Wheel offset

[dkn1997]

I found a set of rims for my 68.  they are 18 x 9's. the guy selling them seems to be used to dealing with imports because he told me that the have a 25mm offset.  I asked him what that was in inches and he said 5.75"  dude was throwing other numbers in there and somehow even came up with 6" at first! then he changed his story to 5.75 but then sounded unsure.  my head hurts now
has anyone ever heard this and is it right?

I was thinking that if they are a 9" wide wheel, then 0 offset would be a 4.5" backspace(1/2 of 9)  using that logic, then 25 offset could mean 25mm added to 0 offset(which is 4.5")  that would mean that these wheels have a 5.5" backspace?
I want to put these on my 68. same 4 wheels all around.  brand new wheels, but they are a close out so no fiddling with backspace. they are what they are.

[Mike DC]

I'm not sure either, but your final guess sounds correct to me.

4.5" as the zero point + 25mm added (moving the rim 25mm farther inwards on the car, past the zero point).  So you're talking about a distance of something like 5.5 inches between the bolt-circle mounting surface and the inner rim lip. 

[Mike DC]

BTW:  If you're indeed dealing with a 5.5" offset, that may or may not fit the front end of a Charger.

The upper balljoint (or the UCA's loop of metal that the upper BJ threads into) may interfere.  I know this is true with smaller diameter rims like 14-15" rims and a 5.5" offset. 

But a much larger rim size (diameter) might very well get you off the hook entirely.  I dunno.

[dkn1997]

Ok, I asked over at moparts too and they said that a 9" wheel is really 10" from lip to lip.  They came up with 6" backspace. I found these wheels listed somewhere else with offset and backspace on a chart.  that confirmed that the 25mm offset is indeed 6" backspace..  I used that 68 charger fitment guide and that puts the wheel a bit close to the leafspring with a 295 tire.  looks like even a 305 width tire would fit.  worst case is either relocating the springs inboard a bit or spacers.  It's a pretty smokin deal on the rims and a style I love that's almost identical to Mass_mopar's wheels which are the best things I have ever seen on an charger ever.  It's 850 for 4 wheels brand new so I dont' see how I could go wrong.

[dkn1997]

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=140296320995&sspagename=STRK%3AMEWNX%3AIT&viewitem=

I bought them!  they are boyd's imperials, chromed, and free shipping for [4] 18 x 9 wheels.  I looked into it more and I believe them to be 6" backspace. I may have to use spacers...there's a guy on moparts who makes them and they will also make the wheels hubcentric for our cars.   once get them and mock them up, I will get some spacers if need be.

I intend to offset the cost by selling my current wheels/tires. they are 16" torquethrust 2's in good shape and tires with almost no wear on them.  they look killer, but I was wanting a change after the accident.  sort of like getting a new car!

[471_Magnum]

You WILL have to use adaptors (not spacers). Those are a late model-type offset. The wheel will sit way too far inboard. If it doesn't contact something (it will) it will still look ridiculous. Even if you clear the ball joint, you'll hit the frame rail long before full lock.

[Mike DC]

Yeah, that seems to happen more often than not with any decent size wheel/tire combo anymore. 

I've got a set of 15" rims with tires that are barely one notch bigger than factory stock, and they already hit the framerails. 

[dkn1997]

I'm pretty sure I will be using just spacers in the back.  6" backspace and I am thinking I will need about 5.5"

Looks like adaptors for the front.  I'm still fired up!!! 

I am choosing to look at it positively....AR engineering makes a 13" rotor kit that uses a hub that pushes everything out so that these wheels would be close to a bolt in.  That could be an option in the future.  I dont' think these will hit the suspension, but the framerail is another story.

We will see when I get them.

[dkn1997]

just took a rim down to the body shop where car is getting prepped for paint.  it clears the suspension easy.  definately need some adaptors for the front but that's not the end of the world.  for the back, looks like a 1/2" spacer will do.  I will probably run 245/45's on the front.  also, these wheels have a 62mm center register diameter.  I read somewhere else that stock mustang was 70.5.  just some trivia

I found this website  www.motorsport-tech.com  that lets you build every aspect of your adapter online and gives you a price quote at the end.  I priced out [2] 1/2" spacers for the rear and [2] 1.5" adaptors for the front (thicker or thinner won't effect price too much)  both sets would be made hubcentric on one side and wheelcentric on the other.  total for me is 265 with shipping.  I still think i did ok having a set of chromed 18" coddington wheels for 1K.  I paid almost that much for my torquethrust 2's a while ago.

[doctorpimp]

I intend to offset the cost by selling my current wheels/tires. they are 16" torquethrust 2's in good shape and tires with almost no wear on them.  they look killer, but I was wanting a change after the accident.  sort of like getting a new car!

How much for the Torquethrusts?    What size/type of rubber?  PM me please !!!

[defiance]

just for the record, I just recently spent a lot of time trying to figure out why the offset and backspace math never worked out on wheel specs - you figured it out and mentioned it briefly, but I just kinda wanted to spell it out so if anyone like me is trying to figure it out and searches this thread in the future ---

Anyway, offset is measured from centerline of the inside of the lip, as is wheel width.  So, for example, an 8" wheel will be 8" from inside lip to inside lip, and a 0 offset wheel will have the mounting surface 4" from the inside lip.
A logical conclusion would be that this wheel would have 4" backspacing, but that's not quite true - backspacing is measured to the *outside* lip of the rim.  Most rims are around 1/2" thick at the lip, so the backspacing of our hypothetical rim would be 4.5". 
Overall specs: 8" wheel, 0mm offset, 4.5" backspacing.

For a second example, let's look at a 9" wheel with 25mm backspacing.  25mm is around 1" (25.4 is exactly 1/2").  Therefore, the backspacing is: 4.5" (centerline) + 1.0"(offset) + 0.5" (lip thickness) = 6.0"  from the mounting surface.

[doctorpimp]

Great explanation!!!
Thanks defiance 

[mauve66]

what are you allowing for the tire to be outside the rim when you took them to "mock up" at the body shop???

[defiance]

Yeah, that's something I didn't mention,the tire will be outside the rim, so backspacing is still not the "furthest back" point

On tire width, I've read that the width measurement (the 235 or 255 or 315 or whatever) is supposed to be the maximum width, but only when mounted on the "recommended" wheel width...  But from what I've seen, they're nearly always quite a bit wider...  Seems like tire manufacturers' "recommended" wheel widths are CRAZY narrow for the tire size, and I've never been able to find what widths are "recommended" for each size to actually match that size.  I believe it's left of to the tire mfg, so it probably varies quite a bit...  Sucks that there's not really a better method out there of getting real width, since that's such an important measure.

[mauve66]

remember the tire ratio numbers are for TREAD width not exactly TIRE width for including the sidewalls unless your doing a rubberband type thing where the rim is so wide the tire sidewall barely makes it to seat

[defiance]

Got it - I was confusing tread width with section width.