FTP using MPH on Turbo

tommy_tommy

I use a cycle computer with a rear wheel sensor to measure speed whilst training on my turbo trainer. I also measure my heart rate with a polar heart rate monitor.

To calculate a rough FTP figure I follow this protocol:

1. Warm up ten minutes
2. Cycle up to 20MPH hold for 15 seconds and then stop pedaling.
3. Measure time for wheel to stop rolling.
4. Perform 2 and 3 times and calculate average roll down time. (10 seconds)
5. Complete 30 min TT on turbo save average speed and average HR

I use these 2 figures to calculate my turbo training zones.

In the last 2 months, since the end of the last racing season, I have only completed 2 weekly 30 min easy sessions with 6 * 30 SEC sprints. I have also completed 2 weekly weights sessions. Please note this schedule was not intended to improve cycling performance.

I have decided to race again this season so conducted an FTP test today to set a starting
point. Here are the figures:

Jan 10
Time: 30 min
Ave speed: 15.2 mph
Ave HR: 157

I compared this result to last year

Jan 09

Time 30min
Ave speed: 17.2 mph
Ave HR: 148 bpm

I followed the same protocol each time so what has gone wrong? I understand why my speed has dropped because I am not aerobically fit. Weights and short sprints do not maintain FTP.

However, how did I maintain such an high heart rate this year compared to last year? Is this normal for a reduction in fitness?

I did a few 10 Mile TT's last year and maintained and average HR of 157bpm each time. Maybe, I did not try hard enough on last years test which means my fitness is even worse than the second test suggests.

Anyway, I'll start the long tempo rides and 2 x 20 minutes etc and test again in 6 weeks.

Bhima

Are your tyres the same?

Same pressure?

Same resistance?

Same room temperature/fans/cooling?

Same hydration?

Maybe you were fatigued...?

Perhaps the power-speed relationship of your setup varies a lot.

I use a similar system on rollers and can do an average speed 1.244km/h more in 30 minutes compared to 60 minutes so your zones could be more accurate if you did a 1 hour test. I'm not sure how wheel roll-down times affect things. Any chance of enlightening me there?:?

I've given up on all these calculations - it's better to just "feel" if you're in the right zone anyway.

chrisw12

Were the roll down tests the same? Did they produce the same figure?

Have you changed tyres from the last test?

Have you put on weight?

Were both efforts evenly paced? Averages can play some funny tricks if you haven't got your maths brain on.

Has your child/partner.cleaner/wife/enemy/other come in and changed the settings?

You performed a roll down test at the start which is good but if that was me I'd be kicking myself that I didn't perform one at the end as well!

and perhaps a suggestion for people using speed as a proxy for power on a turbo, use KM/H instead of mph. You'll get a bit more precision (wont you?)


See I suppose this is the pitfall with using speed as a proxy for power, there can be a lot of what ifs, if things go funny. Saying that, it can work. I'm getting very consistent power-speed readings from my turbo once it's WARMED UP.

chrisw12

'kin hell, I swear I posted mine first!!!!!!!!! :roll:

Bhima

One step ahead, as usual. 8)

Slow1972

When you do your "FTP" test, are you going all out the highest pace you cope with? I don't know how old you are but your average HRs seem quite low for a 'ride as hard as you can session". I appreciate HR is an individual thing though, for instance what is your max HR? If you're nor riding as hard as you can for the period its not really a FTP session (you're under threshold) and means you'll have difficulty comparing the tests.

Other wise if you are riding at threshold maybe your training means you have pushed up where you hit threshold within you HR range (hence the higher avg bpm) but your overall fitness is lower (because, all other things being equal, you're going slower at a higher HR)

Pokerface

I have a powermeter and a turbo. But also look at the MPH when doing my FTP tests (or even just normal training).

Only problem is, the actual wattage and speed will vary greatly from day to day. No way to get consistant readings.

Some days I'll do 250w average for 20 mins at an average speed of 24MPH, the next it might be 200w average at 24MPH average. Just too many variables with a turbo to go off the MPH.

At least there is on mine.

Anonymous

I don't display MPH whatsoever on my power meter. The only time I see it (if I actually want to) is when I download it.

dave35

Seeing as FTP is Functional Threshold Power, how can you even roughly work out FTP without a powermeter???

Anonymous

dave35 wrote:

Seeing as FTP is Functional Threshold Power, how can you even roughly work out FTP without a powermeter???

You can't, not with any degree of accuracy.

You can roughly work out your threshold HR though.

Bhima

The theory is, if your trainer's speed increases linearly with power, you can find your functional threshold speed.

Anonymous

Bhima wrote:

The theory is, if your trainer's speed increases linearly with power, you can find your functional threshold speed.

But power does not increase in a linear fashion for a given speed...

Bhima

NapoleonD wrote:

But power does not increase in a linear fashion for a given speed...

On some indoor trainers it does! Obviously, the speed outdoors would be meaningless...

amaferanga

There seems to be a phase that many people go through where they try to train 'with power', but without the parting with several hundred pounds on a power meter.

Most realise quite quickly that you either buy a power meter or just forget about it.

I went for the former option

andyeb

amaferanga wrote:

There seems to be a phase that many people go through where they try to train 'with power', but without the parting with several hundred pounds on a power meter.

Most realise quite quickly that you either buy a power meter or just forget about it.

I went for the former option

Agreed. And something that I've discovered since shelling out for a power meter, is that the power required to sustain a constant speed on the turbo does not remain the same, even within the same hard interval in the same session. That's on a Tacx Satori, which has magnetic resistance and has advertised linear power curves.

My theory is that the flywheel gets sufficiently hot to change the electrical resistance of the material, which in turn affects the amount of magnetic resistance produced.

Alex99

Pokerface wrote:

I have a powermeter and a turbo. But also look at the MPH when doing my FTP tests (or even just normal training).

Only problem is, the actual wattage and speed will vary greatly from day to day. No way to get consistant readings.

Some days I'll do 250w average for 20 mins at an average speed of 24MPH, the next it might be 200w average at 24MPH average. Just too many variables with a turbo to go off the MPH.

At least there is on mine.

That's a big varyation. Is that at constant speed... tt type of effort?

I find a really good correlation with power and speed on my turbo. I used turbo speed a lot prior to getting a power meter and I have made a power curve for my turbo.

As others have said (and is discussed in detail in Graeme Obrees book), same tyre, same pressure, same roller position are essential. Also, turbo's with wind ressistance may have more variation than magnetic. Of all these, to my mind tyres make a big difference... more so than on the road.

But, to the OP, don't take n of 1. Do the test at least another time.

Alex99

NapoleonD wrote:

Bhima wrote:

The theory is, if your trainer's speed increases linearly with power, you can find your functional threshold speed.

But power does not increase in a linear fashion for a given speed...

Turbo's have power-ressistance curves in various shapes and sizes. Some seems to be quite linear and some curved, presumably to try to be more 'realistic' in feel.

For what it's worth, my turbo's power curve flattens out at higher power ie. the opposite to 'real world'.

Alex99

NapoleonD wrote:

I don't display MPH whatsoever on my power meter. The only time I see it (if I actually want to) is when I download it.

Same here. Some people find that odd, but they haven't got a power meter.