Is there a chart of watts + speed?

Manc33

I just read somewhere "It takes 100 watts to do 15 mph on level ground".

Is there a chart from say 0-40 MPH, with wattages for all of them? 40 MPH is a lot but what must Cav be doing at the end of a sprint? Over 40? :shock:

I wanna see the curve on the chart more than anything else.

Strith

You won't find one because there are to many other variables like aerodynamics, drive train efficiency, rolling losses etc, etc, etc...

Best thing you can do is buy a power meter, find a flat road and see for yourself.

If you want to know how many watts Cav puts out in a sprint I'm sure the information is easy to find with a google search.

Manc33

I need a chart with all other variables factored in except it taking 100W to go 15 MPH on flat ground. :P

I thought boffins could just take the relationship between 100W and 15 MPH. Its something like 200W to go 20 MPH (when "100W = 15 MPH" is true).

Is there an increase in the rate of increase though, I bet. Unless you've got legs like a flea.

JackPozzi

Something like this? http://www.gribble.org/cycling/power_v_speed.html

Not exactly what you want but fairly close

bernithebiker

The aero drag force acting against you increases with your speed squared, i.e.

to simplify; F = .5 x drag coefficient (how slippery you + bike are) x A (frontal area) x ro (air density) x velocity x velocity

so if V = 10m/s you have Force = (constant) x 100

if V = 20m/s you have Force = (constant) x 400

So a doubling of speed has resulted in a drag increase of 4 x.

An increase in your average speed from 25 to 26km/h is much easier* than an increase from 32 to 33km/h.

*required less power

imposter2.0

Manc33 becomes interested in power numbers. Let the thread-fest begin...

darkhairedlord

based on the above and your hypothetical 100W at 15mph, just take the velocity, multiply by 2/3 then square.
P=(V*2/3)^2

so 5mph:11W; 10mph:44W; 15mph:100W; 20mph:178W; 25mph:278W; 30mph:400W; 35mph:544W; 40mph:711W; 45mph:900W; 50mph; 1111W.

And No! Heavy rims will have no effect on this but a dodgy chainline might

ai_1

I'm confused by the unusually reasonable and bike-related nature of your query. However just for the hell of it I'll pretend this thread has a sane future
The shape of the curve you're looking for will be pretty similar for different riders but it will be scaled a bit differently depending on lots of variables. So don't expect highly accurate results from any curve you may find. Kurt Kinetic provide one which they claim to have used to make their fluid resistance units representative of real riding resistances for any given speed. I have one and I have to say it's not a million miles off for me (it's not spot on either).
As you can see from the page, they claim this is a good approximation for their “average rider" and conditions, defined as follows:

https://kurtkinetic.com/technical-infor ... ower-tech/

Rider: 165 lbs.
Riding a 23 lb. bike
With 170 mm crank arms
Up a 1% grade
At sea level
With no wind
On rough asphalt

I'm afraid it only goes to 35mph which equates to approx 1kW.

matt-h

But that doesn't account for the loss of watts from a poorly indexed front mech and rubbing quick links.

rower63

look at my sig - I've got a whole load about it my link there

MountainMonster

You need to also account for rider weight and bike and so forth. How long is a piece of string?

southdownswolf

matt-h wrote:

But that doesn't account for the loss of watts from a poorly indexed front mech and rubbing quick links.

RChung

GGBiker

Have a look for an iPhone app called bike calculator, it gives very good estimates of wattage for various gradients, speed, wind speed, weight and even position on the bike. I have found it to be reasonably accurate compared to power meter result on q climb for example.

chris_bass

GGBiker wrote:

iPhone

I don't think he's a fan

Manc33

Cheers guys this is useful http://www.gribble.org/cycling/power_v_speed.html

According to that its like this:

01 MPH = 2 Watts
02 MPH = 4 Watts (+2)
03 MPH = 6 Watts (+2)
04 MPH = 9 Watts (+3)
05 MPH = 12 Watts (+3)

06 MPH = 15 Watts (+3)
07 MPH = 20 Watts (+5)
08 MPH = 24 Watts (+4 lol)
09 MPH = 30 Watts (+6)
10 MPH = 37 Watts (+7)

11 MPH = 45 Watts (+8)
12 MPH = 54 Watts (+9)
13 MPH = 64 Watts (+10)
14 MPH = 76 Watts (+12)
15 MPH = 90 Watts (+14)

Note how it takes double the watts to
go 15 MPH than it does to go 11 MPH!

16 MPH = 104 Watts (+14)
17 MPH = 121 Watts (+17)
18 MPH = 140 Watts (+19)
19 MPH = 161 Watts (+21)
20 MPH = 184 Watts (+23)

21 MPH = 207 Watts (+23)
22 MPH = 235 Watts (+28)
23 MPH = 263 Watts (+28)
24 MPH = 295 Watts (+32)
25 MPH = 330 Watts (+35)

26 MPH = 368 Watts (+38)
27 MPH = 409 Watts (+41)
28 MPH = 450 Watts (+41)
29 MPH = 497 Watts (+47)
30 MPH = 547 Watts (+50)

31 MPH = 597 Watts (+50)
32 MPH = 654 Watts (+57)
33 MPH = 710 Watts (+56 lol)
34 MPH = 780 Watts (+70)

I was going to do all the percentage increases but I would be here all night.

If I can be arsed I will add them all to the post at some point.

napoleond

Well, it takes me more like 180w to average 15mph on a ride.

cougie

Those figures look bobbins to me.

chris_bass

what did you put in for the other variables (rider weight, bike weight etc)

also - if you want to put percentages in just make a spreadsheet and copy and paste a formula, should take about 12 seconds I'd guess!

chris_bass

Only went to 30 but here you go, use it wisely!

Speed (MPH) Power (W) Difference % Increase
1 2 0 0.0%
2 4 2 100.0%
3 6 2 50.0%
4 9 3 50.0%
5 12 3 33.33%
6 15 3 25.0%
7 20 5 33.33%
8 24 4 20.0%
9 30 6 25.0%
10 37 7 23.33%
11 45 8 21.62%
12 54 9 20.0%
13 64 10 18.52%
14 76 12 18.75%
15 90 14 18.42%
16 104 14 15.56%
17 121 17 16.35%
18 140 19 15.7%
19 161 21 15.0%
20 184 23 14.29%
21 207 23 12.5%
22 235 28 13.53%
23 263 28 11.91%
24 295 32 12.17%
25 330 35 11.86%
26 368 38 11.52%
27 409 41 11.14%
28 450 41 10.02%
29 497 47 10.44%
30 547 50 10.06%

(sorry for the formatting, copy and paste wasn't my friend!)

Manc33

Thats odd, at around 15-20 MPH each MPH gained takes around +15% more power.

Around 25-30 MPH though, each MPH gained only takes around +10% more power.

Typical huh. I mean no one goes 25-30 MPH on the flat... but if you did you could "ease off" a bit lol.

The chart is probably up the wall in that it won't apply to anyone, but it should be right in that the figures are all right compared to each other. I didn't do it exactly anyway, a lot of it was 12.05 instead of 12 etc.

chris_bass

but it is 10% of a bigger number, so the power needed is still more, if you ease off the power you will slow down!

also, I'd imagine quite a lot of people go 25mph on the flat!

disgruntledgoat

Is it me, or if this mystical chart existed and was reliable would we all be wasting our money on power meters, when we could just buy a cheap speedo?

disgruntledgoat

NapoleonD wrote:

Well, it takes me more like 180w to average 15mph on a ride.

150w for me, which just shows you how pointless it is to look for a "one size fits all"

JustBenonstrava

Watts increase with the square of the speed.
If you square 16 and then square 32, you can see the huge power challenge to double one's speed.

bondurant

Will you be replying to any current threads too?

Sutton_Rider

Interesting - These charts seem to show zero wind conditions. What difference would there be if riding into a head wind of say 10 mph? Would you just add an extra 10 mph to your speed?

keezx

A headwind would add nothing to your speed.....

Sutton_Rider

Obviously a headwind would add nothing to your speed. You missed the point. Let me put it another way. If in zero wind you are riding at 16mph with a power of 100 watts, then you ride into a headwind of 10mph but still maintain 100 watts by how much will that headwind reduce your speed? Or the other way 10mph headwind and you maintain 16mph by how much would you have to increase your power?

darkhairedlord

Sutton Rider wrote:

Obviously a headwind would add nothing to your speed. You missed the point. Let me put it another way. If in zero wind you are riding at 16mph with a power of 100 watts, then you ride into a headwind of 10mph but still maintain 100 watts by how much will that headwind reduce your speed? Or the other way 10mph headwind and you maintain 16mph by how much would you have to increase your power?

The wind speed will reduce as you get closer to the road surface, so that will have significant effect.

imposter2.0

Sutton Rider wrote:

Obviously a headwind would add nothing to your speed. You missed the point. Let me put it another way. If in zero wind you are riding at 16mph with a power of 100 watts, then you ride into a headwind of 10mph but still maintain 100 watts by how much will that headwind reduce your speed? Or the other way 10mph headwind and you maintain 16mph by how much would you have to increase your power?

Depends entirely on your position on the bike. More aero = less effect. Less aero = more effect. There is no single answer.