Wheel Diameter vs Time: Does Size Matter?

[svn4svn]

I am not a physics student however I have a random and hopefully SIMPLE question about wheel diameter over time and distance

Basically take a toy car. A Hotwheel 1/64 scale car for example and run a Pine Derby type of event.

If a car was released down a slope from height of 5ft, slope 10 ft long and run flat for approx 30ft (approx 40 ft long track)

A car weighing 41 grams runs on a wheel diameter of 11 mm = average 3.569 sec from start to finish

With the same variables, would a larger diameter of 13 mm run a quicker time?

My question relates to how effective the 11mm tire would run with increased weight vs. adding weight and using a larger 13 mm diameter wheel.
We have a maximum weight allowed of 4oz and want to know if I can stay with smaller tires or MUST i change to larger wheels for a quicker time.

Hopefully I am not sounding silly, but I am very interested in the equation to find out rather than simply testing different times due to variables of friction loss or other factors unable to control.


thank you in advance for helping me learn.

Robert

 

[rcgldr]

If the wheel weight was the same, then the angular momentum factor is the same regardless of the diameter. I don't know about other factors such as rolling resistance and friction at the axle. If the wheel weight is heavier, it slows down the car a tiny bit, but only if the weight is significant compared to the total weight of the car. If the wheel was a disc, it would increase the momentum resisting gravity by 1/3 the weight of the wheel, which I assume is small comparted to the total weight of the car.

For example, if the wheels were solid uniform disks and 10% of the total weight of the car, then they would reduce the acceleration from 1.0000 g sin(θ) to ~ 0.9667 g sin(θ), ignoring all other factors.

 

[K^2]

Generally, larger wheel will reduce rolling resistance, both due to wheel/track deformations and due to axis friction. Whether the difference will be significant will depend on way too many factors. Still, all other things being the same, you are better off with larger wheels.

On a long track, aerodynamic factors will make a much larger difference. Unlike real cars, where you want aerodynamic downforce to improve traction, when racing under own weight, you want to make the body as aerodynamically neutral as possible. So if you are choosing between different Hot Wheels models for the race, body shape should be your first consideration.