Will a car travel faster on larger or smaller wheels?

Question

By car I mean a rolling science project about the size of a shoebox or smaller. It is going to be powered by a small 9 Volt motor, which will rotate the wheel axle. I assume that the wheel size will not affect the RMP of the mini-motor, but please correct me if I'm wrong. Scientific answers or helpful equations would be greatly appreciated.

Answer 1

If your motor turns at a certain rpm, then increasing the wheel size will definitely increase your speed.

Each revolution, you will travel (pi * diameter of wheel). Since speed = distance / time, you can see that if you travel further in the same time (the time for the motor to make one revolution) then your speed will increase.

Of course there are physical limitations. You can't put on really big wheels and exceed the speed of light, for example. And possibly not even 15mph. But when the speed and weight are low and the motor generates enough power to run at full rpm, then the wheel size definitely matters.

Answer 2

Typically when a car maker or tuner fits a range of wheel sizes, the tyre aspect ratio is changed to keep the overall tyre diameter reasonably constant. Example: 150/70/R12 replaced by 165/55/R13 is only 0.6% difference in diameter If the new tyre diameter is larger then the speedo under-reads, the car goes faster (but accelerates more slowly). At some point, the effect of higher gearing and the power output curve of the engine will affect the top speed. Adding significantly taller tyres has a range of effect on the handling, and risks contact between the tyre and the body/suspension.

Answer 3

The wheel size will not affect the RMP of the mini-motor but larger wheel size will increase the contact area between the wheels and the surface it runs on. Larger contact area will yield larger friction force acting on the "car" against the motion and thus slow it down. The best thing for you to do will be to resolve the maximum friction force permissible by drawing a free body diagram of the car (assuming you know all the forces working on the car such as the minimum speed you want it to move at, weight, etc etc and leaving the contact area as a variable).
From the equations that you get from the free body diagram, it will easy to calculate the normal force and thus the contact area that yields the least friction force.

Answer 4

If you have enough power in the motor to ensure the RPM is not changed, then you have to go for the bigger wheel. The bigger wheel has a greater circumference so for each rotation the linear travel of the car is greater.

However, it will require more power to drive the bigger wheels. So if you don't have an excess of power from the motor you might find the RPM drops for bigger wheels. The trick is to optimize the wheel size to maximise the power usage.

Answer 5

Small Car Wheels

Answer 6

Yes it makes a big difference. In real world and on big cars (normal scale) the big diameter wheels (assuming that we keep constant their width) are rotating the axle slower so at higher speeds on runway this should make a difference because the frictions on the bearings rise once with their speed. If you study a wheel you can see that a big one compared to a smaller one has a outside perimeter longer (try it with a wire putting it around the perimeter) than the smaller one. So if you put them in contact with the ground and make them to go for a fixed distance in the same time and same speed, you'll notice that the smaller wheel will rotate faster having less length to cover with its perimeter for one rotation.

But for a project for this size is a question if it will encounter in its path some bumps or edges to make difficult terrain or just go on hard and straight surface?

The bigger the wheel the off-road-er it is, because with its greater diameter does Not enter in any recess of the ground (only in the bigger ones which overcomes the wheel diameter).

The smaller wheels work for extremely high speeds, but for a greater consumption (miles/gallon), if you take a look to Formula one cars or other like this (carting cars), or to a skate board rollers.
Because they have a smaller diameter they can be much faster in movements and that's why they "feel" and respond to any action of their rotation, compared to big diameter ones which respond to a higher one, due also NOT for any inertia but the shorter lever from axle to ground (in this case the radius itself).

So in conclusion, if want to go faster, on straight and smooth surface, choose the smaller ones, but if a bumpy road, choose the bigger diameter ones.
Hope that helped
Dfriend:)

Answer 7

By wheel size I assume the you mean diameter and tire width.

On a vehicle the size that your taking about the diameter will not make a lot of difference. You're talking angular velocity and of course the larger the diameter the more inertia you must initially overcome to get them turning, once they are turning they will go farther using less power.

As far as the width; you want as narrow of tire as possible as the rolling resistance will be reduced. Razor thin tires on a very hard surface would be ideal.

Hope this helps.

Answer 8

The axle, on a small wheel and a big wheel rotate the same speed. The smaller tire has less surface to ride on, and the big wheel has more surface to ride on. So there is more rubber, and more surface so the answer is simple.
A `15" wheel is slower then a 17" wheel . so if you want to save gas, buy a bigger wheel.

Answer 9

I am not an expert on this, but logic and common sense tells me that the size of your wheels will not affect the speed of your mini-car. However, since your car is so small, I guess maybe larger wheels could slow it down if they weighed more.

Answer 10

wheel size won't make for faster car...the wheels, if are small will only rotate faster, if larger will rotate slower but speed of vehicle will be constant, depending upon acceleration.