Frame size, new bike fitting, questions

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wozzo
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Joined: Mon May 09, 2022 1:43 am

by wozzo

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Weber
Posts: 125
Joined: Sat May 15, 2021 11:21 am

by Weber

Assuming bikes with the same seating position and same seatback. How many mm does one get closer to the pedal box using a seat angle of 73, 73.5 and 74? is it considered marginal?

by Weenie


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cpac54
Posts: 93
Joined: Sun Sep 06, 2020 11:24 am

by cpac54

Struggling with a decision re: geometry with a side of aesthetics.

I'm in the process of finalizing an order for a new bike. Due to a fused cervical spine at two levels, an aggressive position isn't in the cards for me.

For a standard geometry I was given two options to achieve my current fit numbers on the new bike: one with 20mm of spacers and a -3.5 deg stem OR one with 30mm of spacers and a -7 deg stem

I was hoping for as few spacers as possible within my fit limitations, but not sure how I feel about the -3.5 deg stem option (example with 22mm of spacers pictured below for reference)
324511547_5949446305112212_5644783705741087252_n.jpg
Full custom geometry is of course an option, which would require a fairly long headtube and an upcharge of approx $1500, but it's an option.

Perhaps I'm just overthinking it all, but I'm grateful for any and all thoughts and feedback!

TobinHatesYou
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Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

cpac54 wrote:
Tue Aug 08, 2023 10:52 pm
I was hoping for as few spacers as possible within my fit limitations, but not sure how I feel about the -3.5 deg stem option (example with 22mm of spacers pictured below for reference)

As much as I love an Argonaut, that -3.5deg stem just doesn't match the TT at all. It wouldn't look good even without the 22mm worth of spacers. I think a -6 to -12deg stem would look good with that particular example.

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cpac54
Posts: 93
Joined: Sun Sep 06, 2020 11:24 am

by cpac54

TobinHatesYou wrote:
Wed Aug 09, 2023 2:47 am
cpac54 wrote:
Tue Aug 08, 2023 10:52 pm
I was hoping for as few spacers as possible within my fit limitations, but not sure how I feel about the -3.5 deg stem option (example with 22mm of spacers pictured below for reference)

As much as I love an Argonaut, that -3.5deg stem just doesn't match the TT at all. It wouldn't look good even without the 22mm worth of spacers. I think a -6 to -12deg stem would look good with that particular example.
Yeah, I've been trying to tell myself that it's not that bad, but my gut tells me if I go with it, I'll regret not just going full custom. Given the upright nature of my fit, I'd need a frame with a fairly tall headtube though - likely around 170mm. Not sure if that would look just as odd in the end.

Weber
Posts: 125
Joined: Sat May 15, 2021 11:21 am

by Weber

Weber wrote:
Tue Aug 08, 2023 3:44 pm
Assuming bikes with the same seating position and same seatback. How many mm does one get closer to the pedal box using a seat angle of 73, 73.5 and 74? is it considered marginal?
I'm asking this because I have a TCR with a 73° seat angle and I have the rails at the front limit to position the seat where I like it, at the 5cm limit of the bottom bracket. Perhaps it is because I have short legs and a long torso that it is difficult for me to position myself more behind.
And I wonder if I would benefit from bikes like the scott foil or other brands that are between 73.5 and 74°. In order not to force the limits of the seat rails

dvdrl
Posts: 111
Joined: Sun Jun 11, 2023 8:55 am

by dvdrl

Weber wrote:
Thu Aug 10, 2023 4:10 pm
Weber wrote:
Tue Aug 08, 2023 3:44 pm
Assuming bikes with the same seating position and same seatback. How many mm does one get closer to the pedal box using a seat angle of 73, 73.5 and 74? is it considered marginal?
I'm asking this because I have a TCR with a 73° seat angle and I have the rails at the front limit to position the seat where I like it, at the 5cm limit of the bottom bracket. Perhaps it is because I have short legs and a long torso that it is difficult for me to position myself more behind.
And I wonder if I would benefit from bikes like the scott foil or other brands that are between 73.5 and 74°. In order not to force the limits of the seat rails
It depends on your saddle height.

The general formula is h ✕ cos α

At 75cm seat height with 73° seat tube angle you get a setback of

75cm ✕ cos 73° ≈ 75cm ✕ 0.292 = 21.9cm

With a seat angle of 74°, this becomes

75cm ✕ cos 74° ≈ 75cm ✕ 0.276 = 20.7cm

As you can see, with a difference of 12mm it's not insignificant for this 1° change in seat angle. But it depends on your seat height.

Also, you cannot interpolate linearly.

Casio20
Posts: 108
Joined: Tue Jul 24, 2018 9:31 pm

by Casio20

Hi dear Mates,

I have a Canyon Ultimate CF Disc in 54 with 100mm Stem and Look 795 Blade RS Disc in L (55) with 110mm stem

I just bought a TREK EMONDA SLR 2021 frame in 54 without a handlebar and stem and need to purchase a specific size.

Can you please support in which size to purchase?
I'm 1,82m and the Canyon and LOOK is fine for me
I just thought about 420mm and 100mm Option to be a little bit more relaxed.

What's your opinion?

Thanks a lot for your support,
Markus

macwatt
Posts: 155
Joined: Thu May 13, 2021 10:09 am

by macwatt

Hi

A bit of advice I've previously had a bike fit at the time I had Pro Griffon Saddle on my Tarmac SL7. Once I completed my fit I got send a video and measurements etc one thing that confused me is at no time during the fit was I sitting near the rear of the saddle.

Over time I found due to narrow sit bones that the Pro Griffon and other saddles I owned were too wide I replaced with a 130mm Power Saddle. On my fit my fore / aft from BB to saddle nose with Pro Griffon was 71mm due to the Power Mirror being 265mm and Power Mirror 240mm I increased fore / aft to 96mm.

I don't have any major issues but seem more comfortable sitting on the nose of the saddle reviewing my fit video at no time was I near the rear of the Pro Griffon therefore is this giving a false fore / aft measurement?

Attached is final fore /aft position
IMG_5258.png

rowdyyy
Posts: 100
Joined: Sun Jan 09, 2022 7:26 pm

by rowdyyy

I tried googling but didn't manage do find anything so maybe your joint knowledge can help me out.

Is there a calculator that lets you predict saddle to bar drop for any given bike? I'm trying to narrow down my future choices. At the moment I'm riding a BMC Roadmachine in 58 with a 140mm stem and no spacers. Reach is not a problem but saddle to bar drop is already at 12,5cm. While I can go lower I don't think I want to go super low.

fogman
Posts: 1069
Joined: Fri Oct 30, 2009 10:36 pm

by fogman

This is what I use.

https://www.velogicfit.com/frame-comparison/


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TobinHatesYou
Posts: 13025
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

rowdyyy wrote:
Mon Dec 04, 2023 10:09 am
I tried googling but didn't manage do find anything so maybe your joint knowledge can help me out.

Is there a calculator that lets you predict saddle to bar drop for any given bike? I'm trying to narrow down my future choices. At the moment I'm riding a BMC Roadmachine in 58 with a 140mm stem and no spacers. Reach is not a problem but saddle to bar drop is already at 12,5cm. While I can go lower I don't think I want to go super low.

You should assume your saddle position on two different bikes is the same, so all you really need to know is the difference in grip reach/stack. This is dependent on frame reach/stack, HTA, headset bearing cover height, spacers, stem stack/length/angle, bar reach, etc.

I like to visualize this with https://www.bike-stats.de/
Last edited by TobinHatesYou on Thu Dec 07, 2023 4:49 am, edited 1 time in total.

rowdyyy
Posts: 100
Joined: Sun Jan 09, 2022 7:26 pm

by rowdyyy

Thank you, that makes perfectly sense!

EtoDemerzel
Posts: 308
Joined: Sun Dec 17, 2023 4:13 pm

by EtoDemerzel

TobinHatesYou wrote:
Wed Dec 06, 2023 10:11 am


I like to visualize this with https://www.bike-stats.de/
wow this is great, thank you!
I'm inbetween sizes and this really helped- the "similar geometries" is really useful as well

by Weenie


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Steve Curtis
Posts: 1358
Joined: Thu Jul 31, 2008 12:20 pm
Location: Hampshire UK, Dublin Ireland and Geneva Switzerland.

by Steve Curtis

Hi all.

I had a bike fit back in nov 2023, two bikes were adjusted to the new measurements. ( same saddle, and components on both bikes )
One frame was ridden and one had been left untouched.

The bike that has been ridden was adjusted to help with a hip issue at the suggestion of the fitter.

I've now recovered so I used bike 2 for the first time yesterday and it felt fantastic, so I now need to revert bike 1 to the same measurements.

So

10cm saddle setback and a hight of 72.5 to the middle of the saddle from the bb centre.

I've fired a vertical laser line from saddle tip which is set to the correct hight, to a marker 10cm from the bb centre.

So, should they now be the same or am I missing something?

This is just a scene check 😂

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