Comparing the fit and trail riding experience on the gravel and fat bikes

First, a bit of backstory… I’ve had issues with my left knee since a junior high injury over 3 decades ago. It plays into my bike riding experience and is the reason I stopped riding twenty years ago. My hope is that by being careful my newfound ability ride bikes again will continue for many years but with that hope comes a caution regarding how I ride.

Fat Bike – look at those big, cushy tires!

I’ve been riding the Poseidon daily since the last week of July and have put on 2,700 miles of road and gravel riding. This past couple of weeks I decided to stay closer to home and return to some trail riding. Naturally I used this as an excuse to pull the fat bike out of the shed for a ride and what a blast! It’s such a soft, cushy ride! But after three or four days I started to get an occasional tension in my left knee. I’d felt this over the summer too when I rode but was careful and adjusted my seat, riding position and a few other things which reduced the problem somewhat. At least enough to keep riding. Then I started riding the Poseidon X in late July and the problem went away. I didn’t even think about it really. Then I started riding the fat bike and the discomfort returned. Hmmm.

Gravel Bike – can narrow tires handle the trails?

My first thought was to try to figure out if it was the fat bike or the nature of riding trails. So, to test I decided to try riding the trails with the Poseidon. It wasn’t too bad. Not as cushy as the fat bike which also meant taking it a bit slower. I figured if I could manage a few days I might see if the discomfort persisted. If it did I would chalk up the different kind of riding required by the trail to be the problem. Lots of standing then sitting and standing and sitting. And more torque and strain on the many little hills, twists and turns. It’s an over-all slower speed but I think more pressure on the knees. If the problem decreased or disappeared I figured the problem would point to some aspect of riding the fat bike specifically. After three days the discomfort had decreased and nearly disappeared. After an additional two days of riding there was no discomfort at all.

So it seems the problem may be the fat bike and I think I figured out that it is the width of the bike to accommodate the fat tires. Wider hubs, chain stays and, most importantly, a wider bottom bracket which means that the pedals stick out further too. The final result is that my feet are also out to each side a bit further and at somewhat of an angle. In the bike measuring world this is often called Q factor or “stance width” which is the better, more descriptive term. I noticed the difference when I got back on the fat bike after 2,700 miles on the narrower gravel bike. I actually felt it in my legs that my feet were farther apart but it didn’t occur to me that it would be a problem until it was a problem. Bummer because I do love riding that fat bike on these trails.

Okay then, to move onto the question, can a gravel bike, specifically the Poseidon X, be a trail bike? After riding the X on the trails for the past two weeks I’m feeling increasingly confident and comfortable using it as a trail bike. In fact, I have to say that I’m enjoying it more with each ride. Comparing it to the fat bike, it feels more agile and gets going more quickly. It feels faster. The fat bike with it’s heavier wheels requires more effort at the start and overall feels more comfortable but also less lively. In the first few days I rode the X with more caution and a bit slower. With less tire cushion and volume comes an overall bumpier feel especially at higher speed. I’d say that I feel a bit more focused when riding the X though as the days go on I’m increasingly more comfortable riding the trails at higher speeds.

I’m still experimenting with tire pressure, currently keeping it at 30 psi and will discuss further in the upcoming review of the Hutchinson Touareg tires and recently discussed the switch from 700c to 650b wheels. But for now I’ll conclude that trail riding (at least my trails) are very doable on the X with this wheel set and these tires.

Aside from tire volume and width of the tires, another notable difference is that the fat bike has a more upright position with higher handlebars which I prefer for comfort and feel. I was already thinking of changing to a shorter, steeper angled stem on the gravel bike to bring the bars closer and raise them up a bit. So, that’s next on the list.

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