Forces acting on a Wheel/Rim?

[Spirits of Senna]

I must apologize to my fellow F1Technical members with my master class of Paint skills.

I am trying to figure out what are the forces acting on the rim wheel the car is moving; unfortunately, vehicle dynamics is not my strong area.

What are the forces I need to correct?


I don't have tyre pressure acting on the rim. Is it realistic for the pressure omission or tyre pressure is jointing with the external forces acting at their directions to act on the rim?

Thank you. [-o<

[Tim.Wright]

Why do you need to know this? As with any engineering problem, we need some context.

If you need this because you are designing your own wheel, then don't forget to take into account the point loads you get on the rim when some hairy mechanic prys the tyre bead over it with a crowbar...

Also:
1. rpm wheel rotation isnt a force
2. Is torque wheel nut the tightening torque of the nut? If so forget that and put the clamping force instead
3. dynamic x and dynamic y, while technically correct need to be somehow defined. Commonly these loads are expressed as x"g"s of acceleration on the sprung mass which produces an inertial force
4. Normal axis systems are X long, Y lateral, Z vert. I had to lie on the ground to fully appreciate your drawing

[Blanchimont]

Don't forget the lateral forces that create a torque around the x axis during cornering!

[Spirits of Senna]

I didn't take into lateral forces to keep things simple and I assume the critical forces on the wheel is from longitudinal acceleration, though I am not sure if it's a valid assumption.

Ok I understand that I should change that RPM_Force into torque with the axle force in respect to radius of the rim.

[Blanchimont]

Estimated max longitudinal force between all 4 tyres and road: 6g*642kg = 37,8 kN

Estimated max lateral force between all 4 tyres and road: 5g*642kg = 31,5 kN

I would not dismiss the lateral forces!

[Spirits of Senna]

I presume those are F1 figures which I see your point. Thank you.

What about road car racing? Any info?

[Tim.Wright]

I didn't take into lateral forces to keep things simple and I assume the critical forces on the wheel is from longitudinal acceleration, though I am not sure if it's a valid assumption.

Critical for what? Again, if we know why you want this data it will be possible to give advice on what forces you need to take into account...

Lateral forces are absolutely not negligible in most cases. The car is accelerating laterally at roughly the same level as longitudinally. Not to mention the load case to the wheel is completely different laterally vs longitudinally.

[Spirits of Senna]

Critical for what? Again, if we know why you want this data it will be possible to give advice on what forces you need to take into account...

I would like to understand how designers develop their rims to keep it as light as possible yet durable enough not to be have fatigue failure, if that helps.

[Tim.Wright]

Ok, thats better. For that I'd say that inflation pressures aren't important but lateral forces absolutely are.

You basically have two application points for the forces/torques:
1. Wheel centre, where the drive pegs are and the wheel nut clamps
2. Rim/tyres bead interface (this is not so easy to define exactly how it is fed into the wheel)

The only job of the wheel is to transmit forces from point 1 to point 2 without deflecting too much.

Once you have the external forces defined, to design a light yet durable wheel you simply put material only where its needed. Same as any part really. Surface finish is also a large factor in durability.

[Jersey Tom]

In series where tire inflation pressures get to the 90+ psi range the stress imposed on the wheel may not be trivial.

[Tim.Wright]

In series where tire inflation pressures get to the 90+ psi range the stress imposed on the wheel may not be trivial.

That's mental... who are doing that?

[Lycoming]

I would like to understand how designers develop their rims to keep it as light as possible yet durable enough not to be have fatigue failure, if that helps.

Easy, bin 'em after 1 race weekend.

Though in all seriousness, some people are of the opinion that wheels as a wear item like tires. Also, it seems you don't have a force from the hub reacting the wheel nut torque.

I would say you should include pressure loads. And also probably the load involved in mounting the tire.

[Spirits of Senna]

Also, it seems you don't have a force from the hub reacting the wheel nut torque.

Sorry I don't understand that.

I would say you should include pressure loads. And also probably the load involved in mounting the tire.

I think you are right for illustration purposes. I presume tyre pressure does not reflect greatly on the force acting on the wheel hub, if of significant, as tyres are designed to expand outward. I would love to put some strain gauges between the wheel hub and tyres to find out the pressure and the change of it.

[rjsa]

I didn't take into lateral forces to keep things simple and I assume the critical forces on the wheel is from longitudinal acceleration, though I am not sure if it's a valid assumption.

Ok I understand that I should change that RPM_Force into torque with the axle force in respect to radius of the rim.

You can't do that. The rim more often than not is not centrally loaded by the spokes, so there will always be moment around your X & Y axis.

And everytime the car is excited on your Z axis (like when it turns) you will have forces along Z and moment around X & Y.

[riff_raff]

There are some stresses created within the wheel structure simply due to the mass of the wheel spinning. There are also stresses produced within the wheel structure from the tire beads bearing against the opposing rim surfaces due to inflation pressures. As for the remaining stresses created within the wheel structure due to braking, acceleration, downforce or cornering, they are limited by the traction capability of the tire.