Author Topic: Please please check my math! 19.5" top tube 49.5cm bike right?  (Read 10280 times)

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Offline John Driz

Hey, not sure if I'm doing my math right so I was hoping someone could double check my work.  I'm looking at a Cannondale T700 frame which measures
Top Tube: 19.5"
Fork: 17"
Seat Stays: 19.5"
Chain Stays: 18"
Down Tube: 24.5"
So this would be 49-50cm's right?  I was really hoping to find a 54.  If it were a 19inch mtb it would fit but I'm just a little unfamiliar with touring bike measurements.  Huge thanks to anyone who responds to this.
19.5inches x 2.54cm = 49.5cm tall right?

Offline Macbeth

Re: Please please check my math! 19.5" top tube 49.5cm bike right?
« Reply #1 on: April 25, 2010, 09:46:54 pm »
 
 I work in a bike shop and am always interested how bikes measures in Inches and bikes in Centimetres never work out the same.....

 I am 5"11' and ride a 19 (sometimes 20) inch moutain bike, but a 56cm Cannondale road or touring bike fits me very nicely...... I think, if a 19ish mountain bike fits you nicely, that a 49-50cm Cannondale touring frame will be WAY too small.... 54-56 cm frame sounds about right.

Offline John Driz

Re: Please please check my math! 19.5" top tube 49.5cm bike right?
« Reply #2 on: April 25, 2010, 09:54:38 pm »
So do you think the conversion from a 19.5 inch top tube means it is a 50cm frame?

Offline DU

Re: Please please check my math! 19.5" top tube 49.5cm bike right?
« Reply #3 on: April 26, 2010, 09:36:42 am »
The size of a bike frame is determined by length of the seat tube not the top tube. Companies usually do this in two different ways, one being center of crank to the top of top tube or seat lug, the other being center of crank to center of top tube. I'd find out how Cannondale measures theirs.
« Last Edit: April 26, 2010, 09:40:57 am by DU »

Offline Tourista829

Re: Please please check my math! 19.5" top tube 49.5cm bike right?
« Reply #4 on: April 26, 2010, 02:12:32 pm »
19.5 X 2.54 = centimeters. or 25.4 millimeters. it comes out to 49.53 cm or 495.3mm. How tall are you?

I would do a couple of personal measurements.

Inseam
Take a book, shove it as far up as it will go between your legs. Stand with your back against the wall and measure in your barefoot feet. Top of the book to the floor.

Thigh Length
Pelvic bone to the top of the knee (good to have but without the bike, hard to tell if you have enough clearance)

Arm Length
Next Measure your arm from the bony part at the top of your shoulder to the middle of your open hand.

Torso Length
Measure from your crotch to the bony part below your neck.

Shoulder Width
Measure from the bony bump of the outside of the right shoulder to the bony bump to the left side.

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Bike Measurements

Ask the person to measure the bike from the floor to the center point in the top tube. Compare that with your inseam. Even though you will be wearing shoes, you want 1-2" of clearance.

Next have him measure the c-t-c top tub length. (19.5" may be correct)
Next have him measure the stem length (usually average 100mm or 3.9 inch) (if at an angle use a ruler and mark the effective length)
Finally have him measure the handlebar width. (convert to cm.)

Top Tube/Stem Measurement
Combine the arm and torso measurements take the inches X 25.4 = your combined arm/torso length. Compare that to the ctc top tube length+stem length combo. If it is off a little you can change the length and angle of the stem.

Example: if the top tube c-t-c is 495.3mm and your stem has an effective length of 100mm = 595.3  if you are close good but if you are more than 20mm, depending on the stem length and if the stem is at 90 degrees versus an angle, I'd say pass.

Stand Over Height
If there is too much clearance or too little clearance in standing over height, pass.

Shoulder Width
Compare the width of the handlebars to your shoulder width. Most men are 42-44cm on a touring bike.

Shoe Clearance
with 18" or 457mm in the chain stays, unless you have size 13+ shoe size or very wide bags it will work.

This is far from perfect, but will give you a general idea of what will work or not work.



Offline paddleboy17

Re: Please please check my math! 19.5" top tube 49.5cm bike right?
« Reply #5 on: April 26, 2010, 03:49:25 pm »
I am a University student. Please please check my math!  19.5" top tube 49.5cm bike right now,Its so important.

Many bike now have a sloping top tube.  So you would have to measure to where the top tube goes if it were level.  Also, there is no consistency in how bike companies measure size.  The norm would be center of the bottom bracket to center of the top tube (assuming level top tube), but that is not how everyone does it.
Danno

Offline John Driz

Re: Please please check my math! 19.5" top tube 49.5cm bike right?
« Reply #6 on: June 01, 2010, 11:47:12 pm »
Thanks everyone.  I ended up taking a pass on the the Cannondale on Ebay and built up a 2010 Kona Jake the Snake with Tiagra parts for $650 brand new and have been to busy riding my new sweet pony to check my posts.  The Cannondale would have been to short anyway, I'm a 52cm cross bike or 54 road.  Thanks again!