HI, I have a higher FTP on my road bike than my TT bike, by approx 20 watts - how can Xert understand this and how will affect the stats etc - should I use the lower one, the TT one, as this is the one I will race on?
What you can do is open the Activity Details / Advanced tab for your TT activity and update the signature on that - reduce all three manually, click Refresh to make sure you don’t see a lot of yellow dots where Power > MPA and then Save/Lock. If your TP is 20W lower, use the same ratio for each signature parameter (say -6% on each parameter for example). This works well if you plan on riding just your TT bike for a while. If you alternate between Road and TT, then you’ll need to update each activity separately. Use the Extract button when power exceeds MPA to look for signature changes on each. This manual MPA analysis method is quite cool when you use it to determine the actual difference there is between riding one bike or position as compared to another.
Quick correction (I think): you’ll want to reduce your road signature, not your TT signature if you want your TT signature to be the one reflected in Xert (good call if you want to use your signature for TT races, with the TTE/TTR and MPA apps, for example).
Hi Jamie (great name BTW!), I may have made it more confusing that I should have. Basically, you have one signature, but you can manually change it for each activity. If you go into your Activity Table view, click on the activity, then click Advanced MPA, you can change the signature for that activity and then click ‘Save’ to lock it. So, for your TT rides, you can knock your FTP down by 20W (and you should do the same relative adjustment to the rest of the signature parameters (PP, HIE)). Know that the next time you have an activity that exceeds that signature you’ll get a breakthrough, raising your signature again, so it can be a little cumbersome if you’re switching bikes often. If you’d like to use Xert to help pace you during a TT race, you could ‘extract’ the signature from a really hard recent TT activity so that you know what your signature looks like on your TT bike, and then the night before your TT race go into your Profile and update your signature with those numbers. Then when your Garmin updates over-the-air the next time it’s turned on and sync’d with your phone, your signature will be ready for the race!
Much appreciated.
Not sure if I misunderstood. I did this for my TT ride the other day and my TP on my Profile page was lowered from 345W to 320W. I thought doing this would only affect the metrics (XSS etc) for the specific ride and not generally. Confused!
Hi Karl, this establishes a new signature that will carry forward until the next breakthrough activity or until you change it back (the next day for example).
Ah! That makes sense 
thanks!