need geometry help from the fit gurus.

Discuss light weight issues concerning road bikes & parts.
chiltonp
Posts: 136
Joined: Fri May 01, 2009 8:48 pm

by chiltonp

I usually ride a 56-57 frame and currently ride a 2017 TCR Advanced SL in M/L, I have the seatmast in the less offset position and I run a 100mm stem with a good bit of post showing, currently running maybe 10mm of spacers. Stack and reach numbers on this frame are 562mm and 398MM respecitively. TCR has a 570 TT and a 168 HT.

I rode an orignal evo in 56 but always ran a good bit of spacers as the HT was relatively low for me and my fit at the time was not as agressive.

On to my next bike...

I've found a good deal on '18 SS Evo HM in a 58. This new ride would have a 575 TT, 175HT, Stack of 584mm, and reach of 399MM.

Reach numbers between the two bikes are almost spot on despite the slighlty longer TT on 58 EVO. Stack numbers vary significantly between the two frames, is this only due to the longer HT on the 58 EVO? If I can run no spacers on the 58 evo compared to running spacers on the TCR would this help to negate the difference in Stack? Anyhting I am overlooking?

by Weenie


MarcFaFo
Posts: 13
Joined: Fri Sep 14, 2018 4:58 pm

by MarcFaFo

Yes you are further away from the handle bars as your leg length determines your sadle position. Use a plumbline that begins at the front of your kneecap and should be going through pedal axis at 3 o' clock position of crank. This determines normally your sabble set-back. As such your position is different.

mattr
Posts: 4673
Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

chiltonp wrote:
Wed Nov 28, 2018 6:33 pm
Reach numbers between the two bikes are almost spot on despite the slighlty longer TT on 58 EVO. Stack numbers vary significantly between the two frames, is this only due to the longer HT on the 58 EVO? If I can run no spacers on the 58 evo compared to running spacers on the TCR would this help to negate the difference in Stack? Anyhting I am overlooking?
Basically, yes. Longer headtube, probably a longer fork too, maybe a lower bottom bracket. Either way, you could account for the difference in stack by simply ditching the spacers and going to a different stem angle (depending what you have now) e.g. going from a -7 and 10mm spacers to -17 and no spacers *should* put your bars within about 5mm of where they are now. Close enough that you are unlikely to notice a difference. if you are already on -17, you may have to live with the bars being ~10mm higher. I don't know if this would be a dealbreaker for you or not.

On the flip side, you won't be able to increase drop if you ever want to.

chiltonp
Posts: 136
Joined: Fri May 01, 2009 8:48 pm

by chiltonp

Thanks for the insight mattr. Would the TCR being run in basically a zero setback position versus the EVO usually sporting a setback post be enough of a difference for you to worry about it? I'm already running my saddle fairly far back.

The reach numbers are almost identaical though.

Mr.Gib
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Location: eh?

by Mr.Gib

chiltonp wrote:
Wed Nov 28, 2018 7:34 pm
Thanks for the insight mattr. Would the TCR being run in basically a zero setback position versus the EVO usually sporting a setback post be enough of a difference for you to worry about it? I'm already running my saddle fairly far back.
The reach numbers are almost identaical though.
Having a trouble understanding your query above.
Your saddle will be positioned where it belongs in relation to the bottom bracket - period. If you can get your saddle in the correct position on a ML TCR, than you should be able to do so on a 58 SS EVO. You need only to select the appropriate seatpost to acheive optimal clamp/saddle rail positioning. All other fit details will be achieved with handlebar positioning via stem length and spacers.
wheelsONfire wrote: When we ride disc brakes the whole deal of braking is just like a leaving a fart. It happens and then it's over. Nothing planned and nothing to get nervous for.

shimmeD
Posts: 487
Joined: Thu Jun 28, 2012 10:52 pm
Location: eNZed

by shimmeD

I'm with Mr.Gib :up: wrt to saddle position in relation to BB being non-negotiable. Also be careful as you need to do more trigonometry when looking at different Reach figures on different bikes, because differing Stack figures may be significant enough to influence where you think your bars will be. Yup, more trigonometry :smartass:
Edit: If you don't get what I mean lets look at the 2 frames you're comparing. They have near identical Reach, however measured from Stacks with ~20mm difference. If you move the horizontal line of the Cannondale down ~20mm and measure the Reach now you're going to get a larger Reach.
Last edited by shimmeD on Wed Nov 28, 2018 8:49 pm, edited 1 time in total.
Less is more.

mattr
Posts: 4673
Joined: Fri May 25, 2007 6:43 pm
Location: The Grim North.

by mattr

chiltonp wrote:
Wed Nov 28, 2018 7:34 pm
Thanks for the insight mattr. Would the TCR being run in basically a zero setback position versus the EVO usually sporting a setback post be enough of a difference for you to worry about it? I'm already running my saddle fairly far back.

The reach numbers are almost identaical though.
The reach numbers are identical, which is why i assumed you already realised that saddle position should be identical! My mistake.

But as per Mr Gib and ShimmeD, get saddle right first. (Ignore MarcFaFo) and then stack is close enough that you should easily be able to achieve the same (or very similar) fit.

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wheelsONfire
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Joined: Mon Jul 07, 2014 8:15 am
Location: NorthEU

by wheelsONfire

Or you go for another frame. Like keeping the stack height you look for, 10mm spacers + height of frame dust cap (how high is this?) and frame stack 562mm.
Perhaps you should use a frame between 572-580mm stack and shorter reach so you can use a longer stem?

Ridleys medium size bike seems to suit you and also new Cervelo R5 size 56.
Bikes:

Ax Lightness Vial EVO Race (2018.12.21)
viewtopic.php?f=10&t=156137
Paduano Racing Fidia (kind of shelved)
Open *UP* (2016.04.14)


Ex bike; Vial EVO D

shimmeD
Posts: 487
Joined: Thu Jun 28, 2012 10:52 pm
Location: eNZed

by shimmeD

As you move your stem up (more spacers on the Giant) you're also moving your bars (and stem) back. To exactly replicate your current setup you'll need a shorter stem on the Evo, shorter than 100mm. Sketch it up and use Right Angle Triangle on-line: this is what I use but there're probably better tools online.
Less is more.

savechief
Posts: 348
Joined: Wed Aug 31, 2011 2:36 am

by savechief

MarcFaFo wrote:
Wed Nov 28, 2018 6:42 pm
Yes you are further away from the handle bars as your leg length determines your sadle position. Use a plumbline that begins at the front of your kneecap and should be going through pedal axis at 3 o' clock position of crank. This determines normally your sabble set-back. As such your position is different.
https://www.sheldonbrown.com/kops.html
Time VXRS Ulteam (7.16 kg)
viewtopic.php?f=10&t=120268

savechief
Posts: 348
Joined: Wed Aug 31, 2011 2:36 am

by savechief

As mentioned by others, your relationship between your saddle and bottom bracket should be set up the same on both bikes.

I had to make some assumptions (such as an 8mm tall top cap on the TCR, based on stock photos, that your current stem is -6 degrees, etc), but to get your handlebars in the same position with the 58 Evo as the M/L TCR, you would need the low (5mm) top cap for the Evo, no spacers plus something more like a -12 degree stem. Even with this, your reach to the bars will be about 6mm longer.

Play around with this tool to compare the two bikes:
http://bb2stem.blogspot.com/
Time VXRS Ulteam (7.16 kg)
viewtopic.php?f=10&t=120268

Hexsense
Posts: 933
Joined: Wed Dec 30, 2015 12:41 am

by Hexsense

shimmeD wrote:
Wed Nov 28, 2018 9:00 pm
As you move your stem up (more spacers on the Giant) you're also moving your bars (and stem) back. To exactly replicate your current setup you'll need a shorter stem on the Evo, shorter than 100mm. Sketch it up and use Right Angle Triangle on-line: this is what I use but there're probably better tools online.
Yes by 2.5mm if you have 10mm of spacer on 73 degree headtube.
See here,
http://yojimg.net/bike/web_tools/stem.php
plot two setting with the same stem length and angle. But adjust one setting to have 10mm more spacer than the other, read the result in reach difference.
savechief wrote:
Wed Nov 28, 2018 9:29 pm
MarcFaFo wrote:
Wed Nov 28, 2018 6:42 pm
Yes you are further away from the handle bars as your leg length determines your sadle position. Use a plumbline that begins at the front of your kneecap and should be going through pedal axis at 3 o' clock position of crank. This determines normally your sabble set-back. As such your position is different.
https://www.sheldonbrown.com/kops.html
Agree with sheldonbrown. I'm disappointed that Myth on KOPS as holy grail that dictate set-back position is still floating around until these days.
Proper way of adjusting Set-back based on body flexibility and weight balance make a whole lot more sense than KOPS myth.
https://www.stevehoggbikefitting.com/bi ... oad-bikes/
Last edited by Hexsense on Wed Nov 28, 2018 9:53 pm, edited 1 time in total.

shimmeD
Posts: 487
Joined: Thu Jun 28, 2012 10:52 pm
Location: eNZed

by shimmeD

Thanks Hexsense. I'm not frigging around with stems and I have a custom frame, so I haven't been bothered with looking for the tools you've linked.
To get more meaningful results you need to input [spacers + ½ stem stack + vertical distance between bottom of stem and frame Stack] into either of those online stem tools; you may have to guess the vertical distance between bottom of stem and frame Stack. This won't work if the frames have different head angles though.
Less is more.

chiltonp
Posts: 136
Joined: Fri May 01, 2009 8:48 pm

by chiltonp

thanks guys for all the insight and the quick fit lesson.

by Weenie


Schulzy
Posts: 9
Joined: Tue Nov 13, 2018 10:45 am

by Schulzy

chiltonp wrote:
Wed Nov 28, 2018 6:33 pm
I usually ride a 56-57 frame and currently ride a 2017 TCR Advanced SL in M/L,..?
I've also just placed an order for a TCR SL but I'm a little unsure on the size I've ordered, just out of curiousity, what is your inseam, and BB to seat measurement on your M/L? I've currently got an M/L on order but wondering if I should go for an M.

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