Hard tread
- Rolls with the least effort
- Resists flat spots better under standing load
- Noisy, and marks soft floors
Molded part guide: wheel hubs
Injection Molded Wheel Hubs
A molded wheel spends most of its life standing still under load. That is the condition that ruins it. Plastic under a constant squeeze slowly flattens where it touches the floor, and a wheel with a flat spot thumps for the rest of its life. Everything else about the wheel is designed around that.
Standing load
Standing still is harder than rolling
Caster wheels, cart wheels, appliance wheels, and equipment rollers.
A loaded wheel is squeezed hard in one small area where it meets the floor. Rolling, that area moves around the wheel and no single spot carries the load for long. Parked, one spot carries the whole load for days or weeks, and plastic under constant strain creeps: it slowly changes shape and does not fully spring back. The result is a flat spot.
The material decides how bad that gets. Unfilled polypropylene creeps quickly under standing load, especially when warm. Filled nylon, acetal, and similar grades creep far less and keep their round shape. Larger diameters help as well, because they spread the load over a bigger area at the contact point, and a harder tread simply deforms less.
The bearing seat is the second concern. The seat has to stay round for the bearing to run true, and it sits in a part that is thick where the hub meets the spokes. Those junctions shrink after the surface has frozen, pulling the seat slightly out of round and leaving sink marks on the outside faces. Keeping the junctions thin and even is what preserves the seat.
Spokes create their own problems. Each spoke joins the hub in a thick spot, and each one shrinks as it cools, so a wheel with a few heavy spokes ends up slightly out of round and unevenly heavy. Feeding the wheel from the hub center so the melt reaches every spoke together, and keeping the spoke sections thin and even, keeps it round and balanced.
Features
Wheel features and what each one needs
Load, roundness, and the axle interface drive the design.
| Feature | Purpose | Design note |
|---|---|---|
| Tread | Contact with the floor | Resin and diameter chosen against standing load |
| Bearing seat | Keeps the wheel running true | Round, and free from nearby thick junctions |
| Spokes | Carry load to the hub | Thin and even, all the same |
| Hub center feed | Even fill to every spoke | Melt reaches every spoke at the same moment |
| Tread overmold | Quiet running and floor protection | Soft layer keyed into the rigid wheel |
Creep
A parked wheel slowly flattens where it touches the floor
Constant load in one small area is the condition plastic handles worst.
- Parked under load, one spot carries everything for days at a time
- Plastic under constant strain slowly changes shape and does not fully spring back
- The flat spot that results thumps for the rest of the life of the wheel
- Filled grades and a larger diameter both reduce how far it goes
Tread
Hard tread or soft overmolded tread
Floors and noise pull one way, rolling effort the other.
Soft overmolded tread
- Quiet, and gentle on finished floors
- Grips and absorbs small obstacles
- Takes more effort to roll, and flattens sooner when parked
Drawing
What to send with a wheel
Load and how long it stands still matter most.
Wheel CAD, or diameter and width you need
Load per wheel and how long it stays parked
Floor type and any noise requirement
Axle or bearing type and its fit
Temperature and anything spilled on the floor
Expected annual volume
Keep reading
Related guides
Casters, rollers, and the wear resins behind them.
Casters
Complete caster assemblies.
CastersRollers
Conveyor and guide rollers.
RollersBushings
Plain bearings in the same wheels.
BushingsGears
Another part that grips a shaft.
GearsNylon vs acetal
Choosing a wear resin.
Nylon vs acetalOvermolding
Soft treads on rigid wheels.
OvermoldingDimensional variation
Wheels that end up out of round.
Dimensional variationIndustrial and transportation
How we support industrial programs.
Industrial and transportationMolded parts hub
Every part-type guide, grouped by family.
Molded parts hubFAQ
Questions about molded wheel hubs
Why do our wheels thump after being parked?
A flat spot has formed where the wheel stood under load. A filled grade, a larger diameter, or a harder tread all reduce it, and moving the equipment occasionally helps a lot. Loading a set of wheels and leaving them parked for a few weeks is the only realistic way to compare grades.
Why does the bearing bind in the seat?
The seat has gone slightly out of round, usually pulled by thick junctions where the spokes meet the hub. Thinning and evening those junctions restores it. Measuring the seat at several angles on the first molded wheels shows which junction is pulling it out of round.
Why is there sink on the outside faces of the wheel?
Heavy spoke junctions behind those faces shrink after the surface has frozen. Thinner, more even spokes remove the marks and improve roundness at the same time. The same change usually improves balance, because spokes that are alike cool alike.
Should the tread be overmolded?
If noise and floor protection matter, yes. If low rolling effort and resistance to flat spots matter more, a hard single material wheel is usually the better choice. Many products use a hard wheel for outdoor carts and a soft tread for indoor equipment on the same hub.
Next step
Quote a wheel with its load
Upload the wheel and tell us the load and how long it stands. DFM feedback covers resin for creep, spoke section, bearing seat roundness, and tread options.