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Home > Forum > Triathlon Forum > [BikeFit] Lowering Cda -> Lower Stack & Shorter Reach?

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[BikeFit] Lowering Cda -> Lower Stack & Shorter Reach?
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ThibThib
Apr 20, 21 4:21
Post #1 of 9 (1093 views)
Hello,

I did a bike fit 6months ago and resulting specs were:

Saddle Height: 721mm (with 172.5mm Crank)
Pad Reach (BB to end of pad): 467mm
Pad Stack: 650mm

Could you please advise me on the 2 following scenarios?

1) Swapping only Crank:

Moving from 172.5mm to 165mm

New saddle height => would think ~729mm

Pad Stack: lower crank should be lower stack I'd imagine (as lower crank would open up hip angle)
Pad Reach: would that shorten reach as well?

2) Swapping Crank + trying to be more aero/aggressive:

New saddle height => would think ~729mm

Pad Stack: how much lower should I try? From 650mm down to 625mm or is that too big a jump? (although the shorter cranks should help)
Pad Reach: Shortening it from 467mm to ~ 457mm? Would I be correct in thinking that it's just a 'geometry' problem that could be solved via cos? Are any websites/sheets which can help?


Thanks,

ThibThib




Last edited by: ThibThib: Apr 20, 21 4:28

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Re: [BikeFit] Lowering Cda -> Lower Stack & Shorter Reach? [ThibThib] [ In reply to ]
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rruff
Apr 20, 21 10:17
Post #2 of 9 (996 views)
Are the photos of your baseline fit/setup?

Nominally you'd move the saddle both up and back a bit (retain max leg extension at the bottom, and also compensate for the reduced "foot reach" at 90 degrees).

What events are you racing, and what issues (if any) did you have with your original fit?
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Re: [rruff] [ In reply to ]
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ThibThib
Apr 20, 21 10:32
Post #3 of 9 (985 views)
rruff wrote:
Are the photos of your baseline fit/setup?

Nominally you'd move the saddle both up and back a bit (retain max leg extension at the bottom, and also compensate for the reduced "foot reach" at 90 degrees).

What events are you racing, and what issues (if any) did you have with your original fit?

Hi rruff,
Photos are with the current fit/setup.

Think it makes sense indeed, if shortening cranks by 7.5mm, then raising saddle height by 7.5mm and back it up by ~1-2mm.
I am less sure on what that would mean for reach&stack though?

I am racing mainly long distance, no real issue with my fit as I am finding it comfortable enough to stay there for long periods.

I'd like to just get it more and more aero with incremental changes (so that I have the time to adapt to it) - to that end, would assume lowering stack would help.. and I'd imagine that means I'd need to slightly shorten reach?
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Re: [BikeFit] Lowering Cda -> Lower Stack & Shorter Reach? [ThibThib] [ In reply to ]
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tilburydavis
Apr 20, 21 10:48
Post #4 of 9 (964 views)
In answer to your question, "it depends".

Victor Campanerts makes some good interesting points in the video below....

https://www.youtube.com/watch?v=nn5wXswY94w
David T-D
http://www.tilburydavis.com
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Re: [ThibThib] [ In reply to ]
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rruff
Apr 20, 21 11:13
Post #5 of 9 (948 views)
I know that short cranks are all the rage, but I wouldn't advocate that change unless it is to solve some discomfort. In other words work on aerodynamics with the cranks you have... then maybe go shorter if you feel it will help solve an issue.

Aero is tricky stuff. Lower is not necessarily better. It would probably be good to increase your saddle to bar drop a little, but I believe turtling (neck pivoted down at the shoulders, and head tilted up just enough to see) and scrunching (torso low with shoulders towards your ears) would have a bigger effect than a lower pad height. These are postural items; there is a massive range of positions possible with no change to your contact points at all, depending on your head, neck, and shoulder posture. At any rate, you will need to test it to know... and adapt.
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Re: [tilburs] [ In reply to ]
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ThibThib
Apr 20, 21 13:51
Post #6 of 9 (895 views)
tilburs wrote:
In answer to your question, "it depends".

Victor Campanerts makes some good interesting points in the video below....

https://www.youtube.com/watch?v=nn5wXswY94w

Thank you tilburs - very interesting indeed! Crazy how he manages to "shrink" his shoulders!

Gonna watch a few more videos from him
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Re: [rruff] [ In reply to ]
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ThibThib
Apr 20, 21 13:55
Post #7 of 9 (890 views)
rruff wrote:
I know that short cranks are all the rage, but I wouldn't advocate that change unless it is to solve some discomfort. In other words work on aerodynamics with the cranks you have... then maybe go shorter if you feel it will help solve an issue.

Aero is tricky stuff. Lower is not necessarily better. It would probably be good to increase your saddle to bar drop a little, but I believe turtling (neck pivoted down at the shoulders, and head tilted up just enough to see) and scrunching (torso low with shoulders towards your ears) would have a bigger effect than a lower pad height. These are postural items; there is a massive range of positions possible with no change to your contact points at all, depending on your head, neck, and shoulder posture. At any rate, you will need to test it to know... and adapt.

While trying to lower the stack, I was noticing that my legs were getting too close to my torso, so would be hoping that with shorter cranks I could dialed in a more aero position.

Fair point on "lower is not always better", guess only way to know for me is to try both and check via bestbikesplit the CDa.
But I'd think it is "likely" that lowering the stack would help me getting faster.


Point taken on the postural items - definitively some work there. I'll try to take a video in the next couple days from side & front to see where I am at currently. Should not be "too bad" as when riding outdoor I tend to get my chin to rest/touch my arms/hands area while still being comfortable and able to see where I am going.
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Re: [BikeFit] Lowering Cda -> Lower Stack & Shorter Reach? [ThibThib] [ In reply to ]
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jimatbeyond
Apr 20, 21 14:13
Post #8 of 9 (872 views)
Which saddle are you using?
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Re: [jimatbeyond] [ In reply to ]
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ThibThib
Apr 20, 21 14:36
Post #9 of 9 (859 views)
jimatbeyond wrote:
Which saddle are you using?

Dash Strike althought I am not 100% happy with it
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