Wheel Spacers - Good, Bad or Dangerous ?

Ian Anderson

Member
Lifetime Supporter
#21
Me again and no more laws etc!

I just spoke with our company's metalurgist and asked his opinion.

He said he would not see a problem with it, you would have to extend the studs to get a coverage on the nuts. The male portion of the joint will show signs of failure first so keep an eye on the studs!

He also said he would only suggest utilising the same material as the original studs and not go higher tensile.

The friction joint between the 2 faces, hub to spacer and spacer to wheel should be as large as possible so as to get the greatest possible friction joints.

He did state that the studs should be tensioned to the correct torque and that under torquing would be more dangerous to over torquing and cause failure much more quickly.

I asked about aluminium for the spacers and he was not of the opinion this would be a good idea - too different compared with steel / iron on friction coefficients.

Now presumably this opens up more questions and I will pose these to Roger - I asked if I could sign him onto the forum and he declined. (By the way Roger was involved in the analysis of stud testing with the ministry of transport UK when they worked on the loose wheel syndrome - this bloke seems to have been involved in loads of testing!)

Ian
 
#22
I would use 7075 T7 or 2024 T3 aluminum. With the proper flanges locating the wheel to spacer to hub the friction necessary is not that relevant and aluminum to steel is quite sufficient.
 

Peter Delaney

Newbie
GT40s Supporter
#23
Thanks guys for all your input. Its hard to try & distill all the info, but my gut feelings are that spacers are ok if :

- they are correctly indexed to the locating lip on the hub & the wheel.

- the rotational torque/stress at the spacer/wheel interface is taken on clear shanks of the studs/bolts & not across threads.

- it makes sense to secure the spacers to the hubs if you can.

- aly vs steel - that's a big question. In a race car setup, unsprung weight savings & regular checks make aly look like the choice, but in a road car, I suspect that the bit of extra weight for steel is worth it for the stability of the hub/spacer assembly.

- stud length is also a controversial issue - do you mount them just thru the spacer or run them right thru the hub+spacer ? My feeling is that spacer-mounted studs would be ok with steel spacers, but that I would be worried about the fairly small flange area of the stud-ends in an aly spacer unless the lug-nut torque was regularly checked.

By now, you have all figured out that I am fairly conservative - I make no apologies for this as I still remember when I first learned of the "factor of safety" concept when studying engineering at uni. Prior to this, I had assumed that engineers just calculated everything correctly, then built stuff. Wrong - they do all the calcs (using slide rules in those days), then ask the question : "what if I got it wrong" ? Simple answer - multiply everything by a "factor of safety - say 2 or 3" !!

Hence my inclination is to take the whole "belts & braces" approach :

- indexed spacers
- spacers bolted to the hubs
- steel spacers
- studs thru hub & spacer

Kind Regards,

Peter D.
 
#24
I didnt read ALL the answers in the treat so I might repeting things.

First, ther is generally no strengh or centration problems involved in a properly made distancer. However, the rest of the A-arm system may not be designed to carry very wide spacer load, but the same goes for big offset wheels.

Big scrub distance is greatley affecting wheelrate if the A-arm system is much cambercompensative. Short and steep angle upper A-arms is not to be used with much scrub if not
she spring system is designed for the matter. On my site
http://hem.passagen.se/hemipanter/ (fare down the site) ther are a number of images that show the influece of scrub distance.

Also, I got a friend hurting his thumb very bad by a rotating steering wheel while driving over a larger road obstruction.

By the way, if wiwiting my site, ther is some images form my latest Pantera design bodywork. A little F40 front influece....

Regards
Goran Malmberg
 
#25
I prefer not to use a wheel spacer because there are greater chances of having problems associated with it. I would strongly suggest getting wheels that have the correct offset from the beginning than trying to make something work. I would choose an adapter over a spacer. aftermarket wheels are made for several types of vehicles the center hole of the wheel is usually larger than your hub. this requires the lugs to center the wheel. adding spacer will cause vibration and will put stress in your lug. longer studs and a specific type of lug nut will make it secure
 
Last edited by a moderator:
#26
All,

The following is an excellent discussion on the use of wheel spacers
by two mechanical gurus of the NorCal Shelby Club, Don Wollesen and
Scott Griffith (Skod).

The discussion took place on Jun 14, 1998.

The internet is forever. :laugh:

Mike


------------------ Dave Dwelley asked: --------------------------

Why are wheel manufacturers so uptight about wheel spacers? I'm at
the point where I'm buying wheels for the Falcon, and because it's
fenders are so tight, I'll need to get the offset just right - that almost
assures I'll need wheel spacers. I can see how a 2" spacer might
overstress the wheel studs, but 1/8"? I don't even lose the ability to
center the wheel on the axle center! Not that most of the aftermarket
wheels seem to care - they all seem to use the lugs, not the center,
to align to the hub.

-------------------- Scott Griffith replied: ---------------------

The same reason that we frown so heavily on wheel spacers on track
cars: they really *are* dangerous, and they really do create
additional loadings in the studs that can quickly exceed the ultimate
tensile or ultimate bending strength of the studs and lead to an
outright, catastophic failure.

When you have a wheel bolted directly to a rotor (or a drum) with no
spacer, there is only one single shear plane. If there is slippage at
that plane, you induce a bending load in the stud. You also increase
the tension load in the stud by a value proportional to the sine of
the bend angle. However, the bending moment is applied essentially
right at the stud root- the loads are contained to the shear plane, so
the total bending load is controllable, and relatively small, since
the offset is nearly zero. It is essentially a pure shear load.

But if you interpose a spacer, then there are now two shear planes.
The makes slippage of the wheel with respect to the drum/rotor much
more likely with braking or drive loads, since there are two sets of
surfaces to clamp. But much worse than that, the bending load is no
longer applied right at the root of the stud. It is now applied
whatever the spacer thickness is *away* from the stud root. The
bending load is thus proportional to the spacer thickness, and if that
thichkess is nonzero, the load goes up *fast*. Even worse, the
increase in the tension load is proportional to the square of the sine
of the bend angle (if I remember correctly), and that value goes up
*unbelievably* fast with increasing bend angle. At that point, the only
question is whether the stud will fail from accelerated fatigue
cracking due to the bending loads, or just fail in a brittle mode from
the tension overload. This is not a contest you want taking place on
your car.

Bottom line is that running a 1/8" spacer probably reduces the
ultimate strength of the assembly by a factor of 2, and the fatigue
life goes to hell as well. With a 1/2" spacer, the loads can exceed
the ultimate strength of even the best quality studs, and the fatigue
life is nonexistent. I have seen an instance where a friend of mine (a
chassis engineer at Ford, in fact) sheared 4 of the 5 ARP 180,000psi
studs on one front corner in a *single stop* with a 1/2" spacer, even
when they were properly torqued- just to prove the point of the risks
involved in running spacers. Moroso studs, or some of the other
somewhat brittle "race" studs, have no chance whatsoever when run with
a thick spacer.

Don't run loose spacers on the front end, at all, ever, on a track
car. They might be acceptable on the rear (since the braking loads are
so much less), or on a delicately-driven street car, but not one that
I own! For a car that will see threshold braking into a corner where a
stud failure is likely to result in a trip to the toolies, they are
just flat unacceptable. While we do not have a blanket prohibiton
against wheel spacers in the tech rules, there are solid engineering
reasons to avoid them like the plague. We've been trying to slowly
educate people about them as time goes on and cars go faster, one on
one- but this is a good time to bring it up again. If somebody shows
up at Nini Nats with inch-thick spacers, we'd probably park them. It's
always fun to look at Super Ford, and see pictures of the drag racers
who've blown their rear studs out at launch, and try to blame the
studs...

If you absolutely, positively *must* run spacers to make the stackup
work on your car, you must machine them for some hardware (perhaps
reamed dowels and countersunk socket-head cap screws) that you can use
to rigidly lock out one of the two shear planes. Studs will handle
single-shear-plane loadings all day long, if properly torqued, but
they die *fast* with two shear planes and the resulting increase in
bending and tension loads.

One of these days I'll pull out a chunk of graph paper and redo the
derivation of the bending/tension load changes for an example case. I
did it once before, and the numbers really are mind-boggling. Maybe I
can find my notes- but it was 10 years ago...

-skod

----------------------- Don Wollesen replied: ------------------------

Good post, Skod.

However, a few comments from the peanut gallery.

IF the studs are well torqued, then the wheel to hub is (well, SHOULD
be) attached by FRICTION and NOT dependent on the shear or bending load
on the studs. i.e. if the spacer doesn't flex any (it does a little)
then there should be no shear load or bending load on the stud. What
this means to non-Engineer types, is that you want to squeeze the wheel
so that it sticks to the hub with friction. So, if you torque the nut to
the stud and place 50,000 pounds of tensile force on the stud ... which
squeezes the wheel to the hub, then if the friction coefficient between
the wheel and hub is 0.9, then you can put 40,000 pounds of shear force
(per stud) on the wheel to hub interface. If the friction coefficient
between the spacer and the wheel is 0.9, then you are down to 36,000
pounds of shear capability. So ... the message here with this comment is
that the surface between the hub and the spacer and the wheel should not
be shiny, it should have surface roughness ... like normal machine
marks.

It is, however, better to think of all metals as plastic and assume that
they do flex some. Since the wheel and spacer does flex a bit, the stud
will bend a bit ... and this will be true even with no spacer. As Skod
points out, any bending of the wheel stud is NOT good. If you use really
brittle studs (as Skod pointed out), they are more likely to break. My
point being here that the discipline of checking wheel bolt(or nut)
torque before each run on a race car is maybe tedious, but is good
practice if you don't want the wheels to fall off.

The fact the studs do break with bigger spacers as pointed out by Skod,
should be evidence that Engineering pontification notwithstanding, it is
an issue.

I run 1/4" spacers on the front end of my Jensen Healey. Of couse it has
500 pounds/wheel with 4 of the same ARP studs you Mustang guys use 5 of
on your well prepared track cars with 900 pounds/wheel.

So ... if you are gonna hafta use a 1/2" spacer, then I would recommend
that the spacer be:
a) dowelled to the wheel
b) screwed to the wheel (with aluminum wheels use coarse pitch threads
because the aluminum can't stand a lot of torque anyway). Note, this is
just to get the spacer to the wheel in close contact and keep it there
when you take the wheel off, the real squeeze needs to come from the
wheel studs-bolts when you bolt the wheel to the hub.
c) Spacer Locktited or epoxied to the wheel (a "permanent" attachment).

Or in other words, you should make sure the spacer is as much a part of
the wheel as you can. Then you approach having only one friction shear
surface (the one from the hub to the spacer). This will be not quite as
good as having no spacer. Of course this is NOT as good as being able to
obtain a wheel with the correct offset in the first place.

My message here is agreement with Skod to try to avoid using thick
spacers, but if you must, do as much as you can to avoid the problems
Skod pointed out. And be extra careful about torquing the studs before
running. Use a torque wrench for sure. Torque to the spec for your wheel
studs.

Don Wollesen

----------------------------------------------------------------------
 
#27
Each problem has its own solution, and its own critics! I needed a thick spacer on peg drive wheels where the car regularly changed to different wheels for different purposes. My solution is shown attached, and works very well indeed, it is secure and quick to change without compromising the original hub pegs. Frank
 

Attachments

Ron Earp

Member
Admin
#28
I agree with Don'w comments. In the race paddock cars are commonly have spacers. Longer replacement studs are the order of the day but most spacers are not the nice hub centric spacers built for the purpose.

While I do agree the spacer should be made as much a part of the hub as possible, like with Frank's example, I wouldn't be scared a bit of running some thin, 1/2" or less, wheel spacers that are not like that. I run some 1/2" skeleton type spacers on my Z and it has been fine for years. Longer studs make sure I have plenty of nut engagement.

Jeff has to run some bigger spacers, about 28mm, on his TR8 and they are of the type that Frank shows. They've been fine for three racing seasons now and work great.
 
#29
On the subject of wheel studs, you should have at least 1/2" of thread showing beyond the lug nut, if not you need longer studs. Some of the long aftermarket studs are not up to the task, having a poor thread fit and not made from the best materials. Of all the aftermarket studs, ARP studs are the only ones I know of that list the tensile strength. Hub centric spacers are available from Baer brakes and Maximum Motorsports.
 
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