Upsizing tyres - what you need to know.


Upsizing your vehicle’s tyres and wheels can be undertaken for a number of reasons.

Perhaps you’re after a sportier look, are track focused or want further control and handling. In this article, we’ll take you through the different reasons why you would upsize, and also the reasons why you wouldn’t. But first, let’s run through some of the terminology used to describe certain aspects of tyre and wheel sizes to fully understand the results of upsizing.

  • Wheel and Rim Diameter: This is the distance across the face of the wheel from rim to rim. It’s usually measured in inches and can be found on your tyre size, which is indicated on the tyre. It should be noted that this does not include the tyre and is the measurement of the wheel only. They are typically 16” – 20” in size however, some larger sizes can be found on modern performance vehicles or after-market wheel sets.
  • Overall Rolling Diameter: The overall rolling diameter is the measurement including both the wheel diameter and the size of the tyre’s sidewall (outside tread). You can easily calculate this by adding the wheel size to the tyre’s sidewall or aspect ratio. Again, this can be found on your tyre’s size information.

So, with these in mind the best way to think about upsizing your tyres is that the wheel and rim diameter increases while the aspect ratio of the tyre decreases. This means that the overall rolling diameter remains the same.

Check out this diagram that explains the above:

Tyres and sizes

By moving into the Plus1, Plus2 categories, you are substituting ride comfort for handling and performance. Most modern sports cars and vehicles with a more aggressive look tend to lean towards the plus sizes.

A larger rim with a lower tyre profile means greater response, handling and braking. The stiffer sidewall of the tyre allows for a much more responsive result when pushing your vehicle hard into braking and cornering.

However, your OE fitment tyre has more sidewall and there is basically more tyre to cushion the ride. It might feel a little spongier than a lower profile tyre and this size is usually common with passenger and people movers, offering a much more comfortable ride for all.

There are some things that you should keep in mind if you’re looking to step in to plus sizes. Your car's speedometer is set to your tyres overall rolling diameter. If you don’t follow the guides, not only will your speed be out but it will also cause other on-board electronics to not respond correctly.

Traction Control and ABS are some key safety features of your car that may malfunction if you upsize your vehicle’s tyres incorrectly.

Wheel arch and clearance can also be an issue with incorrect tyre and wheel sizes. It could result in uneven wear or even rubbing on the vehicle chassis. Other components that rely on correct tyre size fitment are the suspension and brakes.

Tyre Zone Capalaba is your number one fitment centre in Redlands, east of Brisbane. We offer a wide range of services and are experts in tyre fitment. If you are considering upsizing your vehicle’s tyres, drop past our store or call today on (07) 3245 6125 for expert advice.

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