Originally Posted by Ben
Ok, with the recent influx of wheel spacer questions i thought I would post up the knowledge base that I have picked up over the years on this topic, hopefully answering as many questions as possible.
Are spacers the best option? No, when available you should always opt to purchase wheels with the correct backspacing for your particular application, but we all know that it's not always an option to do so.
Do I have all the answers? Hell no, but I do have experience running spacers on and off the track and have put quite a few sets through the grinder in terms of abuse with little to no issue worse than stock hub short comings.
Have I ran them offroad? Nope, I am fairly new to the offroad scene and have never had a set on a trail. However, I really can't see how the amount of abuse when compared to a autocross track car can be all that different. But hopefully we can address all this with other, more experienced, peoples contribution to this thread. So, let's get started!
First, let's go over what these things actually are, and what kind of incarnations exist.
There are basically two categories of spacers. Wheel spacers and Hub adapters. Both options perform the same function, which is placing space between the vehicles hub and the wheel itself in order to achieve a goal. (i.e. Clear a brake caliper, allow for room for wider tires, etc.) A hub adapter also accomplishes another function. Some will allow you to change your bolt pattern from, for example, a 6 lug pattern to a 5 lug pattern and so forth. For this reason, some manufacturers list their wheel spacer sizes with two sets of numbers. One set for the "hub side" (the side that you mount to the vehicles hub) and one set for the "wheel side" (which, obviously is what you bolt the wheel to.) even if these numbers are the same. (no pattern change.). Is it a good idea to change lug patterns? I say it's fine as long as you are increasing your lug pattern. (i.e from four to six, or six to eight, etc.) The reason for this is it's much easier to maintain a center with more lugs and much more difficult to do so with less lugs. I know people however that would argue that it makes no difference. So it's just a matter of what you are comfortable with.
Here is a 5 lug hub, to six lug wheel, 1.25" spacer/adapter, (it has more lug holes than 5 so that you can mount it in multiple patterns.):
Now, spacers and spacer/adapters basically come in two forms:
Those with built in studs (which I prefer d/t ease of installation):
Then we have those without studs or "slip on" spacers. These spacers are actually more structurally sound than the spacers with built in studs, (and some would argue that this is technically the "correct" way to hub space.") but installation is considerably more difficult because these require you to swap out your OEM studs for extended aftermarket studs if you go above 5mm thick. (which most of us will be doing anyway.) Plus you have to have a press to remove your stock studs and press on the new extended ones. Which isn't a big deal, or complicated, but it's much more time consuming.
Now, a warning. Stay Away from universal spacers!! I can't stress enough the disasters I have witnessed because of cheap universal spacers and improper installation (failure to maintain proper length studs, etc.) because someone did not have the correct information when they bought their spacers.
STAY AWAY! These will fail, it's just a matter of when.
Now let's move on to another aspect of wheel dynamics... The centering mechanism.
The OEM hub has to center the wheel on that hub with a very low tolerance, usually 1/1000 of an inch, to prevent premature bearing wear, and unwanted vibration. The hub accomplishes this one of two ways:
Either with the lug nuts themselves centering the wheel (lug centric), or a small lip on the center of the hub that actually centers the rim on the hub by mating to a similar sized hole on the center and back of the rim. (hub centric). I believe our ims are hub centric but AFAIK you can run any even numbered lug pattern, with tapered lugs, either way as long as the spacer you get has a hole in the center with a large enough diameter to fit over the "lip." For instance, a 5 lug pattern can be hub centric ONLY, but a 6 lug pattern can be either hub centric or lug centric. Keep reading, it will make more sense in a minute.
Hub centric spacers come in two forms:
rings built in:
Or rings separate: (known as "loose ring spacers")
So, this brings up another question...is the center hole where the rings fit the same size for every vehicle?
NO, of course not. That would be waaaay to easy.
The technical name for that little hole is called the "center bore." If you are bound and determined to get your wheels totally hub centered you need to know this number. On the h3s I believe (correct me if I'm wrong) the centerbore is 100.6mm. Buy your rings or spacers with a 100.5mm outside diameter centerbore so that the hub of the wheel will fit over the hub ring "lip". Also be sure to buy rings the same thickness as the spacer so that the correct amout of "lip" protrudes. Usually the option for centerbore when purchasing will not be this precise. Mainly they say "100mm" and they automatically know the rest of the tolerances.
Now, the good news is that you don't have to spend a week on the net searching for matching hub rings. In fact, since the lugs are a even number, you don't have to sweat being totally hub centric at all. The number of studs plus the tapered OEM studs will center it good. Just make sure your centerbore is 100mm to clear the stock hub ring.
Ok let's move on to another aspect, wheel "gaps".
You will need a "gap" or hole in the area between the mounting studs for spacers less than 25mm thick.
aftermarket rim without "gaps"
wheel with "gaps"
Now, the stock studs are 25mm long, so any spacer that's less than 25mm will result in stud protrusion through the spacer, and without the gaps demonstrated above the wheel will not mount!
example of stud protrusion through the spacer
Now, could you slice off the extra length? Wink, now your thinkin'!