To learn about how bike geometry effects the feel of a bike, I want to measure bikes that I already ride.
The ideal way would be a nice jig but as a hobbyist I don’t want to invest in one of those.
I’m want to know how to best do this with more common tools. There has to be better ways than just holding a tape measure over what you believe is the center of a tube. If anyone has any advice or input on this topic that would be very helpful for me.
A tape measure and a smart phone will get you far, but if you want to get fancy, get yourself a laser level, a tripod, and a digital angle finder.
For instance, to get the saddle clamp to BB (X) dimension, place the rear wheel against a wall with the bike perpendicular to the wall. Measure from the BB center to the wall and saddle clamp center to the wall. Subtract the two and bam, there’s your number.
Combine that with the direct measurement from saddle clamp to BB and you can trig your way to the perfect seat tube angle for yourself.
The location of your contact points are most important. You can work from there to design the frame of your dreams.
Plumb bobs are handy too if you don’t have a laser level
I like to use photometry. If you take a photo of the bike with a long lens (zoomed) to reduce distortion and with a meter stick. You calibrate the image to the meter stick to pull out dimensions.
I have found this method to be +/-5mm and .2-.3deg accurate. The combination of photometry and cross-correlating with real-world measurements gets that accuracy even closer.
This method works really well for frame-only. It’s much harder to measure a bike when it is not built up with a fork.
I use fusion360 for this, but there are a few other programs that can do this.
Check out Ryden Bikes’ measuring tool for the ‘tape and phone’ method on steroids: https://sites.google.com/ryden.bike/ryden-bikes/bike-setup-tool
This is the method I use too. BikeCAD allows you to place a photo too which makes for a pretty quick process. You can also scale complete bikes easy enough if you know the wheel/tyre size.
Below is an example trace I did on Oddity’s Dirt Cruiser built for NAHBS in 2019, shot but John Watson for the Radavist. Pretty neat to be able to extract that kind of info!