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English => How-To => Topic started by: JUGGARNAUT on June 29, 2010, 12:46:22 AM

Title: How to correctly measure a frame
Post by: JUGGARNAUT on June 29, 2010, 12:46:22 AM
Check it out here;

How to correctly measure a frame (http://www.bikeguide.org/guides/geometry/geometry101.php)
Title: Re: How to Correctly Measure a Frame.
Post by: Scuffy on June 29, 2010, 06:26:10 AM
Nice link Juggs.

I wish I was a more experienced rider and that I had some welding knowledge as I have been thinking alot lately about flatland frame geometry.

Like some people have a preferred chainstay length and some have a preferred top tube length and some have a preferred seat tube or head tube angle.

I've been thinking about finding all the different measurements that seem best to a given rider.

Like how would a frame with a 19" toptube and a really short chainstay feel like,or a frame with an short toptube but long rear end...then factor in BB heights,wheelbase (due to forks being offset or not) head tube and seat tube angle....I'll have to buy a sh*t ton of bikes just to figure all that out...the possibilities are almost endless.

I've heard some people talk before about how their frames have the same toptube lengths but when they try the others bike it feels too short or long to them....they obviously didn't realize that there's more to it then just toptube length,but also head tube and seat tube angles etc.

A frame has a 19" toptube,71 degree seat tube angle and a 75 degree head tube angle and B frame has a 19" toptube,74 degree seat tube angle,and 73 degree head tube angle...hmmm,I wonder which frame would have alonger feeling front end...Bike A I would think.
Title: Re: How to Correctly Measure a Frame.
Post by: kkmk on June 29, 2010, 12:56:03 PM
A frame has a 19" toptube,71 degree seat tube angle and a 75 degree head tube angle and B frame has a 19" toptube,74 degree seat tube angle,and 73 degree head tube angle...hmmm,I wonder which frame would have alonger feeling front end...Bike A I would think.

Bike B will be much longer.
Title: Re: How to Correctly Measure a Frame.
Post by: smiley (Roy) on June 30, 2010, 10:55:58 AM
A frame has a 19" toptube,71 degree seat tube angle and a 75 degree head tube angle and B frame has a 19" toptube,74 degree seat tube angle,and 73 degree head tube angle...hmmm,I wonder which frame would have alonger feeling front end...Bike A I would think.

Bike B will be much longer.

It depends are the standover dimensions the same on both frames ? The bike with the taller standover will have a longer front end...

Measuring frames by toptube length does not work with the way frames are currently built. There are too many variables not taken into consideration. Once upon a time you could compare two frames by toptube length (when toptubes were horizontal).
 
-Roy
Title: Re: How to Correctly Measure a Frame.
Post by: Paradoxium on June 30, 2010, 02:53:00 PM
I always thought tt length was measured from the centre of the headtube to the centre of the seattube, not along the actual tube itself. Great link nonetheless. ;)
Title: Re: How to Correctly Measure a Frame.
Post by: Vic Román on July 16, 2010, 04:20:20 AM
I always thought tt length was measured from the centre of the headtube to the centre of the seattube, not along the actual tube itself. Great link nonetheless. ;)

That`s what I thought. :huh:
Title: Re: How to Correctly Measure a Frame.
Post by: SurfonFlatland on July 23, 2010, 07:11:52 PM
Top tube is measured from the center of the head tube to the center of the seat tube.  Scuffy, bike A would feel longer. KKmk, before you act like you know the answer, why don't you actually think before posting.  A little lesson in geometry, and a 74 degree seat tube (steeper than 71 degree) and a 73 degree head tube (more laid back that 75) would make frame B's ht and st closer together. 
Title: Re: How to Correctly Measure a Frame.
Post by: JUGGARNAUT on July 25, 2010, 06:33:10 PM
I always thought tt length was measured from the centre of the headtube to the centre of the seattube, not along the actual tube itself. Great link nonetheless. ;)

That`s what I thought. :huh:
thats what it says....................:huh:
Title: Re: How to Correctly Measure a Frame.
Post by: Paradoxium on July 26, 2010, 03:57:24 PM
I always thought tt length was measured from the centre of the headtube to the centre of the seattube, not along the actual tube itself. Great link nonetheless. ;)

That`s what I thought. :huh:
thats what it says....................:huh:

Between centres across both latitude and longitude. Picture the centre of the seat tube from the bb to the top where you clamp it. Not just the middle across, but top to bottom as well. Reason being because the hta and sta vary from frame to frame. The difference is minimal anyways....
Title: Re: How to Correctly Measure a Frame.
Post by: Scuffy on July 26, 2010, 05:04:37 PM
Scuffy, bike A would feel longer. KKmk, before you act like you know the answer, why don't you actually think before posting.  A little lesson in geometry, and a 74 degree seat tube (steeper than 71 degree) and a 73 degree head tube (more laid back that 75) would make frame B's ht and st closer together. 

Yeah I knew I was right,I mean I am really horrible with math such as geometry and algebra but simple geometry like that..pfft,please.

Obviously if you have a steep seat tube angle and a lax head tube angle the front end will feel shorter then a bike with a lax seat tube angle and a steep head tube angle.
Title: Re: How to Correctly Measure a Frame.
Post by: kkmk on July 28, 2010, 11:26:22 AM
Between centres across both latitude and longitude. Picture the centre of the seat tube from the bb to the top where you clamp it. Not just the middle across, but top to bottom as well. Reason being because the hta and sta vary from frame to frame. The difference is minimal anyways....

Even that will vary from frame to frame, bb height, seat tube height etc.
Title: Re: How to Correctly Measure a Frame.
Post by: alex@H on November 01, 2010, 12:52:58 PM
you'll need this:
(http://img227.imageshack.us/img227/350/40124448.jpg)
Title: Re: How to Correctly Measure a Frame.
Post by: pwh4130 on December 11, 2010, 06:29:28 PM
The rest of the bike world measures Effective Top Tube length.  The ETT is a horizontal line from the seat post to the center of the steerer tube of the fork.  Things like seat position, stem reach and handlebar sweep are all changeable.  ETT is not.
Title: Re: How to Correctly Measure a Frame.
Post by: Scuffy on February 05, 2012, 07:54:07 AM
Yes,stepover height does make a difference a difference in fork offste will also make a difference in the wheelbase.