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.
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.
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.
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.
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!
Comments
And I always thought that 35” tires makes car faster xD lol
I went for both
Actually, depending on your situation, larger wheels can sometimes benefit your fuel economy. I have a long highway commute in an area where if you go less than 75 mph, you’re asking to be rear-ended, but I drive a 1995 GMC Sonoma with the wheezy but reliable 2.2 four-cylinder. On the original wheels, 75 mph was a difficult speed to maintain, as the little truck’s top speed isn’t much more than that. So I changed the wheels from a 205/75 R15 to a slightly-larger 235/70 R15, which is overall about one inch larger diameter. It’s not a huge difference, but I have noticed a very slight drop in low-end torque. However, I have also had much less trouble maintaining a 75 mph speed because, with that extra inch of diameter, I have 3.1% fewer revolutions per mile, which I have noticed positively impacting my fuel costs when highway driving.
Uhhh
You made your sidewall thinner and your tyre wider.
I did the same to my s10… p235/75r 15. Goodyear Wrangler. I get worse mileage because they are all terrain and not meant for highway speed
I still like 18s on my stuff, performance be damned!
350 nm from an original 1.6 Golf GTI is pretty damn good.
Thats why im not going any bigger than an 18 inch rim when i get new wheels. I want to fill in the fender well but i dont wanna lose performance
You didnt seem to take weight into consideration here. I have 17” x 7” aluminum wheels on my car that came stock with 14” x 5” steel rims. However despite the larger rim there is less un-sprung mass for the engine to roatate, and a larger contact patch. It also looks pretty dang good. Win-Win. Thin wheels also hurt acceleration if they don’t have enough lateral grip to cope with the force of acceleration
Good read man! Even tho i would be lying if i said i wanted smaller wheels now… Call me a show-off i accept it 😂
Depends highly on the car. But ideally smaller wheels = more acceleration. Bigger wheels = more top speed but acceleration suffers highly.
Smaller wheels are less grip and bigger wheels have more grip.
Ideally you should always go with smaller and smaller until you start having issues with grip.
When you’re pushing out 1000hp, you have to get bigger tyres to tone down the speed and increase the grip.
All this hypothetically without even talking about tyre width
What if you switch out 25lb 17 inch rims for 18lb 18’s?
Good question! actually Mopar did a study back in the 70s I beleive (not sure exactly on the time) but they found that for every Lb lost in un-sprung weight was equal to loosing 10lbs of sprung weight on the track. this does not include ets on the quarter mile tho, unspung weight reduction is most bennificial when cornering or conditions where the wheels are changing direction lots. the less un sprung weight you have the more control your suspension has over your wheels and thus allowing them to have more contact with the road over all. one of the best upgrades you can do is anything that will reduce your un sprung weight. there is obviously a fine line though when you start getting into the realm of structural strength though but gennerally one of the often overlooked aspects of suspension tuning is the weight of components.