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Ftp road bike vs aero
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Hi, this week I have done two separate 1 hr max efforts, one on the road bike and one in the TT bike. Both times I was fresh and food the same route. My normalised per for the road bike effort was 267 and for the TT bike 223. My question is...is this difference reasonable/ normal/ to be expected? I'm supprised at such a difference and am wondering if my power meter (garmin vector pedals) might be playing up. The reason I am doing the tests in the first place is that I notice that sometimes hitting my power targets on my training sessions seem easy and other times hard, so I was wondering if my power meter was playing up. I often swop the pedals between the road bike and the aero bike but always re calibrate each time.
Interestingly my average speed on the road bike effort was 31 kph and on the TT bike it was 34, so I'm not doubting the benefit of the aero position, just surprised at such a big FTP difference. Any thoughts, ideas or experiences most welcome.
Steve x
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Re: Ftp road bike vs aero [Boomwhacker1] [ In reply to ]
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Often there's a bit of a discrepancy, maybe 10% give or take but you do have a big difference. How is your tri fit? Are you too low, too choked up? Hip angle really closed?
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Re: Ftp road bike vs aero [coates_hbk] [ In reply to ]
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I've had a professional bike fit on the TT bike but not on the road bike. I feel good and comfortable on both bikes. I wouldn't say the TT is an aggressive or too low position. The main difference I feel is in the hip angle. In the aero position my hips are at a wider angle as I'm in a fatter seat (ism adamo). I've wondered if I might need to put the seat further back and sit right on the nose to close my hip angle a bit? What do you think?
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Re: Ftp road bike vs aero [Boomwhacker1] [ In reply to ]
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I have a theory about power production and recording on bicycles. Maybe I should call it an observation. At higher speeds like on a TT bike, there is more wind resistance relative to rolling resistance. Higher wind resistance takes away the bit of "swing" in your pedal stroke - the very, very slight surge in each stroke. I think power meters report this as lower power. If you are somehow able, see what your TT bike power is up a 20, 30 or 60 min 4% mountain grade. I would predict it's higher. I find my power is highest on a cyclocross type bike with fat 35mm gravel tires. Next a regular road bike. And last my triathlon bike.

This is also why on most home mag trainers, it's impossible to match outdoor power. The mag trainer has a unnatural 360 degree resistance that takes away much of that slight surge with each rotation of the crank.

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Re: Ftp road bike vs aero [Boomwhacker1] [ In reply to ]
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No clue as I've never had reason to test road bike power, but likely only a handful of watts at best.

It's common to put out less in an aero position (i.e. on a TT bike) than sat up though. I know people putting out 50-60w less, but the corresponding drop in CdA is far higher so it's not a big deal. There's a sweetspot for when to come out of the aerobars in order to take advantage of increased power production, so that should be taken into account when you race.
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Re: Ftp road bike vs aero [Boomwhacker1] [ In reply to ]
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Boomwhacker1 wrote:
The main difference I feel is in the hip angle. In the aero position my hips are at a wider angle as I'm in a fatter seat (ism adamo). I've wondered if I might need to put the seat further back and sit right on the nose to close my hip angle a bit? What do you think?


Steve,

From your response I'm wondering if you're perhaps misunderstanding the concept of hip angle. You may want to open rather than close the hip angle to improve power in the TT position. This might entail moving ahead on the saddle and or moving the saddle itself ahead. A 16.5 % difference betwee TT and road position is greater than it needs to be. You ought to be able to bet that under 10% if not even better. The winter I did all threshold work in aero on the trainer I actually was able to bring it down to nearly zero difference.



Genetics load the gun, lifestyle pulls the trigger.
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Re: Ftp road bike vs aero [geoffreydean] [ In reply to ]
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With regards to the 360 degrees of resistance, it makes me think 60 minutes on the trainer is a harder workout than 60 minutes outside as there is no letting off or coasting, 100% pedaling the whole time. This assumes putting out roughly the same power levels.
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Re: Ftp road bike vs aero [Boomwhacker1] [ In reply to ]
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Why are you comparing 'normalized' power? How about average power?

Are you estimating ftp from similar courses and riding conditions (ie, solo vs. Group riding)?

If I'm racing in a crit, my NP is always much higher (~40w) higher than AP. in a tt, however, my NP and AP are almost the same.

When comparing AP from both road and tt riding, I see very similar ftp estimates.
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Re: Ftp road bike vs aero [beston] [ In reply to ]
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Hi beston, AP and NP were virtually the same. Both were solo rides, same course, same conditions.
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Re: Ftp road bike vs aero [sciguy] [ In reply to ]
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Got it! Yeh, I was meaning something different with the seat....wider seat means it feels like my legs are wider apart...which is a different thing to hip angle for sure.
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Re: Ftp road bike vs aero [Grill] [ In reply to ]
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Thanks, it seems that it's fairly common for ftp to be lower on aero, and that mine is particularly lower, perhaps more than average. I'll have to get to work on doing more in the aero position and maybe fiddle around with my fit. As far as the sweet spot you talk about, at what point is that?
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Re: Ftp road bike vs aero [Boomwhacker1] [ In reply to ]
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Going too low at the front is a great way to lose power in an aero position (and isn't necessarily more aero).
Sweet spot is going to be different for everyone, but it's typically around the mid teens. You'll notice it as if your power goes up a lot but speed goes down you've come up too soon.
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Re: Ftp road bike vs aero [Grill] [ In reply to ]
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but it's typically around the mid teens



You mean mph?
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Re: Ftp road bike vs aero [Boomwhacker1] [ In reply to ]
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For me sustained climbs ftp is 10 watts greater than flats on a road bike, which is about 10 watts greater than on my TT bike.
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Re: Ftp road bike vs aero [Grill] [ In reply to ]
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Any idea what the Pro TT guys are pushing out watt wise?
Their positions are super aggressive (and limited by UCI) - given they seem to spin a 55*11 at 90 rpm I get the feeling they push out very big numbers !
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Re: Ftp road bike vs aero [bespoke] [ In reply to ]
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Well into the 400w range (Mullen did 440w for 55 minutes at the Euro champs and Dowsett is around 430w). Spartacus, Wiggo, and Martin are closer to 500 than 400 (reckon Vasil is too)...
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Re: Ftp road bike vs aero [Grill] [ In reply to ]
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Bloody hell
And at these numbers I am assuming they are not down 10-15% on their FTP?
So - how do these guys, riding in much more aggressive TT positions 'lose' less power than Triathletes?
Core strength? Hip flexor flexiblilty?
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Re: Ftp road bike vs aero [bespoke] [ In reply to ]
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They train on their TT bikes.
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Re: Ftp road bike vs aero [Grill] [ In reply to ]
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Yeah - but you would think proportionately a Triathlete spends more % time on a Tri bike than a UCI guy on his TT bike
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Re: Ftp road bike vs aero [Boomwhacker1] [ In reply to ]
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If you are down 10% or more, there is a problem to be solved. Either hip angle or time in the saddle, probably hip angle. You should look to get that delta to less than 5%, 2-3% is better. I've seen this dozens of times. It is correctable. Don't settle.

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Re: Ftp road bike vs aero [Boomwhacker1] [ In reply to ]
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For what it's worth, I have had similar experience too with less power on the TT bike.

Just a random thought - as you are using power pedals, are the cranks the same length, and if not, does your head unit account for that properly? I understand power pedals require the crank length as a variable to compute power from the torque generated.


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Re: Ftp road bike vs aero [Boomwhacker1] [ In reply to ]
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Boomwhacker1 wrote:
Hi, this week I have done two separate 1 hr max efforts, one on the road bike and one in the TT bike. Both times I was fresh and food the same route. My normalised per for the road bike effort was 267 and for the TT bike 223. My question is...is this difference reasonable/ normal/ to be expected? I'm supprised at such a difference and am wondering if my power meter (garmin vector pedals) might be playing up. The reason I am doing the tests in the first place is that I notice that sometimes hitting my power targets on my training sessions seem easy and other times hard, so I was wondering if my power meter was playing up. I often swop the pedals between the road bike and the aero bike but always re calibrate each time.
Interestingly my average speed on the road bike effort was 31 kph and on the TT bike it was 34, so I'm not doubting the benefit of the aero position, just surprised at such a big FTP difference. Any thoughts, ideas or experiences most welcome.
Steve x

Before adjusting your fit, which may well be in order, the first question I would ask is how much time do you spend on your road bike vs. your TT bike. I spend about 25% of my time on the TT bike and my 50 minute power is within 2% on each bike.
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Re: Ftp road bike vs aero [geoffreydean] [ In reply to ]
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geoffreydean wrote:
I have a theory about power production and recording on bicycles. Maybe I should call it an observation. At higher speeds like on a TT bike, there is more wind resistance relative to rolling resistance. Higher wind resistance takes away the bit of "swing" in your pedal stroke - the very, very slight surge in each stroke. I think power meters report this as lower power. If you are somehow able, see what your TT bike power is up a 20, 30 or 60 min 4% mountain grade. I would predict it's higher. I find my power is highest on a cyclocross type bike with fat 35mm gravel tires. Next a regular road bike. And last my triathlon bike.


This is also why on most home mag trainers, it's impossible to match outdoor power. The mag trainer has a unnatural 360 degree resistance that takes away much of that slight surge with each rotation of the crank.

There's a difference between what are errors in measurement and what are differences in physiological capability under varying environmental and riding scenarios.

The only reason a lower inertial load may erroneously inflate power meter reported data is if it results in a significant enough violation of the assumption of constant crank rotational velocity used by crank/pedal power meters to calculate power output.

Assuming circular chainrings, at most the error in power will be of the order of 2-3%, and that's for the extreme scenario of the initial couple of pedal strokes of a maximal acceleration from a standing start. Steep climbs and low inertia trainers are the other scenarios where the crank velocity does vary more than flat road riding but the potential power meter error resulting form these are less than half of the acceleration scenario.

The crank velocity variations in all other (circular chainring) scenarios will be even less, and the resulting power meter error will be negligible.

Here's some detailed assessment of that issue if you are interested in reading more about it:
http://alex-cycle.blogspot.com.au/...-crank-velocity.html
http://alex-cycle.blogspot.com.au/...-crank-velocity.html

http://www.rstsport.com
http://www.aerocoach.com.au
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