the truth about hub fitment

atomic · Postby **atomic** » Thu Jan 18, 2007 12:52 am

So I've read a lot of conflicting opinions about whether or not the hub actually does anything in terms of bearing the load of the car.

Does anyone know the \"truth\" (hopefully substantiated by some conclusive evidence) regarding this issue?

Is it okay for the car to run on wheels that are just held in by the wheel nuts (lugs)?

I have several aftermarket rims I can fit to my car but I'm hesitant since none of their centre holes fit perfectly with the hub of the car. Should I be worried about this?

Thanks

Daz 27 · Postby **Daz 27** » Thu Jan 18, 2007 6:59 am

on my car there is a plastic spacer ring over the centre of the hub to make it the right size for the wheel centre.
the wheel guys told me it's just to line the wheel up properly on the hub but the wheel nuts take all of the load.
my car has been running like this for a couple of years now.

deez · Postby **deez** » Thu Jan 18, 2007 9:27 am

Likewise. When I bought the wheels for my car they didn't have the spacer rings. Went and got some for 8 bucks and they fit into that spare gap perfectly.

RaYmO · Postby **RaYmO** » Thu Jan 18, 2007 9:32 am

U guys talking about the difference between 100 and 113?

deez · Postby **deez** » Thu Jan 18, 2007 9:34 am

atomic wrote:I have several aftermarket rims I can fit to my car but I'm hesitant since none of their centre holes fit perfectly with the hub of the car. Should I be worried about this?

Thanks

I think he means the centre hole, not the PCDs. I could be wrong though

kitkat · Postby **kitkat** » Thu Jan 18, 2007 10:00 am

The hub is meant to take the load of the cars weight... the whee nuts are just there to hold on the wheel.

It doesnt mean the nuts wont do it... we have the rims held on by the nuts and have had no problems. Had the car over a year now, has been around many corners and i've never had any problems.

But as been said... you can get rings to match the size of the hub.

greenMachine · Postby **greenMachine** » Thu Jan 18, 2007 8:02 pm

Rant mode on/

Furphy!

Just another unnecessary americanism ... they call them 'hub-centric' rings, the alleged purpose of which is to ensure that the wheels/tyres are absolutely centred.

Ask yourself what role a piece of plastic is going to play, when the wheel nuts are tightened up ... then the car's weight is loaded onto the wheels ... then the cars is pushed hard through the corners (perhaps on the track with R-spec tyres or even slicks).

And then ask yourself what we did before the yanks 'discovered' them.

As I said, a furphy, but if the yanks use them, they MUST be good - mustn't they?

/rant mode off

What the hell, they are only a couple of bucks, and if you feel better using them, go for it.

Sheck · Postby **Sheck** » Thu Jan 18, 2007 9:11 pm

They're just for centering/locating the wheel on the hub, i've been through a couple of track days and many drift days without hubcentric wheels with no ill effects.
Theres no way a thin bit of metal bout 5mm thick will hold the cars weight better than 4 ~10mm diameter bolts.

It'll be fine, just put the wheels on and post up a pic!

Dave

Garry · Postby **Garry** » Thu Jan 18, 2007 9:50 pm

Theres no way a thin bit of metal bout 5mm thick will hold the cars weight

Have you had a look at what Koni and Bilstein damper's use to support the bottom spring seat? :shock:

Sheck · Postby **Sheck** » Thu Jan 18, 2007 9:54 pm

true, but i did say better than the bolts :mrgreen:

Wouldnt the shock take alot of the weight though???

Dave

Garry · Postby **Garry** » Thu Jan 18, 2007 10:02 pm

Indeed you did but never let the whole truth get in the way of a good story

The weight of the car is supported entirely by the circlip until the damper runs out of suspension travel then the weight of the car is held by the shock body. (Assuming that the springs have been designed correctly and they dont bind before it runs out of suspension travel.)

But hub rings are only used to locate the wheel centrally on the hub to reduce the likelyhood of vibration. If you are using only the wheel nuts to locate the wheel then you need to make sure the taper on the bottom of the nut matches the one on the wheel and to do them up evenly. I have plastic hub rings on my wheels so they wont be supporting much weight.

greenMachine · Postby **greenMachine** » Thu Jan 18, 2007 11:00 pm

Interesting point Garry.

I suspect that the forces acting on that circlip are not as high as you imply. To start with, the gross forces cannot exceed the sum of spring rate times deflection, and all other forces are taken out through the shock rod, bushes and bump stops. It is too late for me to do the maths, but as well as a simple multiplication above, it would also involve the area of the contact surface between spring seat and circlip, and circlip and shock body.

From what I recall of that setup, those forces are acting in shear along the body of the shock absorber, which if I remember my physics is a lot better than some others.

Engineering-wise, I think that the forces there are much more manageable (and moderate) than those at the hub. I think that the dimensions and nature of the materials involved at each location is evidence to support this hypothesis.

Then again, I am no engineer, so what would I know?

EDIT - to calculation above, add in the weight of the car that that corner is carrying :oops:

bruce · Postby **bruce** » Fri Jan 19, 2007 3:37 pm

My understanding is that some cars use the hub to support the wheel. Others use the studs.

No idea what the MX5 relies upon?

Benny · Postby **Benny** » Fri Jan 19, 2007 4:01 pm

I know that many MX-5 race cars do not have hub spacers, and they haven't had any problems.

However, I have always made sure that any aftermarket wheels that I have bought, come with the correct spacer and I do always fit them.
Just about any tyre/wheel place will have them in an assortment of sizes.

Garry · Postby **Garry** » Fri Jan 19, 2007 4:55 pm

I suspect that the forces acting on that circlip are not as high as you imply. To start with, the gross forces cannot exceed the sum of spring rate times deflection, and all other forces are taken out through the shock rod, bushes and bump stops. It is too late for me to do the maths, but as well as a simple multiplication above, it would also involve the area of the contact surface between spring seat and circlip, and circlip and shock body.

Try an experiment.....take the springs out and see how well the shock rod supports the weight of the car. It wont. It will compress until the car is resting on the bump stops. The springs support the weight of the car until they are compressed enough by a large bump (like a pothole) for the bump stop to hit the shock body, the shock body and bump stop then support the car. What is supporting the spring while all this is happening? Nothing but the circlip. All will work fine as I'm sure all the forces involved have been carefully calculated with a reasonable safety margin built in. And you are correct, we are only talking about sheer forces on the circlip. Things start to turn pear shaped however when the wrong springs have been used and the spring totally compresses (binds) Then the larger forces normally taken by the shock body and bump stops are now transmitted through the circlip.