Using Bar XY Cartesian Coordinates
Over the last few years it has become standard practice for bike manufacturers to provide Reach and Stack figures in their geometry charts. As shown below, these metrics give the coordinates of the top of the Head Tube relative to the Bottom Bracket.
This set of metrics was first espoused by Dan Empfield (founder of Quintana Roo bikes and slowtwitch.com) and rapidly adopted by a few, mostly Tri-focussed, brands.
Wide acceptance has taken 10 years but it is now rare not to be given these metrics, which is of great benefit to bike fitters.
Reach and Stack precisely define the size of the frame, compared to Top Tube Length which is an imprecise measure of the length of the frame as it is modified by the Seat Tube Angle.
The example below (from our Frame Comparison tool) demonstrates this effect. The Cervelo R5Ca was built with a slack Seat Tube Angle (to enable the use of lighter Seat Posts) so has a 25mm longer Top Tube than a Felt Z-Series bike. But when we look at the Reach of the Frame there is only a 6mm difference.
Knowing Reach, Stack and Head Tube angle makes it easy to calculate the configuration of the Handlebars and compare the true size of different bikes.
However, the failing of using Reach and Stack to compare frames arises because of the slope of the Head Tube. The example at right demonstrates this effect.
The Reach of these two frames is very similar, which could make them look like they are the same size apart from needing different spacer heights to account for the large difference in Stack.
However – extra Stack has a negative impact on Reach (roughly a 3mm reduction in Reach for every 10mm Spacer).
Once we’ve added an extra 25mm of spacers (thus normalising the Stack of the Frames) the Litespeed turns out to be 9mm shorter Reach than the Felt.
By comparing Bar XY we are able to account for the dimensions of every component that connects the Handlebars to the bike.
This more precise calculation is why we offer the Frame Comparison tool for direct calculation, or the XY bike search in the Advanced Bike Finder (look under Advanced Options).
All results in our Advanced Bike Finder show Bar XY in the detailed specifications, regardless of which input method you use to define the bikes.
Definition of Bar XY
Bar X and Bar Y are measured from the centre of the Bottom Bracket to the centre of the Handlebar.
There are tools available such as:
Our Velogic Studio system digitally captures both Frame XY and Bar XY.
How is Bar XY Calculated?
The traditional method is shown below. This method suffers from a systematic error that gets worse the more the stem is angled. At velogicfit we have a proprietary algorithm that more accurately calculates Bar XY, taking account of the effect of stem angle correctly.
See also:
- Our free Frame Comparison tool
- A guide to Using Frame Comparison
- Our Advanced Bike Finder tool
Related Articles
Frame Comparison - Bar Curve X and Bar Top Y for Road Bikes
In order to enhance the usefulness of our Frame Comparison tool we’ve added additional metrics that aid in precisely matching positions. These metrics are Bar Curve X and Bar Top Y. To calculate these metrics for road bikes we add the handlebar reach ...Using frame comparison
The free velogicfit Frame Comparison tool offers a quick, fully-user-controlled way of comparing two or more frames side by side. You’ll find frame geometry, images (if available) and frame specifications. If you’ve got a target Bar X & Y (e.g. from ...Using the software
Shrink the capture area around the rider – leave space above for sitting up but it can be tight on the sides and ground. Reducing the capture area significantly lowers the processing load on your computer and can help it run much faster. Only the ...Using multiple Kinect cameras
Microsoft Kinect cameras have always had an inbuilt limitation: it's only possible to attach a single Kinect camera to Windows at one time. When we developed Velogic Studio 4 (released early 2024), one of the major enhancements was the ability to use ...Velogic Studio bike measurements defined
Our Velogic Studio system collects a detailed set of bike measurements that combine both traditional relationships and modern XY metrics. Bike measurements as shown in Velogic Studio The definitions for these measurements are listed below. Saddle ...