If you’re new to the bike world, it’s normal to be confused by all the terminology and calculations that get thrown around. Many new cyclists, especially those just looking for a commuter bike, are starting to opt for a single speed bike to simplify the process.
However, single-speed bikes open up a new dilemma: the gear ratio.
The gear ratio refers to how often the rear wheel will turn with each rotation of the crank.
The truth is that there is no best single speed gear ratio that works universally, since the right ratio depends on your fitness level, your wheels, and the terrain you ride on.
The most common single speed gear ratio is the 2:1 straight ratio, which is a simple ratio including the front gear, rear gear, and rear sprocket.
There is another, more complex way of calculating the ratio called the gear inches method.
None of these standardized formulas will necessarily lead you to the best gear ratio, as you also need to account for factors such as your fitness and whether you ride on steep hills.
So how should you set up your single speed commuter or road bike? Belows is a basic guide to get you started, but you might also want to consult our post on how bicycle gears work.
What Is the Gear Ratio?
Before we get into the details of calculating gear ratios, we should talk about what a bike gear ratio is in the first place.
In the simplest terms, the gear ratio is the calculation of how many rotations the rear wheel makes for every time that the crank or bike chain turns. Calculating the gear ratio requires looking at a few different factors, including the rear sprocket, wheel size, and the number of teeth on the chain ring.
A gear ratio is usually expressed in two numbers.
The first number is the number of teeth on the chain ring:
The second number is the number of teeth on the rear bicycle sprocket:
You don’t have to think about the gear ratio as much when riding a type of bike with multiple gears because you can adjust the gears (and the riding experience) as you pedal. However, figuring out the best single speed gear ratio is important because you need to ensure that you can ride easily no matter what terrain you will be covering.
The Straight Ratio
The straight ratio is the most common—and easiest—way of calculating the gear ratio. You just compare the number of teeth of the front gear to the rear gear.
The most common gear ratio is 2:1, meaning that the front gear has twice as many teeth as the rear gear. When pedaling, your rear wheel will turn twice for every rotation of the crank. There are a few common variations on this straight ratio, such as 32:16 and 32:18.
Most newcomers to the single speed bike world start with a 2:1 ratio because it is the most common, and it is the easiest to calculate. If you notice that it isn’t working for you for whatever reason, you can always adjust it.
Calculating Gear Inches
The straight ratio is very useful as a starting point for calculating gear inches, but that assumes everyone is working with a standard 26-inch bike. If you’re working with a different setup or you just like to know everything about your bike, what are you supposed to do?
Enter the gear inches calculation. This formula multiplies the diameter of the wheel with the number of teeth in your chain ring, and then divides it by the number of cog teeth. The resulting number is a relative feel for how many inches your bike will travel with each turn of the crank.
For most cyclists, especially people that are just using their bike to commute, there’s no point in whipping out this more complex calculation. However, if you are swapping parts in your single speed bike, the gear inch calculation is a great way to ensure you keep the same ratio. For example, if you know that you like your current feel but you had to get a bigger wheel, the calculation can help you figure out how to adjust your chain ring to keep the same ratio.
If you need to change your rear sprocket to gear down or gear up, check out this video:
What Do the Different Ratios Mean?
We’ve thrown a couple of different gear ratios at you. You might be wondering what they mean. How can you know which ratio is best if you don’t even understand what the numbers mean in terms of your everyday ride?
A good rule of thumb is that the lower the ratio is, the easier it is to pedal. The higher the ratio, the more effort you’ll have to put in to get the bike to move across the terrain.
Most beginners default to thinking that easier pedaling is automatically a good thing, but that isn’t always the case (you don’t want to be flying down a hill with your pedals whizzing away with no control, for example). In the next section, we’ll cover a few factors that will help you determine whether a lower or higher gear ratio is right for you.
Factors Affecting Your Optimal Ratio
The calculations mentioned above for figuring out your gear ratio are general rules of thumb. You can adjust your gear ratio to make your ride easier once you figure out how your bike feels according to a few factors.
One of the most important factors when adjusting your gear ratio is the terrain that you ride. If you ride frequently up steep hills, you should use a higher gear ratio that is harder to pedal.
This may seem counterintuitive. After all, if you’re going uphill all the time, do you really want to be huffing and puffing as you move your bike uphill? The thing is, if you’re going uphill, you’ll eventually have to go downhill, and that’s when lower gear ratios really start causing problems.
Lower ratios on a single speed commuter bike are harder to control when going downhill, and you’ll notice your pedals will start flailing.
A good rule of thumb is that you should be standing on the pedals when you go up most hills. If you’re able to pedal while sitting comfortably in your seat, your gear ratio is too low. As mentioned earlier, a ratio of 2.75:1 is recommended if you frequently ride over hilly terrain. But be careful that your gear ratio is not so high that you’re having trouble going up the hill.
Besides thinking about terrain in terms of elevation, you should also think about the terrain in terms of the infrastructure you encounter. If you have to stop frequently (e.g., at stop signs) a higher ratio gives you more control.
Another factor affecting your optimal gear ratio is your fitness level. If you are very fit and are used to cycling, a higher gear ratio will give you the resistance you need. However, if you’re just getting started, a high gear ratio will be too demanding, especially if you only use your bike to commute.
Besides your fitness levels, think about the pace you want to ride your bike at. If you’re just riding a slow, leisurely pace, then a lower gear ratio is better. If you want to pick up the speed, increase your gear ratio.
Another factor affecting your gear ratio is the wheel size. Most commuter bikes use a standard 26-inch diameter wheel, but some off-road and road bikes use a 700c wheel, which has a 29-inch diameter.
If you’re cycling on paved roads, usually the gear ratio for a 700c wheel is higher than for a 26-inch wheel.
Your wheels will also affect the feel of the ratio. For example, a high gear ratio is easier to pedal when using high efficiency, better inflated tires than when using older tires that are harder to maneuver. If you know you want a higher gear ratio for better control on hills but are having trouble pedaling, consider stopping by the bike shop to switch out your tires.
Can You Ride Single Speed on All Bikes?
So far, we’ve talked mostly about gear ratio in terms of commuting. But can you use this ratio to make single-speeding work for a road bike or mountain bike?
Yes, you can—even though most serious cyclists and some folks in the bike industry scoff at using single-speed bikes. You might have to make a few adjustments to your setup.
For example, if you are using a mountain bike or going off-road a lot, you can keep the same gear ratio but use a smaller chain ring to reduce the chances of your ring snagging on rocks and other debris on the trail. In turn, this means you will need to find smaller cogs.
The Final Word on Gear Ratios
When you don’t have the ability to adjust gears based on your terrain, the right gear ratio is extremely important. You should choose the right ratio that will make your commute easier, depending on your level of fitness, the terrain, and your bike’s setup. Most people start with a straight ratio of 2:1, but you can adjust this to make pedaling easier or harder.
If you frequently ride a mountain bike uphill, consider investing in some bar ends for mountain bikes to make your ride more comfortable.
Want to add gears to your single-speed bike? See this post.