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Shorter Cranks = Higher Seat Post ?

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Shorter Cranks = Higher Seat Post ?

Old 01-11-15, 10:42 PM
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rekon
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Shorter Cranks = Higher Seat Post ?

This is probably a dumb question. I raised my seat post about 5 inches and have 170mm cranks. If I get shorter cranks, could I raise my seat higher?
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Old 01-11-15, 10:43 PM
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Yes
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Old 01-11-15, 10:56 PM
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Yes.
Do you have a goal for a higher seat post?

Consider when the pedal is at the bottom of the stroke.

Longer cranks = lower pedal at bottom ==> lower seat
Shorter cranks = higher pedal at bottom ==> higher seat
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Old 01-11-15, 10:57 PM
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Originally Posted by rekon
If I get shorter cranks, could I raise my seat higher?
Yes, but I really hope you're not doing so for that reason alone.
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Old 01-11-15, 11:01 PM
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Originally Posted by k_kibbler
Yes, but I really hope you're not doing so for that reason alone.
I want to have a more aggressive position. I'm thinking I could accomplish this by buying a new bike (smaller than my current 52cm) or shorter cranks...
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Old 01-11-15, 11:08 PM
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The effect of 170mm vs. 175mm cranks is going to be pretty minimal (it's only 1/5 of an inch). I'd think you could get a more aggressive position with a change (or adjustment) of your stem that would be much more pronounced.
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Old 01-11-15, 11:13 PM
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I'm not sure sticking your butt higher in the air makes you more aerodynamic.
You're better off dropping the handlebars.

Go with 140mm cranks, and it is about a 3cm difference.
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Old 01-12-15, 12:37 AM
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Originally Posted by rekon
I want to have a more aggressive position. I'm thinking I could accomplish this by buying a new bike (smaller than my current 52cm) or shorter cranks...
You are doing it wrong. Have you removed all the spacers between the headset and the stem (including the large conical spacer)? What is the length and angle of you stem?
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Old 01-12-15, 01:24 AM
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Originally Posted by CliffordK
I'm not sure sticking your butt higher in the air makes you more aerodynamic.
You're better off dropping the handlebars.

Go with 140mm cranks, and it is about a 3cm difference.
Originally Posted by Fiery
You are doing it wrong. Have you removed all the spacers between the headset and the stem (including the large conical spacer)? What is the length and angle of you stem?
ding ding. Sticking your butt higher in the air isn't more aggressive.

I periodically ride with a friend of mine who is a dramatically stronger rider than I am - he prefers speedplay pedals because the stack height is ever so slightly lower and that lets him lower the seat a skosh, to get him out of the wind a little. Since he's so much faster than I am, I pretty much just say "uh huh" and keep pedaling.
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Old 01-12-15, 01:50 AM
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Originally Posted by TrojanHorse
ding ding. Sticking your butt higher in the air isn't more aggressive.

I periodically ride with a friend of mine who is a dramatically stronger rider than I am - he prefers speedplay pedals because the stack height is ever so slightly lower and that lets him lower the seat a skosh, to get him out of the wind a little. Since he's so much faster than I am, I pretty much just say "uh huh" and keep pedaling.
Then he messes that all up by using shoes that require the 3 hole to 4 hole adapter.
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Old 01-12-15, 02:30 AM
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Originally Posted by prathmann
The effect of 170mm vs. 175mm cranks is going to be pretty minimal (it's only 1/5 of an inch). I'd think you could get a more aggressive position with a change (or adjustment) of your stem that would be much more pronounced.
+1. The adjustment for shorter cranks is in the range of 5-10mm. You (the OP) have moved your seat by inches already... ?
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Old 01-12-15, 06:47 AM
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I went to 165mm cranks to get more aggressive. I have a flipped and slammed -17 stem, and I am flexible enough that it is comfortable, but the problem was that I kept kneeing myself in the chest with 170s.

I now graze my jersey with my knees with 165s, so yes, shorter cranks did help me use a more aggressive position.
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Old 01-12-15, 06:50 AM
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Oh, and my seat came up 5mm, of course
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Old 01-12-15, 07:11 AM
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Originally Posted by TrojanHorse
ding ding. Sticking your butt higher in the air isn't more aggressive.
Yeah, but it looks more aggressive, and isn't that all that matters?
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Old 01-12-15, 10:27 AM
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Originally Posted by rekon
This is probably a dumb question. I raised my seat post about 5 inches and have 170mm cranks. If I get shorter cranks, could I raise my seat higher?


Don't forget that you'll be faster if you can reach the pedals.
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Old 01-12-15, 09:19 PM
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Originally Posted by Wesley36
I went to 165mm cranks to get more aggressive. I have a flipped and slammed -17 stem, and I am flexible enough that it is comfortable, but the problem was that I kept kneeing myself in the chest with 170s.

I now graze my jersey with my knees with 165s, so yes, shorter cranks did help me use a more aggressive position.
I think a slammed -17 is still too low.

I'm sure you'll defend the set up but I really hope you're getting a full pedal stroke.
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Old 01-13-15, 03:34 AM
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Originally Posted by KantoBoy
I think a slammed -17 is still too low.

I'm sure you'll defend the set up but I really hope you're getting a full pedal stroke.
Based on what? Do some research before deciding you know what is what regarding crank lengths and pedal strokes

Determinants of maximal cycling power: crank length, pedaling rate ... - PubMed - NCBI

Trained cyclists (n = 16) performed maximal inertial load cycle ergometry using crank lengths of 120, 145, 170, 195, and 220 mm. Maximum power ranged from a low of 1149 (20) W for the 220-mm cranks to a high of 1194 (21) W for the 145-mm cranks. Power produced with the 145- and 170-mm cranks was significantly (P < 0.05) greater than that produced with the 120- and 220-mm cranks.*
Determination of the crank-arm length to maximize power production in recumbent-cycle ergometry | Danny Too - Academia.edu

Note in this study highest peak power was around 165mm

Crank Length - Cervélo
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Old 01-13-15, 03:38 AM
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Originally Posted by KantoBoy
I think a slammed -17 is still too low.

I'm sure you'll defend the set up but I really hope you're getting a full pedal stroke.
Based on what? Do some research before deciding you know what is what regarding crank lengths and pedal strokes

Determinants of maximal cycling power: crank length, pedaling rate ... - PubMed - NCBI

Trained cyclists (n = 16) performed maximal inertial load cycle ergometry using crank lengths of 120, 145, 170, 195, and 220 mm. Maximum power ranged from a low of 1149 (20) W for the 220-mm cranks to a high of 1194 (21) W for the 145-mm cranks. Power produced with the 145- and 170-mm cranks was significantly (P < 0.05) greater than that produced with the 120- and 220-mm cranks.*
Determination of the crank-arm length to maximize power production in recumbent-cycle ergometry | Danny Too - Academia.edu

Note in this study highest peak power was around 165mm

Crank Length - Cervélo
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