The materials used in 1.85 x 18 Motorcycle Rims?

Types of 1.85 x 18 Motorcycle Rims

The designation 1.85 x 18 refers to a rim with a width of 1.85 inches (47 mm) and a diameter of 18 inches (457 mm). This size is commonly found on lightweight motorcycles, off-road bikes, and vintage machines. The following bullet points describe the main types based on construction, spoke configuration, and intended application.

• Steel Spoked Rim with Cross Lacing: This type uses steel rim base with 36 or 40 spoke holes. Spokes are arranged in a three-cross or four-cross pattern. The rim has a painted or chrome-plated finish. Steel spoked rims are standard on enduro and motocross motorcycles from manufacturers such as Honda XR series and Yamaha DT series. Weight ranges from 2.0 to 2.5 kg per rim.
• Aluminum Alloy Spoked Rim: The rim base is extruded from 6061-T6 or 7050 aluminum alloy. Spoke holes are drilled at angles matching the hub flange. These rims are often anodized in black, silver, or gold. The weight is 1.2 to 1.6 kg, representing a 30 to 40 percent reduction compared to steel. Aluminum spoked rims are used on competition enduro bikes and custom vintage restorations.
• Cast Steel One-Piece Rim: Manufactured by casting or stamping, these rims have no removable spokes. The entire rim and hub are a single component. Cast rims are found on low-power motorcycles (under 15 hp) and mopeds. They are less common on modern machines due to higher unsprung weight, typically 3.0 to 3.5 kg.
• Cast Aluminum One-Piece Rim: Produced by low-pressure die casting or gravity casting using A356 or A380 aluminum alloy. Heat treatment to T6 condition follows casting. These rims have integrated spoke-like structures for aesthetics. Weight is 1.8 to 2.2 kg. Cast aluminum rims are specified for small-displacement street motorcycles (125 cc to 250 cc).
• Steel Rim with Undrilled Spoke Holes: Designed exclusively for use with pressed steel hubs. The rim has no spoke holes; instead, tabs or brackets weld to the inner rim well. These rims are found on vintage British motorcycles (BSA, Triumph) from the 1960s and 1970s. Reproduction types are available for restoration projects.

Materials Used in 1.85 x 18 Motorcycle Rims

Low-Carbon Steel (SPHC, SPHD): Used for stamped and welded steel rims. Carbon content is 0.08 to 0.12 percent. Tensile strength is 270 to 350 MPa. Elongation at break is 30 to 40 percent. This material is chosen for its formability during rim rolling. Steel rims weigh 2.2 to 2.8 kg per unit. Resistance to corrosion is low without surface treatment.

High-Strength Low-Alloy Steel (HSLA): Grade S355MC or QSTE380TM. Yield strength is 380 to 420 MPa. This material allows a thinner rim section (1.6 mm wall thickness compared to 2.0 mm for low-carbon steel). Weight reduction of 15 to 20 percent is achieved. HSLA rims are found on dual-sport motorcycles where impact resistance is required.

Aluminum Alloy 6061-T6: Extruded rim profiles use this alloy. Composition: 0.4 to 0.8 percent silicon, 0.15 to 0.4 percent copper, 0.8 to 1.2 percent magnesium, and 0.04 to 0.35 percent chromium. Tensile strength is 310 MPa minimum. Yield strength is 276 MPa. T6 temper involves solution heat treatment at 530°C followed by artificial aging at 175°C for 8 hours. Density is 2.70 g/cm³.

Aluminum Alloy 7050-T7651: Used for high-end competition rims. Composition: 2.0 to 2.6 percent copper, 1.9 to 2.6 percent magnesium, 5.7 to 6.7 percent zinc, and 0.08 to 0.15 percent zirconium. Tensile strength is 510 to 550 MPa. Yield strength is 450 to 490 MPa. This alloy provides higher fatigue resistance than 606However, it is more susceptible to stress corrosion cracking in chloride environments.

A356 Aluminum Casting Alloy: For cast one-piece rims. Composition: 6.5 to 7.5 percent silicon, 0.25 to 0.45 percent magnesium, and 0.20 percent maximum iron. Tensile strength after T6 heat treatment is 230 to 260 MPa. Elongation is 3 to 5 percent. The silicon content improves fluidity during casting but reduces ductility compared to wrought alloys.

Anodized Coating (Aluminum Rims): Type II sulfuric acid anodizing produces a layer of 10 to 25 microns thickness. Hardness is 300 to 400 HV. Color is achieved by organic dye absorption before sealing. Sealing is performed in deionized water at 98°C for 30 minutes. Anodized coatings have salt spray resistance of 300 to 500 hours. Thinner coatings (under 8 microns) are unsuitable for off-road use.

Precautions for Using 1.85 x 18 Motorcycle Rims

• Tire Size Compatibility: The 1.85 inch width accepts tire sizes of 2.75-18, 3.00-18, and 3.25-1Do not mount a 3.50-18 or wider tire. A tire wider than 3.25 inches on a 1.85 rim causes the tread profile to become excessively curved, reducing the contact patch and increasing center wear. The rim width-to-tire section ratio must remain between 0.60 and 0.7For a 3.00-18 tire (section width 3.0 inches or 76 mm), the ratio is 1.85/3.00 = 0.62, which is within the acceptable range.
• Spoke Tension Management: Spoke tension on a 1.85 rim must be measured with a spoke tension gauge, not by hand plucking. Lateral runout should not exceed 1.0 mm, and radial runout should not exceed 1.5 mm. Uneven tension (difference of more than 20 percent between adjacent spokes) leads to rim distortion over time. For off-road use, re-check spoke tension after the first 500 km and every 1,000 km thereafter. Loose spokes produce a clicking sound when the wheel is tapped with a metal wrench.
• Tube Selection and Installation: For non-tubeless rims, use tubes labeled for 18-inch wheels with the correct valve stem type (TR-4 or TR-6). Tube size must match tire size: a 3.00-18 tire requires a 3.00-18 or 2.75/3.00-18 tube. Do not use a tube sized for 3.50-18 tires, as the excess rubber folds inside the tire and chafes. Before installing the tube, wrap the rim band (rubber or fabric tape) over the spoke nipple heads. The rim band must cover all spoke holes without gaps. Apply talcum powder to the inside of the tire and to the tube to reduce friction.