Improving my bike fit using a smart trainer: what I learned

TL;DR

• My saddle was too low because the method I used to determine saddle height didn’t work for me.
• I tried to overcompensate for what I perceived as excessive reach by moving the saddle forward. Moving it back instead and improving my posture worked a treat.

Backstory

In mid-December 2020 another half-hearted lockdown loomed in my region and there was a possibility that exercise outside might actually be prohibited. That made the decision to finally pull the trigger on a smart bike trainer easy and I was lucky enough to snag a mid-range model before they went out of stock in Germany.

I’ve been enjoying the smart trainer a lot and it’s helped me improve my many aspects of my cardiovascular fitness. Something I’ll write about at some point.
The other benefit the bike trainer brought with it, was the ability to slowly but steadily improve my bike fit on both my road bike and my gravel bike. It’s honestly had as much of, if not more of an impact on my riding as the marked improvement in fitness.

There are a lot of good resources for picking the right size of frame and dialling in the right position of the touch points on a bike, to achieve an optimal riding position. The three that have helped me the most since December are,

1. “Bike Fit Tuesdays” on Francis Cade’s youtube channel,
2. “Bike Fitting Series (with Neill Stanbury)” on Cam Nicholls’s youtube channel,
3. And the article “How to Determine the Correct Saddle Height” on the site of the cycling retailer Mantel, oddly enough.

The big issue with attempting to try all of the advice thrown around is that it’s hard to do on the bike when out riding or not being able to pedal while sitting on the bike. That’s where the trainer came in really handy and I’d encourage anyone to either buy or rent one, if you want to improve comfort and efficiency on your bicycle¹.

Side note:
Getting a professional bike fit has been something I considered to be something useful only for racers but I’ve come to change my mind and would now recommend getting one to anybody who either plans on buying a new bicycle or has issues with comfort on their current one.

So here’s what I learned

The resources I linked to above have loads of great information and greatly improved my understanding of how certain changes to a bike influence my riding position. The findings listed here came as a bit of a surprise to me, or were generally counterintuitive based on the information that is out there.

Moving my saddle back

James of Bicycle Richmond often mentions in the Bike Fit Tuesdays videos that many people buy bikes with excessive reach and then try to compensate for that by moving the saddle forward or hunching over the handlebars, which leads to all sorts of pains, mostly a lot of pressure on the hands and wrists.

Well for me it was a bit of a mixed bag. The bicycle frames I have are the right size, from what I can tell. I’ve already equipped my road bike and gravel bike with comparatively shorts stems (~ 7 cm) and the handlebars I use also have short reach figures. Still, I felt the need to use seat posts with no setback and moved the saddles forward, often as far as they went. I did so because of things I read about a good angle between torso and upper arms and a general impression of being too stretched out on my steeds.

The result has always been the aforementioned impression of riding on a stretcher even while I felt hunched over the handlebars and putting a lot of weight onto my hands and wrists. This in turn caused numbness in my hands, sometimes after only 20–30 min of riding. On the bike trainer, when I wasn’t shifting my position as often as I did riding outside, this effect was even more pronounced.

In one of the bike fitting videos I learned about hip position over the bottom bracket and how being too far forward could result in pains and less power output. I gave it a try, gradually moving the saddle back² and carefully tilting it forward a bit. This resulted in me rotating my upper body downward and my hip forward.
I was honestly stunned by how suddenly my core muscles had an easier time supporting my upper body, less weight resting on the hands, and the bike feeling less long even though I technically increased the distance between the nose of my saddle and the handlebars.

Something was still a little off:

My saddle was too low

This realisation was the single biggest revelation to my riding comfort and equally importantly; my cycling efficiency.

One of the most commonly used methods to estimate/determine saddle height is the “heel method”, where you sit squarely on the saddle and place your heel on the pedal, with the leg fully extended. If you cannot extend the leg fully, move the saddle up. If you find that you’re rolling of the side of the saddle trying to extend the leg, move the saddle down until you sit securely on the saddle again.

I’ve been setting my saddle height using this method for years and it Turns Out™ that it doesn’t work for me.

Looking at a video my partner recorded, I noticed that in the lowest pedal position the underside of my foot was pretty much level with the ground and that the angle of my upper leg to my lower leg was larger than typically recommended.

After some reading, I discovered two methods for calculating saddle height (see the article linked above) and they gave me totally different numbers than the heel method and a new starting point for experimentation.

I gradually increased the height of my saddle and ended up with 3 cm more³. Honestly, that’s a lot. The effects of this modification were and are profound:

1. I still feel perfectly planted on the saddle, perfectly secure sitting on the bike.
2. In the lowest pedal position my heel now sits higher than my toes and my leg is extended further. This has led directly to my calf muscles being activated and me being able to put more power down.
3. It made rotating my hip forward and my whole upper body downward even easier and even more comfortable.

Bonus: use a narrower saddle on a trainer

This one was a small but nice surprise.

At the beginning of my time with the smart trainer, I had specifically put a slightly wider saddle on my road bike thinking that the increased surface area would help spread the load I put on it, riding in a more static position than while out and about. After having already gone through the two steps above, I still felt some discomfort after a long time in the saddle on the trainer.

Looking for information, I stumbled across a video on the youtube cycling channel GCN where someone asked for advice with saddle sores/butt pain on a bike trainer. Their guidance was to use a narrower saddle than what one would typically use but obviously something that still supports the sit bones fully, to encourage more movement and better circulation while on a static trainer.

This bit of advice turned out to be bang-on for me and brought the desired improvement.

In conclusion

Using a bike trainer allowed me to cautiously experiment and eventually massively improve my bike fit. I was lucky in the sense that my bicycles have the right size and my basic assumptions about reach and stem length were correct. Honestly, I should’ve gotten a trainer (or better: a proper bike fit) a long time ago.

Cycling on my bikes now, I’m much more relaxed, able to put much more power down at the same perceived exertion, and long rides are more enjoyable because my bikes feel more comfortable.
On the gravel bike in tricky terrain there has been another positive side effect: due to the fact that I’m putting less weight onto the handlebars and being in a generally more balanced forward/aft position on the bike, I’m able to steer more nimbly. That gives me more confidence on technical climbs and descents and makes for a wildly improved and fun overall riding experience.