Intricacies of Bicycle Gear Range and Ratio

Designing the Optimum Drivetrain on Your Bicycle

1. What's the lowest available gear?

2. What's the highest available gear?

3. How much of a difference is there between each available gear?

4. Is the bike geared correctly for the specific rider, environment, etc?

We usually don't describe bikes as "24 speed" anymore. We would typically say what kind of front and rear gearing the bike has. For example, a "24 speed" bike could be a 3x8 (fairly old technology) or a 2x12 (extremely modern technology.)

The highest and lowest definitely effect how fast the bike goes. If you need lower gearing than you have available, it can be hard and slow to climb hills. Worst case, you might not even make it up the hill.

The highest gear you have won't usually affect your speed on flat ground, but can limit how fast you go down hills. Though there are some cases like a 3 speed internal gear hub bike, where the top gear might be a limit even on level pavement.

Gear shift ratios are important, because they effect your ability to make good power. If your shifts are too large, you might find yourself jumping around gears a lot, and you might have a hard time finding a comfortable power output (making you tired.) Most people pedal most efficiently over a 10-20 RPM range. For example, I find that I'm fastest pedaling at 80-90 RPM.

Gear Ratio and Gear Shift Ratio are Different

Let's start with Gear Ratio. The best way to define gear ratio when pedaling a bicycle is how far your wheel will rotate in comparison with a full rotation of your pedal stroke. A pedal stroke can be defined as one pedal starting in the 3 o'clock position and making a complete rotation back to the 3 o'clock starting position. The ratio is determined by the number of teeth on the front ring divided by the number of teeth on the rear cog. More teeth on the rear cog make the wheel rotate less gear easier to pedal, but more teeth in the front chain ring makes the wheel rotate further. gear harder to pedal. It is important to understand this when trying to select components. Big in front is harder. Big in back is easier. For example, a 34 tooth front ring paired with a 34 tooth rear cog results in a 1:1 ratio. In this gear, your wheel will match the rotation of your pedal stroke. So a full rotation of your pedal stroke will also generate a full rotation of your wheel. A 1:1 gear ratio for road cycling has become the standard easiest gear choice for longer steeper roads. 

The distance the bicycle covers within the pedal revolution is based on the wheel and tire size and the gear inches. Gear inches is a combination of the size of your front and rear. We will discuss gear inches in more detail on the next article.

The next option to consider is gear range. Range is the difference between your easiest gear and your hardest gear. Keep in mind, pedal cadence + your gear choice determines your speed. Most cyclists prefer to pedal at a cadence of 70rpms-95rpms. Above or below this range makes it either too difficult to pedal because the resistance (from gravity or wind resistance) makes it too difficult to turn the pedals or there is not enough resistance so achieving and maintaining a high cadence is technically not possible for the cyclist. Ideally, a cyclist wants an easy enough gear for steeper climbs (10%-12%) and a hard enough gear to pedal downhill at a high rate of speed (35mph-40mph). 

Let's add one more concept, gear shift ratio. It is not that difficult to make a wide range. The wider the range, however, the wider the gap can be when shifting to a harder or easier gear. Gear Shift Ratios effect your ability to pedal in an efficient power output. If the gap is too wide, it can be difficult finding the optimum gear when the gradient in terrain changes or a headwind is encountered. Keeping a comfortable cadence is key to riding faster and longer; therefore, a tight gear shift ratio is desired. The challenge is reducing the difference or gap between each gear while maintaining the wide range.

Ways to Achieve a wide Range and Tight Shift Ratio

1. Add more gears. Currently, 11-12 gears in the rear is the maximum with some brands having a 13 geared cassette in the works. More rear gears can reduce the gap between each gear shift.

2. Increase the size of the biggest rear cog while decreasing the size of the smallest rear cog. There are many options available but pairing with the proper front chain ring set up and proper rear derailleur need to be considered. SRAM offers an Eagle Cassette Option with a 52-10. This is typically run on a mountain bike set up or gravel set up but is designed to be paired with a single ring up front.

3. Add more gears to the front chain ring combined with an optimum tooth size of each ring. This was how it used to be done 30 years ago, now the trend in mountain and gravel bike setups is a single ring, while road setups continue to use a 2x or double chain ring combination. A typical road set up would be a 52/36 combination paired with a 30-11 or 32-11 Cassette with 11 to 12 cogs/speeds. Keep in mind, the lower the number of teeth in your front ring will also help reduce the gear shift gap. Some 12 speed set ups will offer a 10-33 or 10-36 in the rear and pair it with a 48/35 or a 46/33.

Understanding the concept of Gear Range, Gear Ratio, and Gear Shift Ratio will help with setting up the perfect drivetrain component options for your bicycle. The first obvious question, is what type of bike and what type of riding will this be optimized for. A mountain bike, road bike, and gravel bike are the 3 most common bikes ridden where the rider is looking to really optimize the gearing for performance. Within each of these categories, a more focused purpose can still be desired. For example, within the road category, is the bike going to be used for riding "epic rides or staged events" that involve lots of mountain climbing? Or will this bike be set up for local group rides where the pace is fast and the terrain does not feature long climbs. Gravel riding has been gaining popularity ever since its introduction 10ish years ago. People are doing rides on a gravel bike that only mountain bikers previously did. Some gravel bikes double as both a road and off-road rig. Choosing the optimum drivetrain for these types of gravel bikes will vary once again. 

Unchained Bicycle Garage works with you and can help put together the optimum drivetrain set up for whatever your build. Mark Bierotte, has plenty of experience from racing triathlons, to long distance mountain bike events, enduro riding, and of course road and gravel riding. Come talk to us about building your dream bike or simply optimizing the gearing  of your current ride.

Note: to the reader who will want to challenge comments in this article regarding speed or power output or riding faster or longer or climbing better. Rider Fitness is a major factor. So it is understood that a rider can always go faster or longer if they become more fit or lose more weight or ride more often or ride longer. This article is written with the assumption that whatever fitness level the rider is currently at is where they are at. If by being able to optimize their bicycle to allow greater enjoyment while cycling and if this in turn causes them to ride more often or ride longer and this in turn improves their fitness and allow them to ride faster. Then lets agree to agree that we both are right.