How To: Measure Bike Fit Exactly

[Reed Kennedy]

Been meaning to write this up for a while, and finally made some time today. Figured some folks here might find it useful!

Ever found a bike that fits great, but not been sure how to measure and record that fit? 

Maybe you got another bike and want the new one to fit the same?

Maybe you moved parts from one bike to another and want to understand why it feels different?

Maybe you want to make small adjustments, but be able to put things back if they don't work out. 

Maybe you just like data.

I can help!

After trying a bunch of methods (spirit level, drywall square, plumb bob, expensive and impossible to buy FitStik) I have a far-and-away favorite method: A relatively cheap and easy to buy laser level. Here's the one I use:

https://www.amazon.com/gp/product/B00OZHIFNS/

Here's how to do it:

Example of bike with laser level aligned.

1. Level the bike:
1. Keep the bike from rolling and the bars from turning by strapping the front wheel to the frame with a toe strap
2. Lean the bike against a wall, as vertically as possible (tie it to the wall for safety if you can)
3. Set up your laser a bit over a 1 foot off the ground (I clamp it to a floor pump)
4. Turn the laser on on
5. Align the horizontal beam with the hub axle of whichever wheel is higher (I shoot for the QR rod at the center of the QR nut)
6. Raise the lower wheel (I use door shims) until the horizontal beam passes through both hub axles (or QR nuts and rods)
7. Your bike is now level, even if your floor isn't:
2. Set up laser for measurement:
   
1. Move the laser to a taller object (I use a repair stand)
2. Align the vertical laser with the center of the crank bolt
3. Align the horizontal laser with the highest point of the saddle
4. Try to avoid moving the bike going forward, realign laser if the bike moves
3. Measure with a meter stick:
1. Measure reach: From the foremost tip of the saddle to the center of the bars (use the horizontal beam as reference to keep the meter stick level)
2. Measure setback: From the foremost tip of the saddle to the cross of the beams above the crank (use the horizontal beam to keep the meter stick level)
3. Measure bar drop (or rise): From the top (or bottom) of the bar to the horizontal beam (eyeball meter stick verticality, this distance is usually too short to introduce much error)
4. Measure saddle height: From the center of the crank bolt to the horizontal beam (measure parallel to the seat tube)
5. Extra credit: Use a digital torpedo level to measure saddle angle

Labeled diagram showing measurements. My bars are near saddle height, so 3.3 is clumsy.

Record that data. Now you know exactly how your bike fits! The above measurements make a fixed set of points: a triangle made by the positions of your butt, hands, and feet. If they match on two bikes, the fit will match. The bikes may *handle* differently, but they will fit the same and support your body the same way.

Now you can adjust your bike, confident you can go exactly back to the old fit if you want to. You can also switch to another bike, take the same measurements, and then adjust and replace parts until it matches the first one you measured. 

Note that step 2.3 has some wiggle room, especially if you don't use the same saddle and saddle angle on every bike. If you tilt your saddle significantly, you may want to align the horizontal laser with the top rear of the saddle instead of the highest point (usually the nose). Just make sure you line the horizontal laser up with the same point on the saddle every time, on every bike.

Saddles: Your posture will still be different on different saddles. To truly duplicate fit you'll want to use the same saddle on each bike. If you don't use the same saddle, give yourself room to fine-tune saddle fore-aft position and angle, rather than blindly following the measurements. I seem to sit further forward on a Brooks B17 than I do on a Berthoud Aravis, even though they're the same length. So I adjust my Brooks saddles a bit further back.

Cranks & Pedals: If you use longer or shorter cranks on different bikes that will slightly change your saddle height. Different pedals can change saddle height too. When using different pedals or different length cranks ride a bit if possible to make sure the seat height feels right, then measure. 

Bars & Brake Levers: Different drop bars have different reach (the distance between the bar tops and where the brake levers mount). Different brake levels have different reach as well. Newer brake lever bodies extend well forward from the bars, while old ones tended to be shorter. If you are changing to a different bar or brake lever, keep reach in mind. Try measuring from the nose of the saddle to the place where your hand rests on the brake hood, and replicating that distance. 

Here are my personal measurements of my bikes, as an example: https://docs.google.com/spreadsheets/d/1c5AetKEaTfJ0w9Mmf163a86AI8TLPTCqgSKSKtr5stE/edit?usp=sharing

Figuring out how to measure fit has changed the way I shop for, build, and enjoy bikes. I now know what will work, instead of having to go through bunches of trial and error. Saves money on parts, too!

I don't mean to suggest that all your bikes should fit the same. Only that it's worth understanding and being intentional about the differences. Give it a try!

Best,

Reed