Jump to navigation Jump to search

Spherical Bearings and Rod Ends

Used on the ends of suspension/steering tubes.


  • Aurora Bearing

Radial and Axial Bearings

Used on shafts. Radial Bearings are very common in Formula Student, while Axial bearings are rare. Typical unit has a hollow cylinder shape, with spherical balls or cylindrical rollers inside.


Bearing Selection

Pre-Selection: Type of Bearing

  • The Schaeffler Pre-selection Chart on page 30 of the HR1 handbook[1] provides a useful overview of the different types of bearings.
  • Ball bearings are usually lighter, can run at faster speeds, and are lower friction than cylindrical roller bearings, but also have lower load capacity. Deep Groove Ball Bearings can take some axial load (see section 1.6, Page 36 of HR1[1]), while non-locating roller bearings cannot take any. There will always be small amounts of axial load on shafts from small misalignments, which is why deep groove ball bearings are so common.
  • Single row deep groove ball bearings come with different sized balls (and corresponding weights and sizes). From smallest to largest: 618XX, 619XX, 60XX, 62XX, 63XX. See section 1.2, page 216 of HR1[1].
  • Suggestions from a FS Wiki Author of what teams could use:
    • Bellcranks: Deep groove ball bearings
    • Steering: Deep groove ball bearings, or needle bearings (in areas with 0 axial force)
    • Drivetrain (such as differential mounting): deep groove ball bearings or roller bearings. Note that at least one bearing will have to be able to take the small axial load.
    • Wheel Hubs: Angular Contact ball bearings or tapered roller bearings in an O configuration, Or buy an off-the-shelf wheel hub.

Picking the Specific Size

Suppliers have helpful tools. Can also use the Schaeffler HR 1 handbook.[1]

Tolerances and Fits

Since bearings are standardized across suppliers, its okay to use a tool that isn't from the same company as the one that manufactures the bearings you actually buy.

SKF Bearing Select Tool Method

  1. Go to SKF Bearing Select Tool Website.
  2. Select Roller Bearing (This includes deep groove ball bearings).
  3. Pick Single or Two on a Shaft.
  4. Pick the Bearing type in the drop down, then in the "Search Designation" type in the supplier part number, such as "608" or "6005", then hit next.
  5. Enter in the loads.
    1. For Single Bearings, Pick Calculations > Equivalent dynamic load AND Fits and Tolerances. Enter in Loads, then Calculate, then Next.
    2. For Two on Shaft, Enter the loads, hit calculate, then Next.
  6. On the Fits and Tolerances page, set "Standard fit recommendation" to ON.

Schaeffler HR1 PDF Method

Follow section 8.3 of the Schaeffler HR 1 Handbook[1].

  1. Search for the supplier part number on a supplier's catalogue like Schaeffler's Medias Catalogue. Bearings have standardized supplier part numbers across all suppliers, so it will be the same part number on SKF or NSK's website as well. Searching without the suffix for the seals (ie. "-ZZ" or "-2RS1") will improve the chances of at least finding the bearing of the correct size.
  2. The catalogue page for the specific bearing (like Schaeffler's Medias) should state the basic dimensions, and min/max radii of the housing etc. It may not contain the tolerances.
  3. In section 8.2-8.3 (pg 145) of the Schaeffler HR1 handbook[1] there will be tolerance info for the housing and shaft. Start with Table 1 to determine the loading condition. Then for radial bearings (the most common type) look at Table 2 for the shaft tolerance, and Table 4 for the housing tolerance.
  4. In the same Schaeffler HR1 handbook[1], Section 8.6 has the more advanced GD&T (Table 10). To use Table 10, look up the Bearing Tolerance Class from the catalogue page specific to the bearings (from step 1 in this wiki guide), or just assume it's "normal 6X" or "PN", then Table 11 has the surface roughness tolerance (The diameter tolerance grade is from 4th column of Table 10).
Tolerances note:

Looser tolerances than those recommended by the manufacturer may be possible.

For drivetrain and wheel assemblies, an increased interference may be possible when seating bearings into aluminum housings. Aluminum's high coefficient of thermal expansion allows it to expand significantly when heated. Do not wreck the heat treatment of the aluminum though. Additionally, having thin, lightweight aluminum bearing seats limits the residual stress from the press-fit and minimizes dimensional changes of the steel bearing race (compared to the same press-fit into thick steel housing), which would cause bearing issues such as friction and wear.

For bellcranks an increased interference may be possible for the same reasons as above. Additional clearance is possible due to the bearings moving at low speeds, only ever rotating <90deg and always being under preload. When in doubt, follow the manufacturer's recommended tolerances.

Just give me some tolerances

If you want some housing and shaft diameter tolerances from strangers on the internet. If you run into issues, you have no one to blame but yourself.

  • Wheel Bearings: N8/k6
  • All Other Bearings: H8/h7

See Also