Getting The Perfect Single-Speed Gear Ratio (Beginner’s Guide)

Last updated: January 21st, 2024

Single-speed bikes are easy to maintain and liberating to ride. But when you only get one gear, it’s got to be the right one!

I advise single-speed bike riders to start with a gear ratio of:

  • 1.8:1–2:1 on mountain bikes
  • 2.2:1–2.4:1 on city & cruiser bikes
  • 2.5:1–2.7:1 on road & hybrid hybrid bikes (with a freewheel)
  • 2.7:1–2.8:1 on fixed-gear road bikes

Many mountain bikers go lower, and many road bikers go higher (especially on fixies). You may also want to go 1-2 teeth lower for frequent stoplights, since it’s tough to start without momentum.

Again, these are just starting points that should be not bad for most people in most situations.

No particular gear ratio is universally the best. A single gear can’t be both fast (high RPM) and easy (high torque) at the same time. Rather, there’s an inherent trade-off between speed and torque.

That’s why the optimal gear ratio depends on your bike, fitness, terrain, and riding style. That’s also why the optimal ratio will change over time.

To find it:

  1. Stick with a reasonable starting ratio (see above) for several rides. It takes time to get used to it, and more time to figure out what terrain it does and doesn’t suit.
  2. Adjust by 1–2 teeth at a time. You’ll eventually hit the right balance between speed vs. climbing ability.
  3. Keep the unused chainrings/cogs on hand so you can test new ratios quickly and cheaply in the future.

When you’re comparing different bikes, it’s helpful to use gear inches, not gear ratios. It’s a simple and wonderfully useful number, so more on that later.

Why “perfect” gearing doesn’t exist

The best gear ratio isn’t perfect; it’s just a good balance of trade-offs.

After all, it’s physically impossible for one speed to feel fast (high RPM) and easy (high torque) at the same time. Otherwise, we wouldn’t need multi-speed drivetrains!

In other words, it’s about realistic expectations. No magical gear ratio lets you climb a mountain and bomb back down with ease. One of the two—and usually both to an extent—is going to suffer.

If you find that too frustrating, then single-speeds probably aren’t for you. And that’s perfectly reasonable!

Follow this process to change your gear ratio

Make small changes, usually no more than 3-4 teeth in the front or 1-2 teeth in the rear. Change only the front or the rear, not both at once, so the change isn’t too drastic.

It gets expensive to swap gears repeatedly. Consider buying lightly used gears for testing purposes, then replace them with new ones (in the same size) once you’ve found the right ratio.

(You won’t want to use the secondhand ones long-term, since they’re often a bit worn or rounded out. This may accelerate chain wear and increase resistance.)

Now, how do you decide which gears to change? Here’s how I approach it:

  • Chainring adjustments are easier to fine-tune, since you can change just one tooth out of 30- to 50-something up front, versus one out of 10- to 20- something in the back.
  • Chainrings are usually cheaper and easier to replace than rear sprockets.
  • It’s easier to chain links than to add them, so move to smaller gears rather than larger, when possible. That means decreasing the front for a lower gear ratio, or decreasing the rear for a higher gear ratio.

Some riders prefer a “dingle-speed” set-up wherein the freewheel and chainring each have two close gears. This allows a manual change between a high and low gear. It’s irritating to change often, but not bad for 1–2 changes from pavement to trails or from flats to huge climbs. You’ll need angled drop-outs (not horizontal track ends) or a chain tensioner in order to accommodate the slight differences in gear circumference.

Caveat: watch for frame limitations

Some frames can only accommodate chainrings up to a certain size. Fortunately, as discussed, you can pair that with whatever rear cog creates the ratio you want.

Let’s say you have a 20-tooth cog and you want a 2.5:1 ratio. That indicates a 50-tooth chainring.

But what if your frame’s chainstays can only clear 46 teeth?

Simple: use a 45-tooth chainring, and go with an 18-tooth rear cog. The ratio is still 2.5:1, but now you’re clear of the frame.

Better still, go with an even smaller 2:1 combination, like 40:16. That leaves a few teeth’s worth of clearance, just in case you want to fine-tune the ratio with a slightly larger chainring in the future.

A better way to compare single-speed gearing

Gear ratios are a fine way to keep track of what works for your bike right now. But they have one shortcoming: they don’t account for wheel size, so they aren’t comparable between bikes.

Instead, you can use gear inches to compare different bikes (or the same bike before/after a tire change). To calculate gear inches, find:

Front teeth x rear teeth / rear tire diameter in inches

The metric equivalent is meters of development, or:

Front teeth x rear teeth / rear tire circumference in meters

(Rear tire diameter/circumference is always measured to the tire tread.)

The math is simple, but rim and tire sizing isn’t always obvious. I like to use this calculator to easily account for them.

How wheel & tire size affect your gear ratio

Larger wheels or fatter tires both mean larger circumference, so each revolution covers more distance (and requires more effort). The opposite applies to smaller wheels or skinner tires.

To give a dramatic example, if you switched to a bike whose wheels are half the size, then the same gear ratio would require half as much effort, and turn the wheel half as many times per pedal stroke.

Consequently, you’d calculate half the gear inches, too.

What about crank length?

If you want to be as precise as possible, then you also need to account for crank length. It varies between bikes, but does affect mechanical advantage (ease/difficulty) of a gear.

The standard way to do this is with a measurement called gain ratio, which is:

(Wheel radius / crank length in the same unit) x (front teeth / rear teeth)

Do you actually need to worry about this? In my experience, not really. Gear inches is sufficient for most cyclists to find the right gear ratio.

Crank length absolutely does affect your gear choices. And if you’re changing your cranks, then you’ll want to change your gears to maintain your preferred gain ratio.

But any two bikes will also have several other differences in feel. In light of all those factors, I personally have never found it worth comparing crank length.

A note on gearing for fixed-gear bikes

Generally, riding a fixie calls for a slightly higher gear ratio than you’d use with a freewheel. Coasting isn’t possible, so you need to be wary of “spinning out” while descending on a fixed-gear.

You might think this would make climbing harder, but that’s not quite the case. The flywheel effect of the rear wheel helps maintain your momentum, so fixed-gear cyclists often report climbing faster despite the higher gear ratio.

Single speed gear ratio table

Gear ratio calculation is easy, but it’s always nice to have a quick reference. To that end, this table provides every gear ratio within common ranges for single-speed bikes.

Bicycle gear ratios for the most common gear configurations.