Rims

A rim is the circular aluminium hoop of a BMX wheel. It holds the tyre, and spokes connect it to the hub. On a BMX the rim takes most of the impact from landings and grinds, so it needs to be tough and true.

What it does

The rim is the outer frame of the wheel. The tyre sits on its outer edge. The spokes pull the rim inward toward the hub, and that tension is what makes the wheel strong.

Rim design affects weight, strength and how the tyre fits. Wider rims support wide tyres better. Heavier rim walls resist dents. A rim with a flat spot or a bend will make the wheel feel wobbly, and spokes can loosen.

Types and standards

Spoke count

Spokes	Notes
36	Lighter. Common on front wheels and many complete bikes.
48	Stronger and stiffer. Often used on rear wheels for street, park and heavy riding.

Rim drilling must match the hub. A 48 hole rim needs a 48 hole hub.

Wall construction

Almost all BMX rims are double wall. Two layers of aluminium form a hollow box shape that resists bending. Single wall rims are cheap and flex more. They are found on very basic bikes.

Brake surface or brakeless

Type	Notes
Brake rim	Has a machined sidewall for a brake pad. Needed if you run a brake.
Brakeless rim	No machined brake surface. A little lighter and cleaner looking. Fine for riders who do not run a brake.

If you run a brake, check the brakes setup and the rim surface. If you ride without one, see brakes or brakeless and the term brakeless.

Joint: welded or pinned

The rim is made from a long aluminium extrusion, bent into a hoop and joined at the ends.

Joint	Notes
Welded	The ends are fused together. This gives a smooth join and a clean brake surface.
Pinned (sleeve)	The ends are joined with an internal sleeve and pins. Often cheaper. The join can be felt on some rims.

Both can be strong. Welded rims are common on higher quality rims.

Sizing and compatibility

Wheel sizes

The size in inches is a nickname. What matters for fitting a tyre is the bead seat diameter (BSD), measured in millimetres.

Common name	BSD	Notes
20 inch	406mm	The standard BMX size.
22 inch	457mm	Used on some larger BMX and "BMX cruiser" style bikes.
24 inch	507mm	Used on cruiser bikes and some larger riders.

A 20 inch tyre will only fit a 406 rim. Always check the BSD on the rim and tyre. It is stamped on both.

Width

Rim width is listed in millimetres. It can be quoted as inner or outer width, so check which one the maker means. Wider rims suit wider tyres. Narrow rims work with thinner tyres. As a rough guide, match a rim to the tyre width range the maker lists.

Other checks

1. Spoke count: match the hub drilling.
2. Valve hole: BMX uses Schrader or Presta valves. Check the rim drilling and your tubes.
3. Hub type: fit the rim to a cassette hub, freecoaster hub or front hub with the same hole count.

How to choose

1. Decide how many spokes your hubs have, and buy rims to match.
2. Pick 48 spoke rear rims if you grind hard or ride heavy.
3. Pick a brake surface only if you will run a brake.
4. Choose a rim width that suits your tyre size. See tyres.
5. For a first build, a reliable double wall rim from a known brand is a safe pick. See how to build a BMX bike from parts.

Rims cost from low to moderate prices. Light, strong, welded versions from known brands cost more.

Maintenance

• Spin the wheel and check it runs straight. Dents and wobble mean it needs truing.
• Keep spokes evenly tensioned. Loose spokes cause wheels to go out of true quickly.
• Look for cracks near the spoke holes. Replace the rim if you find any.
• Check the brake surface for wear lines if you run a brake.
• Replace the rim tape if it slips, to protect the tube from the spoke nipples.
• See BMX maintenance basics.

Related parts

Tyres, cassette hub, freecoaster hub, front hub and brakes.