Benefits of moving the saddle aft?

Equipment
1

Hi all,

I thought I had gotten dialed in to my new bike so I was very frustrated when I found it difficult to hit my normal 90+ rpm, in fact I shortened my cranks to 165mm from 172.5mm so I was expecting a cadence of over 95 rpm. I even chalked it up to being overly fatigued.

I checked online and came across a Bike Fit Adviser video where he suggested that moving the saddle aft always has more benefits that being too far forward. Well I moved the saddle aft about 10mm and behold, my cadence is back up to 95+ rpm and I don’t feel like I’m struggling against the pedals anymore. Another thing to note is that when my saddle was forward my left knee kept wobbling at the top of the pedal stroke, this doesn’t happen after moving my saddle aft.

Does anyone here know why moving a saddle aft helps with pedal stroke? What exactly are the benefits?

3

Indeed, with fore-aft saddle position adjustments, you typically need to do a related change in saddle height.

It is roughly 2:1 so if you move the saddle 10mm aft, you should drop the saddle height about 5mm. This assumes the starting height was “correct” and the goal is to maintain the leg extension after the fore-aft change.

This change is needed due to the roughly 73* seat post angle (typical road bike).

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4

I increased the saddle post height when I got the short cranks, but I didn’t move the saddle back because I was concerned that reach might be an issue for me.

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6

There is a lot of black magic and strong opinion among fitters about proper fore-aft position. K.O.P.S is great… no, it’s the devil… and other sorcery about how to position yourself. Ideas about power delivery and cadence run the full range and it is all a bit maddening if you dig in too deep.

Personally, I start with K.O.P.S. and adjust to suit the needs and preferences of each rider.

With your shorter cranks, even with your saddle 7.5mm height increase (which also moves you back about 4mm at the same time), you “effectively” ended up more “in front” of the pedal spindle by about 3mm after all the changes are done.

That may have lead to a more closed leg angle at the bottom of the stroke for extension. It also leads to a different angle through the majority of the stroke. That may account for you knee popping out, but it’s not the only possible cause.

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