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FixMeUp! Instructions

This page talks about what FixMeUp! does and explains how to use it to find the right gears for your fixed-gear or single-speed bike.

These instructions are written to work for all versions of FixMeUp!, which are similar enough that you'll have no trouble moving between them. There are no separate instuctions for the Java versions or the html version; the downloadable Windows and Mac versions do come with manuals, however.

Caveat: the html version lacks some of the features described here. That said, it's by far the easiest and fastest to use, so you may want to start with it.

Here's a table of contents.

What FixMeUp! Does

Using FixMeUp!
   From a working gear
   From scratch

Other features
   Selection display
   Tire size
   Highlight area

Reading the display
   What gears will fit

What FixMeUp! does

Problem Statement

There are three "problems" that contribute to making it hard to find the right gear for a derailleur-less bike with vertical rear dropouts.

Fixed chain path

First, the chain "path" can't change. Without a derailleur, the chain wraps around the ring and cog and wants to take the shortest path between them. On bikes designed to be used without derailleurs there's a provision for changing the distance between the ring and cog in order to change the length of the path, but of course vertical dropouts don't allow this. fixed chain path

Chains are 1" long

Second, chain lengths can only be adjusted 1" at a time. Chains are made up of links each exactly 1" long (on a new chain, anyway). So far nobody's figured out how to remove less than one link.

The chain must be tight

Finally, the chain must fit snugly. If a chain doesn't fit tightly enough it will be thrown off by bumps in the road, uneven pedalling, or plain bad luck. In the worst scenario, losing a chain on a fixed gear can cause you to crash.


Imagine that you have a chain 47" (47 links) long and that you want to use it on a 42x16 gear (that's short for "42-tooth chainring paired with a 16-tooth cog"). You're going to find a frame, or have one built, to fit that gear and chain. There will be exactly one chainstay length (where "chainstay length" means the distance from the center of the BB spindle to the center of the rear axle) that will fit that gear and that chain.

Now imagine that you're going to be less picky about what length chain you'll be using. All you need now is a frame that will accomodate any length chain on a 42x16. There are a number of chainstay lengths that will work for your chosen gear. Since increasing the length of the chainstay means both the top and bottom runs of chain must be longer, those chainstay lengths will differ by about 1/2".

Now imagine that you don't care what cog and ring you use (as long as the ring fits your crankset and somebody actually makes the cog.) Agree to accept any cog/ring combination and any length chain -- only now let's try to make do with the frame you have. Since there are now a large number of possible chainstay lengths (each corresponding to one of the ring/cog/chainlength combinations), there's only one question left to be answered: What ring/cog/chainlength combinations will fit my frame with its particular chainstay length?

<EM>FixMeUp!</EM> screenshot

This is what FixMeUp! does. You tell it how long your chainstay is and what cogs and chainrings you can use. It then produces a chart like the one above.

Along the top are chainstay lengths, with yours at dead center. Along the left edge are gear inches (or meters, European style) that tell how hard a gear is to push. Each entry on the chart (such as our 42x16 example above) represents a gear and is positioned to show what chainstay length the gear requires and how difficult to push it will be.

All you need to do is select from those gears near the middle the gear whose difficulty suites your riding style and present level of fitness.

How to use FixMeUp!

There's only one difficult thing about using FixMeUp!: you have to figure out very accurately how long your chainstay is. If you still need to measure your chainstays, we suggest you take a look at our page on chainstay measurement.

Copyright 1996-2024 by Eric House & Fixed Innovations
This site was completely rewritten around October 2020. If you notice problems they are probably new!
Please let me know if you find problems or have comments about this site.