Sunday, 17 February 2013

Tires and Wheels

The tires on a car are a critical factor in its performance. Having bad tires on a great car would be analogous to having crummy speakers hooked up to a fantastic sound system.

The wheels on the M5 are forged alloy and are either 19" (1) or 20" (2). This dimension refers to the diameter of the wheel itself, not the wheel+tire diameter. On my M5 I have 19" wheels for the winter tires, and 20" for the summer tires.

It is important that the wheels be as lightweight as possible, because they act like a gyroscope and resist turning if too heavy. Also, they are part of the so-called "unsprung" mass of the car, that part of the car which is isolated from the heavier chassis. Lighter unsprung mass means that the wheels will more readily conform to the road surface, promoting better traction.

The summer tires are Michelin Pilot Super Sports. The front tires are 265/35R20 at the front, and 295/30R20 at the rear. The "295" part is the width of the tire in millimetres, or 11.6" wide. The "30" part is the ratio of tire width to tire sidewall height. So the sidewalls are 295 * 30% = 88.5mm = 3.5". Therefore the diameter of the tire and wheel together is 27". The summer tires are rated for very high speed, and the tire has been customized by Michelin specifically for the F10 M5. The tires would be extremely poor for winter driving, as the grippy rubber compound becomes hard like a hockey puck when too cold.

The tire has two types of tread rubber. The outboard shoulder features a track-type compound to withstand the stresses of high performance cornering while the notched centre ribs and inboard shoulder feature a compound designed for superior performance at very high speeds and in wet conditions. The tire's internal structure has twin steel belts reinforced by a spirally wound Twaron cord. Twaron is a polyamide cord that offers a lightweight, high-strength reinforcement above the steel belts.

The winter tires are Pirelli Winter 240 Sottozer Series 2.

They are 255/40R19 all around. The narrower tire is better for traction in the snow. It concentrates the weight of the car onto a smaller patch to allow for better grip in the snow. However traction on dry pavement is less good due to the smaller contact patch with the road. The rubber, however, stays soft even in the cold. The tire is optimized for winter driving, high speeds, and great handling.

Unlike on most BMWs, the tires are not "run-flat" models.  The very stiff sidewall on a run-flat compromises grip and handling, and so is not deemed suitable for an "M" car. However, neither is there a spare tire in the trunk due to space and weight considerations. Instead we get a "kit" that attempts to seal and re-inflate a punctured tire.



  1. If you want your car to have a greater speed and performance, choose wheels that are lightweight and tires that has a higher performance and long tire life.

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  2. You need high performance tires that are also Multi-Mile tires.

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  6. Your excellent guidelines will be of great help to many unusually snowy winter is main cause of the cancellation of several longer driving trips . Nice post. I enjoyed reading it. Thanks!
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  7. I've been trying to find some insights on what to look for in quality car tires. With so many different kinds it's hard to know what ones are good and what ones aren't. This helped a ton, and I feel confident that I'll be able to find some by this weekend.


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  9. We know that very well how much tires are important for a wheels,if we have a good quality of tires than we can get the better performance by our wheels.That's why we should always care about our wheel's tires. This post is really awesome for making people alert about his wheel's tires.
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  12. This is really informative. I want to know the prices to buy car tyres online for all four tyres of my Skoda car.

  13. Great article but does anyone know the optimum tyre pressures for the following tyres;

    Front tires: Michelin Pilot Super Sports 265/35R20.
    Rear tires: Michelin Pilot Super Sports 295/30R20

    For some idiotic reason the previous owner decided to remove the door sticker.....

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