stack and reach tolerances in a road bike.

Nov 22, 18 6:41

Post #1 of 18 (1345 views)

I have spent 10 minutes trying to figure out the formulas of the stem calculator:

stack=((A+(B/2)*SIN(C)+(D*SIN((90-C+E))
reach= -(D*(-COS(90-C+E))-((A+(B/2)*(COS(C)))

where

A - spacers and headset cap height
B - stem height
C- head angle
D - stem length
E- Stem angle (- for negative)

Then I put them in an excel file and played around with bike geometry, and values, to arrive at my desired numbers... more or less. For the road bike I want to buy, the best I get is -3mm in stack, and +5 mm in reach (long&low! hurrah! ;-), with a 110, -6º stem and 35mm for cap+spacers (not great but acceptable IMO, my rule is "less than the stem height")

So my question is:

What tolerance is acceptable for S&R? will these few mm off be OK? My baseline is my current bike, wjere I feel quite confortable, after riding the same geometry and fit for 5 years.

thanks in advance!

Last edited by: SrSalitre: Nov 22, 18 6:44

Re: stack and reach tolerances in a road bike. [SrSalitre] [ In reply to ]

Nov 22, 18 6:59

Post #2 of 18 (1322 views)

SrSalitre wrote:

I have spent 10 minutes trying to figure out the formulas of the stem calculator:

stack=((A+(B/2)*SIN(C)+(D*SIN((90-C+E))
reach= -(D*(-COS(90-C+E))-((A+(B/2)*(COS(C)))

where

A - spacers and headset cap height
B - stem height
C- head angle
D - stem length
E- Stem angle (- for negative)

Then I put them in an excel file and played around with bike geometry, and values, to arrive at my desired numbers... more or less. For the road bike I want to buy, the best I get is -3mm in stack, and +5 mm in reach (long&low! hurrah! ;-), with a 110, -6º stem and 35mm for cap+spacers (not great but acceptable IMO, my rule is "less than the stem height")

So my question is:

What tolerance is acceptable for S&R? will these few mm off be OK? My baseline is my current bike, wjere I feel quite confortable, after riding the same geometry and fit for 5 years.

thanks in advance!

stems generally come in 10mm increments. so, if you're at 5mm away, probably not much you can do about that. 3mm is not a problem in terms of height. you'll never feel it.

that said, what bike do you want to buy?

Dan Empfield
aka Slowman

Re: stack and reach tolerances in a road bike. [SrSalitre] [ In reply to ]

Nov 22, 18 7:13

Post #3 of 18 (1302 views)

The insanely expensive ENVE aero stem has a +-2.5 mm adjustment (if I remember correctly) and you can always shave spacers with some sandpaper. I find that the difference of the shape of the handlebar. Probably makes a difference as well that you can't anticipate

Last edited by: grumpier.mike: Nov 22, 18 7:19

Re: stack and reach tolerances in a road bike. [Slowman] [ In reply to ]

Nov 22, 18 7:14

Post #4 of 18 (1301 views)

Since this is a road bike, bar reach could make a bit of a difference as well.

Also, I’ve noticed that the newer hydraulic shifters tend to be a bit longer (up to ~10mm). So even if everything to the stem clamp & bar are the same, there still might be some extra length to account for to the hoods.

Re: stack and reach tolerances in a road bike. [Slowman] [ In reply to ]

Nov 22, 18 7:16

Post #5 of 18 (1294 views)

Thanks Dan,

I am going for a Tarmac Disc Pro, size 58. Comes with a 110 stem but I cannot find stem angle or headset topcap info. Not that it makes much difference...

Re: stack and reach tolerances in a road bike. [Andres] [ In reply to ]

Nov 22, 18 7:18

Post #6 of 18 (1291 views)

I see, so maybe it is better to be 5 mm short than 5 mm too long in reach? What do you guys think?

Re: stack and reach tolerances in a road bike. [SrSalitre] [ In reply to ]

Nov 22, 18 7:22

Post #7 of 18 (1286 views)

If you're really fussy, if you look around you can get 2mm and 2.5mm headset spacers. I think Wheels Mfg makes them.

I know I wouldn't notice the difference, but you might.

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Re: stack and reach tolerances in a road bike. [SrSalitre] [ In reply to ]

Nov 22, 18 7:40

Post #8 of 18 (1275 views)

can i ask you the following:

1. how tall are you?
2. are you long in the leg or torso? or evenly proportioned?
3. are you confident the position you have is correct?
4. what do you want to buy this particular bike?

Dan Empfield
aka Slowman

Re: stack and reach tolerances in a road bike. [SrSalitre] [ In reply to ]

Nov 22, 18 7:50

Post #9 of 18 (1269 views)

SrSalitre wrote:

Thanks Dan,

I am going for a Tarmac Disc Pro, size 58. Comes with a 110 stem but I cannot find stem angle or headset topcap info. Not that it makes much difference...

Is your concern whether you need a different overall frame size because you are “close”?

Or are you looking at OEM parts to see if they are close?

It sucks, but personally on a roadie unless you get super lucky I see the original stem and seat as throw aways. It’s too personal for a mfg to get right for everyone.

Maybe even bars. Width, drop, reach. A different bar can alter reach a good bit.

Just ensure it’s something you can ride comfortably for 1000 miles then start tinkering with the “perfect” setup once you know how the bike rides.

Re: stack and reach tolerances in a road bike. [grumpier.mike] [ In reply to ]

Nov 22, 18 7:54

Post #10 of 18 (1265 views)

Thanks, this stem comes in a -12º angle, and using the angle adjustment to make it -7º, no reach adjustments are possible, so it is not a good solution for my specific case.

Re: stack and reach tolerances in a road bike. [Slowman] [ In reply to ]

Nov 22, 18 8:02

Post #11 of 18 (1259 views)

Sure!

1- I am 186 cms tall
2 - I would say evenly proportioned
3 -I got fit into this position 3 years ago, and been riding comfortably ever since. Should I get fitted again?
4- Crashed on my shiv this summer, and I am getting a crazy deal to replace my road bike along with the new TT bike.

Re: stack and reach tolerances in a road bike. [burnthesheep] [ In reply to ]

Nov 22, 18 8:08

Post #12 of 18 (1251 views)

Yes I am trying to validate the frame size and stem to avoid doing things like turning my stem upside down. Luckily this one comes with a 110 stem which is what I need, -6º to -7º make for -2mm in stack and +1mm in reach.

Good thing I wrote this post, I was not even considering bar reach to be a factor... I will ahve to measure my current setup and the potential options.

Thanks!

Last edited by: SrSalitre: Nov 22, 18 8:10

Re: stack and reach tolerances in a road bike. [SrSalitre] [ In reply to ]

Nov 22, 18 8:16

Post #13 of 18 (1243 views)

SrSalitre wrote:

Sure!

1- I am 186 cms tall
2 - I would say evenly proportioned
3 -I got fit into this position 3 years ago, and been riding comfortably ever since. Should I get fitted again?
4- Crashed on my shiv this summer, and I am getting a crazy deal to replace my road bike along with the new TT bike.

i don't think you can go wrong with this bike. but, you're high in the front. and, you're a little bit tight in the cockpit, but, as andres said, it depends on the bar geometry and the hood geometry. like andres, i find that the SRAM hydraulic hoods adds 5mm to 10mm to the length of the cockpit. so, your cockpit distance sounds either 10mm too short or about right. but, in general, i guess i'd question whether your bars need to be as high as they are, realizing i'm saying this without having seen you or your position and i don't know the front end geometry. that's why i'm a little more sure of my height question but not at all confident in questioning the length of your bike's front end.

point is, whether you need 35mm of top cap/headset spacer + -6° stem, or whether you could ride something lower, that bike will still work fine for you.

Dan Empfield
aka Slowman

Re: stack and reach tolerances in a road bike. [Slowman] [ In reply to ]

Nov 22, 18 8:47

Post #14 of 18 (1230 views)

Slowman wrote:

your cockpit distance sounds either 10mm too short or about right

You mean in my current setup or the calculated solution?

I have a 120mm stem laying around at home, maybe I should try it and see if it works for me... that would make me -4mm in stack and +16mm in reach froom my current fit.

Otherwise I would try to gradually reduce spacers, to go lower with minimal increments in reach

Anyway, thanks for stopping by and validating my figures, makes me confident to purchase the bike and gives me a direction to start tweaking to improve.

Re: stack and reach tolerances in a road bike. [SrSalitre] [ In reply to ]

Nov 22, 18 9:09

Post #15 of 18 (1213 views)

https://www.bikegeocalc.com

Re: stack and reach tolerances in a road bike. [SrSalitre] [ In reply to ]

Nov 22, 18 9:54

Post #16 of 18 (1183 views)

SrSalitre wrote:

Slowman wrote:

your cockpit distance sounds either 10mm too short or about right

You mean in my current setup or the calculated solution?

I have a 120mm stem laying around at home, maybe I should try it and see if it works for me... that would make me -4mm in stack and +16mm in reach froom my current fit.

Otherwise I would try to gradually reduce spacers, to go lower with minimal increments in reach

Anyway, thanks for stopping by and validating my figures, makes me confident to purchase the bike and gives me a direction to start tweaking to improve.

i mean in what i suspect is your current setup based on your calculated solution. you have an hx/hy, if i understand your calcs correctly, if 664/488 respectively. mine is 630/500 respectively, and i'm about your height, within a half-inch. not that mine should be yours. just, these bikes, like the venge & tarmac, are very mainstream as road bikes go. so, is your position a mainstream race position? if not, why?

if your position has been working well for you, probably no reason to change it. i just want to make sure your position is dialed before you make any hardware investments that match a position you're liable to change. the good news is, your position is going to fit that bike, regardless what you decide to change.

Dan Empfield
aka Slowman

Re: stack and reach tolerances in a road bike. [SrSalitre] [ In reply to ]

Nov 22, 18 21:25

Post #17 of 18 (1090 views)

SrSalitre wrote:

Thanks Dan,

I am going for a Tarmac Disc Pro, size 58. Comes with a 110 stem but I cannot find stem angle or headset topcap info. Not that it makes much difference...

Stock stem is +/-6 and headset topcap is 10mm.

-SD

https://www.kickstarter.com/...bike-for-the-new-era

Re: stack and reach tolerances in a road bike. [SuperDave] [ In reply to ]

Nov 22, 18 21:43

Post #18 of 18 (1079 views)

Thanks Dave! This is good news to me, so the stem is just the one I need. Can you please confirm that stem height is 40 mm?

Last edited by: SrSalitre: Nov 22, 18 21:48

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