Wheel spacers ... safe or not ?

[MikeLMR]

Right this is a little bit less of a question and more of a start of a debate ?

Now I have read all sorts of things about wheel spacers and would like to get some other opinions on the matter.

This is my way of thinking. Wheels are held onto the hub by the tension in the wheel studs/nuts or bolts. That is their only purpose ... to provide that tension. The wheel is prevented from turning and moving in relation to the hub by the friction between the hub and the wheel ... the studs should take ZERO radial (shear) loads ... they are not designed to do so.

Therefor if a spacer is added between the two (say <5mm) and assuming the friction coefficients are the same there is no difference between the two setups.

any more opinions ? I\'d like to get this one clear in my head  :wiggle

[Tintin]

I\'ve been through this with Pip recently , I couldn\'t get the wheels I liked in the right width for the rear of my car , I needed to soace them out about 1/2" to bring them in line with the body kit

I ordered some spacers and extended studs ( the studs are a bitch to fit as you have to dismantle the hub to get them in )

If you look at the hub you notice it has a shoulder on it and when we actually fitted the wheels back on with the spacers we noticed that the wheel no longer sat on the shoulder , this could pose a problem as the suds are not designed to take the weight or pessures aplied by the wheel they are only to keep the wheel tight to the hub , I did run the wheels like this for a while but you have to check to torque settings of the nuts all the time to make sure there just right , no longer can you just tighten them up as tight as you like . This got a real pain so I spoke to Pip about getting some custom spacers machined up with the shoulder on them , a few weeks and £40 later the new spacers where on and they worked a treat


The wheels are now saftly in line with the kit and it only cost me a small fortune ( rebuilding the hubs with new bearings is quite pricey )

[chrisBoid]

Interesting point, I had never looked at it that way before.
Can the friction under tension be enough to avoid loading the stud at all?

The way I always looked at it was from a simplistic (I\'m simple) physics point of view, the further away from the ?fulcrum? you apply force, the less force is needed to move/break.

The fulcrum is where the stud attaches to the wheel and the force is the weight of the car.  The further the distance between them, the less force is needed to snap the stud.  This reasoning was enough to justify buying new rims when I had my wide arches fitted as I was looking at having to use 20-25mm spacers.  I remember investigating longer studs and found that longer studs were machined thicker meaning drillling of the existing holes.  Would they be machined thicker if they thought no more stress was being applied to them?  Or were they just being safe?

I have no idea what difference 5mm would _actually_ make though.

Are you coming from a racing point of view where the stresses would be greater?

[MikeLMR]

On the hubcentric thing.

The central spigot should not be loaded at all, it is just there to align the wheel and to ensure it is concentric with the hub when the studs/nuts and bolts are tightened ... the shoulder should not be loaded at all. But I agree if the wheel and hub are designed to be hub centred (not all are) it shoud be included in the spacer.


On the friction forces being enough

The tension pulling the two faces together is huge.

say 100Nm of torque is applied to each bolt. Now using online bolt tension calculators thats roughly equal to a bolt tension of 45.58KN per bolt/stud&nut

Say 4 bolts (just because 4 is lower) so thats a clamping force of 182.32KN total.

Now the coefficient of friction is a tricky one as it varies with the materials but a number on the low side of things is about 0.15 for a clamped joint

in this case the force required to make the two joints slip is the coefficient of friction multiplied by the clamping force so

0.15x182.32KN = 27.348KN or 27348Newtons

to give an idea that would support around 2 3/4 tonnes in weight before it would slip.

is that enough ... I\'m not sure (some of my numbers may be more than a little dodgy but its in the ballpark)

[MikeLMR]

a good website with an example of wheel stud failure and backing up what I said ... a wheel hub is just a flanged joint btw so all the same rules apply.

http://www.boltscience.com/pages/failure4.htm

[Mazdarotaryparts]

Hi Mike, Paul n Chris,

We sell 10mm spacers and longer studs but would not sell anything wider but not really for the reasons stated !

As has already been said, its the "clamping" effect that holds wheels on and is nothing to do with spigots as these only locate the wheel in its correct position before tightening .

The reason l won\'t sell bigger is because of excessive load on wheel bearings and also if you shift the wheels to far in this manner you will alter the steering geometry.

I am going from hands on experience when l used 10mm spacers with sticky 10" wide slicks on circuits for a number of years and had no problems.

Hope this helps.

[chrisBoid]

Interesting read.  I always thought that a wheel falling off a lorry was due to the studs all unscrewing themselves  :rolleyes: but all it takes is the studs to slacken off a bit, reducing the tension, causing the studs themselves to be loaded and shearing off.

So as long as you keep your studs tightened correctly, everything _should_ be okay.  But keeping them tight is a constant battle it would seem.

[Gerry M]

The spacers I have on mine have 2 sets of holes, one set counterbored to take the nuts. These bolt into the original P.c.d, The other set are threaded I think, but could be splined, for another set of bolts in correct P.C.D.

H & R make ones similar & are TUV approved. They look like this

I\'ve used longer studs & spacers on other cars & do agree it puts more load on the wheel bearings

[Gerry M]

the centre spigot doesn\'t carry any load, and that there is no shear load on the wheel bolts either. The load is transmitted through the friction between the axle hub and the wheel, and the purpose of the bolts is to clamp the two tightly together to maximise the friction. So the bolts are only subjected to tensile loads, and the only reason for the centre spigot is to centre the wheel before you do the bolts up. Many older cars don\'t have a centre spigot, and the wheels only fall off if you don\'t do the bolts up tight....

Wheel bolts should achieve sufficient clamping force to prevent movement of the wheels. The studs should not be a tight fit in the holes, but should be centred by the tapered seats of the nuts, and/or by the spigot. All these factors are important. Older cars probably survived because cornering forces and wheel loadings were somewhat lower.

Under cornering there is a degree of distortion of the wheel centre as the wheel is loaded. This is why poorly fitted hub caps usually disappear on corners.

Aluminium alloys behave differently under load than steel. They don\'t display a clear elastic limit, and even a high strength Al alloy has an Ultimate Tensile Strength well below even the elastic limit of a mid range steel. Size for size Al alloys exhibit greater deflection for a given load. In some ways not an ideal wheel material, and as has been mentioned, unless of high quality, unlikely to display any great weight saving. This all means that unless alloy wheels are properly designed the distortion in service will be greater than in the steel wheels. Because of the increase propensity for distortion, the clamping load of the wheel studs will be critical. No doubt recognising this, some carmakers specify a greater wheel bolt torque for alloy wheels compared to the steel wheels.

A properly sized wheel will have the close fit on the spigot, and this will tend to limit movement in this crucial area, should the design of the wheel be marginal causing excessive distortion of the wheel centre. This extra restraint will be absent if a plastic spacer is used, as this will only centre the wheel during installation. Therefore it\'s feasible that a combination of marginal wheel design combined with a lack of support at the spigot could lead to problems, and in any case the centre spigot provides some extra security if the wheels are subject to high loadings

[clive]

Interesting read.  I always thought that a wheel falling off a lorry was due to the studs all unscrewing themselves  :rolleyes: but all it takes is the studs to slacken off a bit, reducing the tension, causing the studs themselves to be loaded and shearing off.

So as long as you keep your studs tightened correctly, everything _should_ be okay.  But keeping them tight is a constant battle it would seem.

Your exactly right Chris

[Tintin]

So either I have misunderstood what Pip has told me or his info was incorrect

Probably more likely I haven\'t understood , however I have had no probs with my spacers

[Martiny]

Whilst I find the theory interesting..... no spacers for me, thanks!

[MikeLMR]

some excellent points there

I feel happier now using a 4mm spacer to correct the offset of one wheel (got one odd alloy in a set of 4)