Rear Aluminum Hub/Spindle

[chucked]

Hi there,

We are planning on running rear aluminum hubs for the first time this year. We have run aluminum front hubs and steel rears in the past.

I am worried about the CV ball bearings chewing the aluminum.

we are using CV joints with 6 steel balls of 0.53" diameter.

The hub will be machined out of 7075 T6 aluminum and has 2 AC bearings with an ID of 65mm

We are considering getting it hard anodized to increase wear resistance, but are very worried about its effects on endurance life.

so I am asking for your help,
Has your team run rear aluminum hubs? did they survive the year? were they anodized?

Do you think rear 7075 hubs can survive a race season?

Whats your opinion on getting the hub hard anodized?

thanks for any help.

PS: we are running an F4i with 80-90hp

[fade]

One season? Is that the typical design life of a wheel hub?

[TorqueWrench]

I've heard people say the design life needs to last testing and competition and thats it. Not that I agree with that for most parts, but you could justify it.

[Pico]

We've done similar but with a steel sleeve to give a harder surface for contact. As for the hard anodised surface on the interior you would need to account for the extra 0.001-0.003in added by the coating. Even with the anodised coating you will get increasing play over use (should be allowable for the season). I would suggest a ceramic coating though.

[Kevin Hayward]

A team I was with ran aluminium hubs with tripods. The material in the contact area deformed in operation. The hubs could certainly survive an event, however the team very quickly developed steel inserts.

If you treat it as a Hertzian contact problem you will note that the maximum shear stress in the contact region will be slightly below the surface. With this in mind hard anodising is unlikely to help for the bearing contact stresses, which it certainly didn't in practice for us.

My suggestion is to do some simple contact stress calculations to see if you are in the ballpark of material failure.

The more important questions in this case are:
- Are still opportunities for weight reduction in the steel units?
- Are modifications of the rear hubs one of the best areas for performance increases?


Cheers,

Kev

[Hector]

Because I'm feeling generous...

We tried running Taylor Race tripods in aluminum tripod housings (7075), both anodized and unanodized.

Epic failure within 10 minutes both times.

[Adambomb]

Originally posted by TorqueWrench:
I've heard people say the design life needs to last testing and competition and thats it. Not that I agree with that for most parts, but you could justify it.

Yep, we used to have this design strategy too. Not anymore.

[HoggyN]

We have run aluminium hubs for the last two seasons with no problems. In fact, our budget was so low last year that we reused the same hubs two years in a row. We considered using them again this year.

The CV balls run on replacable (commercially available) steel inserts.

[exFSAE]

Check the Taylor Race website.. Drive Axle Components - Tripod Joints - Housings.

They make aluminum bodies with steel liners to take the contact stress. You can take the same approach.

[RacingManiac]

We ran aluminum hubs in 2005, they are same design front and rear and we've quickly noticed wear in the contact area(tripod style) despite the hard anodizing. The solution at the time was to use it as a replaceable part and we can use the worn one up front(we had 6 hubs made that year) so we were able to use them for the season. But not the cheapest solution and were subsequently back to using steel one in 06 onward. I liked the insert idea but at the time we did not have the time to design for one before I finished school...

[chavez]

Pegasus sells them here:

http://www.pegasusautoracing.c...tails.asp?RecID=5816 (http://www.pegasusautoracing.com/productdetails.asp?RecID=5816)

[BenB]

FYI: I've read somewhere that anodizing reduces the fatigue strength of aluminum.

There was some story in some aviation magazine where some guy anodized some control rod for his helicopter and it failed. Apparently there were thousands of these helicopters made and his was the only one to have a failure. They claim it was because of the ano.

I don't know to what extent it reduces it, but something to keep in mind.

[Richard Pare]

Yes, anodizing reduces the fatigue strength by about 50%. This is because anodizing is brittle, and not very strong. Once it cracks, it starts a stress riser in the substrate. Presto, a part that would normally never break breaks fairly quickly.

The problem with using anodized tulips with your tripods is not hardness, but the compression strength of the substrate. Once it starts to compress, the anodizing shatters and flakes off.

[MalcolmG]

We used aluminium tripod housings in '08 and '09. Our '08 car had a supercharged 600cc engine, lots of torque, big rear tyres (13x8) and won acceleration in Australia. We never had a tripod failure, despite testing for nearly 3 months before comp. The tripods were certainly worn around the balls but still worked OK.

We used 7075 aluminium with no surface treatments or sleeves. We even screwed the design up a bit and ended up with more slop than we wanted and some thin wall sections where we'd counterbored for the attachment bolts.

Obviously it doesn't work for everyone, but it did for us.

[BenB]

Thanks for the information Richard. I had heard that before, but I never heard a good explanation as to what is going on there.

We've done similar but with a new york escort (http://www.newyorkescortsasian.com) steel sleeve to new york asian escort (http://www.newyorkescortsasian.com) give a harder surface for contact. As for the hard anodised surface on the interior you would need to new york escorts (http://www.newyorkescortsasian.com) account for the extra 0.001-0.003in added by the coating. Even new york asian escorts (http://www.newyorkescortsasian.com) with the anodised coating you will get increasing play over use (should be allowable for the season). I would suggest a ceramic coating though.

[RacingManiac]

I think part of the problem may also to do with the kinematics and the amount of plunge and movement the driveshaft experiences due to suspension travel. I think in our case it just always wear the same spot...

The anodizing issue makes sense. Something else to think about...