Rim Design Help

[Simactive]

Hey all,

I was wondering for those team who have designed in house rims out of mystery material. When doing your analysis did you included the K (spring) value of the rubber tires into the calculations for the impact forces, inertial forces etc or was that left out?

I am looking a redesign of our wheel centers for our team and started going through the calculations and life cycle analysis (with worst case scenarios but then it dawned on my I didn't included any effects the tires have on any of this.) I am leaning towards if I run my analysis with all my calculated and measure forces acting directly on the rim that it will just increase my safety factor overall.

Our wheels are too heavy right now but I don't have enough resources to go for a full out CF design.....just yet.

Also regarding too FEA simulations I have been running it through with just the wheel center themselves since we have 3 piece rims. Would it be advised to do it with the whole assembly since that is more realistic (with or without tires) if with tires any suggestions on a decent method to add into the mix?

Thanks any comments are welcomed.

[Charles Kaneb]

The first question is - are you OK with the wheel rim being destroyed if you suffer a blowout, or a puncture with a bad driver at the wheel? If not, then that might drive your rim load case!

[mech5496]

Most importantly, keep in mind that camber compliance would be a much better target when pursuing wheel design, together with fatigue strength. And what if I tell you that you do not need CF wheels at all?

[Kevin Hayward]

I'm with Harry. Design for stiffness and fatigue strength. You can go a very long way to making lightweight Al wheels just by working towards evenly stressed material under expected load cases. Most wheel designs I have seen (commercial and student designed) don't achieve this. Lots of areas around attachments where there is way too much material, and spokes (or equivalent) with obvious stress raisers.

Early on the ECU guys designed wheels using pre-existing commercially available wheels as a standard. These wheels were commonly available and used by a lot of FSAE teams. The first ECU car used them successfully. The goal was to make the new wheels just as strong, reduce manufacturing effort, improve stiffness, reduce weight, and reduce cost. All targets were exceeded considerably. In the end the strength became a non-issue. Due to wanting the wheels to handle a bit of abuse (i.e. limit minimum wall thicknesses) the wheels were strong enough by a large margin, without having to include rubber reducing impact forces. Designing to strength equivalence is a lot easier than determining the proper load cases. The driving loads are pretty easy to figure out, but the big question would be what sort of impact would you design to?

I should note that the team has had much more success reducing weight through careful geometric design and consideration of load paths than by replacing one material with a lighter one.

Kev

[Simactive]

Charles - Hmmm true I never really thought of a tire blowing out since I don't see it often or ever on FSAE.

Harry - True I don't see the need for CF for our vehicle at this time honestly. I am working with what we have at the moment and how much I could afford to donated material haha. Thanks for the tip I am trying to keep those in mind.

Kev - Thanks for all the tips and hints. Yeah I think that is what is taking the most time for me now is to figure out all the best load paths and structure of the whole rim design. See how far I get with the calculations and then test them to see if they match.

Guess I am going to leave the tire out of the calculations for now. Maybe I'll be able to get do some more after Christmas when the workload reduces.