The Weekly Grapevine

Black Technology

It is every scale modeller's biggest challenge: applying decals to the tyres. Strangely, though, whilst Formula One kits are generally more finicky than those of their WRC or DTM counterparts of the same scale, the decals supplied with the former are a comparative doddle.

The reason is simple: real life DTM and WRC cars run tyres with aspect ratios (simply put, the relationship between sidewall height and tread width, also known as tyre profiles) of anything between 25 and 35 (depending on the road surface and application), F1 tyres currently have aspect ratios of 55 (front) and 45 (rear). And, kit makers scale the tyre sidewalls accordingly ...

The actual F1 sizes provided this year are, according to sole supplier Bridgestone: 265/55 R13 (front) and 325/45 R13 rear, where the first number in each instance is the width in millimetres, the second is the aspect ratio and the 13 refers to its inner diameter in inches.

Bridgestone dry tires © XPB

This mixing of metric and imperial units certainly complicates matters, but measured against the history of aspect ratios which are taller than in virtually every other motor vehicle application - including trucks, busses and LDVs - this complexity pales into insignificance.

But, first some technical background: in general - for a particular construction - the lower the aspect ratio, the stiffer the sidewall and the less the deflection between the bead (where the tyre seats against the rim) and the tread, and therefore the better (and faster) the response of the tyre to dynamic changes due to reduced sidewall 'squelch'.

By the same token, the higher the ratio, the more the 'give' in the tyre, leading the sidewall to act as a giant supplementary spring - thereby further complicating spring rate and suspension geometry calculations, and bringing with it certain safety issues, for the amount of stored energy in a sidewall causes considerable 'bounce' when separated from the vehicle.

Flying, bouncing tyres have caused numerous motorsport deaths - with two in the past ten years springing to mind immediately.

Returning, though, to the dimensions: since the early 1980s, aspect ratios for non-F1 applications have shrunk to a point where even contemporary econohatches are fitted with 45 aspect rubber, whilst high performance sports cars have tyres lower by half or more.

Formula One thus very much out of kilter with real world automotive developments, even if there has recently been a trend to move up on ratios (from, say, 45 to 55) in the interests of ride comfort, for the stiffer the sidewall, the harsher the ride - which should, though, be of no consequence in F1 ...

The reason for F1's refusal to reduce ratios in line with all other forms of motorsport - certainly four-wheeled - has its roots in periodic supplier monopolies (voluntary and contractual), intra-sport politics, old-school economics rather than technology, and thus the most technological of all motorsport categories is saddled with tyre profiles hardly any different to those first mandated over 15 years ago.

The (first) departure of Michelin from F1 in 1984, followed by Pirelli following in 1991, left the F1 stage open to Goodyear.

Understandably the American tyre company saw no logic in developing low profile tyres at a time when it had only itself to beat, so why should it, the company's reasoning went, invest in new moulds and technologies for no competitive advantage?

Pirelli wets on a 1991 Benetton © XPB

Then, in 1993, the FIA introduced narrower tyres (maximum width 15 inch on 13 inch diameter wheel rims), which led to the current 45 and 55 (front and rear respectively) ratios, which were about average for high performance road tyres of the time. Goodyear was content for it had no on-track competition, and branded such road rubber as 'Eagle F1' ...

When Bridgestone joined the fray in 1997, it, according to sources within one of the first teams to commit to the company's rubber, wished to introduce low profile technology.

This was summarily rejected by the incumbent supplier, for it would at a stroke lose its hard and expensively-earned advantage by having to chuck out all its data and start with a clean slate. Thus it vetoed the suggestion.

When the sport introduced grooved tyres in 1998 it missed a golden opportunity to modernise this aspect, at the time using the argument that doing so would defeat the very object of grooved tyres - slowing down the sport.

Thus those cars were blighted by lo-tech sidewall dimensions (certainly by the standards projected by F1), with their looks further compromised by the sort of grooves more at home on the tyres of the Routemaster double-decker buses which plied London's suburbs at the time.

Then, at the end of 1998 Goodyear departed, and Bridgestone, understandably, saw no reason to push for a reduction in profiles merely to beat itself, so stuck to dimensions by then already five years old.

When Michelin re-entered the fray in 2001, it, too, wished to go with lower profiles, at the time pushing for the larger (15 inch) wheel rims which would permit Formula One to dump carbon fibre brakes and fit steel rotors - thereby reducing costs and facilitating technology transfer to road cars.

Michelin's suggestion met with predictable resistance, forcing the company to construct tyres conforming to dimensions by then in use for close on a decade. The French company's exit five years later again left the stage clear to Bridgestone, which in any event won the tender to be the sport's sole supplier from 2008 onwards.

For reasons outlined above, it had/has no wish to change moulds or technology to in order to supply the two (hardish) dry weather compounds as required in terms of its contract with the sport's governing body, the FIA.

Next year, though, is likely to bring considerable technical change - 'likely' for, in principle, the 2009 Sporting and Technical Regulations have not yet been approved despite being tabled for last week's World Motor Sport Council meeting in Paris - even without KERS being factored into the equation.

Downforce will (likely) be reduced by approximately 50 percent, with two further (proposed) regulation changes directly affecting tyres: a return to slicks (to increase speeds in compensation for the downforce reduction) and the 'unbanning' of (at this stage still banned for 2009) tyre warmers.

Pedro de la Rosa testing a McLaren with 2009 bodywork and tires © LAT

Sadly, though, no change to tyre dimensions now over 15 years old was on the agenda ...

However, certain factions in the paddock seem to be pushing for change. Without exception the four technical directors (of ten) approached by this column indicated a preference for low profile tyres, regardless of the additional (initial) charges their teams would incur for stocks of 15 inch wheel rims, and redesigned suspension geometries.

Such a move, they said as one, would increase their control over spring rates, and thus virtually every aspect of vehicle dynamics.

Also referred to by one technical director was the question of safety (see above), whilst another suggested that the larger profiles and lower profiles would improve aesthetics of the new-look 2009 cars which will be shorn of various aerodynamic appendages.

Plus he said, larger rims would facilitate steel rotors without compromising safety, which, in turn, would facilitate overtaking under braking whilst reducing the costs of braking systems - which, unlike carbon components, could be economically adapted for road car use.

Bridgestone, though, seems dead set against the introduction of lower profiles, even suggesting that the drivers will be unable to control the present cars if these are adapted for low profile tyres.

The current cars are designed for the present profiles and any tinkering with wheel sizes will result in cars that are 'too fast', believes the company's Director of Motorsport Tyre Development, Hirohide Hamashima.

"I think (the) current car is designed for that (45/55) aspect ratio," he said. "Because a low profile tyre with current car, in that case (the) driver can't control car because turn-in is sharper, making understeer and less grip."

He did concede, though, that some teams were pushing for lower profiles. "They are currently investing in 13 inch wheel for brakes and uprights, (but) of course someone require low profile tyres. But I believe the majority wishes to stay with (the) current profile."

Bridgestone has winning experience with low profile competition tyres, with their products having a proud record in saloon car and sports car racing categories, so this reluctance certainly is not as a result of any doubts over the company's available technology.

"If they (the sport and teams) want, we can produce low profile tyres anyway, but we are producing tyres according to the regulations," Hamashima stressed, before adding that a switch would cost Bridgestone "many money". "Building the machines would mean investing many money anyway, but if they require (it) we can do it."

Ferrari brake detail © XPB

Regarding steel brakes, he correctly pointed out that the present regulations do not ban steel brakes, simply that they do permit carbon-fibre stoppers - and that a switch could be made without a change of rim sizes.

"In case of (the) current car they can use steel brakes, longer term it is not our business, but I want to say that there is no regulation preventing steel brakes."

This view does not, however, take into consideration the longer stopping distances of steel versus carbon rotors of equal dimensions, and that larger rims would allow larger steel rotors with a commensurate reduction in braking distances.

So, the teams are keen - certainly the 40 percent canvassed for this column - and Bridgestone has the knowledge and technology and a contractual obligation to supply whatever the regulations require.

Formula One has an unspoken duty to facilitate technology transfer, and what area is more visible than tyre technology, whilst improved braking for road cars is obviously a safety issue.

Whether the regulatory will exists is, though, another matter - but given that one of the decisions handed down during last week's WMSC meet was to 'enter into a wide-ranging consultation with the Formula One teams to examine plans for improved efficiency, including new technical regulations for the Championship'. Will this include a revamp of tyre dimensions in the near future?

Some scale model kit makers are already wringing their hands in anticipation.