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01 October 2021
BURN RUBBER: Tyres ‘102’ for the enthusiast driver

Ready to go beyond the tyre basics? Learn more about +1 upgrades in our tyres ‘102‘ guide below!


By now, you should already know that there’s a lot more to tyres than just four innocuous black rubber things on each wheel of the car, truck, or bike. If you are an enthusiast driver, you might know a fair bit more about tyres than others. Nonetheless, it‘s good to get reacquainted with some tyre basics; after all, the point is not to go overboard with tyre upgrades.

What we need is to balance our quest to maximise grip with reasonable tyre lifespan and fuel economy. After all, our commutes to and from work are on normal city streets and highways, not the Nürburgring and unrestricted sections of Germany’s excellent Autobahn.

Let‘s say you are an enthusiast-focused daily driven car. We explore the possible tyre upgrades based on the 3.3-litre twin-turbo Kia Stinger GT and the 2-litre turbo Subaru WRX with the following profiles:

Rear-wheel drive KIA Stinger GT

Front tyres: 225/40R19
Front rims: 19X8J ET34 5X114.3
Rear tyres: 255/35R19
Rear rims: 19X8.5J ET46.5 5X114.3

All-wheel drive Subaru WRX

Front and rear tyres: 245/40R18
Front and rear rims: 18X8.5J ET55 5X114.3

Before we begin exploring the upgrades you can add to your tyres and rims, let‘s first have a look at what that complicated string of numbers in the rim size mean. (Meanwhile, you can check what the tyre sizes mean here.)

Understanding rim numbers

Earlier we saw numbers associated with rims such as 19X8J ET34 5X114.3, 19X8.5J ET46.5 5X114.3 and 18X8.5J ET55 5X114.3. At first glance, they seem complicated, so let’s break them down for simplicity.

The WRX in our example runs 18X8.5J ET55 5X114.3 rims. Here are what the numbers stand for.

Diameter and width

In the first set of numbers ‘18X8.5J’, we see 18 denoting rims that accept 18-inch tyres. Next to it, we see 8.5J which denotes how wide the rim is, 8.5-inches in this example.

Offset

The next alphanumeric notation is ‘ET55.’ ET stands for the German word Einpresstiefe, which means offset and describes how much the mounting face of the rim is offset from its centre line. The number 55 is the actual offset in millimetres (+55mm in this case).

Rims with negative offset would show a negative ET number, such as ‘ET-12’ (-12mm offset).

Pitch Circle Diameter (PCD)

The last set of numbers, ‘5X114.3’, shows the PCD of the rim. 5 denotes the rim is for a 5-lug application, and has 5 lug-holes as a result. Next to it, we see 114.3 denoting the PCD, the diameter of an imaginary circle drawn through all of the lug-holes (114.3mm in this case).

Types of rims

There are 2 types of rims in the aftermarket that interest us — forged and cast.

Forged alloy rims are as tough as nails and lightweight to boot. They offer significant weight-savings when it comes to unsprung mass, thereby allowing a car’s suspension system to work more effectively. However, due to their (forged) construction-method, they are more expensive to produce.

Gravity-cast alloy rims are usually cheaper then their forged counterparts and the quality ones are heavier too, by virtue of requiring more metal for strength. Due to their (gravity-cast) construction-method, they are not as strong as forged rims.

Spun-cast, flow-formed and rim-rolled alloy rims are also considered cast rims but use a specific process in their construction, which starts with a low-pressure casting and uses a machine that spins the initial casting, heats the outer portion and uses steel rollers pressed against the rim area to form the rim into its desired width and shape. This process gives rise to a rim with similar strength to a forged item, but without the associated high cost.

For enthusiasts, we recommend spun-cast rims as the relatively budget-friendly everyday option, and forged rims as a top-of-the-heap choice.

We would also stay away from cheaply manufactured lightweight gravity-cast rims, as these are notorious for bending, cracking or breaking under light to moderate usage, such as running over a pothole to time-trial applications.

+1 tyre upgrade

The aim here is to switch to a slightly more grippy compound than the OE tyre from factory. Tyre sizes remain the same and factory rims are retained. This enables us to work within a more conservative budget while still achieving benefits from more grippy tyres.

In our example, this means keeping the Stinger GT’s stock sizes of 225/40R19 and 255/35R19 front and rear respectively, and 245/40R18 on all four corners of the WRX.

The reason this is ideal is because too much (width of) tyre can be detrimental in terms of increased risk of hydroplaning, as well as increased fuel consumption and noise. There’s a good reason — namely balance between grip and tyre lifespan — why engineers at the respective factories have specified these tyre sizes for their cars. However, we can enhance this a bit.

For instance, if the stock tyres are Michelin Pilot Sport 4, a good amount of extra grip can be had from moving to Pilot Sport 4S in the same size.

Such upgrades can also be had with other tyre brands, depending on size-availability:

  • Bridgestone POTENZA RE050 to POTENZA Sport
  • Goodyear Eagle F1 Asymmetric 5 to Eagle F1 Supersport
  • Pirelli P Zero to P Zero (PZ4)

Cross-brand upgrades can also be done, for example from Bridgestone POTENZA RE050 to Michelin Pilot Sport 4S and can serve as a stellar upgrade.

If you are unsure which tyres are the perfect +1 upgrade, our AutoApp team would be more than happy to give you recommendations based on your car, tyre sizes and availability.

+1 rim and tyre upgrade

We know from the earlier sections what the rim specification stands for and what types of rims are available. Now, we can choose a suitable set of replacement rims for our car.

There are many reasons to change a car’s rims to an aftermarket set — aesthetics, lightness and strength being the oft-cited reasons. Many performance-oriented cars these days already come with suitable-width tyres from the factory. We would suggest simply improving upon what’s already there. In other words, choose a set of forged or spun-cast rims with the same diameter, width, offset and PCD as the stock rims, and pair them with more grippy tyres from the “+1 tyre upgrade” section of this article. Easy-peasy.

If the chosen aftermarket rim does not come with the same width and offset as the factory rim, we need to figure out the right offset needed for the width of aftermarket rim available. This is where an online Wheel Offset Calculator comes in handy.

Using the example of the WRX, we enter the width and offset of the stock rim in the respective boxes under Current Wheel Specs.

We then enter the available aftermarket rim’s width and offset into the respective boxes under New Wheel Specs and hit Calculate.

Below the Calculate button, under Results, the calculator presents different clearance numbers to help us ascertain if the aftermarket rim would be suitable for our application.

Ideally, we’d have the same-to-similar inner clearance, plus-minus a few mm, and some protrusion toward the outside. This extra protrusion to the outside would also go toward achieving a ‘flush’ fitment that is so popular with car enthusiasts, without the need for wheel spacers.

We can then physically measure inward to the strut housing and outward to the fender lip to ensure that there would be no interference from the aftermarket rim-and-tyre combination.

Once these measurements are ascertained, the rim-and-tyre combination can be purchased with peace of mind.

Beyond +1 rim & tyre upgrades

The goal here is to blend and balance improved driving pleasure with everyday usability. As such, upgrades that go further than those described above go beyond the current scope, but that‘s a discussion we‘ll table until next time.

Suffice to say, the principles behind going beyond +1 have already been explored. Both the online tyre calculator and the wheel offset calculator would be used to achieve the desired goal.

However, caution is advised, since there have to be overwhelmingly good reasons for upgrades such as upsizing to larger diameter and/or wider rims and tyres. We also recommend that daily-driver comfort and drivability be considered when performing such upgrades.

Some parting tips

The last thing anyone wants after upgrading tyres or rims is for your drive to go oh-so-wrong, so here are some tips to help with your upgrade.

Remember, always change tyres in pairs for 2-wheel drive vehicles, or a set of four for all-wheel drive vehicles. The reason for changing tyres in pairs is simple — the same grip levels side-to-side across the front or rear axles, which allows for more predictable handling.

With all-wheel drive vehicles, the rolling diameter of each tyre affects how differentials and/or the transfer-case operates. Having different rolling diameters front-to-back and/or side-to-side would put these components into slip-states. While differentials and transfer-cases are designed to slip, they are not designed to continuously slip over thousands of kilometres, and can be severely damaged, requiring thousands of dollars in replacement parts.

And there you have it!


Now that you know more about how to choose the right tyres and rims for your ride, head on over to Asia’s Ultimate Tyres, and keep your eyes peeled for the results of the inaugural Asia’s Ultimate Tyres Awards 2022!