Overhead Crane Trolley Wheel Specification and Girder Rail Matching
Trolley wheels are the second wheel population in an overhead bridge crane — distinct from the bridge (end truck) wheels that travel on the runway rail. UTEC Industrial manufactures precision-machined alloy steel crane wheels, sheaves, and industrial components from AISI 4140, 4340, and 8620 billets in the Pacific Northwest, with in-house induction hardening, CNC machining, and chemistry testing on every heat. Because trolley wheels run on rails mounted to the bridge girder rather than a permanent runway structure, the rail section is typically lighter, the wheel diameter smaller, and the load lower than bridge wheels. However, trolley wheels cycle more frequently than bridge wheels on many cranes (the trolley travels back and forth across the span for every lift, while the bridge may travel only occasionally), which affects duty cycle classification and service life. UTEC Industrial produces custom trolley wheels for overhead crane applications to any required specification.
How does trolley wheel specification differ from bridge wheel specification?
Trolley wheels carry the hoist load plus the trolley dead weight, distributed over the number of trolley wheels (typically 2 or 4). They do not carry the bridge dead load or the full crane live load — the maximum trolley wheel load is typically lower than the maximum bridge wheel load for the same crane. The trolley rail section is typically lighter than the runway rail (ASCE 25# to 60# is common for trolley rails vs. ASCE 60# to 175# for runway rails), which means the maximum wheel load per rail is lower. Trolley wheels are often specified with flat tread profiles matching the flat-head trolley rail, while bridge wheels may use tapered tread. Flange configuration is typically double-flange for both, but trolley wheel overall width must fit within the clearance between the bridge girder and any runway obstructions.
How is maximum trolley wheel load calculated?
Maximum trolley wheel load = (rated lift capacity + hoist and trolley dead weight) / number of trolley wheels. For a 10-ton (20,000 lb) crane with a 3,000 lb trolley and 2-wheel trolley: max trolley wheel load = (20,000 + 3,000) / 2 = 11,500 lbs. Service class constant for the trolley wheel: the trolley service class is determined by the hoist duty cycle, which may differ from the bridge service class. A crane where the bridge travels infrequently but the trolley cycles with every lift has a higher trolley duty cycle than bridge duty cycle. Minimum trolley wheel diameter: D_min = 11,500 / 1,600 (Class C constant, if applicable) = 7.2 inches — specify an 8-inch wheel minimum (CMAA Spec. #70, Section 3.3).
What tread profile is standard for crane trolley wheels?
Trolley rails are typically flat-head crane rail or structural flat bar — not the tapered-head ASCE rail standard on crane runways. Accordingly, flat tread is the standard profile for crane trolley wheels. The tread face width must meet CMAA float requirements for the specific trolley rail section, but trolley rail head widths are smaller than runway rail head widths — verify minimum tread face width against the actual trolley rail dimensions. For trolleys running on the bottom flange of a wide-flange beam (under-running trolleys), the wheel profile must match the flange width and surface condition of the structural member.
How does trolley wheel service life compare to bridge wheel service life?
On cranes where the trolley cycles with every lift and the bridge travels only to reposition, the trolley wheels accumulate far more load cycles per unit time than the bridge wheels. This can result in trolley wheels reaching their tread wear limit before bridge wheels, even if both were new at the same time. A proactive maintenance program should track trolley and bridge wheel wear independently and not assume they will wear at equal rates. For high-throughput production cranes where trolley cycling is continuous, trolley wheels may need replacement at intervals 2–3× more frequently than bridge wheels on the same crane.
- Crane Wheel Selection Guide for Overhead and Bridge Cranes — complete bridge crane specification framework
- Crane Wheel Tread Profiles: Flat, Tapered, and Radiused Explained — flat tread for trolley rail applications
- Crane Wheel Load Capacity and CMAA Service Classifications — load calculation for trolley wheel sizing
References
- CMAA Specification No. 70: Specifications for Top Running Bridge and Gantry Type Multiple Girder Electric Overhead Traveling Cranes. Crane Manufacturers Association of America.
Ready to Specify Your Crane Wheels?
UTEC Industrial manufactures forged alloy steel crane wheels and sheaves for heavy industry applications across the US. Tell us your application and we'll help you select the right wheel for your load, speed, and duty cycle.