Why a Tram Curve Can Squeal
On a straight track, the two wheels on an axle can roll at nearly the same speed. Around a curve, the outer wheel must cover more ground than the inner one. A tram’s wheels are fixed together, so they cannot freely spin at different speeds like the wheels on many cars. Their tapered shape helps, but on a tight curve the wheel and rail may still slide slightly against each other.
That tiny, repeated slip can make the wheel vibrate against the rail. The vibration is heard as a sharp squeal, especially where a tram’s flange—the raised inner rim that helps keep the wheel on the track—presses against the rail.
A Small Dose in the Right Place
Melbourne’s curve-lubrication systems apply a friction modifier near the rail before a tram reaches a tight bend. The material leaves a thin film at the wheel–rail contact area, reducing the friction that drives the squeal. It does not eliminate the forces of the curve; it makes the rubbing less likely to set the wheel and rail vibrating loudly.
Placement matters. The treatment must reach the contact where it can reduce noise without making the surface used for braking and traction too slippery. Applying it ahead of the curve lets passing wheels spread the film through the bend.
Noise Control Is Also Wear Control
The same sliding that produces squeal can wear wheels and rails. Reducing friction at the flange contact can therefore help limit that wear as well as make the street quieter. The result is a practical compromise: keep enough grip for safe movement, while easing the intense rubbing that turns a routine turn into a piercing sound.
