Hubcentric Rings
 

No idea what they are or what they do? Heard of them, but aren't sure if you should have them? Here's a quick rundown about Hubcentric rings.

When looking at wheels, you may have seen rings like this:
http://farm9.staticflickr.com/8430/7...32508d8f_c.jpg
Just a circular ring with a flared base.

This is a hubcentric ring. It fits between the center of your wheel and the raised center of your hub.

Here are a before and after:

(Before)
http://farm8.staticflickr.com/7264/7...15a078ac_c.jpg
Parts from the center, outwards:
Axle Spindle
Axle Nut
Hub Lip
gap
Wheel Center
Lug Nuts (fastened to lug studs)
etc.

(After)
http://farm8.staticflickr.com/7247/7...b9c339b5_c.jpg

If you look closely at the Before picture, you will see a gap between the Hub Lip and the Wheel Center. Look at the After picture and you will see that the hubcentric ring fills that gap. The lip on the ring retains the ring behind the wheel.

So no unsightly gap. What else does it do?

That raised lip is part of the hub.
A simple diagram:
http://www.motorera.com/dictionary/pics/W/wheel_hub.jpg
This is a very strong piece as it supports the weight of that corner of the car, holds the wheels on, mounts the brake disk to stop the car, and in the case of driven wheels, attaches to the axle and transfers the engine's torque to the wheels. So it's safe to say it can handle a lot of forces.

When you fill the gap between your wheel and the hub with a hubcentric ring, you're letting the forces acting on the wheel (bumps, potholes, cornering force, etc) transfer directly to the strong hub. Without that gap filled, these forces have to go through your lug studs.

Is this catastrophically bad? Not necessarily. There are plenty of cars with aftermarket wheels that aren't hubcentric that are probably perfectly fine. But these cars might not see pothole-ridden roads or racing. The issue is that OEMs make their stock wheels hubcentric. The wheel centers are the right size on their own to snug around the hub. This makes for a stronger wheel, and the lugs only have to be strong enough to hold the wheel to the hub. Meaning, OEM lug studs are not hardened. They are not designed to bear the entire weight of the car.

So those using the OEM lug studs should use hubcentric rings if they are planning to use their new wheels for racing, off-road use, or just have to deal with a lot of potholes. Not doing so runs the risk of shearing off the lug studs.

So any other reasons to get them?

An added benefit to hubcentric rings is that they will center your wheel on the hub, making sure it is perfectly aligned. This will cut down on the chance of unevenly tightened lug nuts causing the wheel to vibrate. When fitting a hubcentric wheel, you'll be able to spin it slightly back and forth on the lug studs before you tighten the nuts. This will show that the wheel isn't resting on the lugs but on the hub itself and is perfectly centered.

I can't get hubcentric rings for my new wheels that will fit my car, what do I do?

Don't panic. Just don't abuse your lug studs. Try to miss big bumps and potholes. Don't haul @$$ over speed bumps. And don't do track days or heavy AUtoXing. If you do want to do these things, replace your lug studs with hardened ones from ARP or a similar company. They are much stronger and can bear the weight of the car better than the OEM studs.

I hope this helps clear up any confusion. Obviously I advocate hubcentric rings for ANY replacement wheels that aren't naturally hubcentric for the car. I haven't yet seen a modern aftermarket wheel that wasn't able to fit Subaru hubs with a ring.

Thanks, great post. My understanding was non-OEM wheel have a different contact surface to your hubs compared to OEM wheels. As a result, they may cause non-optimal wear to your hubs/bearings. Hubcentric rings help distribute load more evenly to your hub. I've heard the whole bit before about the wheels studs bearing the weight if no hubcentric ring is there; the OP details all of that.

You may have wanted to at least read the first three sentences....

Yeah I edited my post. I sort of skimmed through at first and thought you were confused about their purpose. :bonk:

I'm hearing conflicting facts regarding hub rings. Some (like you) say they carry the load while others say it doesn't. They claim the sole purpose of the hub ring is to help you easily center the wheel while mounting. I kind of agree with you that the hub ring does carry the vertical load but if that is the case, why are most rings made of plastic?

I've bought 5 sets of aftermarket wheels, and all but one used metal rings. The set that weren't were a high-impact composite, kind of what Rhino ramps are made of. Maybe some companies use cheaper plastic to save cost. In that case, then they would only be good for centering the rim. But the good ones will take a hit and direct most of the force of an impact directly to the hub.

If you tighten the lugs down correctly, it's the static friction between the wheel surface and hub which hold things in place. The lug nuts just provide clamping force, they don't carry any load, unless of course you don't torque them down properly. Hubcentric rings do not carry any load either, they are only there to help center the wheel before you tighten it down, in fact most hubcentric rings are cheap plastic or aluminum.

With the tapered lugs on the Subarus if you torque down the lugs in the correct order (star pattern like a flywheel), the wheel will almost always be centered on the hub. I've used non-hubcentric rims for autocross (16x10s...), track, etc. for years and never had any issues. People get in trouble with the plastic rings when doing things like tracking the cars because they can melt or metal ones expand since they aren't the same as the wheel and the wheel gets stuck on, etc...

I'd use them on street wheels, they make the wheel easier to mount and you won't get weird vibrations from screwing something up and the wheel being off-center.

I don't think hubcentric rings bear the load; the bearings do that. The rings merely channel/distribute the load to the hub instead of the studs. Everything touching the hubcentric rings is static and is supposed to be mated tightly together so they don't see drastic impact forces that would cause them to shear/fracture. Most of the impact gets directed to the bearings/suspension.

Well, I would rather have them than not for the reasons outlined above. Lugs can shear, so anything that can help minimize that is a good thing in my book.

Studs generally only shear if the nuts aren't torqued correctly. If everything is true and torqued correctly, they do not carry any load. The wheel sits on the lugnut, people use fairly soft lightweight aluminum lugnuts all the time. If they were carrying sufficient loads they would probably deform.

I will say Subarus are not known for having the strongest wheel studs in history, they are very prone to breaking if they are undertorqued. Not sure if the BRZ is the same but you can find many failures on later gen Subarus. If they are undertorqued then you are putting load on the studs and I've seen someone shear all 5 at one time on a rallyx course. 99% of the failures are with stock wheels, which of course are hubcentric.

For a car seeing heavy track use I would probably just replace the studs with some ARP ones or something similar. With these cars you don't have to press out the rear hub to change the rear studs like the older WRXs, so that's a bonus.

This is what I mean by the conflicting facts but I guess we all agree that using hubcentric rings can't hurt and its a good idea. You can get a set of plastic ones for $8 anyway.

This ^^^

Yeah, they don't bear any load, until they do, and then the difference could be the wheel falling off and going home on a flatbed vs. keep on driving home on a bent rim.

A little off topic, but are those McGard Spline Drive lugs? If so, how do you like them?