Another offset question

[Doc's 280]

I've been reading a lot of threads about wheel sizes, offsets, tire sizes etc. I'm no engineer (maybe someone out there is and can shed some light on this issue), but isn't the matter of safety and stress on the hub a question of where the centerline of the wheel is and not whether the wheel has negative or positive offset? For example: If I choose to go with a 17" X 7" wheel that has a +40mm offset but space it out 40mm, isn't the centerline of the wheel effectively at zero offset? As a result, aren't the stresses located at the same point as with a zero offset wheel? I can understand that if you take a zero offset wheel and space it out 40mm, you will be moving the centerline of the wheel out and adding leverage stress to the mounting point. Am I missing something? I know MSA sells lots of wheels with spacer kits and claims it is perfectly OK yet there have been several threads that suggest this is not a good idea. Does anyone have the definitive answer? Thanks.

[NZeder]

On most cars it is not a good idea to shift the centre line. However Nissan/Datsun has/had a tendency to over engineer. There are a number of Zcars over the years that have run large negative offsets with no issues. In the 70's a lot of racing Zed had large10" rims or more in the rear (some of the US guys can tell you how big the IMSA car had but I think 12" or more) with stock spring perches/sizing. A Zed can handle upto 4.5" BS with stock springs. So if they ran a 10" rim with 4.5" BS (remember rim measured size and edge to edge are different, approx 1" different) this would shift the centre line out 1" from stock. I have read that on a RWD car that has a north/south front engine setup can usually run up to a maximum of 20% of the rim width in + or - offset without causing too much of an issue if the bearing are engineered correctly. So in theory you could therefore run a 10" rim with 3.5" BS on a Zed if the flare is big enough to handle it.

Like you, I am no engineer I am only going by the research I have done.

[Curtis240Z]

I believe what MSA and others who use large offset wheels with spacer kits are saying it is "ok" for street use. The stress on these high offset rims used on cars like ours now is on the spacer kit.

Problem we see with spacer kits is people don't check the tightness of the spacer kit to the hub because it is covered by the wheel, they only check the lug nuts on the wheel. We've seen wheels shear the hub studs at track events because the person was only checking the lug nuts on the wheel (not the nuts holding on the spacer kit underneath the wheel).

I would use proper offset wheels if at all possible, but that is only my opinion. I'm using 17 x 9.5" wheels at all four corners with a 5" backspacing. With my coilover setup I even got the fronts to fit without flares.

[zguitar71]

I am not an engineer either but I will give my 2 cents anyway.

The large spacers seem as though they could be dangerous. The ones that bolt onto the hub and then the wheel is bolted to the spacer seem like an accident waiting to happen. They appear to be a weak link. Even if they are properly torqued down the wheel is not attached to the hub. on cars with good suspensions and sticky tires there is a lot of tourque put on the spacer. I personnaly would not trust them. I would never race on them. The small spacers (1/4 inch or so) do not bother me but I have seen spacers as thick as 2 inches. If the hub was meant to have a configuration like that it would have been engineered that way. I would not run any wheel that was not the right offset.

[Aussie260z]

I spoke to a local engineer and he said that,

If you use a spacer that you bolt onto the hub,

Then make a groove in the spacer that the wheel will slot into,

This will mean that the force of the wheel will not be upon the 4 lugs - but will be transfered through the spacer and into the hub,

This means that the wheel lugs will pretty much just be holding the wheel in place and not taking any of the force, the force is transferred through the spacer and into the hub,

Do this with possibly longer wheel studs if there is not enough thread left for the wheel nuts and he said it would be pretty strong, enough to be RTA approved anyway, but this was only for a 10mm spacer though...........

Anybody got an opinion???

[Mike]

You also have to consider that spacers put a lot of stress on the outside wheel bearing. The outside bearing is designed to hold a certain amount of lateral force and the wheel centering is very important. If you put a large spacer on the disk, I assume the weight on the outside wheel bearing could cause it to prematurely fail.

I am speculating that a properly modified car would include a longer spindle pin and larger outer wheel bearing.