How does a differential work?
One rotating input. Two wheels that can travel different distances.
Gears · Drivetrain
What is a differential?
A differential is a gear mechanism that allows two output shafts to rotate at different speeds while receiving drive from a shared input. This diagram shows an open differential: the basic arrangement used to accommodate the different wheel paths in a turn.
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How it works.
In a turn, the outside wheel follows a longer path. The differential allows it to turn faster while the inside wheel turns slower. For the equal side gears shown here, the average of the two output speeds equals the carrier speed.
Drive the carrier
The input pinion turns the ring gear and carrier. The carrier carries the small spider gears between the two side gears attached to the half shafts.
Travel straight
With equal wheel speeds, the carrier takes both side gears around together. The spider gears do not need to rotate about their own cross-pin axis to accommodate a speed difference.
Allow different speeds in a turn
The spider gears rotate relative to the carrier as the two outputs differ. Watch the outer wheel gain speed and the inner wheel lose the same amount relative to the carrier.
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A speed relationship you can check
In the model, a 1.5 m track width and a 5 m axle-center turning radius make the outer wheel 15% faster and the inner wheel 15% slower than the straight-line value. Their average stays unchanged. These are the illustration’s chosen dimensions, not a universal turning ratio.
About this model
- Equal side gears and ideal kinematics; the illustration does not solve tire forces, torque transfer or friction losses.
- Vehicle speed, track width and turning radius are example settings, not adjustable vehicle specifications.
Select straight, left or right, compare the two wheel-speed readings, then pause or reset.
Version 1.0.0
Frequently asked questions
Does a differential make both wheels turn at the same speed?
It allows a speed difference. Both wheels can turn equally when traveling straight; they can turn differently when following unequal paths.
Does this model explain a limited-slip differential?
No. It shows the speed relationship of an ideal open differential. Clutches, locking mechanisms, tire grip and slipping-wheel torque are outside this model.