I just bought a set of 2008 OEM 20's for my X... high1 has given me all the spacer info I need and a place to get them...

http://www.wheelspacer.com/home.asp

NOW... what is better Aluminum or Steel... both are the same price.

Please advise. Thanks!

 

For one thing, dissimilar metals touching each other can lead to corrosion.

 

The wheel is already aluminum. This means that there will always be contact of dissimilar metals even without the adapter / spacer.
Anyway "galvanic / dissimilar metal corrosion is not such a factor when three important factors are not present.
1. Contact area must be wet with a conductive fluid
2. must have metal to metal contact
3. metals must have sufficiently different potentials.

since the wheels and the hubs have very similar potentials, and they are not wetted with conductive fluid, the corrosion is kept to a minimum.
Think about aluminum heads and water pumps, intake manifolds etc. all bolted to cast iron engines. None have problems.
This really is not an issue.

Now, the spacer. I do not like spacers at all, but have run a few in the past. All have been aluminum and of the bolt on style, not just a slip on unit that just makes the studs too short anyway.
Keep in mind that the use of any spacer is going to move the wheel centerline away from the bearing centerline and create a bunch of additional leverage making the bearing work harder. This is different from just changing the backspacing of the wheel. By changing backspacing, this moves the entire wheel in or out, and the adapter / spacer moves the mounting point away from the hub face creating more leverage and wear on the bearing.
Anyway, for the sake of this reply, I prefer aluminum bolt on style if any of these have to be used at all.

 

Wheels can get wet. And I do remember at least a couple of posts in this forum people seeking help about removing stuck aluminium wheels.

 

usually not wet enough for electolysis to occur. The heat from the hubs and brakes prevent this.
Now I am not saying that corrosion does not occur, but it is not related to dissimilar metals.
In your suggestion that some poeple have requested help for removing aluminum wheels, this is a small percentage of wheels when compared to the amount of aluminum wheels being used. Any number of things can bind a wheel.
Heak how many have asked for help with drum removal? The drum and the axle that it rests on are similar metals and they bond as well. This is just the surfaces obtaining scale and deposits preventing the two from seperating.
Happens with steel wheels that are hubcentric too. Not related to anything galvanic at all.
Galvanic deterioration will result in one metal (lower on the scale above) to dissolve and really not bond.
I am not trying to be arguementative, simply stating that since the wheels are aluminum, the use of any spacer / adapter, or even the lack of use will still result in contact of aluminum to carbon steel.

 

backspacing, spacers ?????
seems to me the wheel centerline moves either way
creating an equal amount of load change regaurdless of method

 

Kickback thru the steering system and steering wheel will be greater.
Lightly coat (slight finger smear your contact areas with anti seize compound.
I'm not a fan of spacers at all, rather have the proper offset rims or bolt pattern.