A Do-it-yourself Tool For Measuring Saddle Setback

When it comes to setting up a new bike, one of the most important steps is setting where the saddle is located on the rails (also known as the ’saddle setback’).

Once you’ve figured out your ideal saddle placement, remember to document that position and be sure to have a good way to recreate it, either on another bike or on your current ride. If you’re switching frames, make sure you understand that not all bikes have the exact same angles and you’ll need to have some way to compare the geometries of each frame with the other.

Of course, after you understand that different frame geometry will mess with your saddle setback, you’ll understand that you can’t use the same position on the saddle rails between the two bikes.

This writeup is meant to give you a fighting chance of recreating your ideal saddle setback on any bike. After the jump, I offer a couple of tips that can make the process more trouble free, as well as showing you how to make a custom setback tool that makes positioning your saddle a breeze.

The easy method for measuring saddle setback

An easy method for measuring setback is to drop a plumb bob off the tip of the saddle and use masking tape or a felt tip pen to mark where the string crosses the frame or crank. After that, you can measure from the marked location to the center of the bottom bracket spindle. While this method is simple and relatively cheap, I’ve also found it to be a difficult one, as the string always bounces around and catches on the frame a little while I’m trying to take the measurement; basically, I never really know if the spot that the plumb line settles on is really the right one.

The do-it-yourself saddle setback tool

I built this tool from scraps based on an idea I saw in a post at roadbike review. The basic idea behind the tool is to reference all of your measurements from the BB axle. The tool can be transfered from one bike to another make it easy to transfer the measurement accurately to multiple bikes.

This method requires that the same exact saddle be used between bikes. The DIY saddle setback tool is setup to work by removing one of your bike’s crank arms, and then threading the tool into your installed BB axle.

If you don’t want to remove your crank arms, you can modify it to work with them in place by using a different method for attaching it onto the BB. The tool I saw on the forums used an 8mm allen wrench that had been cut down to a stub and glued to piece of wood. If you use 14mm crank bolts you could take a socket head and glue it into a piece of wood.

Also note that my measurement is actually being referenced off one of the faces of the angle bracket and not the actual center point of the BB spindle. This measurement can easily be determined by measuring from the center point of the tool (which represents the center of the BB axle) to the edge of the angle bracket.

  • Materials
  1. You need something long and thin to connect to the BB. I used a piece of aluminum angle bracket I found next to a dumpster at work.
  2. You’ll need a level or something to ensure that you have the unit perfectly vertical when you measure to the saddle. I used a cheap bubble level.
  3. You’ll need a method of attaching the unit to your bike. Either directly onto the BB axle, or onto a crank bolt. I just drilled a hole in the angle bracket and used a crank bolt.
  4. Finally you will need some sort of ruler to make the actual measurement. I used a square which allowed me to use the angle bracket as a reference point to measure accurately to the tip of the saddle.
  • How to use it

Attach the unit to the bike. For me, this part can be a bit of a a pain because I have to remove the crank arms and attach it directly to the BB. After you’ve attached the tool to your bottom bracket, rotate the unit until your level says that it is perfectly vertical.

Next, place the t-square against the side of the angle bracket, slide the ruler until it just touches the tip of the saddle, and then lock the t-square down. As you continue, remember to keep the t-square / ruler locked because its measurement was taken from your original saddle position; it is this dimension that you want to replicate on your other bike.

After you’ve established your point of reference, transfer the unit to your second bike. Place the t-square on the angle bracket and rotate the unit until the ruler touches the tip of the saddle. Check to see if the level indicates that the tool is vertical before sliding the saddle fore or aft until the ruler hits the tip of the saddle.

This tool will help you get very close to matching your saddle positions between multiple bikes. While it is crude, and with a few modifications it could be even better, it does the job.

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