Help with saddle position and shorter cranks?

Triathlon Forum
1

I have read extensively on riding shorter cranks. I understand the value in opening the hip angle and the top of the pedal stroke. My questions for the fit experts are these:

If I currently run 170’s and go to 165’s should I?

  1. raise my saddle and by how much
  2. move my saddle back and by how much

The reason I ask these is that my saddle height is determined by the position of my leg at the bottom of the pedal stroke. Assuming my saddle is currently at the correct height I would want it to be higher with a shorter crank. However, assuming my saddle setback is determined by having my knee over the spindle with the crank horizontal to the ground wouldn’t I want to move the saddle back?

2

I just switched to shorter cranks.

Yes you’ll want to raise your saddle assuming your current height is correct. However, you’ll want to move your saddle forward ( relative to the BB ) on its rails since moving the seat up moves it back due to the seat tube angle.

3

Saddle up 5mm and forward Xmm. However that X amount is very small but you could figure it out mathematically if you know your seat tube angle.

4

Makes sense that moving saddle higher will move it back relative to the bottom bracket but doesn’t having shorter cranks move my leg back at the most forward crank position as well?

5

I have read extensively on riding shorter cranks. I understand the value in opening the hip angle and the top of the pedal stroke. My questions for the fit experts are these:

If I currently run 170’s and go to 165’s should I?

  1. raise my saddle and by how much ?

5mm vertically relative to the BB. Don’t forget to also raise your bars by the same amount.

  1. move my saddle back and by how much ?

5mm horizontally relative to the BB. Don’t forget to also move your bars back by the same amount.

The reason I ask these is that my saddle height is determined by the position of my leg at the bottom of the pedal stroke. Assuming my saddle is currently at the correct height I would want it to be higher with a shorter crank. However, assuming my saddle setback is determined by having my knee over the spindle with the crank horizontal to the ground wouldn’t I want to move the saddle back?

Exactly!

6

Tom, your response troubles me very much. I know you are a knowledgeable stud, but I need to disagree with you this time.

First: The OP needs to know that KOPS is not the right fit metric to be using for determining saddle position fore/aft. Especially not on a tri bike. It all needs to flow from hip angle. To maintain his hip angle he should be counseled to use trig to determine how far forward to move the seat based on his current STA and a 5mm increase in the hypotenuse…or just about as good to play with the seat position per feel.

Second: The OP was wrong about moving the seat backwards, it is forwards and you should have corrected that.

Third: this might then have him moving his bars (or just pads) foward, not backward.

7

Tom, your response troubles me very much. I know you are a knowledgeable stud, but I need to disagree with you this time.

First: The OP needs to know that KOPS is not the right fit metric to be using for determining saddle position fore/aft. Especially not on a tri bike. It all needs to flow from hip angle. To maintain his hip angle he should be counseled to use trig to determine how far forward to move the seat based on his current STA and a 5mm increase in the hypotenuse…or just about as good to play with the seat position per feel.

Second: The OP was wrong about moving the seat backwards, it is forwards and you should have corrected that.

Third: this might then have him moving his bars (or just pads) foward, not backward.

Your response troubles me as well…because I’m right! :wink:

Seriously, though…I wasn’t so much worrying about the KOPS part of the OP’s statement (it’s actually not a bad starting point for any bike fit) since I realized that the intent was actually to keep the relationship of the leg to the pedal constant through the “power stroke” of the pedal cycle.

When moving to a shorter crank, the foot will be closer to the center of the BB during the power stroke…hence, the need to move the saddle back to keep the leg-pedal relationship the same. The bars move back as well to keep the saddle-bar relationship the same.

Lastly, if the locations of all of the “touchpoints” are recorded in horizontal and vertical measurements relative to the BB (which is why I used that specific language in the response), then NO trig is necessary.

8

Fist off, listen to Tom’s advice. I have been to the School of Tomology and it’s dead nuts on. So sayeth my ride and my bud’s Planet X we copied over from his Litespeed.

Secondly, DO the shorter crank experiment you won’t be sorry. I’m 6’1" and went to 165’s and it was just heaven for ‘me’. In my sphere of influence it’s 4 for 4 happy customers by going to shorter cranks. Plus you can dump them in a second if you don’t like 'em.

9

Ok Tom…so I understand what you are saying and agree there’s a bit of logic to it.

But you are implying that proper bike fit (and we are talking tri bikes I assume rather than road bikes) all hinges from the vertical axis rather than being relative to the body of the person on the bike. And then you are arranging the touchpoints from there. It seems that this would thereby disparage the concept of rotating the body forward around the bottom bracket which is how we always think of obtaining a good TT position…because darnit, the knee would now be more forward relative to the pedal! And we can’t have that!

If you are to be totally consistent in your advice to the OP, you will have to also have him move his elbow pads UP to complete your exercise of basically rotating him backwards around the bottom bracket.

I would assert that you are wrong to keep the leg to pedal relationship the same. First, on what axis would you be maintaining it? When interfacing with a circular crank the angle of attack versus vertical means nothing. It’s the angle of attack versus some point relative to the body that is meaningful. And with a shorter pedal it’s maintained by moving the seat foward and the elbow pads down.

Of course you may still be right. :wink:

10

Ok Tom…so I understand what you are saying and agree there’s a bit of logic to it.

But you are implying that proper bike fit (and we are talking tri bikes I assume rather than road bikes) all hinges from the vertical axis rather than being relative to the body of the person on the bike. And then you are arranging the touchpoints from there. It seems that this would thereby disparage the concept of rotating the body forward around the bottom bracket which is how we always think of obtaining a good TT position…because darnit, the knee would now be more forward relative to the pedal! And we can’t have that!

If you are to be totally consistent in your advice to the OP, you will have to also have him move his elbow pads UP to complete your exercise of basically rotating him backwards around the bottom bracket.

I would assert that you are wrong to keep the leg to pedal relationship the same. First, on what axis would you be maintaining it? When interfacing with a circular crank the angle of attack versus vertical means nothing. It’s the angle of attack versus some point relative to the body that is meaningful. And with a shorter pedal it’s maintained by moving the seat foward and the elbow pads down.

Of course you may still be right. :wink:

I’m not Tom but IMO what he is talking about is maintaining the same position on the bike but with a shorter crank length. I think of it this way by visualizing a side view of the cyclist with the near leg fully extended along the line from the hip to pedal. Now decrease the crank length by X mm and move the cyclist in the same position up that line. What happens ?? The saddle and elbow pads must move up and back. The combination of saddle moving up and the shorter crank results in the position of the opposite knee at full contraction (for want of a better word) is ~ 2X mm lower. The benefit is that the hip angle is opened up possibly permitting better breathing and more supply power.

IIRC Tom did mention moving the elbow pads up.

The shorter cranks may result in an opportunity to effectively get into a lower position and so lower CdA at the same power.

11

I have read extensively on riding shorter cranks. I understand the value in opening the hip angle and the top of the pedal stroke. My questions for the fit experts are these:

If I currently run 170’s and go to 165’s should I?

  1. raise my saddle and by how much ?

5mm vertically relative to the BB. Don’t forget to also raise your bars by the same amount.

  1. move my saddle back and by how much ?

5mm horizontally relative to the BB. Don’t forget to also move your bars back by the same amount.

The reason I ask these is that my saddle height is determined by the position of my leg at the bottom of the pedal stroke. Assuming my saddle is currently at the correct height I would want it to be higher with a shorter crank. However, assuming my saddle setback is determined by having my knee over the spindle with the crank horizontal to the ground wouldn’t I want to move the saddle back?

Exactly!

is it a fool’s errand not to raise the handlebars as well? Part of the reason for me to get shorter cranks was that my stem was already slammed against an ungodly tall 16.3cm effective HT, and i can be quite a bit lower. getting 7.5mm was part of the equation

12

Ok Tom…so I understand what you are saying and agree there’s a bit of logic to it.

But you are implying that proper bike fit (and we are talking tri bikes I assume rather than road bikes) all hinges from the vertical axis rather than being relative to the body of the person on the bike. And then you are arranging the touchpoints from there.

No. All I’m describing is what the OP is asking about, i.e. when switching to shorter cranks, what adjustements to the other touchpoints need to be made to keep the relationships between the saddle, the bars, and the foot in the power stroke the same?

I’m getting the impression that you’re over-thinking this…

It seems that this would thereby disparage the concept of rotating the body forward around the bottom bracket which is how we always think of obtaining a good TT position…because darnit, the knee would now be more forward relative to the pedal! And we can’t have that!

Not at all. See the explanation above. My advice was given under the assumption that the OP has his touchpoints currently where he wants them to be and is merely looking to gain some “room” between his leg and his torso at the top of the pedal stroke. My advice for how to move the other touchpoints had nothing to do with the original fitting exercise.

If you are to be totally consistent in your advice to the OP, you will have to also have him move his elbow pads UP to complete your exercise of basically rotating him backwards around the bottom bracket.

I did say to raise the bars, didn’t I? I didn’t explicitly state to raise the pads, but I’m assuming they’re attached to the bars, which is pretty reasonable, no? :wink:

I would assert that you are wrong to keep the leg to pedal relationship the same. First, on what axis would you be maintaining it? When interfacing with a circular crank the angle of attack versus vertical means nothing. It’s the angle of attack versus some point relative to the body that is meaningful. And with a shorter pedal it’s maintained by moving the seat foward and the elbow pads down.

Again, you appear to be overthinking things. The important thing about the pedal/foot interface is the path that the pedal takes through the power stroke (downstroke) portion of the pedal cycle. The “return path” on the upstroke isn’t as important. The power stroke is close enough to being a vertical that the adjustments I described above are perfectly acceptable using horizontal and vertical references. Being a practical sort of engineer, sometimes being close enough is…well…close enough :wink:

The point of the adjustments when moving to a shorter crank (and not changing the touchpoint relationships) is not to rotate about the BB…the point is to translate the body relative to the BB in the longitudinal plane of the bike so that the relationships to the touchpoints (with the pedal touchpoint being at the point of max torque application) are kept constant while also keeping the orientation of the upper torso relative to the horizontal plane consistent.

The whole point is to not *just *make adjustments to saddle position when changing between crank lengths. That’s how you end up with people saying things like “I swapped from 175s to 170s and it just didn’t feel right”.

If one wants to make other adjustments (for example, lowering the angle of the torso relative to the ground) that moving to shorter cranks might help accomplish, then that’s an slightly different issue than what the OP was asking about.

Of course you may still be right. :wink:

Of course :slight_smile: Then again, if you search enough, I think you’ll find cases where I’ve stuffed the direction of adjustments before…but, I’m pretty sure I learned from the pain of those experiences enough that I’m not making that mistake again here…I hope… :slight_smile:

13

I have read extensively on riding shorter cranks. I understand the value in opening the hip angle and the top of the pedal stroke. My questions for the fit experts are these:

If I currently run 170’s and go to 165’s should I?

  1. raise my saddle and by how much ?

5mm vertically relative to the BB. Don’t forget to also raise your bars by the same amount.

  1. move my saddle back and by how much ?

5mm horizontally relative to the BB. Don’t forget to also move your bars back by the same amount.

The reason I ask these is that my saddle height is determined by the position of my leg at the bottom of the pedal stroke. Assuming my saddle is currently at the correct height I would want it to be higher with a shorter crank. However, assuming my saddle setback is determined by having my knee over the spindle with the crank horizontal to the ground wouldn’t I want to move the saddle back?

Exactly!

is it a fool’s errand not to raise the handlebars as well? Part of the reason for me to get shorter cranks was that my stem was already slammed against an ungodly tall 16.3cm effective HT, and i can be quite a bit lower. getting 7.5mm was part of the equation

No. Your intent was to also effectively lower the angle of your torso relative to the ground, correct? Sounds good to me…

14

I’m getting the impression that you’re over-thinking this…

I think I agree.

I did say to raise the bars, didn’t I? I didn’t explicitly state to raise the pads, but I’m assuming they’re attached to the bars, which is pretty reasonable, no? :wink:

I missed that. I only remembered you saying to move them back. Apologies.

And I wonder if adjusting the entire set of touchpoints for a 5mm change in crank length might not be overthinking. There’s a decent amount of flexibility in the human form to absorb this I think. My personal experience switching from 175 to 165 only had me reposition the seat and everything felt great.
Thanks for your willingness to dialogue about it.