How Does Wheel Size Affect Performance?

One of the first and easiest modifications to a car can be to slap some larger wheels on, but what what affect does it have on acceleration and overall performance?
How Does Wheel Size Affect Performance?

You see it at every car meet and cruise; VW Golfs and Audi A4s turning up with their arches filled and scraping with wheels four inches larger than stock. Aesthetically, it is completely understandable to want to fill the wheel arches for a more aggressive and hunkered look. Your car can be made to look badass and more compact in side profile. I’ve even seen 19-inch Lamborghini wheels crammed into a Scirocco’s arches. But how does a big set of wheels affect your car in terms of performance? Are you needlessly sapping the life out of your 0-60 time and your handling?

To start off with, let’s look at the simple fundamentals of wheel dynamics. To get a wheel spinning, you need to apply a torque through its axis. This torque value can be calculated using the radius of the wheel and the tangential force produced by the wheel.

We can treat the torque value as a constant (assuming your engine produces a stable torque figure) which therefore means that if the wheel radius changes, the driving force acting from the wheel must also change.

How Does Wheel Size Affect Performance?

So let’s say you start off with a 15-inch wheel on your 1.6-litre VW Golf GTI which produces a maximum torque output of 350 Nm. Assuming that the torque is split between the two wheels (175 Nm each) and discounting drive ratios so that all the engine’s torque makes it to the wheels, the force can be calculated to be around 460 Newtons. Now, increase that wheel diameter to a set of 19-inch Need for Speed style, fake diamond cut rims from your local Halfords. Run the calculation through again and that driving force will decrease to 360 Newtons.

How Does Wheel Size Affect Performance?

Newton’s Second Law dictates that the force on an object is equal to its mass multiplied by its acceleration. So, increasing your wheel size will decrease the driving force from your wheels which will culminate in a decrease in acceleration of said wheels.

To summarise, a car’s engine finds it more difficult to rotate larger wheels, making for a decrease in overall acceleration. This is all assuming that every other component like the engine, driveshafts, gears and differentials are kept stock, making them specifically engineered for the original wheel size. Fuel economy will inevitably suffer as well due to the engine having to work harder to rotate the wheels, but I’d imagine that’s the least of worries for the generic modifier.

Car and Driver ran an interesting test a few years ago to show just how much difference wheel sizes can make to acceleration using a VW Golf. The car was tested with varying wheel sizes, with the 0-60mph times ranging from 7.6 seconds for the smallest wheel size (15-inch) and 7.9 seconds for the 19-inch option. That lag in time was emphasised with the 0-100mph times as well, with the large-wheeled car taking over a second longer than the 15-inch variant.

How Does Wheel Size Affect Performance?

Another area affected by wheel diameter is the tyre that has to be mounted to it. Since the speedometer and gearing are finely tuned to the entire diameter of the alloy and tyre combined, as wheel size increases, the profile of the tyre must decrease to not mess this calibration around. This therefore means that the sidewalls of the tyre have to be stronger to withstand the lateral forces applied through cornering, decreasing ride comfort and feedback to the driver.

But it’s not all bad. Increasing wheel diameter normally means increasing its width as well, making the contact patch between tyre and road larger, hence increasing grip. On that note, you should really stiffen your suspension along with increasing tyre width as body roll will increase substantially if the car is able to dig much harder into corners due to the added friction leading to corner stability.

How Does Wheel Size Affect Performance?

Differences in handling will also vary with wheel size. Smaller diameter wheels will make for more concise handling as each rotation of the wheel covers a shorter distance, meaning more acute adjustments can be made during cornering compared to a larger diameter tyre, which will try to push further on into the corner and provoke understeer. On the contrary, the increase in grip for the larger, wider wheels will culminate in faster and more composed handling as stated above.

So the real question is, do you go for aesthetics or performance? Comment below, we’re interested to see what you all think!

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Comments

Marty Pierro

What about tire width, I see people with stretched tires and such to make super wide tires, what does that do for performance?

04/23/2016 - 19:56 |
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A-dree-N

i try to strike a balance between both. Go figure though, my V6 Challenger came with the Sport package, which included performance suspension, brakes, and bigger wheels (20” VS base model 18”). Meanwhile I bought a set of 18’s for some snow tires, and i swear my car launches faster with those on VS the summer tires on the 20’s.

04/23/2016 - 20:00 |
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Anonymous

decreased acceleration, increased braking distance, harsher ride, laughable aesthetics, way more expensive tires - are there no down sides to bigger wheels? :D

Ok seriously, I don’t care what size wheels people run - I’m not in charge of anyone’s happiness but my own - but I will giggle at people who tell me “it’s for increased performance”

04/23/2016 - 20:03 |
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nandee

And what happens when you increase the size of the rim, but decrease the size of the tirewall, so that it equals out? Because that way the tire itself won’t be bigger, it only will be heavier.
And on another topic, how much does the weight of the tire count? If only performance is important, than how much can you benefit from changing the factory alloys to steelies? Because light weight alloys are not cheap…

I’m asking this because it feels that the car was faster with the winter tires which are 185/60R14 steelies, instead of 195/55R15 factory alloys. And the summer tires are older and a bit more worn.

04/23/2016 - 20:15 |
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Nick 29

Don’t get it say my wheel is 18 inch and they tyre add another 4 or 3 what if I change the wheel to 19 or 20 and new tyres off 2-3 will it be the same as written above or will it not affect my car

04/23/2016 - 20:46 |
0 | 0

Then what he wrote doesnt apply to you since the overall diameter hasnt changed. By doing that youll get more response and a more progressive oversteer/understeer since youve effectively got a stiffer sidewall. Obviously theres such a thing as too stiff, just like suspension

04/24/2016 - 01:57 |
2 | 0
Axel Trainwagon

I prefer smaller wheels aesthetically anyway so that’s what I go with.

04/23/2016 - 20:52 |
0 | 0
Dani 3

17” are easily enough for my taste. I dont like cars with huge rims, especially cause you know immediately that, if it’s a fast one, it doesn’t get driven properly ^^

04/23/2016 - 21:45 |
0 | 0
Anonymous

The VEX robotics wheel as an example made me smile.

04/23/2016 - 21:45 |
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FLixy Madfox

Looks like engineering explained has a rival now…

04/23/2016 - 22:10 |
6 | 2

Really doesn’t.

04/30/2016 - 20:18 |
4 | 0

Not at all. This article is one of the worst I have ever read on CT. Half of it is wrong…

01/01/2017 - 15:21 |
6 | 0
riceralero

9’ S anyone?

04/24/2016 - 00:38 |
0 | 0