on a CT all winter. I don't even check one set of data against the other (my PM v. the CT) because I don't trust the CT to be all that accurate (and my power on the road is my power.....period).

I was just curious as to how much credence people give FTP's gleaned from only indoor tests.....and, what that number means in practical terms.
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Re: If you haven't tested your FTP - ouside [nc452010] [ In reply to ]
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I only test indoors and only do 20 min test with same exact protocol every time. But i have leaned how that relates to my racing numbers.

2024: Bevoman, Galveston, Alcatraz, Marble Falls, Santa Cruz
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Re: If you haven't tested your FTP - ouside [nc452010] [ In reply to ]
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My n-1

I can hold more power outside (both racing and training) than I can indoors. For me, it's psychological.

@floathammerholdon | @partners_in_tri
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Re: If you haven't tested your FTP - ouside [cloy26] [ In reply to ]
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cloy26 wrote:
My n-1

I can hold more power outside (both racing and training) than I can indoors. For me, it's psychological.

I think indoors vs outdoors is interesting

4 things to look at

1) FTP on trainer
2) FTP going uphill
3) FTP going downhill
4) FTP on flat road

My belief, all 4 will produce different numbers, with similar effort.

However, trying to match Numbers on all 4 (say consistent riding at 200 watts) will create variability in effort.

200 watts downhill is harder to hit that 200 watts uphill, while on the flat is maybe between?

Merge Multisport Founder & Head Coach
USAT Level 2 - Short & Long Course
Ironman Certified
Brevard, NC
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Re: If you haven't tested your FTP - ouside [nc452010] [ In reply to ]
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nc452010 wrote:
I have a PM on my tri bike. I've been training on a CT all winter. I don't even check one set of data against the other (my PM v. the CT) because I don't trust the CT to be all that accurate (and my power on the road is my power.....period).

I was just curious as to how much credence people give FTP's gleaned from only indoor tests.....and, what that number means in practical terms.

Got it, So for me I always use the same power meter for my indoor vs outdoor tests to eliminate the variable of my kickr being different than my garmin vector (though, they are consistently within 1% of each other). I also try to standardize as many variables as possible. I tend to eat the same meals before FTP tests and races, every time. I also try to get the same amount of sleep, etc. Same bike indoor vs outdoor, etc.

Indoors I always use the same testing protocol. Outdoors I generally don't do a traditional FTP test, but I base my FTP off of 10TT or 40k TT. I've learned, in general, how my race numbers correlate to to my indoor FTP and vice versa. My indoor FTP and Outdoor FTP are slightly different, but it is marginal and sometimes I will use the same number for both indoors/outdoors since we're talking about a few watts.

Curious though, why don't you trust the CT to be accurate? I ride CT with my team and while I don't get any of the data files from the CT, looking at the rider display the numbers generally agree with my PM. We do indoor 10TT's and the CT is generally within a few watts of my vectors (depends on how recently I cleaned my chain).
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Re: If you haven't tested your FTP - ouside [nc452010] [ In reply to ]
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The number one biggest difference between riding indoors and outside is cooling. Outside you have the wind that cools you as you ride through it. I initially thought I had a 5-10% difference between indoors and outdoors (outdoors being higher), but after getting a big commercial fan to use on my trainer, I've found my power is virtually the same now.

As was alluded to earlier, some folks get to know their numbers so well that testing FTP really isn't all that necessary. I haven't done an actual FTP test in 5+ years, yet I have a very good idea of where my FTP is. I use intervals, HR (in relationship to power), and races to see where I am at. That said, I've done a few indoor and outdoor TT's that are pretty close to what an FTP test is, and they have given me an accurate estimate of where I'm at.

My FTP generally decreases by around 15-20 watts over the winter. This is going from 6-8 hrs of riding a week to around 1-2 hrs a week (Oct - Jan). It takes me a few months to build up and get the FTP back to where it was at the end of the previous season.

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Re: If you haven't tested your FTP - ouside [racehd] [ In reply to ]
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During the last three minutes of my indoor FTP tests, I tend to look down at the floor, close my eyes, and scream (uncontrollably) very loudly with every exhale.

My indoor FTP #s will always be way higher than outdoor. There is no need to handle my bike, or even look at were I am going for that matter. I also usually have Metallica on mix extremely loud... again, something I cannot do outdoors.

I don't even think I could find a 20 minute segment in my area that I would not have to yield to traffic... probably not even a 10 minute segment for that matter. And even if I came close, it would be rolling hills which is not good.

For me I just test indoors for safety, accuracy, and consistency. I just need to continue to be mindful and learn how that relates to my outdoor abilities.

"If it costs you 30 minutes at Maryland so what" -dwreal
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Re: If you haven't tested your FTP - ouside [racehd] [ In reply to ]
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racehd wrote:
Curious though, why don't you trust the CT to be accurate?

CTs have been known/shown to be all over the place since the mid 1990s. Basically, they have never really cared about accuracy, preferring instead to just make marketing claims. The sad part is (aside from heat-related drift and coast-down issues), assuring accuracy would only require that they spend a bit more time tweaking the potentiometer that hides behind the decal on the load generator.
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Re: If you haven't tested your FTP - ouside [bluestacks867] [ In reply to ]
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bluestacks867 wrote:
I don't even think I could find a 20 minute segment in my area that I would not have to yield to traffic... probably not even a 10 minute segment for that matter.

Same for me. The last formal test I took the day off to travel an hour north of the city to a stretch of road a cycling coach/friend suggested. I started in a rural point and I finished the 20 minute test just before getting into the small town. Only to end up with about the same swagFTP that I had been using already based on 20 and 60 minute indoor sessions. Haven't done another one since.

I wish I had an outdoor spot closer as I do tend to overheat inside.
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Re: If you haven't tested your FTP - ouside [Andrew Coggan] [ In reply to ]
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Andrew Coggan wrote:
racehd wrote:

Curious though, why don't you trust the CT to be accurate?


CTs have been known/shown to be all over the place since the mid 1990s. Basically, they have never really cared about accuracy, preferring instead to just make marketing claims. The sad part is (aside from heat-related drift and coast-down issues), assuring accuracy would only require that they spend a bit more time tweaking the potentiometer that hides behind the decal on the load generator.

Couple of reasons I'm skeptical with them (CT's)....

1. One day I'll be in a smaller gear, sitting up, to work at 50% of my FTP (warmup interval). Next time, I'll be 3 gears down my cassette, pedaling harder, to achieve the same power.

2. If 3 of us are doing the same workout (different FTP's, of course), one guy is (according to the CT) riding at 29 mph at much fewer watts than the other 2 - riding at (again, according to the CT) 20 mph. I know this metric means nothing in the big picture, but it further erodes my confidence in the data.
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Re: If you haven't tested your FTP - ouside [nc452010] [ In reply to ]
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This is why it is important to understand and know how to apply all three measures of intensity.
1.) Power
2.) Heartrate
3.) RPE
If you understand all three than you have something to go by if one of them changes or goes away.
Also- training levels are zones (ranges)- you don't have to blindly go out and hold exactly 90% of FTP.
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Re: If you haven't tested your FTP - ouside [Andrew Coggan] [ In reply to ]
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Andrew Coggan wrote:
racehd wrote:

Curious though, why don't you trust the CT to be accurate?


CTs have been known/shown to be all over the place since the mid 1990s. Basically, they have never really cared about accuracy, preferring instead to just make marketing claims. The sad part is (aside from heat-related drift and coast-down issues), assuring accuracy would only require that they spend a bit more time tweaking the potentiometer that hides behind the decal on the load generator.

Can I safely assume that Racermate's Velotron doesn't have these issues and is more accurate and consistent?
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Re: If you haven't tested your FTP - ouside [nc452010] [ In reply to ]
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just curious as to how much credence people give FTP's gleaned from only indoor tests.

I've seen as much as 25w variation between indoor & outdoor power. Sometimes indoor is higher (usually) sometimes out door is higher.

Don't forget about your internal power meter.....PRE when racing

Brian Stover USAT LII
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Re: If you haven't tested your FTP - ouside [Felt_Rider] [ In reply to ]
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Felt_Rider wrote:
I started in a rural point and I finished the 20 minute test just before getting into the small town. Only to end up with about the same swagFTP that I had been using already based on 20 and 60 minute indoor sessions. Haven't done another one since.

I wish I had an outdoor spot closer as I do tend to overheat inside.

I did my first trainer FTP test this past weekend. The result was pretty much what I thought it would be based on past tests and my current fitness. I guess I'm lucky, I have a 10 mile stretch of uninterrupted rural highway about 11 miles from the house (perfect warmup).

My rural highway is not flat, so I've always kinda thought I was "cheating" by pumping more watts climbing the hills. I think the FTP test may be more "fair" in that I was able to put my head down in aero the whole time. But "fair" doesn't necessarily mean more realistic.

Proud Member of Chris McDonald's 2018 Big Sexy Race Team "That which doesn't kill me, will only make me stronger"
Blog-Twitter-Instagram-Race Reports - 2018 Races: IM Florida 70.3, IM Raleigh 70.3, IM 70.3 World Championships - South Africa, IM North Carolina 70.3
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Re: If you haven't tested your FTP - ouside [desert dude] [ In reply to ]
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desert dude wrote:

Don't forget about your internal power meter.....PRE when racing

I wish I'd read this, last September :)

Great stuff, guys. Thanks for all of the replies.
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Re: If you haven't tested your FTP - ouside [nc452010] [ In reply to ]
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nc452010 wrote:
Andrew Coggan wrote:
racehd wrote:

Curious though, why don't you trust the CT to be accurate?


CTs have been known/shown to be all over the place since the mid 1990s. Basically, they have never really cared about accuracy, preferring instead to just make marketing claims. The sad part is (aside from heat-related drift and coast-down issues), assuring accuracy would only require that they spend a bit more time tweaking the potentiometer that hides behind the decal on the load generator.


Couple of reasons I'm skeptical with them (CT's)....

1. One day I'll be in a smaller gear, sitting up, to work at 50% of my FTP (warmup interval). Next time, I'll be 3 gears down my cassette, pedaling harder, to achieve the same power.

2. If 3 of us are doing the same workout (different FTP's, of course), one guy is (according to the CT) riding at 29 mph at much fewer watts than the other 2 - riding at (again, according to the CT) 20 mph. I know this metric means nothing in the big picture, but it further erodes my confidence in the data.
I have two computrainers and a powertap wheel. According to my powertap wheel one reads about 2-3% high and the other about 5% low. They are relatively consistent though and since I use the same one all the time I don't think it's a big deal.
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