Go Back  Bike Forums > Bike Forums > Road Cycling
Reload this Page >

How significant is 20mm stem difference?

Notices
Road Cycling “It is by riding a bicycle that you learn the contours of a country best, since you have to sweat up the hills and coast down them. Thus you remember them as they actually are, while in a motor car only a high hill impresses you, and you have no such accurate remembrance of country you have driven through as you gain by riding a bicycle.” -- Ernest Hemingway

How significant is 20mm stem difference?

Old 06-26-19, 02:51 PM
  #1  
nesdog
Senior Member
Thread Starter
 
Join Date: Nov 2003
Location: Conejo Valley, CA
Posts: 2,670

Bikes: Domane SLR7 Disc

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 66 Post(s)
Liked 56 Times in 34 Posts
How significant is 20mm stem difference?

I did a bike fit with the LBS last year. Zero setback post on that bike. Change was made to swap out to a 70mm stem.

My new bike (exact same frame and geometry) has a 20 mm setback. The saddle was set up to be in the same relative position.

I can't quite tell if I should also change out the OEM 90 mm stem for another 70. It's fractions of an inch. Is a 20mm difference considered to be significant?
__________________
[insert clever quote here]
nesdog is offline  
Old 06-26-19, 02:54 PM
  #2  
jideta
Senior Member
 
Join Date: Apr 2019
Location: Honolulu
Posts: 262
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 94 Post(s)
Liked 138 Times in 74 Posts
yes
jideta is offline  
Old 06-26-19, 02:56 PM
  #3  
DrIsotope
Non omnino gravis
 
DrIsotope's Avatar
 
Join Date: Feb 2015
Location: SoCal, USA!
Posts: 8,553

Bikes: Nekobasu, Pandicorn, Lakitu

Mentioned: 119 Post(s)
Tagged: 0 Thread(s)
Quoted: 4900 Post(s)
Liked 1,715 Times in 952 Posts
Yes, 20mm is significant.

My question is why would you put a 20mm setback post on a bike with the same geometry as one that fits you with a 0mm setback post? Don't change the stem, change the post. The post is how you set your knee angle. Trying to accomodate for the extra 20mm of saddle setback with a shorter stem is likely just going to put more weight on your hands, and your knees still won't like it.
__________________
DrIsotope is offline  
Old 06-26-19, 03:29 PM
  #4  
Seattle Forrest
Senior Member
 
Seattle Forrest's Avatar
 
Join Date: Mar 2010
Location: Seattle, WA
Posts: 22,255
Mentioned: 79 Post(s)
Tagged: 0 Thread(s)
Quoted: 15918 Post(s)
Liked 7,523 Times in 4,195 Posts
Yes, 20 mm is huge.

Is the new seat post better than the old one? In terms of how it positions you in relation to the BB?

70 mm is unusually short for a road stem. As a rule of thumb, shortening your stem will make the bike a little twitchier.
Seattle Forrest is offline  
Old 06-26-19, 03:45 PM
  #5  
Kedosto
Ambulophobic
 
Join Date: Nov 2008
Location: St. Leander
Posts: 1,248
Mentioned: 12 Post(s)
Tagged: 0 Thread(s)
Quoted: 492 Post(s)
Liked 204 Times in 122 Posts
I think the saddle is 'in the same relative position?" Yes? Which, in itself, would be odd because it would mean the saddle is slid forward to mimic the same position as a zero setback post. As a matter of aesthetics you can do what you choose, but I'd be looking to swap out the seatposts. Get your saddle position dialed in relative to the bottom bracket in a way that works for you, THEN start looking at your stem for reach/height based on your final saddle position. IOW, you fix reach and bar height issues at the stem, not at the saddle or seatpost.

As for the 20mm difference in stem length, depending on your fit issues it could be about as bad as a mile off. Millimeters matter.

So if I'm understanding correctly, you have the same frame with the same geo. The new frame came with a 20mm setback post, but you have the saddle slid way forward to mimic a zero setback post so effectively the saddle is in the same position relative to the BB. The new frame came with a 90mm stem and you're wondering if you should trade it for a 70mm stem like your old frame (all other things being equal)? Well, if you were comfortable on the old frame then yes, you're gonna want that 70mm stem. 20mm is over 3/4 of an inch. I doubt you'd notice a 5mm difference, but 20 is a whole 'nuther thing.


-Kedosto
Kedosto is offline  
Old 06-26-19, 04:34 PM
  #6  
Dean V
Senior Member
 
Join Date: Oct 2009
Posts: 2,812
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 1037 Post(s)
Likes: 0
Liked 227 Times in 135 Posts
Originally Posted by nesdog View Post
I did a bike fit with the LBS last year. Zero setback post on that bike. Change was made to swap out to a 70mm stem.

My new bike (exact same frame and geometry) has a 20 mm setback. The saddle was set up to be in the same relative position.

I can't quite tell if I should also change out the OEM 90 mm stem for another 70. It's fractions of an inch. Is a 20mm difference considered to be significant?
I am just wondering why you are on such short stems?
Unless you are rather short or something it would suggest you may be on the wrong frame.
Dean V is offline  
Old 06-26-19, 04:46 PM
  #7  
rubiksoval
Senior Member
 
Join Date: Nov 2015
Location: Music City, USA
Posts: 4,434

Bikes: bikes

Mentioned: 52 Post(s)
Tagged: 0 Thread(s)
Quoted: 2610 Post(s)
Liked 1,410 Times in 705 Posts
I wouldn't ride with a 70mm stem. Even 90 is a bit short for my tastes, but sometimes that's the only option I guess.
rubiksoval is offline  
Old 06-26-19, 05:08 PM
  #8  
nesdog
Senior Member
Thread Starter
 
Join Date: Nov 2003
Location: Conejo Valley, CA
Posts: 2,670

Bikes: Domane SLR7 Disc

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 66 Post(s)
Liked 56 Times in 34 Posts
What I'm gathering from the responses is that it matters. And that 70mm is more unusual rather than common.

The old bike was a 4.3 Domane, new one an SLR7. I'm not short at all, being 5'9. Now I'm wondering if the LBS really wasn't all that swift on this task last year. The fit was more informal, rather than hours long and I assumed the guy knew his stuff. Maybe not!

I'm mostly okay on the bike as it is. Actually one of my concerns was if we shortened the stem, that now may put more pressure on the hands.

The point of the question was that I thought I would be duplicating whatever had worked last year. Now I'm not so sure and will think the solution.

Thanks...
__________________
[insert clever quote here]
nesdog is offline  
Old 06-26-19, 05:40 PM
  #9  
BengalCat
Senior Member
 
Join Date: Dec 2015
Location: Brentwood WLA
Posts: 326

Bikes: 50/34, 11-40, 11 Speed

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 141 Post(s)
Liked 71 Times in 51 Posts
Yes, 20mm is as others have stated a significant amount. My stem is 120mm which IIRC is 10mm longer than the stock stem that came with my 62cm bike. (I am 6'4")
BengalCat is offline  
Old 06-26-19, 06:05 PM
  #10  
jideta
Senior Member
 
Join Date: Apr 2019
Location: Honolulu
Posts: 262
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 94 Post(s)
Liked 138 Times in 74 Posts
Originally Posted by nesdog View Post
What I'm gathering from the responses is that it matters. And that 70mm is more unusual rather than common.

The old bike was a 4.3 Domane, new one an SLR7. I'm not short at all, being 5'9. Now I'm wondering if the LBS really wasn't all that swift on this task last year. The fit was more informal, rather than hours long and I assumed the guy knew his stuff. Maybe not!

I'm mostly okay on the bike as it is. Actually one of my concerns was if we shortened the stem, that now may put more pressure on the hands.

The point of the question was that I thought I would be duplicating whatever had worked last year. Now I'm not so sure and will think the solution.

Thanks...

That 20mm on the stem is a lot.
Just think what 20mm setback on seat post means.

I used to think cyclists were crazy; but fit is literally a game of millimeters.
jideta is offline  
Likes For jideta:
Old 06-26-19, 07:50 PM
  #11  
jadocs
Senior Member
 
jadocs's Avatar
 
Join Date: Jul 2018
Location: USA
Posts: 2,192

Bikes: Ti, Mn Cr Ni Mo Nb, Al, C

Mentioned: 22 Post(s)
Tagged: 0 Thread(s)
Quoted: 941 Post(s)
Liked 519 Times in 345 Posts
70mm stem is short, like mountain bike short. I consider 90mm to be short. What size frame did your LBS put you on?
jadocs is offline  
Old 06-26-19, 08:29 PM
  #12  
GrainBrain
Senior Member
 
GrainBrain's Avatar
 
Join Date: Aug 2017
Location: Central Io-way
Posts: 2,085

Bikes: LeMond Zurich, Giant Talon 29er

Mentioned: 15 Post(s)
Tagged: 0 Thread(s)
Quoted: 1067 Post(s)
Liked 362 Times in 270 Posts
Wow really? That's almost an $8k bike and the shop seriously slammed the seat forward and now you're considering a short stem? Yikes

Did you buy the 56cm version when probably the 54 would've been better?

FWIW I've been working on my fit in my old LeMond, that has a top tube length a couple cm longer then it should. I swapped a 110mm stem that was level (-17°) for a flipped up 17° 90mm stem and it is noticably more "fast turning". I wanted a more upright position for longer days in the saddle. Also I replaced my setback post for a zero setback. The LeMond is a 55 ST x 56 TT so in the future I'll be looking at TTs that are 54CM.
GrainBrain is offline  
Old 06-26-19, 09:06 PM
  #13  
puma1552
Senior Member
 
Join Date: Jul 2016
Posts: 728

Bikes: '17 Colnago C-RS (Full 5800); '16 Specialized Sirrus Elite

Mentioned: 4 Post(s)
Tagged: 0 Thread(s)
Quoted: 351 Post(s)
Liked 54 Times in 35 Posts
70mm stem for a guy 5'9" tells me something isn't right.

For reference, I'm 5'5" and ride an 80mm stem (on a 52cm bike that came with a 90cm stem), and it's just right.
puma1552 is offline  
Likes For puma1552:
Old 06-27-19, 08:05 AM
  #14  
Rides4Beer
Senior Member
 
Join Date: Oct 2018
Location: VA
Posts: 1,405

Bikes: SuperSix Evo | Revolt

Mentioned: 12 Post(s)
Tagged: 0 Thread(s)
Quoted: 707 Post(s)
Liked 769 Times in 396 Posts
Yup, as everyone already mentioned. I didn't think there would be that much of a difference, but 10mm was a huge difference for me.
Rides4Beer is offline  
Old 06-27-19, 11:27 AM
  #15  
69chevy
wears long socks
 
Join Date: May 2015
Posts: 1,614
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 503 Post(s)
Liked 18 Times in 10 Posts
A guy my height posted he rides a bike 45mm bigger than mine with the same length stem.

A guy 280mm shorter rides a bike 55mm smaller than mine.

Just based on that alone, I'd have to say 20mm isn't that significant in the grand scheme of bike fit, however a 70mm stem is rather short and may feel sketchy.

It is also true that if you needed a zero setback post on bike A, you need it on bike B, and C, etc... Most bikes will have the same seat tube angle for a given size. (about 72-74 depending on bike size) meaning at your "fitted" seat height, nearly all road bikes your size, will require a zero setback post.

Where your butt is, is what matters in a bike fit. The rest is about your own comfort. I could swap my 120mm stem for a 100 or a 140 and id be used to either after a few miles.
69chevy is offline  
Old 06-27-19, 11:30 AM
  #16  
nomadmax 
Senior Member
 
Join Date: Jun 2018
Location: SW Ohio
Posts: 1,905
Mentioned: 93 Post(s)
Tagged: 0 Thread(s)
Quoted: 851 Post(s)
Liked 1,162 Times in 585 Posts
Originally Posted by jideta View Post
That 20mm on the stem is a lot.
Just think what 20mm setback on seat post means.

I used to think cyclists were crazy; but fit is literally a game of millimeters.
All of that ^^^ right there. And the older you get, the more the millimeters matter
nomadmax is offline  
Old 06-27-19, 11:51 AM
  #17  
69chevy
wears long socks
 
Join Date: May 2015
Posts: 1,614
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 503 Post(s)
Liked 18 Times in 10 Posts
Originally Posted by jideta View Post
That 20mm on the stem is a lot.
Just think what 20mm setback on seat post means.

I used to think cyclists were crazy; but fit is literally a game of millimeters.
Moving your seat changes the geometry of your hip, knee and ankles, which are all under load and constantly moving while cycling.

Moving where your hands rest isn't anywhere near as significant. If it were, the drops wouldn't be there and we couldn't drop our stack and shorten our reach mid ride (by switching to the drops) or shorten our reach (by holding the tops) without consequence.

Where your butt is affects your performance and wear and tear on your joints.

Where your hands are... not so much.
69chevy is offline  
Old 06-27-19, 07:34 PM
  #18  
Kapusta
Cyclochondriac
 
Kapusta's Avatar
 
Join Date: Feb 2017
Posts: 4,850
Mentioned: 26 Post(s)
Tagged: 0 Thread(s)
Quoted: 2108 Post(s)
Liked 1,569 Times in 881 Posts
To pile on.... yes, 20mm is significant.

Whether a 70mm stem is appropriate really depends on your fit needs. Also depends of the reach of the bar you are using. Needing a stem that short puts one on the tail of the bell curve, but does not mean it is necessarily wrong. But it does warrant making sure you are on the right size frame.

I have atypical fit needs. I run a 70mm stem on my road/gravel bike. Handles fine.
Kapusta is offline  
Old 06-27-19, 07:53 PM
  #19  
AlmostTrick
Tortoise Wins by a Hare!
 
AlmostTrick's Avatar
 
Join Date: Feb 2006
Location: Looney Tunes, IL
Posts: 7,397

Bikes: Wabi Special FG, Raleigh Roper, Nashbar AL-1, Miyata One Hundred, '70 Schwinn Lemonator and More!!

Mentioned: 21 Post(s)
Tagged: 0 Thread(s)
Quoted: 1546 Post(s)
Liked 920 Times in 497 Posts
What many here are saying is it's important you have the same length stem as everyone else, or you're doing it wrong. What a load.

If your setup is working for you, that's what matters. If it isn't, then it's time to re-evaluate.
AlmostTrick is offline  
Old 06-27-19, 08:00 PM
  #20  
Kimmo 
bike whisperer
 
Kimmo's Avatar
 
Join Date: Dec 2009
Location: Melbourne, Oz
Posts: 9,447

Bikes: https://weightweenies.starbike.com/forum/viewtopic.php?f=10&t=152015&p=1404231

Mentioned: 15 Post(s)
Tagged: 0 Thread(s)
Quoted: 1443 Post(s)
Liked 658 Times in 468 Posts
One aspect not mentioned yet is that you can have some wiggle room in stem length if you look at bars with differing amounts of reach. You can move the top of the bars up to 30mm or so, while the hoods and drops stay where they are. Something to consider...

I tend to go for a longer stem (I'm 5'10" and rock a 120) with shorter reach bars, cause I don't mind leaning over a fair bit (stem's slammed) as a minimum, and I like how the 120 makes the steering feel on the tops.
Kimmo is online now  
Old 06-27-19, 08:02 PM
  #21  
GlennR
On Your Left
 
GlennR's Avatar
 
Join Date: Nov 2011
Location: Long Island, New York, USA
Posts: 8,294

Bikes: Trek Emonda SLR, Sram eTap, Zipp 303

Mentioned: 34 Post(s)
Tagged: 0 Thread(s)
Quoted: 2963 Post(s)
Liked 2,345 Times in 1,150 Posts
I'm 5'10" and ride a 56cm with a 110"mm stem.

70mm will be really twitchy on a steep decent.
GlennR is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
mooder
Road Cycling
15
06-13-16 01:35 PM
mooder
Road Cycling
5
06-02-16 07:47 AM
bobbyl1966
Fitting Your Bike
6
08-05-15 07:26 PM
MxChino
Road Cycling
9
08-03-15 07:37 PM
mazdaspeed
Road Cycling
30
10-08-10 08:08 AM

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.