Bridgestone pile on the pressure 06 Jun 2007
Tyres, even Bridgestone Potenzas, cannot hold air on their own but pair them with a wheel and their air retention abilities get immeasurably better
Tyre pressure retention is vital for any tyre and wheel combination, but given the high speeds and loads experienced in Formula One racing any air escape possibilities need to be minimised.
There are many areas where air leakage can occur, says Kees van de Grint, Bridgestone Motorsport Head of Track Engineering Operations, and these vary from design to poor fitting to pure mistakes to punctures from an external object. We work very hard to minimise all of these areas.
For example, its a difficult job to fit the tyres to the rim as its very easy to damage the tyre bead. If there is a small bit of damage and the engineer is not informed, and the tyre is not replaced, then air could escape from that small area of damage. The consequences could be very big if the air escaped at 300 km/h.
Formula One racing is about maximising performance and every component has many precise requirements placed on it. The wheels to which Bridgestones Potenzas are fitted are no different and the teams supply these to Bridgestone for fitting with the tyres. The rims are made by different manufacturers and each presents its own challenges.
A wheel is not merely a wheel in Formula One, explains van de Grint. It is part of the car as a device to improve brake cooling and aerodynamics and minimising weight in this area is a primary design consideration. The rims are extremely thin and I can remember one occasion where a driver had a brake problem and the temperatures went so high that the rim almost melted. The rim actually changed its form from a round wheel to more like an egg shape which meant that air escaped.
Wheels have a hole in them, one for the valve that is used to inflate, deflate and change the tyre pressure. This too is an area where tyre leakage can occur. The valve itself has to be able to satisfy its air retention requirements, and even the simple factor of having a valve cap on is essential.
It is extremely important with the speeds attained that a valve cap is put on, confirms van de Grint. And indeed this is very important on road cars too. In Formula One this area is the responsibility of the teams. It sounds very simple but even in Formula One in the stress of a race weekend this sometimes gets missed. An example of where this could occur would be on the grid just before the race where there is a lot of pressure and the cap could get forgotten after the tyre pressures are taken.
The most referred to means of losing air - or indeed, whatever gas is used to create the pressure between the tyre and the wheel - is when a foreign body comes into play to penetrate the tyre and a puncture is the result.
Of course, there can always be debris on the circuit, which can make a cut in the tyre, and that is very unfortunate, says van de Grint. For me it doesnt matter too much if it is done by a nail or piece of carbon fibre, it is a cut or a hole and the tyre has lost air. That for us is the easy part as we can determine the reason.
Lack of tyre pressure, from whatever means, causes problems as the tyres are designed to work in a certain pressure range, and the loads they are subjected to are very high.
When tyres are running with too low a pressure this can cause the carcass to break up and this is more difficult to determine, says van de Grint. We had this situation in Barcelona with one car which had a very small air leak which caused it to run with too low a pressure and finally the tyre broke up.
Fortunately in Formula One all the teams have pressure sensors so if they notice in time they can call the car in. If they dont notice in time we can analyse and see the trend of the pressure stabilising, or still increasing or in the worst case decreasing, from the data and then we can understand why such an occurrence has happened.
With so many possibilities for loss of air and with over 2000 tyres brought to every race weekend and thousands of high speed laps covered during the course of a race meeting its a wonder that more air doesnt escape.