Let's play a quick little game. Guess the watts.

Moderators: robbosmans, Moderator Team

How many watts to hold 32mph/51.5kph Additional details below.

250W-
2
2%
300W
5
6%
350W
11
13%
400W
19
22%
450W
22
25%
500W
14
16%
550W
12
14%
600W
2
2%
650W
0
700W+
0

maxim809
Moderator
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Even before talking about the impact of wind, which I hope by now everyone at WW is well aware of.

For me, 300w is 30mph at a very shallow gradient of -1%

And at -2% it’s 32mph.

Some TTs are point to point, others out and back. The course makes for significantly different pacing strategies if it’s even the slightest bit of gradient differences exist.

I guess I’m just saying a lot of obvious stuff. Anyway.

Andrew69
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Location: ɹǝpunuʍop
robeambro wrote:
Fri Dec 02, 2022 11:19 am
I answered 350w as I was fully expecting this question to be a trap - I thought it was going to be more like 400-450. I guess it shows that I am not used to holding these wattages..
I also think 350w is about right judging by what it takes me to (try) and hold 50km/h and knowing my CdA isnt that good (too wide and heavy due to years of weight lifting and working in construction)

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TobinHatesYou
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Andrew69 wrote:
Wed Dec 07, 2022 6:47 am

I also think 350w is about right judging by what it takes me to (try) and hold 50km/h and knowing my CdA isnt that good (too wide and heavy due to years of weight lifting and working in construction)

It takes me about 290W to hold 42.5km/h on California roads, ridden on a circuit so should mostly negate wind direction.

350W gets me to 45.5km/h. I consider myself pretty damn aero.

Andrew69
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Joined: Thu Feb 19, 2009 10:52 am
Location: ɹǝpunuʍop
TobinHatesYou wrote:
Wed Dec 07, 2022 7:03 am
Andrew69 wrote:
Wed Dec 07, 2022 6:47 am

I also think 350w is about right judging by what it takes me to (try) and hold 50km/h and knowing my CdA isnt that good (too wide and heavy due to years of weight lifting and working in construction)

It takes me about 290W to hold 42.5km/h on California roads, ridden on a circuit so should mostly negate wind direction.

350W gets me to 45.5km/h. I consider myself pretty damn aero.
Soooo, youre saying that 350w isnt enough?

Andrew69
Posts: 593
Joined: Thu Feb 19, 2009 10:52 am
Location: ɹǝpunuʍop
TobinHatesYou wrote:
Sun Nov 27, 2022 2:16 am
Assume a very, very good road bike CdA of 0.25, 80kg system weight, typical bling aero road bike kit (helmet, roadsuit, deep wheels, etc,) fast tires, average quality flat road, calm conditions, sea level air density for 20C/68F. Do not consult a speed/CdA/power calculator.
So now youve kept us idiots in suspense for many weeks, care to share your answer?

TobinHatesYou
Posts: 12113
Joined: Mon Jul 24, 2017 12:02 pm
Andrew69 wrote:
Wed Jan 04, 2023 2:40 am
TobinHatesYou wrote:
Sun Nov 27, 2022 2:16 am
Assume a very, very good road bike CdA of 0.25, 80kg system weight, typical bling aero road bike kit (helmet, roadsuit, deep wheels, etc,) fast tires, average quality flat road, calm conditions, sea level air density for 20C/68F. Do not consult a speed/CdA/power calculator.
So now youve kept us idiots in suspense for many weeks, care to share your answer?

Andrew69
Posts: 593
Joined: Thu Feb 19, 2009 10:52 am
Location: ɹǝpunuʍop
I see that now, thanks.

I will have to try it out for myself.
Have a short strava segment that it essentiallt flat (well, very slight incline then very slight decline, starts and ends at the same elevation) and I know I can hit and hold 50+ there as there as it is slight downhill leading into it.
Problem is the wind as it is rarely still there and as its a main road, passing cars can give you assistance.

spartacus
Posts: 1003
Joined: Mon Apr 04, 2011 6:53 pm
I have a KOM that's 32.3mph and avg 404w

Karvalo
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Joined: Fri Aug 10, 2018 6:40 pm
spartacus wrote:
Mon Jan 09, 2023 5:05 pm
I have a KOM that's 32.3mph and avg 404w
Wind exists.

spartacus
Posts: 1003
Joined: Mon Apr 04, 2011 6:53 pm
Karvalo wrote:
Mon Jan 09, 2023 8:35 pm
spartacus wrote:
Mon Jan 09, 2023 5:05 pm
I have a KOM that's 32.3mph and avg 404w
Wind exists.
"average quality flat road, calm conditions, sea level air density for 20C/68F."

Just saying it was close to that. The more I've thought about this, the less I think it's 500 watts so I checked some of my efforts and found that one. One other piece of info I have is I did a bunch of laps on an outdoor velodrome on a non-aero road bike and averaged 23-24mph on 240-250w on my flying 4k times so I guess I'm reasonably aero. Maybe the gradient and wind conditions are too hard to account for IRL...

TobinHatesYou
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spartacus wrote:
Mon Jan 09, 2023 11:30 pm
Karvalo wrote:
Mon Jan 09, 2023 8:35 pm
spartacus wrote:
Mon Jan 09, 2023 5:05 pm
I have a KOM that's 32.3mph and avg 404w
Wind exists.
"average quality flat road, calm conditions, sea level air density for 20C/68F."

Just saying it was close to that. The more I've thought about this, the less I think it's 500 watts so I checked some of my efforts and found that one. One other piece of info I have is I did a bunch of laps on an outdoor velodrome on a non-aero road bike and averaged 23-24mph on 240-250w on my flying 4k times so I guess I'm reasonably aero. Maybe the gradient and wind conditions are too hard to account for IRL...
If you’re only averaging 240W on a 4K, then I’m guessing your 404W effort is a minute or less…that is subject to a lot of noise, especially if you have an aided lead-in.

Also 240W @ 23.x mph is about right.

Difference in power required ~ the difference in speed cubed, roughly since there are other scaling factors like rolling resistance.
Last edited by TobinHatesYou on Tue Jan 10, 2023 5:10 am, edited 1 time in total.

maxim809
Moderator
Posts: 792
Joined: Sat Feb 25, 2017 6:28 am
For the temps* quoted at 0.250 CdA, it is 450w just to push through the air to achieve 32mph/51kph.

If you run fast tires and have an optimized drivetrain, that is another +45w-ish to hit just shy of 500w (450w aero + 35w rolling resistance + 10w drivetrain). If you run super slow tires like Gatorskin tubs on terrible tarmac at horrible psi, you might push yourself into 530~540w territory. But TBHY stipulates fast tires on average roads.

If spartacus is running laps in a velodrome, a few things must be considered:

1. You state road bike, but is it truly a road bike or a fixed gear track bike? Fixed gear bikes have the potential to be more aero than road bikes because it does not have shifters, FD, outer cables, bottle cages, bottles, etc. At 32mph, the sum of these parts can be pretty consequential to aero drag.

2. Regardless of bike type, is your position for your flying 4k the same as your roadie? Some people have both a Track fit and a Road fit.... and that will obviously play the biggest role to aero drag. Extending the question is if your kit and helmet are the same.

I think those are the 2 big ones I'd look at first. There are a few other aspects, such as wooden boards in an indoor velodrome helping to reduce Crr. And how those boards can heat-up over time and be slightly faster even still. And usually with ideal surface conditions you can pump up deep section rims with narrow tires to extra high pressure and get better drag reductions. Which hopefully are clincher/tubeless and not tubulars.

But you state outdoor velodrome and those can have wild variation in tarmac conditions.

*We don't know the dew point and thus the actual density, but we can handwave at 1.200 kg/m^3 for 20°C.

TobinHatesYou
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Joined: Mon Jul 24, 2017 12:02 pm
Also I don't know how much spartacus weighs, but 23.5mph at 240W is closer to .30, not .25. So in the same position he'd have to be putting out somewhere around 575W to hold 32mph on a geared bike depending weight and tire choice.

spartacus
Posts: 1003
Joined: Mon Apr 04, 2011 6:53 pm
Interesting information. I was on a touring bike with 32c tires (lol) not a racing or track bike, does have a power meter though, I was surprised how fast I was going. I was just cruising around though at those speeds and staying towards the bottom.

I could go out on my fastest bike and try for 32mph but nothing will satisfy anyone here because the conditions can't be known apparently, I believe the math I suppose.

maxim809
Moderator
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spartacus wrote:
Tue Jan 10, 2023 5:36 am
Interesting information. I was on a touring bike with 32c tires (lol) not a racing or track bike, does have a power meter though, I was surprised how fast I was going. I was just cruising around though at those speeds and staying towards the bottom.
Yes it actually doesn't take "too much" power to hold ~20mph once you look at it on a closed circuit like a velodrome. I think often what happens out in the real world, is there are lots of stops and goes which kill average speed. And also the safety and management with traffic and pedestrians -- all of which can tank average speed for an inflated average power with zero's removed, once you look on Strava.

Those who ride quiet country roads and never have to brake for gravel or potholes will probably have closer experiences to the one you had at the velodrome, compared to say someone trying to get out of downtown Sydney/New York/Sydney/Tokyo proper.
spartacus wrote:
Tue Jan 10, 2023 5:36 am
I could go out on my fastest bike and try for 32mph but nothing will satisfy anyone here because the conditions can't be known apparently, I believe the math I suppose.
You should!

Here's an actual checklist of additional data that should be enough to get rid of a tough crowd:

1. Average Power of run
2. Date & Time the sample was taken
3. Avg Wind speed and direction information sourced from Wunderground for the location of your outdoor run
4. Rough temp & Weather conditions at time of run (can also be sourced from Wunderground)
5. The direction you traveled 32mph into (need to reference against 3)
6. Tire brand/model/size/psi

Those should be the big ones, and the minimum needed to get a rough estimate. There are other things we can look at if the data looks off, but I would start with these 6.

That said, Tobin back-calculated your CdA as 0.30 with the data you already provided. This is a very, very realistic coefficient of drag number for the nominal sized, nominal roadie. This can either be a very small rider sitting up, an average sized rider starting to get low, or a larger rider in an aero position. If you were doing loops in a velodrome, then as long as the wind wasn't blustering crazy, we can squint and hand-wave the conditions out.
spartacus wrote:
Tue Jan 10, 2023 5:36 am
but nothing will satisfy anyone here
Put differently, for a first glance with minimal data I'm pretty satisfied with the analysis! The rabbit hole can of course go as deep as you want.

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