Bigger Wheels Side Effects
 

The aesthetic appeal of larger wheels and tires is undeniable, but what about the alleged performance benefits? In general, larger wheels are heavier, and additional weight hinders performance. To examine the effects of installing larger wheels and tires, also known as “plus-sizing,” we tested five wheel-and-tire combinations—ranging from 15 to 19 inches—on a 2010 Volkswagen Golf and got a good sense of what is gained and lost in the process.

The plus-size concept basically works like this: As the wheel gets larger in diameter, the size of the tire’s sidewall must shrink to maintain the tire’s overall diameter. Keeping the overall tire diameter roughly the same is crucial to keeping the gearing the same and the speedometer accurate, as well as for making sure the wheels and tires fit within the fenders. But larger-diameter wheels and tires are often available only in enlarged widths as well.

We used the stock steel wheels for the 15-inch test and went to the aftermarket for the larger wheels, as most owners would do. The aftermarket wheel we chose was a cast-aluminum ASA GT1, which is available in 16- to 19-inch sizes on the Golf. It’s obvious from the test that as wheels and tires grow in size, they also grow in weight. Here’s how the test shook out:
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What’s immediately apparent from the results is that as the wheel-and-tire packages get larger and heavier, acceleration and fuel economy suffer. Neither is a huge surprise, but we measured a 10-percent drop in fuel economy and a four-percent degradation in 0-to-60-mph acceleration from the 15s to the 19s, which is worth considering should you be thinking about “going big.” Increasing wheel diameter and width, in turn, requires wider tires with shorter and stiffer sidewalls, which we found will increase skidpad grip, but as our test shows, there is a limit to this assertion. The 19-inch package came with the widest tires (235/35R-19) mounted to the widest wheels (8.5 inches), but this setup had less grip around the skidpad than the narrower 225/40R-18s on 8.0-inch-wide wheels. We asked the folks at Goodyear why that might be, and they postulated that the added width may have given the outside tire more grip, which would increase body roll and could therefore decrease the load on the inside tire enough to lose 0.01 g on the skidpad.

Subjectively, both the 17-inch and 18-inch wheels and tires were in the sweet spot of grip, braking performance, ride comfort, and steering feel. Moving from 17-inchers to 18s barely degrades ride quality, and the additional grip is welcome. We’d guess that a W-rated Eagle GT in the 17-inch size would come close to matching the grip of the W-rated 18, but we can’t say for certain without testing. Even with V-rated rubber, the per-form*ance of the 17s felt *similar to that of the 18s. But since the 18-inch setup costs only $112 more than the 17-inch package, we’d probably opt for the 18s if we lived in a region with smooth roads and looks were a priority.

The 19-inch wheels definitely look the coolest. But the 17- and 18-inch setups offer a better compromise of grip, acceleration, price, and ride harshness, so we’re not surprised.

ABOVE FROM: Effects of Upsized Wheels and Tires Tested - Tech Dept. - Car and Driver

MY .02 Worth. :eek: If a car comes with 16", 17" and 18" tires, the 17's will be best overall for all seasons. the 18's will be a bit wider which is great for summer only. Going to 20" is just stupid----you're ride will be harsh and you may bend the rim. Try not to go too wide as you will lose traction, especially in the rain and snow! I have 17's on my car and will probably go to 18's and a bit wider as I have a set of 16's for winter tires (if $$$$$ comes). :p :D :eek: :)

I never did like the look of low profiles myself, other downside to them is if you get a flat your pretty much running on the rim and not the sidewall of the tire, yes you will destroy your tire by running on it while flat but if it saves your rim its a good sacrifice. Also if you curb your car often the low profiles will not save your rim either.

It is not simply 'larger and heavier' that causes a negative when it comes to larger diameter wheels and tires.

Even a lighter, but larger wheel & tire combo can reduced HP at the wheels. One of the laws of physics is that the further a mass is from the point of rotation, the more force that will be required to accelerate and sustain that mass. Even though the wheel and tire may be lighter, the majority of its mass is still at the outer edges of its diameter, and being a larger diameter that mass is further from its point of rotation.

There used to be a TV show on Speed called 'Sport Compact Revolution'. They put a lighter, but larger, wheel & tire combo on their project WRX. The difference was significant- something like 4-5 lbs per corner. Imagine their surprise when they went back to the chassis dyno and found out they lost something like 7 hp at the wheels...

In simple terms Karl, you are talking about taller tires.:p Unless you can re-program your computer, taller tires should never be put on!

Didn't have a thing in the world to do with 'taller tires'.

As I clearly stated above, as weight is moved further from the point of rotation, the more force that will be required to move and maintain the mass. A 16" combo vs. a 17" combo of the same overall size still moves the majority of mass further form the point of rotation. Even if it is lighter, the 17" combo will still require more force to move (it). The obvious exception is if you had an absurdly heavy 16" combo.

Doesn't have a thing to do with 'taller' or larger overall height/diameter.