Frame Stack and Reach sizing- What is your tolerance?

Discuss light weight issues concerning road bikes & parts.
RyanH
Moderator
Posts: 2001
Joined: Tue Jan 17, 2012 4:01 pm
Location: Los Angeles, CA
Contact:

by RyanH

Wait, are you comparing retul numbers to quoted numbers? You know you have to factor in the stack height of the cups and headset bearing cover? That both increases actual stack and decreases actual reach. Let's not forget that stack is sometimes measured to some arbitrary point in the head tube.

Also, just because you have fit numbers, doesn't mean it's right. I think the only thing fits are good for is to tell you if something is really wrong. For example, I thought I could run 13cm of drop by my fitter showed me the difference in my shoulders and how I was actually less aero than with a higher stack. BUT, even with that being the case, there's still a chance I could adapt to the position and be relaxed in it too.
Strava
Current Stable. The Snob Machine
The Ex's. LS Siena: 6.21kg | Parlee Z5 SLi: 5.9kg | LS Xicon: 5.76kg | C59: 5.7kg | Cervelo R5ca: 5.09kg | Fuji Altamira SE - 6.2kg | Scott Foil - 6.2kg | Evo - 5.18kg | LS Classic - 6.7kg | The Crumpton - 5.9kg

by Weenie


User avatar
silvalis
Posts: 392
Joined: Mon Sep 07, 2015 1:02 am
Location: Aus

by silvalis

Is standard retul practice to incorporate headset cap? Because my retul frame reach/stack numbers don’t...

Also isn’t he talking about bar reach/stack anyway, not frame?

My tolerance is maybe 5mm in all directions. Don’t forget about bar and shifter reach too.
Chasse patate

cyclenutnz
Posts: 768
Joined: Tue Jul 18, 2006 5:18 am
Location: Cambridge, New Zealand
Contact:

by cyclenutnz

My personal tolerance ~3mm on Bar XY, I know that I won't detect bar placement differences on that scale.
5mm gets noticeable.

Most of my fit clients already have a model in mind, so we necessarily have to work to a slightly looser tolerance, though it's usually possible to find a solution within 5mm radial error.
http://www.speedtheory.co.nz
http://www.velogicfit.com - 3D Motion Capture and Frame Finder Software

davidalone
Posts: 590
Joined: Fri Feb 10, 2012 4:27 pm

by davidalone

fa63 wrote:
Sun Jan 07, 2018 4:11 am
davidalone wrote:
Sat Jan 06, 2018 5:34 pm
My old bar stack and reach figurs were 603/473mm
The stack seems to make sense, but 473mm for reach doesn't. Did you mean 373mm, or are you including the stem length in your reported reach as well?

For me, I can make +- 1 cm work (preferred numbers are Reach = 380mm, Stack = 600 mm).
I'm quoting Bar stack and reach, so yes, that includes stem. the frame stack and reach doesnt matter so much so long as you can get the desired bar stack and reach without a huge number of spacers or a weird stem length.
RyanH wrote: Wait, are you comparing retul numbers to quoted numbers? You know you have to factor in the stack height of the cups and headset bearing cover? That both increases actual stack and decreases actual reach. Let's not forget that stack is sometimes measured to some arbitrary point in the head tube.

Also, just because you have fit numbers, doesn't mean it's right. I think the only thing fits are good for is to tell you if something is really wrong. For example, I thought I could run 13cm of drop by my fitter showed me the difference in my shoulders and how I was actually less aero than with a higher stack. BUT, even with that being the case, there's still a chance I could adapt to the position and be relaxed in it too.
again, quoting bar stack and reach. so all those are included already.

davidalone
Posts: 590
Joined: Fri Feb 10, 2012 4:27 pm

by davidalone

Multebear wrote:
Sat Jan 06, 2018 9:00 pm
This is a perfect opportunity for you to get a more aggressive fit on the bike. I'm not a great believer in bike fitting, since bike fitters tend to find the fit, that is most healthy for you regardless of how fast the fit is. I would look at it the other way around. You need the fastest fit, that wont hurt you. And that isn't necessarily the most comfortable one.

Regarding your question, IMO everything evolves around stack. Reach is adjusted with different stem lengths and angles. Stack needs to be as low as possible, since you'll always be able to adjust seat post position and fit spacer under the stem if you go too low. If stack is to big, you will need to have a stem with negative angles, like above 17 degrees. And that looks awful. When you've found a frame with the right stack, then everything else should be a question of installing the right components.

If you have a lot of confidence in your bike fitted fit, then keep the stack the same or within 10 mm lower. Then you should be fine because it would a question of adding or removing a few spacers under the stem.
you're right- the fastest fit isn't the most comfortable one. I am not in a sit up and beg position. ~11cm of saddle to bar drop, can ride in the drops all day and get low. but it's certainly no armchair ride and my core strength certainly doesn't do it justice. it's a good position, mainly because my fitter listens to what I want.

djwalker
Posts: 165
Joined: Sat Oct 31, 2009 7:35 pm

by djwalker

My experience in ~40 years of riding is that I can feel 1cm differences in stack and reach. Less than that and I think it is more my imagination than reality.

My personal opinion is that, unless you are always on the very front of the peloton, you should get a fit that is as aggressive as possible while still being comfortable. And not accept an uncomfortable fit. An uncomfortable position will just make riding your bike less fun. The ONLY times being super low or efficient really matter is if you are going super hard while in the wind. Like TTs, in a break in a race, or at the front of the peloton. Those situations rarely come up for most of us so living with an uncomfortable fit to be marginally more aero and, supposedly, faster isn't worth it. Also, low is not necessarily faster. Look at the TT bikes of World Tour riders. Lots of them have the armrests 75-100mm above the base bar. Fast is being aero while maximizing power output at the same time. Your power is rarely maximized if you are uncomfortable.

seansis
Posts: 47
Joined: Fri Sep 23, 2016 9:58 am

by seansis

Hello. Sorry for my English.

I choose a new road bike for myself, because it seems to me that now it is very big for me.

Now I'm riding the Simplon Nexio 55 size
ett 555mm,
reach 396mm,
stack 555mm,
stem 105mm (-6 angle),
10mm spacer,
seat tube 530,
head tube 145
But the KOPS method is not followed, my knee is behind the pedal.
And me completely uncomfortable on this bike.
My height is 183cm, weight 67kg, inseam 86cm. I have long arms and legs.

Now I look closely at Pinarello Dogma 65.1 think 2 53 size,
ett 545
reach 386,
stack 542
stem 135mm ( i dont know angle)
5mm spacer
seat tube 545
head tube 139
But I'm afraid that the fall of the saddle-handlebar wheel will be simply huge, because the head tube is very low.
But in theory, the knee should be in the right position on Pinarello. Or I'm wrong?...
I just want to get compact position on road bike.


Any help
Thanks

User avatar
TonyM
Posts: 2495
Joined: Thu Jan 22, 2015 4:11 pm

by TonyM

Changing the bike is a good opportunity to try different stack and reach as your body may have changed (better flexibility/ fitness or less...) :thumbup:

However a few years ago I decided to "try" to go more "modern (more "lead" positon as they said it is the current fit compared to my "old" fit from the 80s). I tried as hard as I could and tried it for 1.5 years. Finally I gave up and went back to my fit of the 80s with a long reach and a low stack; I slammed my stem and bought a longer stem. Less comfortable for many but my body after so many years and km is so used to it. And finally I enjoy more the bike I purchased. At least I tried... :P

User avatar
Rick
Posts: 2035
Joined: Sat Aug 29, 2009 4:30 pm

by Rick

I have made some pretty wildly different frames fit me with seatpost setback, saddle height, stem height and length.
But when I got them all fit, the actual touch-point dimensions always ended up within about ±7mm; which surprised even me. Saddle-to-pedal length, in particular is pretty sensitive to about ±2mm.

For a frame that "fits me well" the correct answer is always a 12cm stem.

DCcyclist
Posts: 42
Joined: Tue Aug 22, 2017 2:09 am

by DCcyclist

I am looking at a new bike. Reach 14mm longer than my current frame and Stack 45mm shorter. Is there a way to compensate for the shorter stack or should I be looking for a different size frame?

User avatar
TonyM
Posts: 2495
Joined: Thu Jan 22, 2015 4:11 pm

by TonyM

DCcyclist wrote:
Wed Jan 31, 2018 9:44 pm
I am looking at a new bike. Reach 14mm longer than my current frame and Stack 45mm shorter. Is there a way to compensate for the shorter stack or should I be looking for a different size frame?
45mm in spacers is to much.

What would the next size in terms of reach and stack?

Are you going from an endurance to a race geometry?

djwalker
Posts: 165
Joined: Sat Oct 31, 2009 7:35 pm

by djwalker

You can always flip your stem to be a +6 degree, +10 degree, or whatever. Flipping a 120mm stem from -6 to +6 will raise the bars by 25mm. Make of the rest with spacers. Or get a frame with more stack.

DCcyclist
Posts: 42
Joined: Tue Aug 22, 2017 2:09 am

by DCcyclist

TonyM wrote:
Wed Jan 31, 2018 10:01 pm
DCcyclist wrote:
Wed Jan 31, 2018 9:44 pm
I am looking at a new bike. Reach 14mm longer than my current frame and Stack 45mm shorter. Is there a way to compensate for the shorter stack or should I be looking for a different size frame?
45mm in spacers is to much.

What would the next size in terms of reach and stack?

Are you going from an endurance to a race geometry?
Yes TonyM, a more race geometry. I also think I have gotten better at riding more aero past year. So figured out I should be (maybe) alright with shorter stack.

DCcyclist
Posts: 42
Joined: Tue Aug 22, 2017 2:09 am

by DCcyclist

djwalker wrote:
Wed Jan 31, 2018 11:37 pm
You can always flip your stem to be a +6 degree, +10 degree, or whatever. Flipping a 120mm stem from -6 to +6 will raise the bars by 25mm. Make of the rest with spacers. Or get a frame with more stack.
Thank you, will keep these in mind. Altho have an appointment with me bike fitter in a week so will put all of these options on the table and find the best bike.

User avatar
TonyM
Posts: 2495
Joined: Thu Jan 22, 2015 4:11 pm

by TonyM

DCcyclist wrote:
Yes TonyM, a more race geometry. I also think I have gotten better at riding more aero past year. So figured out I should be (maybe) alright with shorter stack.
If you go for a race geometry you will end up having a longer reach and a lower stack. The question is just how far can you go. I would suggest you to go to a fitter and check on the bike which reach/ stack is ok for you.

1-2 cm spacer is ok. Stem length as from 100 mm usually.

by Weenie


Post Reply
  • Similar Topics
    Replies
    Views
    Last post