Go Back  Bike Forums > Bike Forums > Bicycle Mechanics
Reload this Page >

frame size clarification - easy question, I think

Notices
Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

frame size clarification - easy question, I think

Old 05-20-10, 09:38 AM
  #1  
Member
Thread Starter
 
Join Date: Jan 2010
Posts: 48
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
frame size clarification - easy question, I think

Ok, I thought for a while that I know what I'm doing, but by no means an expert. Now while shopping for a new frame this very novice question has caused me to scratch my head so I need clarification.

When reporting a frame size based on the traditional center-to-top measurement; is that from the center to the top of the top tube or the top of the seat tube? When shopping online (so I'm unable to actually measure it myself) for a frame and it has a sloping top tube or compact frame I got confused on what this center-to-top measurement actually meant.
sprocket47 is offline  
Old 05-20-10, 10:01 AM
  #2  
Senior Member
 
Join Date: Aug 2005
Location: Pittsburgh, PA
Posts: 33,656

Bikes: '96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '20 Surly Midnight Special, All are 3x10. It is hilly around here!

Mentioned: 39 Post(s)
Tagged: 0 Thread(s)
Quoted: 2026 Post(s)
Likes: 0
Liked 1,096 Times in 742 Posts
For a traditional level top tube frame, it's most always based on the center of the bb spindle to the top of the top tube. Sloping top tube bikes will sometimes give a "virtual" size based on where the top tube's level intersection would be if it were level. Likewise, they give a virtual top tube length based on a hypothetical level top tube.
HillRider is offline  
Old 05-20-10, 10:07 AM
  #3  
Senior Member
 
Join Date: Apr 2009
Location: New Rochelle, NY
Posts: 38,910

Bikes: too many bikes from 1967 10s (5x2)Frejus to a Sumitomo Ti/Chorus aluminum 10s (10x2), plus one non-susp mtn bike I use as my commuter

Mentioned: 140 Post(s)
Tagged: 1 Thread(s)
Quoted: 5891 Post(s)
Liked 2,746 Times in 1,533 Posts
All questions are easy, it's the answers that are sometimes difficult.

In my 40 years in the bike business, there's never been agreement on how to measure frames. On traditional road bikes some measured from the center of BB along the seat tube (there's a consensus on that at least) to the center of the top tube, others to the top,so already there was a half inch difference in how folks measured.

Then they started extending the seat tube above the toptube and using a clamp band, and some measured to there, so another half inch or so. Then they started extending the seat tube even higher, and all bets were off.

Today with frame design all over the place, most folks are measuring to the top of the seat tube, and some are also giving stand-over height (top of the top tube to the ground) which is helpful. Read the spec carefully, and if there's a picture you can estimate the distance down to the sloping top tube to estimate the stand over clearance.
__________________
FB
Chain-L site

An ounce of diagnosis is worth a pound of cure.

Just because I'm tired of arguing, doesn't mean you're right.

“One accurate measurement is worth a thousand expert opinions” - Adm Grace Murray Hopper - USN

WARNING, I'm from New York. Thin skinned people should maintain safe distance.
FBinNY is online now  
Old 05-20-10, 10:10 AM
  #4  
Thrifty Bill
 
wrk101's Avatar
 
Join Date: Jan 2008
Location: Mountains of Western NC
Posts: 23,541

Bikes: 86 Katakura Silk, 87 Prologue X2, 88 Cimarron LE, 1975 Sekai 4000 Professional, 73 Paramount, plus more

Mentioned: 96 Post(s)
Tagged: 0 Thread(s)
Quoted: 1244 Post(s)
Liked 988 Times in 636 Posts
In my experience, it varies by manufacturer. Some are center to center, some are center to top, some with sloping tubes estimate a virtual top tube, etc. Best to check with the individual manufactuer. Even if shopping on line, they should have a help desk of some kind that can answer email questions. Best to go with their answer.
wrk101 is offline  
Old 05-20-10, 10:19 AM
  #5  
Senior Member
 
Join Date: Aug 2005
Location: Pittsburgh, PA
Posts: 33,656

Bikes: '96 Litespeed Catalyst, '05 Litespeed Firenze, '06 Litespeed Tuscany, '20 Surly Midnight Special, All are 3x10. It is hilly around here!

Mentioned: 39 Post(s)
Tagged: 0 Thread(s)
Quoted: 2026 Post(s)
Likes: 0
Liked 1,096 Times in 742 Posts
Originally Posted by FBinNY
All questions are easy, it's the answers that are sometimes difficult.
Ain't that the painful truth.


Originally Posted by FBinNY
.....and some are also giving stand-over height (top of the top tube to the ground) which is helpful.
Stand-over height is useful for a level top tube frame but can be misleading for a sloping top tube. Riders can pick a much too large frame (from a top tube length standpoint) by thinking the stand-over is adequate since the top tube is well below where it would be on a level frame. These days picking a frame size based on (virtual) top tube length has become more important since it isn't as closely related to frame size and stand-over as it used to be.
HillRider is offline  
Old 05-20-10, 12:53 PM
  #6  
Senior Member
 
Join Date: Feb 2005
Location: Oklahoma
Posts: 9,438

Bikes: Trek 5500, Colnago C-50

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 4 Post(s)
Likes: 0
Liked 7 Times in 6 Posts
Learn to measure the frames with a metric tape (I use my wife's cheap fabric tape).
Compare frame size diagrams with actual measurements. Don't count on the diagrams to be accurate.
Measure the effective top tube length c - c. This is just as important as the seat tube length.
Example: My son's 52 cm c-c Specialized with level top tube had the same stand over height as my 56 cm c-t Trek.

Of the frames I've measured most c-t measurements are actually c BB to top of ST.
Al1943 is offline  
Old 05-21-10, 02:15 PM
  #7  
Senior Member
 
Join Date: Jul 2006
Location: El Segundo, Ca.
Posts: 214

Bikes: '93 Performance R203, '83 Bianchi 980

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
bottom bracket drop directly effects standover height, also.
roberth33tiger is offline  
Old 05-21-10, 02:52 PM
  #8  
headtube.
 
zzyzx_xyzzy's Avatar
 
Join Date: Sep 2008
Posts: 803
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Likes: 0
Liked 3 Times in 3 Posts
center of the BB to the top of the top tube is the most sensible way (ATMO) to measure, since that's the dimension you would use if you were calculating standover, frame stack, etc. However if you're using someone else's measurements there is no consistency.
zzyzx_xyzzy is offline  
Old 05-21-10, 06:24 PM
  #9  
Retro-guy
 
Join Date: Oct 2006
Location: Danville, CA
Posts: 285

Bikes: 1980 Raleigh Super Record

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
I would say that the bike makers whose products I researched a few months ago, as part of my bike-buying process, tended to use seat tube length as their "frame size" measurement, measured in most cases from BB center to top of seat tube. But this is getting less and less useful as a frame size indicator, with sloping top tubes, seat tubes that extend a fair amount above the top tube, etc. Some makers also quote an "equivalent to" frame size, but this doesn't seem to be done uniformly, either.

To some extent, when deciding on which frame size to get, it is perhaps more useful to look at both top-tube length and perhaps head-tube height. At least in the case of top-tube length MOST makers quote an "equivalent" top-tube dimension, assuming an imaginary flat top-tube that ends at the seat post.

Stand-over height is of some use, but again there seems to be a lot of variation as to where it gets measured, with a sloping top-tube.

One or two makers quote a saddle-height range, basically from BB center to the top of their provided saddle, and positioning the provided seat post at its min and max positions. You can then compare this to your existing bike's saddle height, and get a feel for whether your preferred saddle height is likely to be in a reasonable range for the frame size. I think Trek does this. (Maybe I'm the only one, but I found this useful. Even though I didn't end up buying a Trek....)

And obviously riding the bike first is always best.
rschleicher is offline  
Old 05-21-10, 06:24 PM
  #10  
Senior Member
 
Join Date: Apr 2006
Location: Vero Beach FL
Posts: 1,102
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
And you thought this would be easy.
ScrubJ is offline  
Old 05-21-10, 07:07 PM
  #11  
headtube.
 
zzyzx_xyzzy's Avatar
 
Join Date: Sep 2008
Posts: 803
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Likes: 0
Liked 3 Times in 3 Posts
If you want my pie-in-the-sky opinion the most useful way to measure a bike is by "stack and reach" as described in these links:

https://www.sicklines.com/2008/12/18/...k-a-good-idea/
https://www.slowtwitch.com/mainheadin...ctr/stack.html

However it seems to be catching on only slowly... of major manufacturers I've only seen Trek and Salsa listing stack and reach numbers. So I have to do a bunch of trigonometry to convert the numbers they do list into stack and reach. A lot of the time it turns out to actually be impossible to convert given figures into stack and reach, because the manufacturer forgets to list the fork length, or maybe the headtube length, or maybe they give a standover or bottom bracket height figure without mentioning what tire size they used or where along the top tube is the standover measured.
zzyzx_xyzzy is offline  
Old 05-22-10, 06:57 AM
  #12  
Senior Member
 
Join Date: Sep 2008
Location: Loveland, CO
Posts: 7,239

Bikes: Cinelli superstar disc, two Yoeleo R12

Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 1102 Post(s)
Liked 560 Times in 447 Posts
Don't worry about how it's measured, because the frame size number is worthless. The dimensions that define how the frame fits are the head tube length, BB drop, seat tube angle and TT length. Fork length is also an issue, but not many brands list it.

What really defines a frame's vertical size is the stack (as defined by Cervelo), but since that's rarely available the next best thing is the head tube length with the headset. Integrated headsets only add 8-20mm to the head tube length, while conventional press-in cup models add 25-35mm. You can compare this total length directly, unless one frame has a significantly different BB drop. The greater the drop, the shorter the head tube can be and still produce a given bar height.

The reach of a frame is determined by the TT length and the seat tube angle. If two frames have the same TT length, but one has a 74 degree STA, while the other has a 73, the later frame will have about a 1cm shorter reach.

https://www.cervelo.com/en_us/bikes/2010/R3/geometry/

The only other thing to consider is the standover height. It doesn't affect the fit, but you don't want your crotch touching the TT when you standover it.
DaveSSS is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
mostafizrahman
Bicycle Mechanics
8
07-31-17 08:31 AM
Fear Before
Singlespeed & Fixed Gear
3
04-26-12 03:47 PM
zenith
General Cycling Discussion
7
03-20-12 04:31 PM
damnable
Road Cycling
3
06-09-11 05:33 AM
Stickney
Framebuilders
2
07-30-10 07:48 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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.