[Closed] Multiple FTP's

Fairly common to have different FTPs indoor and outdoor even when using the same equipment. If using different setups then all bets are off. Short of knowing which of your values is "correct" or at least closest to the correct value I wouldn't worry about it.

If the proportion of indoor/outdoor riding remains fairly constant then while the calculated TSS is inaccurate it's consistent which is all that really matters since you use TSS to manage the changes in stress.

Consistently inaccurate TSS doesn't really work though.

For example, my FTP in Strava & TP is currently set at my indoor FTP value. Last night I rode outdoors and did my efforts at my outdoor FTP value but Strava and TP then then calculated my TSS based on the indoor FTP value and significantly overstated it.

A solution would be to adjust my FTP values in Strava / TP etc each day to match if i'm training indoor or outdoor that day but that's a pain.

Alternatively I guess I could just accept that the TSS value for either indoor or outdoor is going to be c10% up / down.

Its quite normal, not just the equipment but the environment.   Its a bit of a rabbit hole but for example there's Thermal efficiency issues on a Turbo - you run hot and are less efficient, you aren't engage in balancing a bike etc etc.

The only way I found to work with this is to use a PM - in my case a 4iiii crank arm - with Offset settings to closely match my power readings on my turbo with that on the bike.

Use TSS as a guide not a metric, its not accurate.  Its only a guide TSS - and strava algorithms are reputably not very accurate - but daily TSS is also effected by other physical and mental effort e.g. a hard day at work has just increased your TSS albeit invisibly.

I've not heard of the ability to offset power readings on powermeters before. That could be a solution, any ideas if it's available on Stages?

Just for info - I have x3 Stages that are all pretty consistent with one another (for now!!!). They're all reading about 10% higher than the Wattbike. If I could offset the stages to read 10% lower then that would be helpful?

You misunderstand "accuracy" and "consistency". If, when playing darts, I always aim for the bullseye then if I hit the treble 19 nine times out of ten throws then I'm inaccurate but consistent. If I always hit the bullseye I'm accurate AND consistent. If I hit the bullseye five times out of ten with the others in the outer bull then I'm accurate but inconsistent. If all the arrows are spread around the board then I'm inaccurate and inconsistent.

As I said before: "If the proportion of indoor/outdoor riding remains fairly constant then while the calculated TSS is inaccurate it’s consistent" and where TSS is concerned consistency is more important than accuracy.

No I do understand but not sure it'll work for me. I do ride indoors and outdoors but over the winter I might do 75% of riding one month indoors and if the weather is good I might ride 75% outdoors the next month. Pretty sure that would screw up CTL etc up a fair amount.

I've e-mailed Stages to see if there's a way to manually offset their powermeters like you can with the 4iii's. I can't see an option in the stages app to do it.

The TSS can’t be consistent (within 10%?) with itself anyway.

The method of scaling effort in relation to FTP is not going to account for the stress varying depending on your condition. Sometimes a few minutes over FTP is barely going to tax, sometimes it’s going to destroy. The TSS calculations aren’t smart enough to cover that.

Can I ask why TSS matters to you? (I’m assuming you already scale your intervals based on the expected capacity so this is just about booking numbers?)

Trainer Road have power match

https://support.trainerroad.com/hc/en-us/articles/204631294-PowerMatch-Using-Power-Meters-with-Smart-Trainers

I think this will mean the power indoors and outdoors will be the same but as kryton says there are loads of other factors that will change. As above consistency and accuracy are key

I have the same difference when doing FTP on rollers vs outside on the road. I use the outside number as it’s the higher of the two so if I’m doing indoor sessions I’m working slightly harder than I should be but that’s no bad thing! A possible solution could be to take the average of the two and use that, the error really isn’t that big

Cheers all, I think @claudie 's solution to take an average between the two is probably the most sensible and easiest. Unless of course i can offset the Stages to match the Wattbike.

@teamslug Powermatch wouldnt work for me as I don't use the same power meters both indoor and out.

@speccyguy I've used Trainingpeaks to track CTL for several years now and I scheduele my sessions according to my desiered weekly TSS goal.

The next question then has to be if there is a better way of allocating time than just booking TSS? (->CTL)

If I was just looking to increase my CTL I could do a ton of Z3 as my physiology means I can tolerate a stupid amount of work just below threshold and I have the time to do it = max CTL.

Thankfully I've broken my CTL fascination and now do the sessions that make sense to reach my goals and TSS is just an interesting artefact.

As long as you're scaling your intervals inside vs outside because of your physical response (and power meter) then you're doing the right work. TSS is so rough as to barely be more than an idea.

p.s. Slightly wonkish but my inside vs outside power is so influenced by temperature that '% FTP' is not something that is even slightly consistent in vs out. For example doing VO2 max intervals doesn't raise my core temp inside as much as long threshold intervals, so my VO2 max and above power/HR is pretty similar inside and out. But long threshold workouts inside (I avoid them!) are dramatically different to outside because they raise my core temp so much.

That sounds like you've been using TSS as the driver (CTL is the same thing, just averaged over a period). TSS/CTL is the result of what you do. Periodisation does mean that TSS has an input, i.e. values of 500, 600, 700, 300 and so on but 550, 600, 700, 300 is still valid. A TSS of 50 is something like an hour's Z2 work for me or it could be fifteen minutes of anaerobic sprints - not all TSS is created equal as the saying goes. So long as you aren't seeing 800, 400, 800, 300 then there's nothing to worry about.

Indoor temperature: most people have a frontal area on the bike of around 0.5m^2. If you ride at 10m/s (36kmh) then you've five cubic metres of air passing over you every second. Now look at the throughput of your fan(s), you will be lucky to have 10% of that. I've a Cleva Vacmaster Air Mover with a flow of 266 litres/sec and it feels like a hurricane!

VO2max intervals are short and have recovery valleys so there's both a lag in your body's responses and the opportunities for some cooling down. Threshold efforts are longer so you are still working hard by the time your body responds and there's this positive feedback going on. For sustained efforts I've a level, around 70-75%, where I won't raise a sweat. 80% and above I'll be dripping!

Will there not be a difference between the readings given by your power meter vs the Wattbike due to drivechain losses etc as well?
What's the difference when using the crank based power meter indoors?

Most people naturally get higher FTP outdoors, but using the same power source, you can get very similar indoor value with some perseverance...

You need to allow your body to adapt to indoor training, because outdoors it is used to heat easily being taken away.

For me, it takes 2-3 weeks, doing 3+ turbo sessions a week with at least a 20min z4+ per session, drinking lots of water (~1.5 litres per hour) and two decent fans... Maybe it helps that an FTP of 290-298W at ~3.5-4W/Kg is as good I've got, but my best figures are usually from indoors.

I tried to square the indoors/outdoors TSS differences a couple of years back. Looked at trying to apply offsets to my Stages (nope) or recording TSS differently and inputting it manually into TP (ughhh). I reckon I spent an extra 100TSS of effort each week trying to figure it out.

My conclusion? TSS is a fairly broad metric, and I was wasting my time. As long as you're doing the work, your CTL will trend appropriately and the exact TSS really isn't that important. The goal of TSS is to make sure you're doing enough but not too much - the window for this is pretty big. Just use it as a guide, and be mindful that your 'outdoor' weeks will have a higher TSS than your lower ones.