Another generic question, this time about wheel spacers and related stresses

[BTF/PTM]

Yo,

Another fundamentals question that others may be interested in. Again, mods please move the thread if it's valid enough to be put into the wheels/brakes forum.

My questions are in regard to using wheel spacers to adjust where the wheels sit.

1) Is there any difference in added stress when a wider-than-stock wheel with a custom, properly fitted offset is used compared with when the same wider-than-stock wheel with more offset than necessary that is moved outward using a spacer is used? My query is specific to performance driving.

2) Is there a threshold of too much for using spacers where performance driving is involved?

Thanks, everyone, hopefully someone other than myself has been wondering and will also find this information useful.

[Walter Moore]

There are a lot of good wheels available for the Z right now that do not require spacers. I personally don't think that spacers or adapters are a good idea. However some people do use them, apparently with success.

As far as the question of "stress" the centerline of the wheel would be the same with a custom wheel or a "proper" spacer/adapter so most of the suspension isn't going to be exposed to any force difference, except as follows:

A spacer sits between the wheel and the mounting surface, and requires longer wheel studs. The studs will see more shear force when a spacer is used because the spacer doesn't carry any of the vertical load, and the wheel will be held in place only by the studs. Further, the vertical load will be at a distance from the mounting surface, creating a lever arm effect on the stud. Normally the wheel bore pilots on the hub (at least on the front wheels) which carries most of the vertical load. The studs are intended to just hold the wheel in place horizontally.

An adapter has built in studs, and is bolted to the standard studs with thin lug nuts. Once the adapter is mounted the original studs are cut off flush with the adapter. Depending upon how they are designed, adapters could reduce the shear force on the wheel studs, but most don't. They nearly always raise an eccentricity concern relative to wheel mounting. You are at the mercy of the manufacturing tolerances of the adapter as far as whether or not the wheel ends up being mounted on center. The stock wheel stud circle and hub is never going to be perfectly concentric to the wheel bearings. Adding an adapter is almost guaranteed to exaggerate the small error that existed initially.

My concern about shear forces on the wheel studs is based on the knowledge that the shear strength of any bolt is rarely more than about 10% of the force it has in tension. In my opinion, using wheel spacers, and potentially wheel adapters, in a high stress application like performance driving is asking for trouble.

But others may disagree.

[BTF/PTM]

I hadn't thought about the hub center being eliminated when a spacer is used, in that light it does seem like spacers can be risky. This is exactly why I ask these questions. Thanks!!

[5thhorsemann]

I agree with everything walter has stated here. There is a reason that almost every wheel spacer set I have ever seen has "Not intended for highway use" stamped on it or somewhere in the directions. It is just one more (or 4 more) things to go wrong.

[jmortensen]

I ran wheelspacers on my Z with slicks last time around and intend to do so again. Widening front track is particularly useful to eliminate understeer.

The Z is lugcentric, so you don't need hubcentric spacers, but you do need spacers that fit tight on the lugs. Cheap arse Mr. Gasket style spacers are not good enough.

The problem with the Z studs is that they aren't long enough to use spacers, so if you're going to run spacers, you need longer studs. You can use 2nd gen RX7 studs, Quest van studs, or ARP Camaro or RX7 studs. The RX7 studs have 12 x 1.5 threads where stock is 12 x 1.25. Not sure about the Quest studs. If you're using a Nissan mag wheel they have a slightly different size lug nut, so a generic lug nut from the store doesn't work. However, Toyota truck lug nuts have the correct size shank and they come in 12 x 1.5. So if you want long studs and Nissan wheels, there's your answer. I had to cut the end off of the nuts for the studs I was using, YMMV.

I used to work on a Porsche race car that had 1" or 1.5" lugcentric spacers, cant remember. To be fair though, the Porsche did have 5 14mm lug studs.

[BTF/PTM]

Thanks yet again, guys.

Longer studs are easy, I can put those in when I do wheel bearings.

In light of needing high-quality spacers (hopefully I won't need them at all, but it's safer to ask anyway), and without turning the thread into a billboard, are there recommendations for good lugcentric spacers out there?

[gnosez]

Have them made to order as the generic ones have enlarged holes that can float around and cause issues. The fronts are hubcentric, it's just the rears that need to be made specific to your needs.

We're in the process of putting flares on our 240 putting 10-inch wheels with 275/35/15s under them for non-vintage race events. To fill up the flares for vintage events (only 15x7 wheels are allowed) we will have 1/2-inch spacers inserted.

Porsches have been winning races with spacers for more than 40 years....