All About Sidecar Racing Tires

All About Sidecar Racing Tires

© 2002, Roadracing World Publishing, Inc.

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From a press release issued by the World Superside (sidecar) Championship series:

Sizes and compounds for the world championship

Do you want to know more about the specially made equipment used in world championship sidecar racing? Read on…

Wheel sizes for sidecars evolved in the 1970’s to pretty much what we have today. Tyres on the other hand have evolved a great deal, mainly due to the development by Yokohama Rubber Co, Japan.

The tyres are specifically designed for sidecar racing use and each tyre is hand made in the factory in Japan to stringent quality control, before export to Germany for distribution.

The major changes to Yokohama tyres in the previous decade have included the change to the 14″ rear rim size and the evolution of the Yokohama wet tyres. The 14″ rear was designed because the 13″ rear suffered from traction vibration – a problem that occurs on the exit of corners under hard acceleration. The unique design of the 14″ rear by Yokohama engineer, Ihno san, drastically reduced this problem via a complex construction.

Yokohama wets, renowned throughout the wet race circuits of the world, were designed with a specific ‘bounce’ factor. This allows the tyre to better contact the track surface for better wet weather grip and control.

Each wet tyre is hand cut to a specific pattern by the Yokohama tyres service crew.

World championship sidecars currently use 210mm wide front tyres on either 8.5 inch or 9 inch rims. Three compound options for slick tyres (dry weather) were available for use in the 2002 season; I, P and Q compounds.

I compound is the hardest of the three fronts, and only used by some at circuits with either very hard right hand corners or a combination of abrasive surface, tight corners and high track temperatures such as Oschersleben and Misano.

P (medium) and Q (soft) are the everyday compounds for the world championship contenders. The choice between the two depends on driver ability and corner speed, chassis setup and even the type and power of the engine.

The sidecar tyre is often overlooked to the detriment of the overall performance. In fact, they are often considered to be the most important wheel on the machine. High corner speed through right handers for the length of the race can only be achieved through correct use of the sidecar tyre.

Setup problems are increased by the variety of options for negative camber and toe in for the sidecar wheel (which must change between different circuits) as well as the different wheel size options between chassis. The current model Windle chassis uses a 14″ side wheel whereas LCR, ART, Klose and Hock chassis all run 13″ rims.

Camber and toe in are generally increased for circuits with tighter right hand corners, but this will reduce top speed. Circuits such as Assen, for example, with fast, flowing right hand corners would run much less toe in than Oschersleben which, consists of tight corners.

Sidecar tyre compounds for 13″ rims are either P (medium) or T (soft) compounds, made with a very stiff construction to control sidewall flex. Windle runners with 14″ rims have been found to be less sensitive tyre compound choice, and have the rear tyre construction and compound available.

Choice of tyre compound for the sidecar wheel is predominantly dependent on driver style and chassis setup.

The rear tyre gets the most bad press, and often without just cause. A damaged tyre, or blistered as it is described, is one that has grossly overheated causing the rubber to boil on the surface of the tyre, dramatically lessoning the grip as seen in 2002 in Misano.

Excessive heating of the rear tyre can only be caused by wheelspin. The wheelspin can be caused either by violent throttle action or improperly set rear suspension, but abrasive surfaces and higher track temperatures accentuate these factors.

14″ rims are widespread throughout even national championships, with compounds including S04 (hard), B (medium plus), C (medium minus), and P (qualifier).

The S04 compound replaces the S compound of previous years, providing increased traction with the same tyre life in extreme conditions such as those seen at Misano. Most Suzuki 1200cc runners would generally use B compound as a rule, but the change to lighter 1000cc engines, coupled with the slightly reduced race distance at world championship level, has the C compound predicted as the new favourite. P compound is not an option for race distance, as it only lasts for three or four laps when placed in the right hands.

Armed with this information, you might think that it would be just a matter of fitting the correct tyres for the race, once the chassis has been set up through the practice settings. But there is more to do to ensure the proper use of the rubber.

Measuring the tyre temperature during a practice or qualifying session is crucial to setup for two reasons; to determine if the tyre is within operating temperatures and to determine if the tyre is working with an even temperature spread across the available tread. The results of these measurements outside the set parameters indicate the need for some adjustment of tyre, chassis or both.

The tyre pressures must also be set correctly to allow the rubber to work at optimum temperatures for grip and tyre longevity.

The crucial measurement involved is the setting of the optimal air pressure at operating temperature. By setting the tyre pressure to 1.1 bar when at operating temperature and then measuring again when cold, the cold starting pressure can be obtained.

So next time you watch a race, have a think about the preparation and the individual choices that each team has to make before each race. But then sit back and smile as the rubber is put through the most extreme test, leaving big black lines and more than a faint hint of tyre smoke.

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