# Real World Physics and my Wheels

1. Sep 25, 2015

### cDuck28Z

Good evening,

First Post here on PhysicsForums! I'm building myself a 1939 Chevy HotRod and have encountered a slight problem with my build. I'm trying to find a wheel that will fit my project, but the problem is that they don't make it! There are numerous forums online with people both for and against wheel spacers, but I want to know the physics behind these little devices. The concept is simple: add a spacer between your wheel hub and the mounting surface of your wheel.

I'm trying to figure out if there is actually any difference in force on my lug studs (green) between having a -47mm offset or a 0 or +10mm offset. On one hand, I look at it an think 'Of course there's going to be more force, the wheel is so much further away from the hub'. On the other hand however, all of the forces of the vehicle, both while at rest and while driving, are located in the exact same location in all three scenarios. So would there actually be a difference?!

Please note, my diagram is off just a bit with regards to the lug studs. The holes are offset (see example image below) so there is more than enough metal to transfer the force of the vehicle.

PS. My hotrod will weigh an estimated 1400kg with aprox 850kg over the front wheels. Aprox 1.37m track (center point to center point of front tires) and 2.84m wheelbase.

2. Sep 26, 2015

### Simon Bridge

There is s difference, it means the components are more prone to fatigue.
Generally you need to keep a closer eye on them than normal.

3. Sep 27, 2015

### mrspeedybob

By spacing the wheel out you are creating more leverage against the suspension components, and therefore, applying more torque to them. suspension components apply a proportionally greater torque holding the wheel down against the ground, so the net force on the car remains the same, but the component forces that add up to that net force are greater, thus, the wear on the components is greater.

I doubt this will be of much concern on a hot-rod that is likely to be a fair weather weekend cruiser. You can tolerate a little sloppier engineering on a car that sees 1000 miles a year then a daily driver that sees 10,000 miles a year.

4. Sep 27, 2015

### cDuck28Z

The centerline wheel is in the exact same position in every scenario. No part of the system is moving at all. The only change is that the offset that would be comprised of the negative offset of the wheel is replaced with a spacer filling the void and adapting the wheel to the positive offset creating a net 0 change in position. So how would this effect the entire system as a whole?

Last edited: Sep 27, 2015
5. Sep 27, 2015

### mrspeedybob

Ok, I mis-understood the scenario. In that case, you are right.