I’ve read all over the internet that “an hour on the trainer is worth 1.5hrs of outdoor riding” but can’t find any science behind this.
If I ride for 1hr at 65% indoors today, and then do the exact same ride outdoors tomorrow, the TSS will be exactly the same. I understand that the road will never be as consistent as the trainer, but surely it can’t make THAT much of a difference. Anyone know of any science that quantifies his trainer time/tss compares to outdoor time/tss?
Some related discussions:
Forget science, the argument is really about being a) time efficient, and b) sticking with the plan. Indoor rides have little or no coasting, and so they are time efficient. Many people use erg mode, so they stick with the plan. Those are the primary reasons.
That said, I’ve got plenty of country roads nearby where I can ride without interruption. A recent 2.5 hour outside ride only had 6% coasting due to getting in and out of town. It included 10 second “full gas” sprints which I find difficult to do on the trainer. Excellent workout, perfect for outside. But if I wanted to do an hour of 30/15s or 40/20s, those I find easier to do inside.
I’ve seen the 1:1.5 ratio but also 1:1:15 ratio from popular coaches. Also, the lower the intensity, the closer the ratio gets to 1:1.
Plus, there’s a difference between “moving time” and “power time” (not a real term, but let’s go with it). My last 5hr Z2 outside ride was actually 5.5hrs with ~10% of non-moving time (so many nature breaks!). However, I had only 1% of coasting/zero power time. That said, only 60% of the ride was in the desired power zone (92% in the desired HR zone, which is what I was training to); on an indoor trainer it would have been much closer to 100%. Then again, a 5hr outdoor ride is always going to be worth 1,000% times more than a 5hr indoor trainer ride.
At the end of the day it’s going to be based on your personal results. Troll your data to extrapolate your own ratio.
even that is workout dependent. I recently did Garrowby-2 which has 39 minutes of sweet spot, and the breakdown on my trainer (Kickr 2017 wheel off) was:
which is roughly 43% in the target power zone. But does hitting precise power targets really matter? Practically speaking, in my experience the answer is “no” as I’ve made the same improvements doing a training block inside and outside.
In my personal opinion, training inside is about:
I sacrificed Day 1 of a long weekend doing an experiment for you. Yeah…YOU! 
My weekend Z2 endurance rides are usually 5hrs long but I decided to stay inside and do an horrific 4hr trainer ride, y’know, just to see. Compared with a 4hr ride of 3 weeks ago (at same HR), the indoor ride resulted in:
+19% more power (NP)
+50% more TSS/hr
+40% more kJ/hr
No idea what this means, just putting it out there.
I can see moving from an outside time based training scheduled in the summer to a kJ based winter program on the trainer (i.e. 15 outside hours reduced to 10 inside hours). Of course this pertains to my data only, YMMV.
Awesome experiment, Cap.
For me, even for endurance stuff, I find the trainer a better way to hit the higher end, for whatever reason I have trouble getting a steady 70-75% outdoors, I seem to always default between 60-70%. I rode a solo (almost) century yesterday, my IF was 0.67, it gets easier to put power down on some sustained hills but otherwise it requires a ton of concentration from me to get to the upper z2 range that is just so much easier with erg mode. Not that I’m riding 5hrs indoors to know for sure, but maybe someday I’ll try 5hrs at 0.7 lol
Agreed. On my outdoor Z2 rides I really have to keep an eye on things or I start to go too easy.
Also just read an article about TSS vs kJ:
https://wattmatters.blog/home/2006/12/tss-vs-kj.html
Will have to investigate further in regards to outdoor vs indoor rides of similar length & zonage.
Just the opposite here, I have to concentrate to stop an outside endurance ride from becoming tempo.