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!
Here’s what you need to know about single-speed gear ratios, so you can tackle more terrain with less pain.
What’s the best single-speed gear ratio for me?
There’s no universal answer, but start with a gear ratio of about 2.5:1 for road riding or 2:1 for mountain biking. Use it for a few rides, then adjust 1-2 teeth at a time until it feels like a good balance of speed vs. climbing ability.
If you use gear inches—more on that below—then that’s about 67″ for road and 55″ for mountain.
Many mountain bikers go lower, and many road bikers go higher (especially on fixies). These are just starting points that should be not bad for most people in most situations.
Your ideal gear ratio may change along with your riding routes, fitness, and preferences. Testing and changing gears isn’t a one-time task, so it’s worth keeping any unused spares on hand.
Caveat: “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, multi-speed drivetrains wouldn’t exist!
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!
What exactly is a gear ratio, anyway?
It refers to the ratio of front teeth to rear teeth. For instance, if you have a 44-tooth chainring and a 22-tooth cassette/cog/freewheel, then the ratio is 44:22, which simplifies to 2:1.
That tells you how many times the rear wheel turns for every pedal revolution. For example, the rear wheel goes around twice per pedal stroke with a 2:1 ratio, three times per pedal stroke with a 3:1, and so forth.
This has two important implications:
- The higher the ratio, the more work you’re doing with each pedal stroke, and the less torque you produce. That’s why it feels faster but tougher when you use a larger front gear and/or a smaller rear gear.
- Any gear combination with the same ratio will feel the same to ride. For instance, 44:22, 32:16, and 52:26 all equal 2:1, so they’re functionally identical. That’s why we just say “2:1” instead of the exact number of teeth.
(Geeky technical caveat: they’re not exactly the same. Smaller gears make the chain curve more sharply, which creates ever so slightly more mechanical resistance. In a laboratory setting, 34:17 might actually be harder work than 40:20. In reality, the difference is imperceptible.)
What’s the best way to change gear ratios?
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 freewheel 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.
Secondly, secondhand chainrings (for testing) are widely available and take just minutes to install.
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 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 wheel diameter in inches
The metric equivalent is meters of development, or:
Front teeth x rear teeth / rear wheel circumference in meters
Rear wheel 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.
Conclusion: the right single-speed gear ratio for you
No single-speed gear ratio is perfect, since you’ll always struggle on climbs or descents—or even both, to a degree.
However, 2:1 is a good starting point for MTB, and 2.5:1 is good for road. From there, plan on swapping gears a few times (never more than 1-2 teeth each time) until it feels like the right compromise between speed and climbing ability.
Gear ratio is a useful number, but it’s more helpful to use gear inches, which accounts for wheel and tire size. Those vary widely, so the same gear ratio may feel wildly different on any two bikes. Conversely, difference gear ratios may yield the same gear inches and therefore (roughly) the same feel.
So, to convert the starting gear ratios above, we’d get roughly 55″ for MTB and 67″ for road. Again, these shouldn’t be too bad, but you’ll almost certainly want to adjust from there!