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Upsizing your Alloy Wheels

Alloy Wheel Plus sizing or Upsizing is increasing the size of the alloy wheel of your car. Upsizing is achieved by keeping the outer diameter of the tyre constant, decreasing the sidewall height of the tyre and thereby increasing the inner diameter of the tyre. This increase in the inner diameter of the tyre accomodates the upsized alloy Wheel.

Lets understand this with an example. You must have noticed on our website that many of the cars have multiple options in Rim Diameter (R). For example if you check the page of Suzuki Swift LDi you will notice that the Rim Diameter options are 14 inches, 15inches and 16 inches. Here the 14 is the stock size of the Alloy wheels that comes with the LDi variant.

This is the 2nd picture of the ZDi wheel. The wheel radius is of 15 Inches.

Increasing the size of the the Alloy wheel by 1 inch is called Upsize +1. Though in this case the upsize has been offered by the manufacturer itself.

So coming to the most important part How is upsizing done?

Upsizing is done by keeping the outer diameter of the tyre unchanged. The inner diameter of the the tyre is increased to accomodate the bigger size of the Alloy wheel. All confused? Lets start again

So to start with as you can see in the picture above. The outer diameter of the tyre is the height of the tyre calculated from end to end. This outer diameter is suppose to be fixed. The accepted variation in the outer diameter is only 3%. The outer diameter is so important as this is the basis of the speed shown by your speedometer, kilometers counted by your odometer, the configuration of torque, configuration of your cars ABS and a few more things. So whenever you are changing the size of your tyre make sure that the outer diameter does not switch by more than 3%.

So hoping that you are clear with the first bit "Outer Diameter" to be in 3% moving to the 2nd part of the story. You need to find tyres which have bigger inner diameter. In the picture below we have increased the size of the inner diameter keeping the outer diameter. Hence making space for accomodating the bigger Alloy wheel.

While in the process of upsizing when you are increasing the inner diameter of the tyre you might also have to increase the width of the tyre. This is done as the low profile tyres (Tyre with biger inner diameter and slimmer section height) usually come with higher width.

In this example we have only increased the Alloy wheel size by 1 inch from 14 inches to 15 inches. However there are people who like to upsize by 4 or even 5 inches. Here is a picture of a Swift with 18 inches Wheels.

We hope with this iteration we hope that we have thrown enough light on the subject. We will soon add another article about the calculation of the tyres while doing upsizing. 

How is upsizing done

Now as we have understood what is upsizing lets talk about how is upzing done. Lets start this example with the same car Maruti Suzuki swift. As already discussed the cars LDi model comes with 14 inch alloy wheels. In this example we will increase the size to 16 inches (upsize +2).

Before we start with the upsizing calculation we should first learn about calculating the outer diameter of the existing tyre. So that whatever upgrade we choose it should be in the 3% range of the original tyre.

The swift LDi model comes with  165/80R14 tyres. For the newbies here 165 is the width of the tyre in milimeter(mm). 80 stands for the section height in percentage value of the width of the tyre. Wow that was quite a mouthful. in layman terms the section height/side wall height is actually equat to width of tyre * the number after the / and divide it by hundred. So in this case the section height is 165*80/100 which is equal to  132 mm. Dont blame me for the tricky calculation I definetly did not design this!


So now we know the Section height/side wall i.e. 132 mm now multiply this by 2 one section above the wheel and one section below the wheel. Also we need to add the height of Alloy Wheel. Here the height or rim diameter is 14 inches. we will convert the 14 inches by multiplying this by 25.4 so it comes up to 355.6. 

As discussed in the start we will be upsizing the tyre wheel to 16 inches. Hence 16*25.4 = 406. mm will be the height of the alloy wheel so remaining divided by 2 will be the section height of the new tyre. We take all the tyres that we have in our database and calculate which tyre will be in the 3% range of the section height. So we shortlist the options to 

TyreOuter DiameterVariation %
195/50R16        601.4      -2.94
225/45R16608.9-1.73
205/50R16611.4-1.32
195/55R16620.90.21
215/50R16621.40.29
225/50R16631.41.9
205/55R16631.91.99

This is a really long process and we have already sorted all this for you. On our site you can simply go to a cers page. Select the wheel size. Click on "recommended tyre" link and voila you have all the tyres that are compatible with your upsized alloy wheels.