This has been rolling around in my head for a while and I finally got time to put together a prototype proof of concept.

The problem:

The miata front wheel bearings are rather small for 1.5G loads and regularly fail under severe use. The hub itself is also weak for the loads imparted on them at high G loads. We've all seen the scary failed hubs floating around here and the bent up cars that go along with them.

Possible solution:

Spec E30 is arguably the next most popular racing series behind spec miata. Those guys don't seem to have the bearing life problems we have and no one has ever broken one, at least not that I've been able to find, you'll see why here in a min. I'm seeing life expectancy 10-20 race weekends, 100-150hrs or years in auto-x / HPDE duty. Same as us they seem to get better life out of good known quantity bearings such as ***, Timken, and OEM. They too also get better life when they are re-packed with good grease. They also seem to run in the 80-120$ range for bearings. This is all on a minimum weight of 2700 lb's. Knock 500+ lb's of weight out of the car and these numbers can only go up.

You can see why they don't break them. Beef....it's whats for dinner

These are a ball bearing design but the bearing diameter looks to be bigger than ours by a large margin. The fact that they are lasting as long as they are in a heavy E30 chassis is encouraging.


Luckily the bolt pattern is the same as ours......and that's about the only thing that is the same between them.
Problems:
Bearing ID is too big
Bearing height is slightly shorter
Offset is too shallow
Rotor register is the wrong size
Wheel register is the wrong size
Uses wheel bolts instead of studs

To address the issues first you need a sleeve to get the spindle up to the bearing size.

There's some funkiness in this because of the radius at the bottom of the spindle snout.

Now that bearing fits on the spindle, the bearing stack is shorter than the miata bearing so the nut won't seat. Another bushing/adapter fixes this.


Now that the bearing is firmly attached to the spindle......the rotor won't slide on and it's no where near the right offset. Enter.....a wheel spacer. This will address the rest of the issues. The bearing side of the spacer is machined to fit the BMW specific rotor register. I machined the wheel side to fit the miata rotor register which is slightly larger than the wheel register. Now there was one problem, the wheel register on the BMW bearing was too long and would have protruded into the area taken up by the miata specific hub centric registers which is smaller. I had to machine that off leaving only the rotor register to center the adapter. I really wanted to be able to use an un-altered bearing so I could grab one from the store and slap it on at the track. The good news is this can be removed rather crudely and not affect anything, in theory you could lop it off with a hacksaw.



Finished pieces in a pile.



I've got my wheel stud conversion kit on order, when it gets here this setup is ready to be installed and tested. This is a cheap 20$ bearing I bought for mockup purposes, so I'll replace it once I know there are no hidden gotcha's. I don't have any other track days lined up for the year so it'll be some time before I can track test it, but there are 1000's of hours of E30 use to backup the strength of the bearing. Even if the bearing life isn't forever I don't see any chance of a failed hub with this setup.

Thoughts? Suggestions? You think this might be an alternative to the plethora of tapered roller bearing setups hitting the market?

 

I think that the failure point has now moved to the spacer/adapter. Aluminum, stress raisers and fatigue do not work well when combined.

 

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Pretty common place to run wheel spacers and no one breaks those, granted this mock up has quite a few unnecessary holes that I wouldn't have if I started from a billet. How would you think it would fail?

Art, not sure I follow.... Are you just saying a spacer will freak people out?

 

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Gotcha.....yeah I wouldn't think joe blow would have the means to make this themselves. I wanted this discussion to be a technical review in nature, if there's interest in something like this in a bolt on kit that's a whole nother discussion that starts with the mods responding to my PM......

 

I have used spacers in the past myself in a street car. They are not necessarily a bad thing per se, but I would hesitate to use those in a highly stressed racing application. IMO, and totally by eyeballing the whole thing, the material left around the bolt recesses seems too thin. I can always be proven wrong, but if I had to take a bet on what will fail 1st, that would be the spacer

 

Well wheel spacer failure theories are a huge topic you can find a lot of opinions on and not a whole lot of facts. You have to dissect any failure down to the forces involved and the strength of the materials. A slip on spacer which is what this one is now that I've removed the studs is only really loaded in compression, of course that's a bit of a simplification but the wheel studs are compressing the wheel and rotor hat against the spacer and the friction on the faces is transferring that force to the hub. This is the basics of any bolted connection, the shear of the bolts/studs themselves also play a role. This is what holds your wheel on the car. The hubcentric nub in the middle is there only to line everything up, this is why you see plastic hubcentric adapters provided with wheels when needed. If you google wheel spacer failure you'll see that with bolt on spacers the studs will pull out of the spacer, this is because the spacer is loaded in tension from the second set of studs. When you go into a corner you have one set of studs pulling at the spacer towards the wheel and another set pulling it towards the hub setting up a shear situation. In that case the spacer has to be sufficiently thick enough and of the right metallurgy to not fail.

Told you all that to say, because the spacer is largely loaded in compression and not tension the spacer will not fail. It takes a tremendous amount of force to crush a chunk of aluminum like this. Yes getting rid of the unnecessary holes and making a smooth spacer with just the needed 4 holes for the studs would be ideal, I'm not equipped with the right tools to be able to drill bolt holes with the precision needed so I skipped a few machining steps by starting with a spacer with the right bolt pattern and at least one of the right hubcentric diameters.

 

It is not just compression. Cornering loads (perpendicular to the wheel plane, at the tire contact patch) should be counter-reacted by the wheel nuts/studs, which see a cyclic load from compression to tension; it's frequency can be calculated from the speed and tire diameter at any given point. Preload acquired through torqueing down the wheel nuts, results in studs being permanently under tension, however, think what happens between those two bolted connections (wheel to spacer, spacer to hub) if you had a really long lever bolted at the same points as your wheel, and pulling/pushing it really hard

 

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Of course cornering loads will affect load, on a loaded corner the wheel will add compression to the bottom of the spacer and pull on the studs at the top. If you torqued your lug nuts sufficiently the total sum will not go below zero at the top and the additional force on the bottom will in compression. Again are you suggesting this spacer is going to crush from the leverage? We haven't even began to talk about axial torque from braking. In the end this is all the same loads the wheel to hub interface sees and you don't see rampant failures. It's VERY common to use slip on wheel spacers in racing, it's one of the main reasons that most if not all racing oriented wheel studs are so long.

I guess I'm not following how exactly you think this is going to fail.....

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Never got one.

 

I think people are assuming that you're using them as bolted spacers, since that's what they started out as / still resemble. Maybe you need an "I AM NOT USING THESE AS BOLTED SPACERS" disclaimer for attention

 

Nothing wrong with this thread, discuss away. If you get tons of interest or enough for a group buy then vendor status will be needed.

I think you'll need to put in some serious track/testing time for anyone to really get excited about this, since so far all I see is "welp, it looks beefier, and doesn't fail on a heavier car as much...so....."

 

Oh. Crap. I was 100% sure these were intended as bolted spacers. If not, please ignore my rant.

 

Lol, ohh hell no this won't be bolted, I don't have a death wish.

Aidandj, sorry missed you on the initial blast.

18psi, thanks for the input and I get your point. After I get some initial street testing done I'll get a set into the hands of a track junky for testing this year hopefully. I guess I just looked at these bearings as a known good commodity in the BMW world, they just needed adapted to fit.

 

Interested in seeing how these hold up. You should find a wrl or chump or lucky dog endurance team to give them a real test.

 

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Yeah but did it handle like it was on rails?

 

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