You may have longer or shorter legs than someone else who has 170cm
Here is what I do when someone ask me for a build.
If you know your ideal saddle height. Good.
If not. Measure your inseam.
Multiply it by 0.883
This will be the length of the line between the crank axle and the top of your saddle.
Or any other method to get your saddle height as described here
http://www.bikeradar.com/gear/article/how-to-get-your-seat-height-right-14608/Report the saddle height directly on the geometry file, PDF or image.
I import the PDF or PNG, in Sketchup and scale it to the right dimension to draw on it directly.
Any other graphical tool familiar to you will do it.
This should give you something like this:
Then measure on the drawing:
- the horizontal distance between the end of the saddle and the bar: here 874mm
- the vertical distance between the saddle and the bar: 78.7mm
- the horizontal distance between the end of the saddle and the crank: 369.3mm
Compare all this with your current bike, or a bike you like.
You should quickly see if the 17" or the 15.5" is better
(1) and (2) are the most important.
You have some room to play with:
- The seatpost offset or moving the saddle forward/backward for (1) and (3)
- The stem length for (1)
- The stem angle, spacers or a riser bar for (2)
