Offset, Spacers

["Carl Buckland" <buckland@xxxxxxxxxxxx>]

There has been a lot of confusion, including in my own head, what "offset" 
means.  It is not an issue when fitting small, OE wheels and tires to your car. But 
when you are trying to squeeze as much rubber as possible into the wheel wells, 
it becomes critical. 

Offset, Defn:  the distance between the the bolt plate and the center of
the wheel.

If the offset is 8mm, there is very little offset, or distance from the bolt plane to 
the center of the wheel.  The wheel stands OUTboard from the bolt plane. To 
take it further INboard requires a LARGER offset, such as 30mm.  

A wheel with a "large offset," say, 45mm, might rub on the inside, while a
wheel on the same car with a "small offset," like 25mm, might rub on the
OUTside.

This might help:

WHEN YOU ADD SPACERS, YOU REDUCE OFFSET

If you add a 10mm spacer to a 38mm wheel, you end up with 28mm of offset.


For another approach, see:

http://www.tirerack.com/wheels/tech/offset.htm 

There seems to be a "fear of spacers," which I don't understand.  They are a 
standard tuning item for anyone who is using anything other than absolutely 
stock wheel/tire sizes (how boring).  H&R Springs also makes spacers in all sizes, 
from 5mm to 30mm.  They also make the extra length lugs that spacers require.  
The spacers are hubcentric, so balancing is not a problem.  I applying a dab of 
glue on mine so that they don't spin around when I am putting on wheels.

To fill the rear wheel well, you usually need to go to a higher offset (say, a 38 or 
a 45, vs a 25 or a 30).  That puts the wheel INboard so that you can utilize all 
your INBOARD  space,  yet without rubbing on the fender lip.  Then, you have 
to use spacers to push the wheel OUT, so that you can get strut clearance, and so 
that you can utilize all of that OUTboard space that we have (unless the car is 
severly lowered, or are not running any negative camber).

I absolutely do not understand why people would want to have two different
sized wheels, or wheels with different offsets, unless they have to.

Carl Buckland

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