Question #1 - Yes, that's positive offset, which means the tire is in further
towards the centerline of the car.
Question #2 - In reality, you have to consider both. But it depends on the tire
that is mounted on the wheel, and whether you have stock springs or comp
springs.
Some people forget about the width of the tire when measuring backspacing. If
the sidewall sticks out farther than the rim (most common), and they just flop a
yardstick down across the sidewall and measure to the mounting face, they aren't
getting an accurate measurement of backspacing.
Since two wheels of the same technical width (say, 14 x 6) can have different
overall widths due to the shape and thickness of the bead, just taking the
backspacing measurement isn't really enough to be accurate. You really need to
measure backspacing and frontspacing, then subtract frontspacing from
backspacing and divide the difference in half. The resulting number is the
offset. If the frontspacing is larger than the backspacing, the resulting number
will be negative, meaning it has negative offset (see Question #1). You need
positive offset for a roadster, generally around 3/8" or about 9mm, although
anything from 0 to 15 seems to work depending on the tire, suspension, etc.
The brake lines should fit inside the wheel, although this can be very close, so
measuring from the mounting flange shouldn't be relevant. Make sure there is
room here. I had a near-disaster once when a taped-on wheel weight caught the
line and ripped it off the caliper. Zero brakes in 75mph traffic can be real
exciting! 8^0
Question #3 - Only a clear answer to the question "Will this combination fit?".
;-)
Gordon Glasgow
Renton, WA
> -----Original Message-----
> From: owner-datsun-roadsters@autox.team.net
> [mailto:owner-datsun-roadsters@autox.team.net]On Behalf Of
> WisslerJon@aol.com
> Sent: Wednesday, May 01, 2002 5:23 PM
> To: "Gordon Glasgow"
> Cc: datsun-roadsters@autox.team.net
> Subject: Re: RE: Wheel Fitment
>
>
> Gordon and all,
>
> Thanks a bunch, and I hope to put this issue to rest with a series of
> stupid questions. It seems to be common knowledge that 0 to 15
> offset works best on the Roadster.
>
> Question #1 = Is that Positive offset (I thought so) or negative offset.
>
> Question #2 - Why wouldn't it make more sense to consider how much
> distance from the back of the mounting flange to the inner edge of
> the wheel/tires in combination with the distance from the back of the
> mounting flange to the outer (street side) edge of the wheel/tires?
>
> It seems that the Roadster configuration is limited by how much room
> you have from the mounting flange to the brake lines on the inner and
> the mounting flange and the inside fender edge on the outer. I think
> I recall someone providing these measurements a few years back. That
> way I could consider 14 x 5.5, 14 x 6, 15 x 6, or whatever x
> whatever. It seems that everytime I ask someone what the offset of
> their wheels is they don't know what the heck I'm asking, but they
> know how to take a ruler and measure from the mounting plate as I've
> suggested.
>
> Question #3 - Am I missing something here?
>
> Thanks in advance.
>
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