The Great Debate: BMX Gearing

September 22, 2021 8 min read

The Great Debate: BMX Gearing

Nowadays, it seems as though everyone in BMX is talking about gearing. Since the advent of the first geared BMX bike, racers and factory dads locked themselves into an arms race seeking the fastest combination. 

All of this talk about rollouts and chainring teeth is enough to make a new rider’s head spin. But what does all of this really mean, and how much time should you spend seeking the right gear?

For this article, we’ll explain how gearing ratios are measured and altered. We’ll also provide you with a list of appropriate rollout ranges so that even the newest riders can select their next gear with confidence.

If you’re impatient or just don’t enjoy reading, scroll down to the section labeled “Rollout Suggestions” to get your information and run. For those seeking more information on the topic, continue reading! 

How Gearing Ratios are Measured

A gearing ratio is the combination of a Chainring, Cog, and Drive Wheel.

An example of a gearing ratio would be: (44-16/ 20x1.75 rear tire)

The example listed above is a 44 tooth Chainring, 16 tooth Cog, with a 20x1.75 Rear Tire or Drive Wheel. The pairing of these three components produces a Rollout. 

The Rollout defines how far the bike travels through a single pedal stroke. Rollouts are measured in inches and represent how hard or easy a gear combination is.

(Note: When we refer to a gear as “light” it means that the gear is easier to push. Essentially the gear is easier to pedal and takes less force to spin the cranks. When we refer to a gear as “tall” it means the opposite of “light”. The gear is harder to pedal and takes more strength to get the bike going.) 

For the sake of simplicity, let’s us a 54inch Rollout as our example.

A total Rollout of 53.9 and lower produces a ‘Lighter’ gear. It’s easier to push from a standing start but doesn’t travel as far with each pedal stroke. A sub 54 inch Rollout provides increased acceleration capabilities compared to the 54 and requires less effort from the rider to push each pedal down.

Rollout larger than 54 (54.2 and up) produces a ‘Taller’ or harder gear. These ratios travel further than the 54 inch Rollout with each pedal stroke. Higher Rollouts can achieve the same speed of the 54 inch Rollout but at a slower pedal cadence.

If two riders pedal at the same exact RPM, the rider with the larger Rollout will be traveling at a higher top speed than the rider with a smaller Rollout

The bigger Rollouts provide increase top speed, but require more physical effort to accelerate. Typically, high Rollouts are reserved for bigger and stronger riders.  

How Rollouts are Changed

In order to change the Rollout, one of three things must be altered. 

1.) Chainring 

The Chainring is the largest gear within the drivetrain and attaches directly to the crank arm spider. Adding a tooth to the Chainring increases the overall Rollout producing a harder gearing (needs more muscle power). Removing a tooth decreases the overall Rollout making the gear lighter (easier to push the pedals). 

2.) Cog

The Cog is the smallest gear and attaches to the hub driver. Increasing or reducing the Cog size produces an inverse effect when compared to the Chainring.

Adding a tooth to the Cog decreases the overall Rollout. The 1 tooth addition to the Cog is equivalent to removing 2 teeth from the Chainring producing a much lighter gearing (much easier to push). Removing a tooth from the Cog increases the overall Rollout equivalent to adding 2 teeth to the Chainring producing a harder gear (requires even more muscle power to push). 

3.) Drive Tire Diameter (the overall diameter measured from the edge of the tire)

Tires come in multiple sizes, but the most important measurement for gearing is the external diameter of the tire. The external diameter is the total measurement of the outside of the tire. The rear wheel (drive wheel) is what impacts the gearing. The front tire diameter can marginally impact gearing but it’s so small that for basic understanding it’s irrelevant.   

Selecting a tire with a larger external diameter than your current tire increases the overall Rollout. A tire with a smaller external diameter than your current tire decreases the Rollout.

However, we can’t identify all 20x1.75 tires from multiple manufacturers as identical in size. While these tires feature the same internal diameter (20) and identical tire width (1.75) they could still posses different external diameters, meaning each tire impacts your overall Rollout differently!

For example:

A Maxxis DTH 20x1.75 has an external diameter of 61.17mm. A Tioga Powerblock 20x1.75 has an external diameter of 62.55mm. The Powerblock is larger than the DTH tire meaning it increases the Rollout more than the DTH tire. 

The “Evolution” of BMX Rollouts

Now I wasn’t around during the early days of BMX racing, heck, I wasn’t even born yet! But my sources tell me that 54 inch rollouts were the industry standard. We’re talking the 1980’s, over 40 years ago! A Pro size complete bike from that period would likely feature a 44-16 on Tioga comp III 20x1.75 rear tires. That’s a 53.92 inch rollout to be exact. 

What makes this all sort of funny is that despite the large gap in time, Pro size bikes are STILL equipped with a 54 inch rollout! many feature the same 44-16 and 20x1.75 rear tire combination of the past. The rollout can slightly decrease or increase depending on the brand of rear tire, but we’re still looking at an average of 54 inches.

Some might chalk this up as an accepted industry standard or a method for companies to save money through simplicity. But if we take a look at today’s pro bikes, we see a puzzling outcome. 

Higher Speeds Mean Bigger Gears…Right?

The modern BMX Track looks vastly different from its predecessors. Tracks are smoother than ever, feature asphalt corners, and taller starting hills. These additions increase the overall speed of the sport with the Pros pushing close to 40mph down certain 8-meter hills.

With tracks being so much faster, you’d be safe in assuming that racers are running taller gears to push even higher speeds.

That isn’t the case…

The vast majority of Pro bikes on the gate are also equipped with an average rollout of 54 inches. There’s a bit of variation with some being as low as 53 and others pushing high 55s. But across the board, the masses haven’t strayed too far from the traditional 54 inch gearing.  

(Factory Pro Cameron Moore’s 2021 VISION F1 with a 44-16 on a Powerblock 20x1.60 equal to a 53.60 Rollout! Not far off of a 54 Rollout!) 

But if the tracks are faster, and athletes are stronger, why haven’t things changed?

Despite the advancements in track grooming and the wide acceptance of clip pedals, the fundamentals of the sport remain unchanged. BMX Racing is a battle to the first turn where grabbing the Holeshot (first rider out of the first corner) provides an 80% chance of winning. Even though the tracks are faster, the 30ft line is still in the same place!

Many racers (myself included) have learned the hard way that harder gearing ratios serves no purpose from the back of the pack. If you can’t get an elbow on the competition out of the gate, then it doesn’t matter how much faster your harder gear can go. The Pros recognize the importance of clear track and the first 30 feet. It’s crucial to win the first portion of the race so we all prioritize first straight performance whenever altering our gearing ratios. 

BMX gears are considered to be light when compared to other disciplines of cycling. In downhill MTB, you have the whole trail to yourself. Road Biking is too long of a competition to make cut offs an effective strategy. BMX racing is unique in that the total race time is a fraction of other disciplines. In our sport, prioritizing acceleration over top speed generally leads to better results because you have hungry competitors itching to cut you off!

Some of you may remember Twan Van Gendt’s Olympic bike that featured a multi geared derailed system. At the time it sparked mass controversy, but it wasn’t the first time multi speed BMX bikes were used.

Brain Lopes lead the charge with his multi-speed GT. Before the creation of the 8-meter hill, downhill BMX Racing was all the rage. To account for the higher speeds and bigger jumps, racers looks for something that had both acceleration and top speed

These systems worked by featuring multiple cogs. One cog would produce a traditional BMX Race gearing while the other cogs decreased in size to make the gearing harder. Once the rider clears the gate and gets up to speed, they would shift into a harder gear for even more speed! 

Barry Nobles also tried a multi-speed bike during the early SX days. This bike followed the same concept as the others but for one reason or another the multi-speed BMX bike never caught on. 

Perhaps with even more innovation and time, multi-speed bikes could be the next step for BMX. However, it has yet to be proven effective at the pinnacle of the sport. For now, racers stick to the relatively light rollout as the first straight is king!

But What About Me?

Now we realize that not everyone reading this article is an Elite Pro. Some of you may not even own a Pro sized bike yet. So what gear should you be running?

We can’t give you an exact number, rather, we can provide you with a starting range! From suggestion listed below, you can tweak the rollout to your liking but avoid straying too far from these recommendations. If you run a much harder gearing than your competition, you run the risk of getting cut off. And before you think about running the lowest gear possible, that too can get you cut off as you won’t have the top speed necessary to keep everyone behind you! 

Rollout Suggestions

(Based on Bike Size) 

Micro: 45-47 inches

Mini: 47-49 inches

Junior: 49-52 inches

Expert: 51-53 inches

Pro: 52-55 inches 

We recommend that you stay within the ranges provided above for each size bike. These are by no means scientifically tested but the last 40 years of racing proves these rollout to still be effective.

If you are interested in determining your current rollout, you can plug your info into a gear calculator linked here. These programs, ask for your chainring size, cog size, and rear tire size & model. After entering the information, you’ll be provided with a rollout measurement.

You can also use this tool to scout out other gearing ratios. If you can’t get the exact number you want, try mixing and matching different cogs and chainring sizes until you find the sweet spot!

For the newer riders, don’t get too crazy with this. Pick something you like from the list above and use most of your energy towards becoming a better rider. There’s no need to spend mental energy on perfecting your gear just yet. Growing your skill-set and developing bike skill will yield the best results.  

If you’re swapping gears, be sure to give your body time to adapt to each gear. It takes multiple sessions before the body becomes comfortable with a new gear. Swapping out gears every day or week isn’t an effective strategy. Look to train the body first, then think about changing the gear.

If the gear feels too light, practice sprinting at high pedal cadences. If the gear is too hard, work on developing more leg strength. If the gear still doesn’t feel or look right after some time, then it may be time for a swap!

- Written By, Jonnie Vance



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