How do I work out what space saver size I need for a spare wheel?

space saver size

Space saver spare wheels are skinny wheel/tyre combinations that go in the boot. You fit them when you have a puncture. Some cars come with them when you buy them new. Others have inflation kits. In the latter instance, owners might want to have a spare wheel instead and if that’s the case, they need to know what space saver size they need to buy.

First thing to consider when buying a new wheel

Whatever wheel you buy – and that includes a space saver ‑  it has to sit on the wheel hubs that are at the ends of your car’s axles.

The first thing to find out is your car’s PCD. This stands for Pitch Circle Diameter (PCD) and it tells you how many wheel nuts your car has and how far apart they are in millimetres. A PCD of 4 x 115 indicates that your car has four wheel nuts (bolts) and they’re 115mm apart.

What is rolling radius?

The new space saver size also needs to be as close in diameter to the car’s existing wheel as possible. This is calculated according to the rolling radius, the distance from the centre of the hub to the ground.

Does the space saver size have to be the same?

The wheel part of a space saver (excluding tyre) might be a different diameter to the wheel on your car. If that’s the case, the tyre’s greater sidewall height (shown by the aspect ratio) might make up the difference in rolling radius. In theory then, a car with 15-inch wheels might be able to take a 17-inch space saver.

For example, a 205/55 R16 tyre has the same diameter (631.8mm, radius of 315.9mm) as a skinny 125/80/R17 space saver. In an ideal world, the space saver rolling radius will be the same as the full-size wheel/tyre already fitted to the car. But they can run within 2.5 to 3% of the car’s proper wheels perfectly safely.

There’s a great calculator here to help you work our rolling radius.

Where to buy space savers from?

You could try getting one from the manufacturer of your car but it’s likely to be very expensive. The cheaper option is to find a company on the internet that specialises in selling space saver spares.

space saver size
Getting a puncture is miserable, whatever the solution you’re carrying…

Space savers are temporary

Space savers are a temporary fix to get you home or to somewhere that the car can be fixed safely. As space savers are skinnier, they have more weight going through them onto the road and can run hotter. For this reason, the speed you’re allowed to travel on a space saver is restricted to 50mph.

Although the distance you can cover on them isn’t restricted by law, it should be limited by drivers. This is because the tread on a space saver tends to be a lot less than on a regular tyre and they’re made of a softer material.

Or if you want a cheaper option…

Go on eBay, Amazon or visit a scrapyard and buy a full-size wheel for your car. That’s always assuming your car has the space in the boot for a full-size spare. Many these days don’t.