Civic type r 18 inch wheels

Why 18-Inch Wheels Could Harm the Civic Type R's Handling

Photo credit: Honda

From Road & Track

Wheels have gotten bigger over the years, and even compact sports cars like the Honda Civic Type R now come with 20-inchers. There's recently been discussion about how 18-inch wheels might improve the look and feel of the car. Thing is, such modifications need to be approached in a calculated manner as they can often make a car handle worse.

Smaller wheels will usually weigh less, which translates into less rotational mass and, occasionally, a better handling car. But if the wheel and tire selection is not approached with suspension setup in mind, it can make the car handle or steer worse. This is especially important when it comes to the Civic Type R, as Honda specifically designed the suspension to prevent torque steer.

To understand how the Type R mitigates torque steer, you need to understand tire scrub radius and the kingpin (or steering) axis. The kingpin axis on something like the Civic Type R extends from the highest pivot point (the upper balljoint) to the lowest pivot point in the suspension (the lower balljoint). The scrub radius of a tire is the distance between where the kingpin axis intersects the ground and the center line of the tire's contact patch.

In high-torque front-drive cars, the goal is to get these two points very close to each other, without overlapping-a car with zero scrub radius can have a lot of tire squirm and handle strangely. Many modern cars, especially those that are front-wheel-drive, actually have negative scrub. This type of setup usually requires less steering effort and often helps to counteract torque steer in cars like the Civic Type R.

Photo credit: Honda

Compared to the standard Civic, Honda was able to bring the steering axis closer to the wheel center line in order to minimize the tire scrub radius in the Type R. That angle is narrower because the kingpin axis is much closer to being parallel with the tire center line.

Wheels and tires are an important part of this equation since the center line of the contact patch changes as wheel offset and tire size are changed. In the case of the Civic Type R, changing to the 18-inch wheel in the Instagram post above would cause a positive tire scrub value. That likely means an increase in torque steer along with changes in handling.

Using the excellent suspension calculator at Racing Aspirations gives us a rough estimate of what the stock setup on the Type R looks like compared to the 18-inch setup shown above, as well as another popular wheel and tire combination for the Type R: the 19-inch front wheels and tires from the Acura NSX.

We know some measurements for the Type R's factory wheel and tire, along with track width and factory camber settings, and we'll estimate the other measurements to get a general idea of how each wheel and tire combination works. We will start with -2 mm of scrub radius for the factory setup, a 20x8.5 wheel with an ET60 offset and a 245/30R20 tire.

Photo credit: Honda

If we enter the details for the Desmond wheel and Advan tire shown in this Instagram post, we see that the 18x9.5 ET45 wheel and 265/35R18 tire combination alters a lot of measurements. The ride height goes down by 7 mm and the track width increases by 30 mm. Our scrub radius goes from -2 mm to +11 mm, a pretty significant change that's highly likely to induce extra steering effort along with more torque steer.

Going to the option of the 19x8.5 ET55 Acura NSX wheel with its stock 245/35R19 tire seems to be a better option, though it's not optimal either. Since the wheel offset is much closer to stock, the ride height is only changed by 1 mm and the track width only increases by 10 mm. Our scrub radius is again positive, but this time it only goes up to +4mm.

Photo credit: Honda UK

A common response to criticism of downsizing wheels on a Type R is that even Honda runs an 18-inch wheel on its TCR touring car. While you can run an 18-inch wheel on the Civic Type R and have it perform as well or better than the stock 20-inch setup, it requires the wheel size and offset to be proportional to the original setup. In the case of the race car, the rest of the suspension is also modified, adding things like adjustable dampers and sway bars, so there is really no comparison. Even if all of that wasn’t the case, the TCR technical regulations don’t allow a wheel any bigger than 18x10, so the stock wheel could not be used anyway.

The most optimal combination for a street car would be a wheel and tire combination that doesn't alter the suspension geometry at all. Something like the NSX wheel would be perfect with just a little more offset, and even the aftermarket 18-inch combination could work if the offset was increased to around ET60 and if tire size was changed to something like a 245/40R18.

Checking through various OEM and aftermarket options, the only downsized wheel for sale right now that offers a perfect match for the OEM Type R wheel is the 19x8.5 wheel that came on the previous generation Type R, as it has the same ET60 offset. Paired with a 245/35R19 tire, it is basically a perfect match for the original setup. The scrub radius would only go down by 1 mm. That should be an imperceptible change. This wheel is about three pounds lighter than the 20-inch wheel, so it'll save some weight along with adding more sidewall.

Photo credit: Honda

There are many aftermarket vendors that are offering wheels for the Civic Type R, and some even claim that theirs are designed specifically for this car. But after looking through many of the options, it appears that a lot of the wheels were originally made for BMWs with the same 5x120 lug pattern. This is very apparent when you look at the offsets, as many OEM BMW wheels fall into that ET43 to ET48 offset range.

Our calculations here are simplified, but they show how chassis tuning can be greatly affected by seemingly small changes. All variables of the suspension and tires should be considered when making any aftermarket upgrades. Once you start digging in, even smaller variables like the flex of the tire sidewall can affect the overall result. You really need to consult someone knowledgeable about chassis setup if you want the maximum performance from your car.

So, even though an 18-inch wheel might be lighter, it may not necessarily make the car perform better. Choose your wheels carefully so you don’t unwind all the suspension setup that was done by the Honda engineers.

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