STILL need help on this whole wheel thing...

[ZeroNilNada]

Ok, I think I've gotten most of this offset/backspace/hole pattern thing worked out but I still have questions.
I've been digging around the posts for some specific info but haven't had any luck. And, unfortunately, the TechWiki page for this subject is WOEFULLY inadequate (I read somewhere that lots of info was lost?).
So here are my issues/questions:
On my car I have 175/70R14 tires on some aftermarket chrome wheels with fake spokes. The fit is good (that is, they don't rub and the wheel/tire location on the car is appealing to me) but I hate the wheels and would like to go with some 15X7 alloy wheels with a lower profile tire.
I've measured the wheels and from what I can tell they're 7" wide with an offset of only about 8mm.
But... Is the width of the wheel measured from the flange on the outside of the tire or at the bead where the tire seats? I'm beginning to think that it's the bead since that's where the tire diameter is measured.
I'm also not sure I've calculated the offset correctly. From the back of the wheel at the flange to the mounting face it's 80.9625mm. The centerline is at 88.9mm. Subtracting the backspace measurement from the centerline measurement gives me an offset of 7.9375mm. Again, this is taken from the flange and not the bead.
This page was helpful:
http://marksink.com/tire_wheel_offset/offset.html" onclick="window.open(this.href);return false;
But without the correct starting data it's useless so I want to be sure I've got good info.
Any expert help is appreciated!
Mannon

[datsunrides]

How about some not quite expert help? The rim width is measured at the bead. If you measured 7" outside to outside, your wheel is actually closer to 6" wide. As for your offset calculation, that would seem to be about right as Roadsters seem to like +12-15 mm offset based on others findings with a 6"-7" wide wheel. 15x7 with +15 offset will be close. May need to roll the lips, or maybe not. There seems to be a bit of variation on the bodies.

Mark

[ZeroNilNada]

Great info. Thanks!
This whole tire/wheel thing is kind of new to me. I've never put a set of aftermarket wheels on any of my previous cars.
Your input will help in my wheel search!
Mannon

[Alvin]

For 6-7" wide wheels try to find an offset close to +15mm
Anything less than that, ie 0 or +6mm will push the wheel outward towards your fender lips.

Wheels with +22mm offset or higher will push the wheel inward, and you risk caliper/leaf spring/sway bar clearance issues

Remember, if wheels fit perfectly on someone elses roadster they may/not fit yours. Each roadster's frame/body make for some interesting fitments clearances, model years/fender changes make things worse!

[Victor_laury]

There's no problem with using the entire rim with (from outsid lip to outside lip) for measureing offset - unless - the inbord lip has a different profile that the outboard. If all things are equal, measuring offset is a breeze and souds like you did it right.

1st over all width.
divide that in half and you have you center line
2nd measure from a straight edge down to the inside hub surface
That's your backspace
3rd subtract centerlne from backspace
That's your offset

Now - here's an example - I have, right here in my hand a very nice 10 pound japanese wheel - Hoshino 14X5.5
Overall - 164mm
164/2=82 =centerline
backspace = 96mm
96-82= 14mm
This wheel is 14X5.5 @+14

[datsunrides]

Pretty clear right there!

Mark

[Linda]

And here's some links for you:

http://www.tirereview.com/?type=cc&id=179&53L3c73d=179" onclick="window.open(this.href);return false;
https://www.rsracing.com/tech-wheel.html" onclick="window.open(this.href);return false;
http://www.yokohamatire.com/customer_se ... izing.aspx" onclick="window.open(this.href);return false;


Linda