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Why in the heck can't wheel builders for older cars use offset measurements instead of backspacking??? I am looking at some Wheel Vintiques Series 30's. I want an offset of .5" less than what I have now. Their fitting diagram shows backspacing as the mounting face to the edge of the lip of the wheel, but the text says it's the mounting surface to the inside lip of the wheel. OK, there's about .5" difference between the two. So, I could order some wheels, and have them be the same as I have now just because no one can define backspacing.

The civilized world describes this relationship as offset. You have the measurement between the beads which is the width, and the offset describes the distance from the centerline of the width to the mounting face. My current wheels are .5" negative offset. I need 1" negative offset. Do ya think Vintiques will be able to tell me which wheel that will be??? I doubt it, they will tell me a backspacing....

 

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Highway Star: I looked at that site, yeah, it's all that stuff I already am familiar with. That means I am familiar enough to know that this is a stupid measurement system as evidenced by the lack of a uniform definition. That site's description of offset is different from Vintiques description. In my wheels' case, .5" different. .5" is what I am trying to change. So, I could order something and get exactly what I have due to variance of definition.

Dyno John: I have measured my wheels. But measure what? As mentioned above, by Vintiques' diagram, they are 5" backspace. By Vintiques' descriptive text, they are 4.5" backspace. But one thing is absolutely crystal clear, my offset is .5". No arguing that.

So I called Vintiques. They said backspace is the measurement to the outer edge of the lip. I pointed out that the lip on a steel wheel and an alloy wheel is very different. So they said backspace depends on the wheel type. I asked if they could just give me the offset measurement, and they said they "don't mess with that metric stuff". It's a relational measurement, not metric... :clonk: That makes me not want to deal with them. Does anyone else make "Covette Ralleye" type wheels?

 

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I guess backspacing goes back to the days of putting the widest meats you could on a car, when that meant using real estate on the inside of the wheel well, and you didn't want to hit stuff.

I am going to sketch my wheels and fax them to the WV people for their blessing of my understanding. The ultimate goal is to get 15x8's the don't rub inside or outside on the back, and 15x7's with the same "front spacing" so that looking at the car, the wheels look like they're the same size.

This over-analysis all goes back to experience with FWD econoboxes. Honda used to be 38mm offset. If you put a 45mm aftermarket wheel on them, it caused all kinds of goofiness! But if you wanted to put a 1" wider wheel on, with the stock 38mm offset, no problem, the tire patch still ended up in the exact same relationship as stock. That would be impossible to determine with just backspacing specs.

 

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1" wider wheel with the same "offset", then the wheel will be 1/2" further from the mounting on each side... 1" wider wheel with 38MM offset, versus 1" narrower wheel with 45mm offset, there should be no problems, because the increased offset of 7mm (45mm vs. 38mm) is less than the increased width of 12.7 mm per side...

Sorry, should have been clearer, my example was with respect to the centerline of the tread patch, not clearance to the inside. It's when you move that centerline in or out that the suspension geometry on the finicky little beasts gets ugly.

General concensus is that back spacing is from the mounting surface to the extreme edge of the wheel lip. But a 5" BS steel wheel and a 5" BS alloy wheel will put the centerline of the tire in (slightly) different positions because the lip configuration is different.... Being a mechanical engineer, those slight differences interest me.

It's dead nuts exact science where the tire will end up if you use offset measurements.

 

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Sorting through the Wheel Vintiques models, I am going with the Series 30 Corvette style. I have that style now, just the wrong offsets front and rear. I need to move my rear tires inward a bit cuz they can skim, so I am getting 15x8, 4.5 bs (I currently have 4 bs).

For the front, they don't have a 15x7 with a 3.5 bs to match the rear wheels' front space perfectly, the closest is 3.75 bs (which is .5" more front space than I have now).

The front wheels' front space will be .25" shallower, but I doubt anyone will notice.

Or I could go 5 BS on the rear and 4 bs on the front and have the front spaces match.....

 

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I am an engineer too, so I tend to be too precise when measuring stuff. For the BS measurements, I usually used my trusty old vernier calipers (but not big enough for total width)...

Once I bought a pair of Florsheim shoes that felt different after wearing them a while. You should have seen the guy at the store when I returned with a digital caliper to show that the insteps were different. He sarcastically asked, "What are you, an engineer or something? Yup.

Update, I got backspace terminology all confirmed. The fronts are going to be 15x7 with a 3.75 BS, and the rears will be 15x8 with a 4.5 BS. Tires will be 255/60 front, 275/60 rear. The tire "bulge" will look about the same front and rear, as will the front spacing.

 

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Thanks Keith, for taking the time to set the pic and post it. I checked and that part number is described as a 4" backspace, so I know exactly what to order. Hey, as a techno guy yourself, doesn't offset make more sense to you?

Oh yeah, how is the quality of Wheel Vintiques? Good enough given that it's a steel wheel? They say they are powder coated...