Would having a very low rear tyre pressure have a significant affect on your ftp test result on trainerroad?
Very low as in 35psi…
It didn’t dawn on me till the cool down section!
Not done much riding since ride London in August last year, but apparently I’ve lost 20% of my ftp. Sure I’ve lost some but I’m hoping that it was partly the pressure!
Going to retest in a couple of days.

Tyre pressure does have an effect but the vast majority of that 20% is going to be genuine loss of fitness if my own experience is anything to go by. 🙁

I can deal with that, been in the gym a lot but no legs and very little cardio.

I was kind of hoping it was the tyre but at least I know what to aim for now!

What are you waiting power with? If a crank arm pm then none at all. But if your taking it from a turbo it will potentially make a big difference.

I’ve not done one for years but I used to calibrate the turbo before any tests.

Power is just the virtual power figure from trainerroad, so calculated from cadence/wheel speed/known turbo resistance curve.

Tyre pressure does make a big difference so don’t be too disheartened until you’ve tested again properly. I have friends who make their rollers sessions harder by nudging the pressure down on the tyres.

In that case I reckon tyre pressure will have a huge effect. At 35psi I’m surprised the tyre wasn’t slipping.

If it’s a road bike then it could easily make up almost the entire 20% difference.
The Virtual Power curve that TrainerRoad uses is based on known figures for resistance for the specific trainer, which is why they recommend the Kurt Kinetic trainers for virtual power use as they have a very consistant resistance curve over time which doesn’t change as it heats up.
Anyway, for a roadbike trainer tyre, recommended pressure is usually between 110-140psi so having only 35psi will have a massive effect on the power output you actually have compared to what TrainerRoad is assuming you have given the virtualpower curve.

TLDR – You need to pump the tyre up and do another FTP test I’m afraid.!

Well, its good news that hopefully it was the tyre!

I’ll empty the bucket out ready for the next test in a couple of days! 😡