Frame Geometry

[campy man]

Any Paceliners with a suggestion to measure frame angles at home? Other than sending to a frame builder, is there a way to determine head and seat tube angles?

[sokyroadie]

Angle finder or I phone

[prototoast]

I use a digital angle gauge (such as https://www.amazon.com/Wixey-WR300-Type-Digital-Backlight/dp/B00T6YZ0K6).

They're quick and easy to use, and though the ultimate accuracy can depends on how controlled the environment you're measuring the frame on (level surface, equal-sized tires, etc.), it gets you a pretty good range for real-world conditions.

[Mark McM]

Angle finders like the ones suggested work great on bikes made with traditional straight round tubes. Unfortunately, many frames today (particularly carbon ones) don't use straight round tubes. On these bikes, you can probably measure the seat tube angle off the seat post (which are still mostly straight). but you may have to get more creative to measure the head angle. You may end up having to take the stem off and measuring the angle off the steerer tube.

[David Tollefson]

Another vote for the digital angle gage. I use one in setting up my building jig, as well as measuring bikes. I think it cost all of $20.

[David Tollefson]

Angle finders like the ones suggested work great on bikes made with traditional straight round tubes. Unfortunately, many frames today (particularly carbon ones) don't use straight round tubes. On these bikes, you can probably measure the seat tube angle off the seat post (which are still mostly straight). but you may have to get more creative to measure the head angle. You may end up having to take the stem off and measuring the angle off the steerer tube.

Or use a framing square and measuring tape to measure the X- and Y-offsets from the BB to the center of the saddle rails and calculate the angle.

[pdonk]

Lots of options for phone apps.

[mt2u77]

You can do it optically, if you are careful. Take a square sideview picture of your bike with a telephoto lens from a long ways away. It's important to be far away (like 100ft+ if you can) to reduce parallax error, and you don't want distortion from a wide angle lens. Make sure the fork is aligned straight ahead. Add a ruler or some other scaling object to the shot, or just use a known dimension on the bike.

Load the image into ImageJ (free NIH download). Set a scale using the reference (X pixels = Y known cm), mark all the frame points you want, draw reference lines, and use the angle and measurement tools to measure every bit of frame geometry you could possibly want. Save the marked up image for future use.

[djdj]

You may be able to calculate them from other measurements by using something like bikegeocalc.

[Plum Hill]

Don’t forget to check the floor the bike is setting on if using an angle finder. If not level you need to take into consideration but adding or subtracting to the measured angle.
Probably could have explained that better....

[David Tollefson]

Don’t forget to check the floor the bike is setting on if using an angle finder. If not level you need to take into consideration but adding or subtracting to the measured angle.
Probably could have explained that better....

This is why using a framing/drywall square is helpful -- it takes any floor slope out of the equation.

[dddd]

Don’t forget to check the floor the bike is setting on if using an angle finder. If not level you need to take into consideration but adding or subtracting to the measured angle.
Probably could have explained that better....

A sure-fire way to cancel out any out-of-level condition of the ground
(and/or of the top tube as a zero-degree tare reference) is to:

1) measure from one side of the bike, record the angles.
2) Turn the bike around 180-degrees and put the tires on the same two spots on the ground.
3) Measure again, this time of course from the bike's opposite side. Then average the measurements.

This doesn't help with molded frames and those with tapered head tubes, offset seat tubes, etc.
There, you will have to get creative (or cheat and look up the bike's published geometry table).
But, more then once I have discovered significant discrepancies from a bike's published geometry data in the size frame that I was looking at.

There may also be reversal-hysteresis errors in the instrument's readings, but which also cancel out if the instrument is applied identically (same side of inclinometer facing the same side of the tube in question).

[Peter P.]

Don’t forget to check the floor the bike is setting on if using an angle finder...

I use a Tilt Box II (http://www.bealltool.com/products/measuring/tiltbox.php).

To counteract crooked floors, take your measurements, then flip the bike around so it's pointing in the other direction. Average your two measurements.

[OtayBW]

I use this thing all the time for related measurements: https://play.google.com/store/apps/details?id=com.plaincode.clinometer&hl=en