Force diagrams for an automotive rim 1

[RaverWaldoEE]

I am trying to design a custom automotive rim, but I am not a mechanical engineer and I would like some help in finding an existing drawing or diagram outlining the forces acting on a rim and how to balance them out with thickness and structure. I understand moments about the axes and simple physics, but an existing drawing would be much easier than starting from scratch. I'm not looking to infringe on any patents, just somewhere to start.

thanx

rich

 

[GregLocock]

You might want to check out the Tyre and Rim Association's handbook. That at least covers the internal profile of the wheelwell. Get that wrong and you will struggle to fit a tyre.

As to the forces. Things you need to consider are one off events like potholes and kerbs, and then the rotating fatigue events.

Are you designing a steel wheel or an aluminium one? each has particular problems. fatigue of the flange is surprisingly common, as it flexes with each rotation. design of the spider for steel wheels is also a big fatigue issue. Alloy wheels tend to have more trouble with the impacts.
Cheers

Greg Locock

 

[RaverWaldoEE]

I was planning on designing an aluminum or alloy wheel for its weight and because it is so widely used. The wheel should allow for oversized brakes and be relatively sporty, designed for mild road racing situations. I also wanna design it to allow for many different bolt patterns and sizes should range from 16 - 19. I haven't decided on the width yet, and that will depend on whatever works well for a variety of vehicles. I would also like to allow for truck and SUV applications, for dress or speed opposed to off road capabilities, but if the added weight will cause a problem then I can do without.
I have another question, if I wanted to design a remote PSI sensor,to be installed in the rim, what is the best way to machine a hole or threads in a rim without worrying about it leaking? I know that it is a lot, but I am ambitious!

thanx

rich

 

[GregLocock]

I think you'll need to accept that one wheel designed to do all that won't be optimal for anything.

In an alloy wheel the structure of the webs around the bolt holes is crucial to maintaining the stiffness and strength across the spider. Therefore you will find it difficult to design a spider that can accomodate much variation in the bolt pattern.

If you want a leak proof seal in the rim just use a valve body - the T&RA book specifies the dimensions, and the mating part is easy to obtain. Unscrew the valve's guts from inside the body and you have a perfect leaktight pressure port. T&RA gives the thread size, which is some weird combination of inches and millimetres.

I think you will also find that there is very little in common between a 15 inch wheel and a 17 inch wheel. As a guide the spider for a 14 inch steel wheel is made from 3 or 4 mm steel. That for a 16 inch wheel for the same car is made of 6 mm plate.
Cheers

Greg Locock

 

[celrifai]

Were Can I find the tire and wheel association Handbook?

 

[celrifai]

This is the website for the tire and wheel association.

http://www.us-tra.org/main.html

The handbook can be bought on CD-ROM and will set you back $65.50 .

 

[fxengine]

RaverWaldoEE, I realise that one of your original posting is well over a year old...do you now design your own car rims. It's a field I have been trying to get into but with no luck. I want to design rims, no one seems to know how to get started in that field. Anyones help would be appreciated, thanks.

 

[GregLocock]

OEM rims are mostly styled in the styling studio. The resulting sculpture is then flicked over to the wheel manufacturer, who attempts to design a manufacturable wheel behind it. Then we do some CAE work to see if it is strong and stiff enough. Inevitably it will fail someone's requirements and you go round that merry loop a few times. Finally when the stylist has been beaten into submission we make a wooden pattern and sand cast a few to see if they look any good on the car. If they are then a proto diecast tool is made and we test them properly. The sandcast step is a luxury, you don't learn much. I don't know how to get into styling, it's its own little world.

Aftermarket wheels seem to be designed by copying other wheels, or developing fresh shapes (it must happen somewhere!) in-house. The obvious approach there is to send your designs in to a wheel manufacturer.

Cheers

Greg Locock

 

[MASSEY]

RS Technologies Ltd. & Caesar Data Systems build really cool wheel force transducers to measure force on rims. If you do come up with a design or want to know what forces you are going to encounter - they could be very helpful.

Let me know if you want more information.