Australian Cycling Forums - Bicycles Network Australia

Reading some peoples posts on what power they make and how fast they go is making me wonder if my power meter is out of whack.

I did a short TT on my road bike last night, averaged 256 watts for a speed of 33.6 kmh.

My last hard ride on my TT bike I did a section at 245 watts for a speed of 34 kmh.

Do those wattages sound about right for those speeds. Both were ok days wind wise, the roads here aren't great.

I know it is a bit of a how long is a piece of string question...but just doubting myself.

Might help.
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Can you check the calibration of your PM? Best way to confirm it is reading correctly...

Is a bit of a how long is a piece of string and really depends on how aero you are. I went into the windtunnel thinking I had a reasonable position and left with an estimated 43 watt saving mostly due to position changes!

Looks pretty good to me if you are a slightly less aero than me (184cm 79kg)

In comparison 16km TT on a rough road, 8km into a headwind, 8km back with tailwind, riden 15 times, 5 times on road bike, last 10 times with TT bike.

best on a road bike: averaged 235 watts and 34kph,
last ride on a TT bike, full aero gear, 245 watts, 37.5kph average

dalai47 wrote:Can you check the calibration of your PM? Best way to confirm it is reading correctly...

Is a bit of a how long is a piece of string and really depends on how aero you are. I went into the windtunnel thinking I had a reasonable position and left with an estimated 43 watt saving mostly due to position changes!

but could you still make the same power in that position?... What were the changes?

nickobec wrote:Looks pretty good to me if you are a slightly less aero than me (184cm 79kg)

In comparison 16km TT on a rough road, 8km into a headwind, 8km back with tailwind, riden 15 times, 5 times on road bike, last 10 times with TT bike.

best on a road bike: averaged 235 watts and 34kph,
last ride on a TT bike, full aero gear, 245 watts, 37.5kph average

Thanks for that. I am a bit shorter but a bit heavier. Looks like on the TT bike I am giving up 3.5 kph to you for the same wattage. I did not any aero gear so I guess that makes a bit of sense. Sounds like the numbers might be ball park in the right area.

toolonglegs wrote:but could you still make the same power in that position?... What were the changes?

10 Watt saving was changing Aero helmets. The rest wasvia a 2 cm drop in spacers and the majority of the savings turtling and shrugging.

Didn't have a PM at the time, but didn't find it took too long to adapt to the drop in spacers. Harder was to remember keeping the noggin out of the wind whilst on the rivet.

Unfortunately I had to change the front end after this session courtesy of UCI rule changes (Visiontech bars weren't 3:1) and still tinkering with my position even to this day...

I wrote up about the day if interested - http://climbinglama.blogspot.com.au/201 ... -from.html

Toolish wrote:Thanks for that. I am a bit shorter but a bit heavier. Looks like on the TT bike I am giving up 3.5 kph to you for the same wattage. I did not any aero gear so I guess that makes a bit of sense. Sounds like the numbers might be ball park in the right area.

When I first start racing the TT bike, I was down 20 watts and slower than my road bike. It took 12 weeks of solid work on TT bike + aero helmet, skinsuit, shoe covers & bike fitting to get that 3.5 kph and the 20 watts back.

I had a friend query my power output of 235 watts for my last TT (at a different circuit) 25km (AT) 37kph, he thought it was a bit low. But I looked at both our outputs over same circuit during a road race, he averaged 225 watts & I averaged 185 watts, he is a good 20% heavier than me.

Toolish wrote:Reading some peoples posts on what power they make and how fast they go is making me wonder if my power meter is out of whack.

I did a short TT on my road bike last night, averaged 256 watts for a speed of 33.6 kmh.

My last hard ride on my TT bike I did a section at 245 watts for a speed of 34 kmh.

Do those wattages sound about right for those speeds. Both were ok days wind wise, the roads here aren't great.

I know it is a bit of a how long is a piece of string question...but just doubting myself.

G'day Toolish,

I did some testing recently in Preparation for BOTB

I used a 4.5km loop and I kept my watts the same. the results were

1. road bike (AT) 355watts = 39kph
2. TT bike (AT) 354watts = 41.8kph (the only change was the bike)
3. TT bike + bling (AT) 356watts = 43kph (I added skin suit, aero helmet, shoe cover, but NOT wheels)

My next test will be with wheels, then I intend on tweeking my setup. The goal is to get over 45kph.

PM if you want my infor on this...

Cheers
Paul

dalai47 wrote:

toolonglegs wrote:but could you still make the same power in that position?... What were the changes?

10 Watt saving was changing Aero helmets. The rest wasvia a 2 cm drop in spacers and the majority of the savings turtling and shrugging.

Didn't have a PM at the time, but didn't find it took too long to adapt to the drop in spacers. Harder was to remember keeping the noggin out of the wind whilst on the rivet.

Unfortunately I had to change the front end after this session courtesy of UCI rule changes (Visiontech bars weren't 3:1) and still tinkering with my position even to this day...

I wrote up about the day if interested - http://climbinglama.blogspot.com.au/201 ... -from.html

That was interesting reading. While not on a TT bike, I discovered much of this from trial and error on my road bike. In a certain position that I use, with arms quite bent (in a similar position to those TT images) - I could go the same speed for less effort needed, or faster for the same effort - perhaps about 3-4km/h was what I noticed. Not only fast but comfortable for me.

I was using a powercal so I won't try to compare power figures as it is not accurate enough.

Toolish wrote:Reading some peoples posts on what power they make and how fast they go is making me wonder if my power meter is out of whack.

I did a short TT on my road bike last night, averaged 256 watts for a speed of 33.6 kmh.

My last hard ride on my TT bike I did a section at 245 watts for a speed of 34 kmh.

Do those wattages sound about right for those speeds. Both were ok days wind wise, the roads here aren't great.

I know it is a bit of a how long is a piece of string question...but just doubting myself.

Even more confused now.

Same section of road last night, same bike, same set up, average power was up 5 watts, NP up 3 watts, went 2 seconds slower over a lap of 7.7km.

I know they are only small differences, wondering if it is just tyre pressure or something like that.

Toolish wrote:

Toolish wrote:Reading some peoples posts on what power they make and how fast they go is making me wonder if my power meter is out of whack.

I did a short TT on my road bike last night, averaged 256 watts for a speed of 33.6 kmh.

My last hard ride on my TT bike I did a section at 245 watts for a speed of 34 kmh.

Do those wattages sound about right for those speeds. Both were ok days wind wise, the roads here aren't great.

I know it is a bit of a how long is a piece of string question...but just doubting myself.

Even more confused now.

Same section of road last night, same bike, same set up, average power was up 5 watts, NP up 3 watts, went 2 seconds slower over a lap of 7.7km.

I know they are only small differences, wondering if it is just tyre pressure or something like that.

It could be any number of things.

A variance that small (approx 0.25 seconds per km), with absolutely everything else the same, could easily be the result of:
- air 2 degree C cooler, or
- barometric pressure only 10hPa higher, or
- a net headwind of 0.05 metres per second (which is so small that you could not feel it, would be rated a dead calm day and smoke would still appear to rise in a vertical line), or
- an increase in air resistance of 0.8%, which would easily be a different jersey, or any number of small things like gloves, how you held your hands, keeping head up/down a little more than before, and so on, or
- loss of tyre pressure (or way over-inflated compared to previous), although it would have to be enough to add a quite lot to your Crr and that's probably not as likely, or
- carrying extra mass, how much depends on type of terrain, but on dead flat, an extra 5-6kg would do that, and less if there are any gradients other than zero on your loop.

and so on... and of course any number of a combination of the above, which can sometimes net each other out


Unless you take some care in measurement of such things, you cannot really know. It is however possible to do this to a reasonable level of precision with a power meter.

Alex Simmons/RST wrote:

Toolish wrote:

Toolish wrote:Reading some peoples posts on what power they make and how fast they go is making me wonder if my power meter is out of whack.

I did a short TT on my road bike last night, averaged 256 watts for a speed of 33.6 kmh.

My last hard ride on my TT bike I did a section at 245 watts for a speed of 34 kmh.

Do those wattages sound about right for those speeds. Both were ok days wind wise, the roads here aren't great.

I know it is a bit of a how long is a piece of string question...but just doubting myself.

Even more confused now.

Same section of road last night, same bike, same set up, average power was up 5 watts, NP up 3 watts, went 2 seconds slower over a lap of 7.7km.

I know they are only small differences, wondering if it is just tyre pressure or something like that.

It could be any number of things.

A variance that small (approx 0.25 seconds per km), with absolutely everything else the same, could easily be the result of:
- air 2 degree C cooler, or
- barometric pressure only 10hPa higher, or
- a net headwind of 0.05 metres per second (which is so small that you could not feel it, would be rated a dead calm day and smoke would still appear to rise in a vertical line), or
- an increase in air resistance of 0.8%, which would easily be a different jersey, or any number of small things like gloves, how you held your hands, keeping head up/down a little more than before, and so on, or
- loss of tyre pressure (or way over-inflated compared to previous), although it would have to be enough to add a quite lot to your Crr and that's probably not as likely, or
- carrying extra mass, how much depends on type of terrain, but on dead flat, an extra 5-6kg would do that, and less if there are any gradients other than zero on your loop.

and so on... and of course any number of a combination of the above, which can sometimes net each other out


Unless you take some care in measurement of such things, you cannot really know. It is however possible to do this to a reasonable level of precision with a power meter.

It was a bit cooler. Same jersey, gloves, knicks, socks and shoes. Attempted to keep the same position.

Wind was similar both days, but hard to measure exactly. It is a loop course so net elevation is 0 but there are a couple of small rises around the loop.

What really has me interested is that last comment. Using a powermeter to work on aero is part of the plan, need to find a suitable venue as a 8km loop is a bit long.

A loop of 300-500 metres that you can ride without changing position and without need for braking and has no traffic is ideal.

If that's not possible, then a 1km stretch of straight flat road, again no traffic, can be used, although a different data analysis technique is required.

Early morning when there is no breeze is typically best.

Alex Simmons/RST wrote:A loop of 300-500 metres that you can ride without changing position and without need for braking and has no traffic is ideal.

Think I have found the spot after a couple of days scouring map my ride. Going for a recon ride tonight.

I have read a bit about the Chung method and Golden Cheetah, is that the best way to go? Seems like data wise ride a few laps holding position and I have what I need, or is there anything else I need to know to get good data?

Toolish wrote:

Alex Simmons/RST wrote:A loop of 300-500 metres that you can ride without changing position and without need for braking and has no traffic is ideal.

Think I have found the spot after a couple of days scouring map my ride. Going for a recon ride tonight.

I have read a bit about the Chung method and Golden Cheetah, is that the best way to go? Seems like data wise ride a few laps holding position and I have what I need, or is there anything else I need to know to get good data?

Like any science, you need to control for or measure as many relevant variables as possible. Typically though, the first times you perform such tests you make mistakes, and find out from that where you can improve. So just do it, see what you find and go from there.

There are many subtleties which I don't propose to go into here, one of which is working out how to assess how precise your estimates are, and hence determine what level of difference you can reliably detect, and what might just be noise.

With a (good) power meter, you can get exceptionally good CdA estimates (as good as a wind tunnel) but it requires no wind to achieve that, and a quality data collection process. More wind reduces precision. You can also attain estimates of rolling resistance as well.