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ITI/NCVT Mechanic Motorcycle (AITT Theory) study materials
ITI/NCVT Mechanic Motorcycle (AITT Theory) study resources

ITI/NCVT Mechanic Motorcycle (AITT Theory): Frame, Suspension, Steering and Wheels

ITI/NCVT Mechanic Motorcycle (AITT Theory) · Work through your exam, one topic at a time.

All guide sections

Frame, Suspension, Steering and Wheels

What this domain tests

Questions cover frame types and materials, rake and trail, wheelbase, telescopic forks, swingarm and monoshock suspension, spring preload, damping, steering-head bearings, wheel runout, spokes and balancing. The exam expects you to link geometry and adjustment to stability and handling.

Core rules

  • Rake is the steering-axis angle from vertical; trail is the horizontal distance between the steering-axis ground point and the tyre contact patch. More trail generally improves straight-line stability; less trail quickens steering.
  • Wheelbase is the distance between axle centres. Longer wheelbase favours stability; shorter favours turning.
  • Telescopic forks may have spring preload, compression and rebound damping. Fork oil level and viscosity affect damping; both legs must be equal.
  • Static sag is measured with the bike supported and then with the rider aboard. Excessive sag means insufficient preload or a weak spring.
  • Steering-head bearing play is checked by lifting the front wheel and feeling for fore-aft movement; overtightening notches the bearing.
  • Wheel runout is checked with a dial gauge; radial runout is out-of-round, axial runout is side-to-side wobble.

Worked example

A front wheel shows 0.35 mm radial runout against a 0.50 mm limit, so it is acceptable. If the same wheel shows 0.80 mm axial runout, the rim is outside limit. Adjusting spokes must correct both readings progressively, because tightening one side pulls the rim sideways as well as inward.

Traps that cost marks

Measuring runout with a dirty rim; mixing fork oil grades between legs; setting preload before measuring free sag; overtightening steering bearings to remove play; ignoring a bent axle after a wheel wobble complaint.

Key points

  • Trail affects stability; rake affects steering effort.
  • Fork legs must have equal oil level and grade.
  • Sag is measured unladen and with the rider.
  • Radial runout is out-of-round; axial is side wobble.
  • Steering bearings need free play, not preload.