Speeds5

I need to put a 10mm spacer in the rear of my 86 Carrera. It’s not hubcentric and I’d like to avoid purchasing a new set if I don’t have to.. Any experience/issues with flat spacers at the track? Say any vibrations?

Thanks

Frank 993 C4S

It's not safe if your wheel center is not held by the hub flanges. Get hub centric spacers. Otherwise your wheel is only held by your wheel studs and they are not designed to take that load.

Edit: I have seen wheel studs fail on a car at Road Atlanta this year for just that reason.

Kevin Fennell

This isn't right. Your wheel is held to the hub by FRICTION between the hub and the wheel surface, or in this case between the hub, the spacer, and the wheel. This friction is the result of the studs applying a normal force to the surfaces by pulling them together. The studs themselves are NOT loaded in shear if they are properly tightened, if they were they would fail immediately as they are not strong in that direction at all compared the the loads a wheel sees. If the wheel and the nuts/bolts have a matching profile such that the wheel is still centered on the studs, there should generally be no problem.

Failures still happen with spacers, but they are the result of improperly torqued bolts/crappy stud extensions, etc.

Frank 993 C4S

You are of course entitled to your opinion and this is why everything on the internet needs to be taken with a sense of caution.

ProCoach

Nope.

"Nearly all OEM Wheels are designed to be hub-centric. The automaker designs an OEM wheel to fit on a certain car or range of cars. The center bore of the wheel is sized to fit perfectly onto the axle of that car. This is a hub-centric connection, as the wheel is centered by its connection to the axle hub. The lugnuts hold the wheel firmly to the mounting plate, but it is the wheel-to-axle connection that actually holds the weight of the car. This is quite an important distinction, as the lugnuts are designed to handle lateral forces that push the wheel away from the mounting plate. The forces that the hub and center bore connection are designed to withstand – the weight of the car forcing downward and impacts forcing upward – are at right angles to the forces that the lugnuts are designed for."

Thundermoose

I can't speak for Porsches or Lotus's , but on BMW's, 10mm spacers are problematic. They are typically too short to have hub extenders and too long to provide an adequate lip for the wheels. I run a 12mm in the front and 15 mm in the rear. Both spacers have hub extenders.

Kevin Fennell

Maybe I wasn't clear, the lugnuts are ONLY loaded in tension on any wheel hub centric or not, I was just saying in order to get the wheel centered correctly you need to have the lugnuts profile matching the wheel correctly so that they will keep the wheel centered while you are tightening it. All of the forces from the wheel to the car go through the friction between the two surfaces.

Think about this. 90% of all aftermarket wheels that you see driving around have PLASTIC hub centering rings. This is because they are only loaded when you are installing the wheel to keep it centered. Once you drive down the street these do not see ANY load.

If this was not the case answer this: How come I have completely intact PLASTIC hub centering rings on my car after doing 30+ sessions at COTA with A7 tires. The load is all held by the friction between surfaces while you are actually driving the car.

OEM's use hub centered wheels because they have a number of benefits, they are easier to install. They give you some backup if the studs come loose, and people expect it. Hubs DO NOT carry load while you are driving.

Kevin Fennell

Another thought experiment. If the load is NOT held only by friction think about what happens when you hit the brakes. Do the wheels spin on the hub until they hit the stud, then go to the other end of the travel when you get on the gas, and over and over again? No... The studs are never loaded in anything but tension, and that tension creates a friction between the mating surfaces.

Thundermoose

I never thought of it that way. Thanks.

Kevin Fennell

Has anyone ever seen a tolerance posted for the hub opening on an aftermarket wheel? If it's carrying such loads certainly it is a very very tight fit? The $100 wheels that every Miata in the world is racing on have that level of hub machining?