Negative offset

[Diseazd]

All of my Panasports (3 sets) are "0" offset. When the car is lowered there is a lot more room on the inside strut side to go wider with the rim and tire size. How do you go about taking a wheel from "0" offset to say -10mm? Who would you take it to and can it be done?

[Arne]

You want to tuck it in closer to the strut? That's not negative offset, that's positive. And there's really no way to do that, on most wheels. You'd need to have the mounting face milled, which would reduced the thickness of the center of the wheel by the amount milled. Most wheels don't have enough thickness there to allow that. Cast wheel manufacturers generally have different molds for different offsets to allow the proper thickness and strength in the wheel center.

[Diseazd]

I always thought that positive offset gave you a wider stance, therefore moved the wheel out from the hub.....thanks for clearing that up and answering my question.

[Arne]

Oddly enough, we've noticed recently that the definition of positive/negative when discussing offset has flip-flopped since the early '70s. Way back then, positive did mean wider stance, at least here in the USA. But since everywhere else in the world used positive and negative in the opposite way, the US wheel manufacturers conformed. These days, positive offset is what flat-face FWD wheels have. As an example, a typical FWD VW wheel will have +38.

[Diseazd]

That explains it.....I'm definitely still living in the 70's........Thanks Arne.

[Carl Beck]

All of my Panasports (3 sets) are "0" offset. When the car is lowered there is a lot more room on the inside strut side to go wider with the rim and tire size. How do you go about taking a wheel from "0" offset to say -10mm? Who would you take it to and can it be done?

Hi Guy:

That's easy. As Arne mentioned you want a 10mm off-set, not a -10mm off-set. You take the wheel to a wheel widening speciality shop and have them add 10mm to the width on the back side of the wheel. Street rod'ers have wheels made wider all the time.

Just google "widen aluminum wheels" and most likely find someone in your area. If not, try the Yellow Pages..

BTW the stock steel wheels on the 240-Z's had a 15mm off-set {.59"}.

FWIW,

Carl B.

[jmortensen]

I don't do offset, but you can probably go 5.25" backspace with the coilovers you're installing. Measure to be sure, as it depends on the diameter of the wheel, but 0 offset is what you use when you have the bigger stock coils on there, and gaining room for wider tires is one of the benefits of the coilovers.

[Diseazd]

My dilema.....I've got a set of Panasport 16x7" wheels that worked great with the Eibach and Illuminas on the stock struts but with G/C coilovers, I believe that I'm gonna be limited to how much I can drop the car by the outside fender, not the inside strut. What kind of offet would you look for for this new application with the same size rims?

[Carl Beck]

A 7" wide wheel with a "0" offset will have 3.5" to each side of the centerline that runs across the mounting surface of the wheel/hub interface. Because a 7" wide wheel measures 7" inside the rim lips, it is usually 8" wide measured to the outside of the rim lips.

Backspace - is measurement taken from the mounting surface of the wheel to the outside of the rim lip on the back side of the wheel.

It is always better to actually measure the wheel for "Backspace" - but you can usually get close by calculating it. On the wheel above with "0" offset, you would add the 3.5" width inside the rim lip determined by the offset being "0" - and the additional 0.5" thickness of the rim lip itself - to get a 4" backspace.

Jon said you can use a 5.25" Backspace. So if you wanted to stay with the 7" wide rims which should be about 8" wide measured outside the rim lips - your new wheel would have 5.25" of the 8" width to the inside of the car and 2.75" to the outside. Converting "Backspace" to "offset" then, you would subtract 0.5" from the 5.25" and get 4.75". That would then be 1.25" {31.75mm} offset. {3.5" of the "0" offset wheels from 4.75" = 1.25"}

That however might leave your wheels looking like they are set too far to the inside.... Do you need an additional 1.25" of clearance on the outside to get the tires past the fender lips? Maybe go to a 7.5" width with a 5.25" Backspace and/or a 32mm off-set. Or don't use the full 5.25" Backspace and go with a 7" wheel with 15mm offset.

Just keep in mind that "offset" deals with the width of the wheel measured inside the mounting lips. "Backspace" deals with the the distance from the wheels mounting surface to the outside of the rim lip on the back side of the wheel. Most aluminum rims have at least 0.5" thick lips.

Another option for tire clearance is to simply have your body man roll the fender lips under. In the old days, we simply cut slots about 12" apart around the fender lips, so they could be bent up inside the fenders. Then we put a baseball bat between the tires and the fender lips and rolled the car forward/backward... adjusting the bat to use an ever thicker part to roll the fender lips up...

hope that helps...

FWIW,

Carl B.

Edited July 3, 2009 by Carl Beck

[Diseazd]

You guys blow my mind! All the info is much appreciated......I'll post pics when it's all done. Carl I still haven't got the P79 head back from Doc yet (you wanted to see pictures of the head shaved .080")......will update my L28 build when I get them. Also re much earlier questions re the L28 in my 70, I now have access to a dyno and will let you know results from tests with the SU's with SM needles. Thanks Guy

[doradox]

Another consideration is the effect of non stock offset, and overall tire radius, on the scrub radius.

http://www.hrsprings.com/technical/scrub_radius

Steve

[CDM]

The Panasports cannot be widened as i have seen suggested but we do have a 12MM offset in the 16s but it is for guys who have converted to coilovers. Remember that the panasports are forged wheels and cannot be repaired and unless you have the 3 piece wheels you most likely would have to change wheels to move them.

Les