Frame Stack and Reach sizing- What is your tolerance?

Discuss light weight issues concerning road bikes & parts.
davidalone
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Joined: Fri Feb 10, 2012 4:27 pm

by davidalone

Killed my bike the other day when the hangar snapped and smashed the seat stays while riding. Currently looking around for a new bike.

What's your tolerance when putting together a new bike? My old bar stack and reach figurs were 603/473mm - obviously it's not always possible to get 'spot on' with different stem/spacer combinations- so what is the tolerance? 3mm? 5mm?

have my eye on an oltre, I can get within 0.6mm of the stack (higher) and 1.5mm of the reach (longer) with a -6 degree 100mm stem and 25mm of spacers. so I;m thinking it should fit.... possibly could 3D print a spacer to 4mm and hit it spot on

by Weenie


boots2000
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by boots2000

You can buy 2mm spacers- bag of 10 on amazon.

https://www.amazon.com/Profile-Design-B ... ile+design

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jekyll man
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by jekyll man

You assume your current set up is correct to that amount?

From a personal point of view, I find reach easier to compensate for than stack.
Check STA angle as well.
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davidalone
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by davidalone

I trust my fitter, he's the best in my country and very good at what he does. his resume is impeccable- Ex-UCI continental bike racer, trained in RETUL, FIST, serotta, geobeomized, ... you name it. also happens to have a degree in mechanical engineering and has started to build his own brand of bikes (Ti and carbon- he was trained at the bohemian bikes framebuilding school)... he also happens to be my brother in law.... so if you're asking if I think my fit is good, I'm pretty damn sure it is...

STA is not a problem for me- I have plenty of room for saddle adjustment and oth bikes are within half a degree of TSA, so around about 5mm difference of saddle adjustment is no biggie.

mrlobber
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by mrlobber

Given that reach is usually compensated by different stem length and sometimes by different bar reach, I personally find it easier to compensate for stack, as stem length does have some (at least perceived) impact on handling. Actually, I,m not even deliberately trying to make stack similar between my bikes, so they easily have 10mm or more differences, even more so because they're serving different purposes and to equalise stack between aero race bike and a commuter / cross bike would be quite difficult anyway unless you want a real spacer tower on the first one.

Multebear
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by Multebear

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.

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wheelsONfire
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by wheelsONfire

I find i don't appreciate reach at +/-5mm difference.
But as there are extremely few stems with 0.5cm increments and as handlebars are not spot on the numbers given,
it's not easy to get pin point match between bikes.
I'd rather live with a change in stack than reach.
Last edited by wheelsONfire on Sat Jan 06, 2018 9:05 pm, edited 1 time in total.
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wingguy
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by wingguy

davidalone wrote:
Sat Jan 06, 2018 5:34 pm
have my eye on an oltre, I can get within 0.6mm of the stack
I doubt that even Marco Pantani could tell the difference between 0.6mm higher or lower. :wink:

(And on a serious note - there's no point planning for exactly how many mm of spacers you'll need until you know if the headset caps are the same height.)
Last edited by wingguy on Sat Jan 06, 2018 9:08 pm, edited 1 time in total.

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wheelsONfire
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by wheelsONfire

For OP
Do you mean 6mm / 0.6cm?
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wingguy
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by wingguy

Multebear wrote:
Sat Jan 06, 2018 9:00 pm
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.
What exactly would you do to seatpost position if your bars were too low?

Multebear
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by Multebear

wingguy wrote:
Sat Jan 06, 2018 9:07 pm
Multebear wrote:
Sat Jan 06, 2018 9:00 pm
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.
What exactly would you do to seatpost position if your bars were too low?
Nothing. I would fit spacers under the stem or decrease the stem angle.

My point is, that you need the head tube to be as short as possible, since you can't compensate for a head tube that is too long. But you can compensate for a head tube that is too short.

wingguy
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by wingguy

Multebear wrote:
Sat Jan 06, 2018 9:12 pm
Nothing. I would fit spacers under the stem or decrease the stem angle.
Oh I see, the two comments weren't connected. Ok.
My point is, that you need the head tube to be as short as possible, since you can't compensate for a head tube that is too long. But you can compensate for a head tube that is too short.
Meh. Depends what you're aiming for and how far you've missed it by. I see loads of people with bikes that are too low that they just can't get high enough even with 5cm of steerer and a positive stem. I'd much rather run a slammed -17 than have the leaning tower of Pisa on the front of my bike, but to each their own!

Multebear
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by Multebear

@wingguy; I don't see the disagreement here. Obviously you want to limit the amount of spacers, but since the difference en stack on most frames, when you move through sizes varies between 1 and 2 cm, you'll never need more than 2 cm of spacers, unless you have very odd body proportions.

Below the cannondale super six evo hi mod:

If you look at a size 54 and 56, the difference en stack is 1.6 cm. And the difference between the two head tubes is 1.6 cm. This obviously means, that a size 54 with 1.6 cm spacers would give you the same effective stack as a size 56, and obviously you'd have to move the seat post 1.6 cm as well. If you are on a bike with 5 cm of spacers, then it's obviously too small. You need to move two sizes up and get a shorter stem to compensate for the larger reach.

Image

wingguy
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by wingguy

Multebear wrote:
Sat Jan 06, 2018 9:58 pm
@wingguy; I don't see the disagreement here. Obviously you want to limit the amount of spacers, but since the difference en stack on most frames, when you move through sizes varies between 1 and 2 cm, you'll never need more than 2 cm of spacers, unless you have very odd body proportions.
Yeah I know, and for someone like the OP who's already quite precise in his measurements you're right - I'm just thinking of other people who sometimes get things way off (and may be looking at different geometry bikes as well as different sizes so there's a lot more than 2cm in play) and in general terms I see more people who are stuck too low. Although now that I think about it I tend to see small people very often on bikes that are too big and big people very often on bikes that are too small, which I guess is for pretty obvious reasons. Anyway, bit of a tangent, sorry.

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fa63
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by fa63

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).
Last edited by fa63 on Sun Jan 07, 2018 4:47 am, edited 1 time in total.

by Weenie


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