How fast you go on a bike is not down to one thing — it is the product of three: how quickly you turn the pedals (cadence), how big a gear you are pushing (gearing), and how far your wheel rolls in one turn (wheel size). Get all three working together and a relaxed-looking spin can carry you along at a brisk pace; get them out of balance and you can be hammering the pedals yet going nowhere fast. This guide explains exactly how cadence, gear and wheel size combine to produce speed, gives you the formula with worked examples, shows why a bigger gear isn't automatically faster, and helps you find a cadence that works for you. At the end, we show how to get instant answers with the cadence-to-speed tool on the Convert.bike home page.

The three ingredients of speed

Think of your drivetrain as a chain of multiplications. Each pedal stroke turns the chainring; the gear ratio multiplies that into wheel turns; and the wheel circumference turns each wheel rotation into metres on the road. Put formally:

  • Distance per minute = wheel circumference × (chainring teeth ÷ cog teeth) × cadence (rpm)

Here cadence is your pedalling rate in revolutions per minute, the chainring-over-cog fraction is your gear ratio, and circumference is how far the wheel travels per rotation. Multiply them and you get metres travelled each minute. Converting to the units we usually quote:

  • Speed (km/h) = distance per minute × 60 ÷ 1000

That is the whole engine. Everything else in this guide is just exploring what happens when you change one of the three inputs.

A worked example

Let's ride a road bike with a 700c wheel (circumference about 2.1 metres), a 50-tooth chainring and a 16-tooth cog, pedalling at 90 rpm.

  • Gear ratio = 50 ÷ 16 = 3.13
  • Distance per minute = 2.1 × 3.13 × 90 = 591 metres
  • Speed = 591 × 60 ÷ 1000 ≈ 35.5 km/h

Now shift to a harder 50×13 gear (ratio 3.85) at the same 90 rpm: distance per minute = 2.1 × 3.85 × 90 = 728 m, giving about 43.6 km/h. The taller gear is faster — provided you can keep spinning at 90 rpm. That proviso is the heart of the next section. If you want to dig into ratios, gear inches and development behind these numbers, see our guide on gear inches, ratios and development.

Why a higher gear isn't always faster

It is tempting to think the answer to going faster is simply "bigger gear". But the formula has three terms, and pushing a taller gear almost always forces your cadence down, because each stroke takes more effort. If shifting from 50×16 to 50×13 drops your sustainable cadence from 90 rpm to 70 rpm, let's see what really happens:

  • 50×13 at 70 rpm: 2.1 × 3.85 × 70 = 566 m/min ≈ 33.9 km/h

That is actually slower than the 35.5 km/h you managed in the easier 50×16 at 90 rpm. The bigger gear lost you more in cadence than it gained in ratio. This is why experienced riders talk about "spinning" rather than "mashing": a slightly easier gear that lets you keep your legs turning quickly is often faster, and far kinder to your knees, than a monster gear that grinds your cadence into the ground. Speed is a product, not a single lever — the trick is finding the gear where ratio and your achievable cadence multiply to the highest figure for the effort you can sustain.

Finding your ideal cadence

Most riders are most efficient somewhere in the 80–100 rpm range on the flat, with many settling around 85–95 rpm. Climbing often pulls cadence a little lower, while track sprinters can spin well past 110 rpm in short bursts. There is no single "correct" number — it depends on your fitness, muscle make-up and the terrain — but a few principles help:

  • If your legs burn and you're grinding, your cadence is probably too low; shift to an easier gear and spin faster.
  • If you're bouncing in the saddle and breathing hard with little power, your cadence may be too high; select a slightly taller gear.
  • Aim to keep cadence roughly steady and change gear to suit the gradient, rather than letting cadence swing wildly.

A practical way to discover your sweet spot is to ride a familiar stretch at different cadences and notice where you feel you could hold the effort longest. Then use gearing to keep yourself near that cadence whatever the road does. The home-page calculator makes this easy: enter a target cadence and see what speed each gear delivers, so you can pick gears that keep you in your comfortable rpm band.

It is also worth practising deliberate cadence drills. On a quiet, flat road, spend a few minutes spinning at a noticeably higher cadence than feels natural — say 100 rpm in an easy gear — to teach your legs to turn smoothly without bouncing. Then do the opposite, settling into a slightly bigger gear and a steadier rhythm. Over a few weeks this widens the cadence range you can use comfortably, which means more gears feel usable and you can respond to changing terrain without ever being stuck spinning out or grinding to a halt.

How wheel size fits in

Wheel size enters through circumference. A bigger wheel rolls further per rotation, so for the same ratio and cadence it goes faster. A 700c/29er wheel (622 mm bead-seat) has a larger circumference than a 26-inch wheel (559 mm), which is one reason 29ers feel like they hold speed so well. If you change wheel size, your speed at a given gear and cadence changes too — something worth remembering if you swap wheelsets or compare bikes. Our guide to understanding bike wheel sizes explains the standards and how each diameter affects rolling distance.

The mph and km/h relationship

Speed comes out of the formula in km/h, but plenty of riders, especially in the UK and US, think in miles per hour. The conversion is fixed and worth memorising:

  • 1 mph = 1.60934 km/h, so to go from km/h to mph you divide by 1.60934 (or multiply by about 0.621).

Our 50×16 example at 90 rpm came to 35.5 km/h; dividing by 1.60934 gives about 22.1 mph. A common everyday cruising speed of 20 mph is 32.2 km/h, and a strong group-ride pace of 25 mph is 40.2 km/h. Mixing up the two units is a classic way to over- or under-estimate how fast you are really going, so it pays to be clear which one your computer is set to. For more on switching cleanly between the two, see our mph to km/h cycling speed guide.

Using the Convert.bike cadence-to-speed tool

The cadence-to-speed converter on the Convert.bike home page does all of this arithmetic for you. Enter your wheel size, chainring and cog teeth, and a cadence, and it returns your speed in both km/h and mph instantly. Because you can change any input and watch the result update, it is ideal for answering real questions: "What cadence do I need in this gear to hold 30 km/h?", "Will a 52-tooth chainring noticeably raise my top-end?", or "What's my speed if I spin this climbing gear at 95 rpm?" Experimenting with the tool quickly builds an intuition for how the three ingredients trade off against each other.

Next steps

Begin by finding the cadence you can hold comfortably on a flat road, then use the home-page cadence-to-speed tool to see which gears keep you near that cadence at the speeds you ride. Resist the urge to simply fit a bigger gear; check whether you can actually spin it before assuming it will make you faster. If you are weighing up a wheel or chainring change, read gear inches, ratios and development to compare gears fairly, and the mph to km/h guide to keep your speed figures straight.