The debate about smaller tires vs bigger tires, and how the size of tires affects essential metrics of the cars like speed, traction, acceleration, etc. is always ongoing. One such metric is Torque. And you have come here to know if smaller tires give more torque?
Smaller tires don’t produce more torque. Torque doesn’t change with tire size, it’s the acceleration that increases with smaller tires due to shorter distance from the center of the rotation which results in increased force to produce the same torque and hence increased acceleration (F=ma).
Torque is the measure of a force that can cause an object( in our case, a tire) to rotate about its axis. Torque is measured in Newton-metre as it’s a product of tangential force to leverage(distance, which in our case will be the radius of the tire).
Don’t get too overwhelmed with this technical definition. It’s gonna get pretty simple once you have gone through this article to the end.
How Does The Tire Size Affect The Torque?
To better answer this question, we first need to understand what torque actually means and how it works in the case of car tires. I would recommend that you watch this video first.
So, I hope you pretty much got the idea about what torque is and how it works in the case of car tires. Let’s have a look at its formula again:
τ = r F
|r||radius (radius of the tire)|
From this formula, we can see torque is dependent on both the radius of the tire and the force applied to lug nuts by the axle.
Back to our original question, How does the tire size affect the torque? Well, it doesn’t. let’s see how.
Tire size doesn’t affect the torque. Tire size only changes the force applied on the lug nuts( where the torque acts). For a larger tire, the force decreases as the radius of the tire increases, and vice versa for the smaller tires, the force increases as the radius of the tire decreases. (τ = r F)
Torque for a vehicle is always specified by its manufacturer and must not be changed. That’s the reason why your mechanic asks you to get your tires retorqued either after 50 km of your new ride or within the next 1-2 business days whenever you have changed tires.
That is to ensure that the lug nuts have been tightened to the required measures. Once your tires are changed the mechanics ensure that your wheels have been gauged with specified torque.
However, after driving for the first few (around 50 km) the lug nuts might get lose or too tightened, and hence your tires need to be retorqued to the specified torque.
Do Smaller Tires Go Faster?
Smaller tires do accelerates a car faster than bigger tires. This is due to the higher force applied by the axle on the lug nuts to compensate for the shorter radius to produce the required amount of torque. Hence, the increased force results in increased acceleration. (by Newton’s 2nd law: F= ma)
Let’s have a look at this video, which pretty clearly explains why a smaller car accelerates faster.
To understand the above video better, Let’s first have a look at the fundamentals of wheel dynamics. The wheels are attached to your car via an axle with the help of lug nuts. This axel produces a torque on the axis of the wheels which then results in the spinning of the wheels.
As we have already discussed above that the torque must not be changed and always be equal to the manufacturer’s specification due to safety concerns. We will assume the torque to be a constant value.
So according to the formula of the torque τ = r F, if the τ(torque) remains constant, we know that with the change in r(radius of the tire), F(force) must change to maintain the value of τ(torque) which is measured in Nm(Newton-metre).
Let’s imagine that a car produces a constant torque of 80 Nm on each wheel. And the size of the wheel is 15″, which means the force required to produce 80 Nm torque is approx 210 N.
Now let’s change the tire size to 19″, the Force required to produce 80 Nm torque is now reduced to 166 N.
|Property||Car with Smaller Tire||Car with Bigge Tire|
|τ (Torque)||80 Nm||80 Nm|
|r (radius)||15″ OR 0.38 m||19″ OR 0.48 m|
|F (Force)||210 N||166 N|
We can see a significant drop in Force in the case of a bigger tire. Force is directly related to acceleration according to Newton’s 2nd Law – F = ma.
So, from this, we can conclude that smaller tires produce greater acceleration than bigger tires. This is due to the fact that greater force is required to produce similar torque in the case of smaller tires.