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Making Wheels Fit--General Rules?

New User
Posts: 1
Joined: 02/11
Posted: 02/28/11 07:48 AM

IMHO, this would make an excellent subject for a magazine article.  Or at least a sticky post by the editors.  There are lots of wheel and tire sites out there who can tell you what fits your vehicle.   What I want to know is how to MAKE something fit that's a little outside the normal parameters of tire diameter or width, or wheel backspacing or offset.   In some cases, there will be more than one possible approach.  I'd like to know them all, along with the positives and negatives of each possible solution.  

My project truck is a '93 GMC C1500 extended cab pickup with an 8' cargo box.  It's going to be a daily driver, and I live in Chicago(read: snow and rust), so I'll need to keep the ride height up, at least in winter.  I'd like air bags, but for the ride improvement, not to lay frame or hop.  Eventually, I'd like to get a big brake conversion, and put disc brakes on the rear as well.  

Stock, I can mount 22" wheels (29" high) with -15 to +15 offset(but 0 to +15 if I want big brakes) and 4 1/2 backspacing, IIRC.  I don't think skinny tires make much sense on a truck that is used as a truck, so 20" would be my practical limit at 29" tire diameter.  
  So, I'm looking at increasing the overall wheel diameter to 31" or 33" in order to mount 22" or 24" wheels with an acceptable sidewall profile.  I expect I'd be tubbing the fenders, and I need info on relocating the brake system parts under the hood.  Is it possible to relocate the PS booster without relocating the pedal?  If not, switching to a hydraulic booster seems called for.  What about the proportioning valve?  If it isn't adjustable, I'd think that it needs to be replaced with one that is in order to make the switch to disc brakes in the rear.  Any suggestiions on a mounting location?  
 Building up new wheel openings on the sheetmetal is something I'm looking forward to doing.

What about switching to a different lug pattern?  I'd like to go to the 6 X 5 1/2 that most of the newer GM'S use.  It seems to me you'd be able to just switch out the front hats, assuming the spindles are the same diameter.  If not, new spindles would take care of that.  Am I missing something on the front wheels?

For the rear, it looks like an axle swap (or the whole rearend) would be needed?  

Lastly, the topic of offset.   I've seen some sellers listing that as low/medium/high/negative.   Is there some conventional numerical range for these categories, or are they just trying to keep this subject incomprehensible?   Others give a more useful number.  I've seen some wheels I really like, but they have a +18 offset.  What can be done to make these work?  

Any and all info or links appreciated.  I'm a total noob at automotive stuff, and craving knowledge.   Thanks.  

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