3 piece comp wheels and wheel construction

[sbrats]

Wheel questions
It seems that it used to be that a lot of comp wheels were 3 piece construction. Now it seems that most are 1 piece, any particular reason for this?

Wondering out loud – if one where to look at (and the word is ‘look’ at) making a set of custom wheels – having the required lip data, stress calculations etc. What would be the material selection process and manufacturing process – also post machining and finishing.

You see the custom one off designs from Boyd or Foose (and others) / CNC’d and polished and away they go, just wondering what is involved.

Thanks

 

[CoryPad]

The reasons to use one-piece rather than three-piece wheels are function and cost. A one-piece wheel can be made less-expensively, and it can have higher stiffness/strength since there are no joints.

Regards,

Cory

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[ahbugeye]

Yes, CoryPad has good points. But another one is safety. A one-piece wheel is inherently safer, since there is no connection to come apart.

 

[patprimmer]

I agree with the above comments, however, in addition to the advantages of one piece, there are several advantages to 3 piece wheels

That the rim and the spider or center disk can be in different materials, hence, stiffer higher tensile material might be used for the spider, and a lighter or tougher material might be used for the rims.

It is relatively easy to change rim width and offset.

A damaged rim can easily be replaced without replacing the entire wheel. This allows for much greater flexibility with a limited spare parts inventory.



Regards

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[GregLocock]

Specifically, a steel rim on an alloy centre makes a great deal of sense.



Cheers

Greg Locock

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[sbrats]

I guess then I could ask what problems would be preventing making machined centers out of [late for a one off set - assuming rim details are avaiable

Thanks
Steve

 

[GregLocock]

So long as it is a sensible design then there is no reason not to. After all, many whels are already custom made.


The trick with aluminium is to design something that is strong enough in impact. The trick with steel is to design something that is fatigue resistant.

Cheers

Greg Locock

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[patprimmer]

I was thinking more along the lines of cast aluminium centres, with sufficiently deep ribbing in the design to give suitable rigidity, and spun aluminium rims to give light weight with ductile kerb impact qualities. Spun steel would certainly be more impact resistant, but somewhat heavier. It all depends on what you are really chasing.

Regards

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[GregLocock]

Spinning the aluminium improves its mechanical properties as well. I haven't used a spun aluminium rim, but I have had a lot of steel ones made and they were fine, once we got the thickness right.

http://www.elanfactory.com.au/pdf/technical_information/Re-inventing the wheel.pdf

For some insight. I think I used the same spinners and laser people.



Cheers

Greg Locock

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[sbrats]

Greg - great article. Funny I used to have an Elan and was wondering about the wheels as well.
I was thinking more along the lines of using the front and back rim from a comp wheel - with the required offset and make up a center and bolting these to a center as the Compomotive FF wheels (years ago)

If I treat this as a mental project, I can have some fun with the artistic design and 3d modeling isn't a problem.

1) I am not sure who may have dimensional information of these rims - I used to at one time have an extensive catalog showing the available sizes - but alas no longer. - any idea?

2) Trickier would be the analysis - determining loads to design the center. - suggestions for reading?


Thanks

Steve

 

[GregLocock]

1 T&RA manual specifies rim dimensions , but that leaves a lot of options open. You could do as the Elan guys did and buy rims from a wheel manufacturer.

I strongly recommend this - getting the weld across the rim right is very tricky. If you are in Australia then ROH wheels in Melbourne are a great bunch to work with. (Amazing, Greg enthusiastic about a vendor!). Or more crudely, buy a complete wheel and unweld the spider from the rim.

2 There's an SAE spec for a rolling fatigue load. For a steel wheel that seems to be worst case. It applies a load at 45 degrees to the rim. More generally, design for 6 times the corner load, but you should find that fatigue is the killer. Note that all those fancy bends in the spider are there for a reason - you have to make the thing flexible so that the loads get shared among all the welds. Designing spiders is fairly tricky, more than one manufacturer has had problems with them.

Cheers

Greg Locock

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