Topic: Wheel backspacing

[socal1200r]

Okay, I've tried to figure this out, based on some web searches and diagrams and such.  So I'm throwing this out to the crowd, in the hopes that someone can explain this to me in simple english.  Here's the scenario:

I bought new tires for my 2000 GMC Sonoma (rwd small pickup) with a V8 conversion.  It has the same size wheels all around, 17x8, with what looks to be the same offset and backspacing.  I have 245/45s on the front, and 285/40s on the rear.  The rears just didn't look quite right, so I ordered a new set of wheels, with 17x8 on the front, and 17x9 on the rear.  The fronts have 4.5" backspacing, and the rears have 5.25".   So based on some research, I'm thinking the fronts have just about zero offset, meaning the mounting hub on the back will be at the centerline of the rim width, so there will be the same amount of wheel behind and in front of the mounting hub?  But the rears, with 5.25" backspacing on a 9" wide wheel, will have more of the rim behind the mounting hub, and less towards the front? 

Comparing this 17x9 rear wheel with 5.25" backspacing with another 17x9 rear wheel with 6.75" backspacing creates another question.  I'm assuming the wheel with the lower amount of backspacing will have more of the wheel going out from the hub towards the outside, i.e. having more of a "deep dish" look than the wheel with the higher backspacing?  So in this case, all other things being equal, the rear wheel with 5.25" backspacing will have 1.5" more of the rim going out from the hub than the wheel with 6.75" backspacing?   

[seanbarney41]

I believe everything you said is correct.

[70CB750]

[socal1200r]

Okay, maybe it's just me, but this diagram is all wrong.  Take the picture on the far left, where it says "brake side".  I think the wheel as shown is reversed, in that the mounting hub is on the other side, not the side that faces the brake.  If that wheel was reversed, and the "hub" is pointing towards the brake, then that wheel would have a positive offset, or a "deep dish" look. 

[Retro Rocket]

That diagram is correct, It is what it says, "positive offset"... Look at the hub position on all three wheels, its exactly the same, its only the rim that has changed position....

[RAFster122s]

Rear wheel drive cars are typically using a negative offset or deep dish look as you call it. Some are neutral, it really depends on the clearance you have between the tire and the lip of the fender or in some cases the inner fenderwell. When upsizing the wheels you may be able to getaway with a couple inches further out and the rest of the width has to go towards the center of the vehicle.  You can run into fitment issues of calipers not clearing the backside of your rim and even hitting brake lines and things like that.
Sometimes you are not going to be able to tell until you bolt it up. Most shops can lookup the vehicle and the wheel makers database to see if it fits. Sometimes they are no help.

There's also wheel designs that are hub centric from the manufacturer where the wheels are mounted the same way every time with locator pins on the hub and the hub center fitting into a matched recess in the wheel.  They support the hub and wheel joint and it ensures that the wheel is centered.  Most aftermarket wheels are not hub centric to have a wider range of vehicles they can be used with...


S

[70CB750]

You always have the flat side to go against the hub.