Monaco Grand Prix: Suspension With Bells On

By Craig Scarborough on at

This weekend, the Formula 1 circus makes it annual trip to the principality of Monaco. It's not news to anounce that this is street circuit; it is in fact the most recognisable track in the world. With the cars dancing between the barriers, it's famed as a track that's demanding on the cars, with the slightest error causing a brush with the armco and immediate retirement from the race. But what's probably less well understood is that as the track is on public roads, the car's suspension has a lot more to cope with.

With a cambered road, littered with bumps, manhole covers and aggressive curbs, it's utterly different from purpose-built tracks that are billiard table smooth.

For a handful of years now, F1 cars have had the assistance of a new form of suspension element, the inerter. A little-known technology which is currently used purely in F1, what is surprising about this technology is that its mechanics are akin to a bicycle bell. It's quite hard to get your head around the fact that cars can get better grip from simply spinning a weight.

Despite the importance of aerodynamics, F1 cars still rely a lot on the grip from the tyres at lower speeds. This is known as mechanical grip, and is a function of the work of the suspension controlling the tyre's contact patch. Rules in F1 have evolved over the years to specify a large 66cm-diametre tyre with tiny 33cm (13") wheels. This creates a large bulbous tyre with tall sidewalls.

Additionally, F1 car design has evolved to give the suspension tiny amounts of suspension-travel, in order to keep the car at the perfect altitude to the track in order to the keep the aerodynamic surfaces working efficiently. Thus, the squashy tyres provide a large proportion of the car's suspension movement. Unfortunately, due to the fact the tyres are effectively like inflatable rubber balloons, when they hit a bump they produce a bounce that feeds back into the chassis. This bounce can sometimes reduce the tyres' contact patch, reducing grip in the process and slowing laptimes.

Back in 2004, McLaren was approached by Dr Malcolm Smith, a Cambridge University Don. He had a solution that could absorb the sudden bounce from the tyres, in a way that conventional shock absorbers cannot. In addition to the exisiting complex arrangement of springs and dampers within an F1 car's suspension, an additional element was added that spins a metal weight. The first prototypes of this device, which was termed an "inerter," were based on the same mechanism that's in a rotary bicycle bell.

If you've ever opened a bicycle bell, or more likely had the bell lid fall off, you'll see the finger lever has gear teeth on it. These spin the bell's hammer. As you thumb the lever, the gears spin the hammer; the bell rings, and the effort from your thumb is absorbed by the mechanism.

This same process is used with the racecar's inerter. With the tyres' bounce being the same as your thumb on the bell and the bell itself being the inerter, as the suspension suddenly compresses from the bounce coming from the tyre, a geared rack spins a round metal weight. The inertia of this weight absorbs the bounce, and prevents the tyre contact patch varying too much. This will not give any more maximum grip from the tyre, but it will ensure the maximium potential grip of the tyre is delivered most of the time. And so, the driver is better able to place his car on the track with less fear of losing control over bumps and curbs.

McLaren raced the inerter for the first time at San Marino in 2005. At this point, McLaren had been using this technology exclusively, and secretly, for several years. Soon after, the patented technology was available to all teams, plus commercially through the racecar damper supplier, Penske.

Nowadays, all the teams run inerters on both the front and rear suspension, with this weekend proving no different. Watch as the humble bicycle bell rings around Monaco on all 24 cars in the Grand Prix.

Craig Scarborough is a London-based freelance F1 journalist and illustrator who blogs here and tweets here.

Image Credit: Ferrari Media