While the winter tire change over
is one of the most common automotive spring traditions, many consumers are seeking to do more than just switch to a new set of all-seasons or summers – they want an upgrade.
And we’re not just talking about a step up in quality or cost, but in size too. In fact, going bigger, or plus sizing as it is known, is often the most important upgrade consideration. A car comes equipped from the factory with 16-inch wheels, but could they be swapped out in favour of a sharper set of 17- or 18-inchers? The answer is it depends.
As an aside, my own car, a 2010 Honda Civic Si coupe, is a common platform for these upgrades. My fellow Si owners routinely put bigger wheels and lower-profile tires on their cars than the stock 17s I’m currently riding around on. In the nearly seven years I’ve owned my car I’ve never seriously considered following suit, but that has more to do with my own personal preferences than the car itself. Bottom line, it’s just not something that matters to me.
But for many others it is a serious consideration, so with that in mind, I cobbled together a few factors to keep in mind based on research and conversations I recently had with the Canadian head office for Toyo Tires, one of the world’s largest original equipment and replacement tire manufacturers.
Size matters, but it also has to fit
One of the most basic factors to keep in mind is the amount of available space, and not just in terms of what will fit in the wheel well. One also should consider the size of the brakes, both rotors and calipers, along with space between articulating suspension components which can impact steering and other safety concerns. Contact with bodywork is also something to watch out for, as is the vehicle’s bolt pattern, both in terms of the number of lugs and their spacing.
“Rim width and Load Index are the main points,” according to Jonathan Scott, technical services specialist at Toyo Tire Canada.
“When upgrading one’s tires size they should ensure the Load Index meets or exceeds the factory tire size equipped on the vehicle. When choosing wheels for the application the end user should be aware of the selected tire sizes minimum and maximum rim widths. These measurements are important so that the tire is safely run within the manufacturer’s specifications,” he said.
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2020 Chevrolet Corvette Stingray[/caption]
What’s the Load Index?
The Tire Load Index determines how much weight a vehicle can safely carry based on correct tire size and pressure. The following figures are per tire: Standard Load (SL) runs from 62 (584 pounds) through 125 (3,628 pounds), while Extra Load (XL) goes from 66 (661 pounds) to 125 (3,668 pounds). The load index figure multiplied by four produces the total carrying capacity for the vehicle. These figures are calculated by auto manufacturers, but it is worth noting the total figure is much higher than what most newer vehicles weigh even when carrying passengers and cargo.
One tire for several rims
Rim width is an important consideration because, due to their flexible sidewalls, a single tire size will fit on rims of varying widths. For example, a tire designed for a wheel that is 6-inches wide, could also be mounted on rims ranging in width from 5.5- to 7.5-inches. This is important because the width of the rim determines the width of the tire, and a tire mounted on a rim not approved by the manufacturer could cause irregular wear and handling issues.
Common upgrade mistakes
As one might imagine, there are many ways to go wrong when it comes to selecting bigger wheels and tires, many of which flow from not carefully considering factors previously mentioned. I asked Toyo for their input on the subject and was told that they commonly see plus-sized tires being selected without the correct load-carry capacity and that have a reduction in speed rating.
So how does one avoid these pitfalls? Selecting the right tire is a good place to start. Scott summed it up this way: “We want users to ensure they are purchasing the correct tire for the application. If a driver is looking for a performance tire with good rain traction [they should consider the] Proxes Sport A/S, whereas if someone is looking for a safe, budget-friendly tire the Extensa AS2 would be a great option.”
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2020 Chevrolet Corvette Stingray[/caption]
Do your homework first
Before putting one’s money down on new set of wheels and tires it’s important to do the homework first. Apart from the items previously mentioned, more mundane things such as cost, driving habits and weather conditions should be accounted for. Is the vehicle going to be driven year-round or will it be taken off the road at summer’s end? Will it need winter tires? Would other modifications, such as brakes and suspension, be impacted by a switch to a bigger wheel and tire package? On that last point, Scott recommends doing suspension modifications, such as lifting or lowering, before tackling wheel and tire upgrades.
Remember this rule of thumb
Given the many options, and pitfalls, regarding plus sizing, one of the first questions that crossed my mind when I sat down to write this is what about a rule of thumb? Is there one? I asked Toyo, and they said yes.
Essentially, the rule of thumb for plus sizing is an increase of one inch in wheel diameter will push the tire’s section width (sidewall) up by 10 mm, while the aspect ratio (section height divided by section width) decreases by 10 points. Ideally, a plus-size tire should have a diameter increase that isn’t greater than three percent compared to the original tire. Diameter size increases of greater than three percent can negatively impact a vehicle’s safety and performance systems, including anti-lock brakes, differential and drivetrain.
In the end, there are many factors to consider regarding plus-size wheel and tire upgrades. As it is for many vehicle modifications, aesthetics often governs the decisions that are made, but they are far from the only factors in play. Cost, safety, performance and driving habits should also be given just as much, perhaps even more, consideration.
The bottom line is that when it comes to upgrading wheels and tires, it’s about so much more than appearance alone.