Frame size, new bike fitting, questions

Discuss light weight issues concerning road bikes & parts.
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silvalis
Posts: 680
Joined: Mon Sep 07, 2015 1:02 am
Location: Aus

by silvalis

don't forget that 10mm or so of that tarmac stack is a headset cap
Chasse patate

CEVelo
Posts: 106
Joined: Tue Mar 24, 2015 5:22 pm

by CEVelo

If between sizes, optiong for the smaller frame with a few spacers will typically feel and work best, its easier to make a bike 'bigger' - very hard typically to make it smaller without wonky stuff (e.g. too short stems etc.) General rule and can't replace a proper fitting on the exact frame with online advice.

by Weenie


mf22433
Posts: 19
Joined: Sat May 10, 2008 8:35 am

by mf22433

CEVelo wrote:
Sat Aug 10, 2019 9:40 pm
If between sizes, optiong for the smaller frame with a few spacers will typically feel and work best, its easier to make a bike 'bigger' - very hard typically to make it smaller without wonky stuff (e.g. too short stems etc.) General rule and can't replace a proper fitting on the exact frame with online advice.
Thanks, makes sense :D

alanyu
Posts: 80
Joined: Thu Jun 06, 2019 1:10 pm

by alanyu

CEVelo wrote:
Sat Aug 10, 2019 9:40 pm
If between sizes, optiong for the smaller frame with a few spacers will typically feel and work best, its easier to make a bike 'bigger' - very hard typically to make it smaller without wonky stuff (e.g. too short stems etc.) General rule and can't replace a proper fitting on the exact frame with online advice.
"If between size" usually means, one 5mm reach shorter and another 5mm reach longer, resulting in roughly 10mm stem difference and 10~15mm spacers difference.
What the hell can you get the conclusion of a too short stem?

If the stem is really too short and the bar is not too low or too high, e.g, 60mm stem, that's a bike with a reach too too too long. It may need to cut down three size to use a 90mm stem, which can induce more than 40mm spacers to compensate the stack. That's not the situation which can be described by "between sizes".

CEVelo
Posts: 106
Joined: Tue Mar 24, 2015 5:22 pm

by CEVelo

:popcorn:

zefs
Posts: 438
Joined: Sat Aug 05, 2017 8:40 pm

by zefs

Thing is it's not only the stack and reach which plays a role on how a bike feels small or large and how it rides, so the whole geometry is important depending on what you are looking for.

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corky
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Joined: Thu Jul 06, 2006 5:53 pm
Location: The Surrey Hills

by corky

zefs wrote:
Mon Aug 12, 2019 6:02 am
Thing is it's not only the stack and reach which plays a role on how a bike feels small or large and how it rides, so the whole geometry is important depending on what you are looking for.
Absolutely, if you consider that 1 deg of seat tube angle equates to 1 cm of top tube length that is not take into account when considering reach, just shows how limiting stack and reach measurements can be,

alanyu
Posts: 80
Joined: Thu Jun 06, 2019 1:10 pm

by alanyu

corky wrote:
Wed Aug 14, 2019 1:32 pm

Absolutely, if you consider that 1 deg of seat tube angle equates to 1 cm of top tube length that is not take into account when considering reach, just shows how limiting stack and reach measurements can be,
Totally wrong. If you have any experience of decent fitting such as Specialized retul, you will know one should first consider his correct seat position and then the correct bar position. 1 deg difference of ST with the same reach and stack won't influence the spacers and stem, as you should pull forward or backward the saddle to keep the correct position relative to BB. This actually shows the limit of the old school TT and ST sizing.
zefs wrote:
Mon Aug 12, 2019 6:02 am
Thing is it's not only the stack and reach which plays a role on how a bike feels small or large and how it rides, so the whole geometry is important depending on what you are looking for.
Sure not only R and S make the "feeling" of large and small, but also rake, BB drop, etc can make a totally different handling, but we are talking about "between sizes", where BB drop, rake, etc should be the same or similar.

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fa63
Posts: 2373
Joined: Mon Feb 19, 2007 7:26 am
Location: Atlanta, GA, US

by fa63

No, he is actually totally right; reach as frame manufacturers define it does not consider seat tube angle. For example, a frame with a 73 deg STA will have an effective reach ~1 cm more than a frame with 72 deg STA, even if the reach is identical between the two frames.
alanyu wrote:
Totally wrong. If you have any experience of decent fitting such as Specialized retul, you will know one should first consider his correct seat position and then the correct bar position. 1 deg difference of ST with the same reach and stack won't influence the spacers and stem, as you should pull forward or backward the saddle to keep the correct position relative to BB. This actually shows the limit of the old school TT and ST sizing.

alanyu
Posts: 80
Joined: Thu Jun 06, 2019 1:10 pm

by alanyu

fa63 wrote:
Wed Aug 14, 2019 7:24 pm
No, he is actually totally right; reach as frame manufacturers define it does not consider seat tube angle. For example, a frame with a 73 deg STA will have an effective reach ~1 cm more than a frame with 72 deg STA, even if the reach is identical between the two frames.
alanyu wrote:
Totally wrong. If you have any experience of decent fitting such as Specialized retul, you will know one should first consider his correct seat position and then the correct bar position. 1 deg difference of ST with the same reach and stack won't influence the spacers and stem, as you should pull forward or backward the saddle to keep the correct position relative to BB. This actually shows the limit of the old school TT and ST sizing.
Please understand what I've said or do/watch a retul fitting or other decent fitting. ST angle can influence TT with the same reach, but it can not influence the stem and spacers. ST angle will only determine the offset of the seatpost to keep the correct saddle position.

Add: Give a picture which can illustrate the difference of ST angle with the same R and S.
1.PNG

zefs
Posts: 438
Joined: Sat Aug 05, 2017 8:40 pm

by zefs

This asummes that you would have pushed the saddle forward if you had switched to a bike with a difference of -1.5deg on the ST angle to achieve the same position. But if you dont, the extra reach to the handlebars can affect the stem and spacers since you will be on a lower position/back angle because of the extra reach.

alanyu
Posts: 80
Joined: Thu Jun 06, 2019 1:10 pm

by alanyu

zefs wrote:
Thu Aug 15, 2019 6:49 am
This asummes that you would have pushed the saddle forward if you had switched to a bike with a difference of -1.5deg on the ST angle to achieve the same position. But if you dont, the extra reach to the handlebars can affect the stem and spacers since you will be on a lower position/back angle because of the extra reach.
One's fitting result is almost universal for the same purpose in a period, e.g, race. It depands on one's body and ability, not the geometry of the bike. A lower bike doesn't mean one can use a lower bar position if that's beyond his ability. If you had done a retul fitting, would you make a different setup comparing to the fitting results?

zefs
Posts: 438
Joined: Sat Aug 05, 2017 8:40 pm

by zefs

I am only mentioning the difference the ST angle makes if you don't move the saddle to the same position as before (if everything else remains the same). If you had a fit you would probably make that change, but if you are trying another position and want bigger saddle setback it would also be a good idea to raise the handlebar a bit (to achieve the same back angle).

flimsy
Posts: 4
Joined: Thu Jul 25, 2019 12:47 am

by flimsy

Hi, I'm looking at getting a specialized tarmac sl6
I currently ride a felt f5 (2015) size 54 with a 110mm stem

I'm 179cm and according to the "general" charts I'm a 56 in the tarmac. My inseam is 81cm which is quite small for my height but my reach isn't exactly compensating for that, which is just average.

As for additional factors I can touch the floor with my legs straight but I do get back pain while cycling which is due to hip tilt which a chiropractor is helping me with, what frame do you think I should go for?
Last edited by flimsy on Fri Aug 16, 2019 11:57 pm, edited 1 time in total.

zefs
Posts: 438
Joined: Sat Aug 05, 2017 8:40 pm

by zefs

Your inseam is not small for your height, 54 seems like the better size as the 56 has longer reach and stack by a bit, compared to your F5.

by Weenie


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