Transmission BMX Black Friday : crowns on sale

What does the BMX transmission of the Black Friday include?

This section is covered on one page, that of BMX chains, sprockets and freewheels. The chainrings, ranging from 35 to 49 teeth, are listed under the name of sprockets, next to rear race sprockets, from 13 to 18 teeth, chains and single-speed freewheels. A few items for geared bikes sneak in, like a 7-speed freewheel or an 8-speed chain: they cannot be mounted on a BMX.

Calculating your gear ratio

A BMX has only one ratio. To find it, relate the teeth of the chainring to those of the rear sprocket: the result gives the number of wheel turns for one turn of the crank. Here are some examples:

• 43 teeth in front and 16 behind: 2.69;
• 40 and 15: 2.67, almost the same gear ratio with a more compact transmission;
• 41 and 15: 2.73;
• 36 and 13: 2.77.

The sprocket matters much more than the chainring: with 44 teeth in front, changing from 16 to 15 teeth at the back raises the ratio from 2.75 to 2.93, whereas adding just one tooth at the front increases it only to 2.81. So, change the sprocket for a big difference, and the chainring for fine-tuning.

Chain width and fittings: compatibilities

• Width: all BMX chains have a pitch of half an inch, but there are two widths, 1/8 inch (referred to as Wide by KMC) and 3/32 inch (Narrow). Chainring, sprocket and chain must share the same width.
• Chainring fitting: most race cranksets have a 4-bolt spider, on a 104 mm pitch circle, others have 5 bolts on 110 mm; the mentions 4pts or 5pts in the designations indicate this.
• Rear sprocket: it mounts on a cassette hub whose body must be compatible; a freewheel, it, screws onto a threaded hub.

Comparing two promotions on transmissions

Race chainrings come in many sizes and several anodized colours: two strikethrough prices side by side rarely refer to the same part. Compare them with an identical number of teeth, 4 or 5 bolt fitting, and chain width, then read the product sheet. A discount on a freewheel or a geared bike chain is useless on a BMX, regardless of its strikethrough price.

Which BMX transmission brands?

Excess offers race rear sprockets from 13 to 18 teeth, allowing you to adjust the gear ratio tooth by tooth.

KMC, a Taiwanese chain manufacturer, offers its K1 in Narrow for racing and Wide for 1/8 inch transmissions, alongside the Z1 Wide.

Insight supplies racers with 4-bolt chainrings on 104 mm, from 35 to 44 teeth, in several anodized colours.

Elevn designs the Flow chainring, tested by Chase team riders: mounted on 4 bolts and 104 mm, for a narrow 3/32 inch chain, with tooth counts from 39 to 49 teeth on this page.

Forward, a French specialist in BMX racing, offers its Joyride chainrings with either 4 or 5 bolt fittings.

Other BMX and transmission pages

The permanent page for BMX transmission details chainrings, cranksets, sprockets and chains all year round. A new transmission works better on a wheel in good condition: check out the BMX wheels from the Black Friday, then all sections from the BMX page of Black Friday. For a geared bike, the MTB transmission and the all-purpose transmission take over. Outside of promotions, check the clearance and new arrivals.

Frequently asked questions

What chain width for my BMX?

Look at the thickness of the teeth on your chainring or the reference of the chain in place. The 1/8 inch fits most freestyle and children's BMX, while the 3/32 inch fits many race bikes. A narrow chain doesn't fit on a wide tooth setup, and a wide chain floats on a narrow tooth setup.

What do 4pts and 5pts mean on a chainring?

The number of attachment points for the chainring on the crank spider: 4 bolts or 5 bolts. Count the bolts on your current chainring and measure the pitch circle, as a 4-bolt chainring cannot mount on a 5-arm spider.

When to take advantage of discounts on BMX transmissions?

The Friday after Thanksgiving kicks off Black Friday, and Vélo-Store extends its discounts on chainrings, sprockets, and chains throughout November. Count the teeth of your chainring and sprocket before choosing: the gear ratio depends on it.

What is a BMX transmission chart for?

It crosses the sizes of chainrings and sprockets to show the ratio for each combination and identify those that provide the same gear ratio. You can create it yourself: divide the teeth of the chainring by those of the sprocket, then compare the results.

How to tension a BMX chain?

Without a derailleur, the tension is adjusted by moving the rear wheel back in the dropouts, then tightening the axle nuts evenly on both sides. Keep a slight slack in the chain between the chainring and sprocket, and check that the wheel remains straight.