Offset and Backspacing
Made Simple:
This is an area that can easily cause
much confusion. While these terms are often used interchangeably,
they are not the same. Further confusing all of this is the fact
that rim width is the distance between the rim flanges (where the
tire bead contacts the rim), so that the actual wheel width from edge to edge is
1.0" greater that the stated wheel width, making a 6.0" rim actually measure
7.0" wide at it's widest point.
- Backspacing refers to the distance from the mounting surface of the wheel (where it contacts the hub) to the back side (inwards-facing) edge of the rim. The easiest way to measure this is by placing a bare wheel on the floor upside down. Place a straight-edge across the wheel, then use a ruler to measure the distance from the bottom of the straight edge to the mounting surface of the rim. Stock 510 wheels have about 4" of backspacing, and this is a good measurement to shoot for. You can try to measure backspacing with a tire mounted on the wheel, but you will have to adjust your measurement if the tire sidewall extends beyond the rim.
- Offset refers to how much the hub mounting surface of the wheel is offset from the wheel's center, usually given in millimeters. Wheels can be positive or negative offset. Datsun 510s like anywhere from zero to up to +25mm of offset. To get this measurement requires a bit of basic math. First measure overall wheel width from the outside edges of the wheel lips, then divide this measurement in half. Next measure the backspacing as above. A 7" wide wheel is actually 8" wide from wheel lip to wheel lip. If the hub mounting surface were exactly in the center of the wheel, it would have zero offset. It would also have 4" backspacing. Many of the 13" x 7" American Racing Libre wheels are just like this. If the backspacing on this wheel were 3", then the wheel offset would be +25mm (1 inch = 25.4 mm). Panasport made 13" x 6" wheels for the 510 in both +9mm and +15mm offsets, and both fit fine, so you don't need to be super-precise with these measurements. As wheel diameter and width increase, you can usually get away with a bit more positive offset, as the 15" and 16" Panasports are +22mm offset. Most FWD cars use wheels that range between +30mm to +45mm offset.
-----Original Message-----
From:
[EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]]On
Behalf Of Adam Jackson
Sent: Monday, 25 March 2002 8:48 PM
To:
[EMAIL PROTECTED]
Subject: Re: TRX
Wheels
Terry,
I've never really understood much about back
space, offset etc. How can i
tell the amount of backspace or offset a certain
rim has when buying second
rims?
cheers,
Adam
----- Original
Message -----
From: "Terry Rudd" <[EMAIL PROTECTED]>
To:
<[EMAIL PROTECTED]>
Sent: Monday, March 25, 2002 6:23
PM
Subject: RE: TRX Wheels
> Adam,
>
> I just read
this again - big blooper on my part in the last post (I
> shouldn't reply
to these on busy work days)
>
> The backspace needs to be more than
100mm on the rim so it sits closer to
> the A arm and clears the guard lip
by more.
>
> regards
> TR
>
> -----Original
Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED]]On
Behalf Of Terry Rudd
> Sent: Monday, 25 March 2002 2:05 PM
> To:
[EMAIL PROTECTED]
> Subject: Re: TRX
Wheels
>
>
>
> Adam,
>
> 205's will fit
depending on what offset wheels - specifically TRX rims?
> I don't know -
anyone know what the backspace is on them. If they are less
> than 100mm
then they've got some chance with 205's but they would be tight
> as mine
is moderately low and i had to massage the rear guard lip with
>
195/60's
> and 100mm backspace wheels.
>
> TR
>
>
> Terry,
> >
> > Thanks very much. I think i'll have a look
for some 195/55 tyres and
check
> > out what sorts of prices are
about. Do 205/55 fit under the rear of a
1600
> > easily enough? ie
with no flaring and lowered suspension?
> >
> >
cheers,
> > Adam
> >
> > ----- Original Message
-----
> > From: "Terry Rudd" <[EMAIL PROTECTED]>
>
> To: <[EMAIL PROTECTED]>
> > Sent: Monday, March
25, 2002 12:18 AM
> > Subject: RE: TRX Wheels
> >
>
>
> > > Adam,
> > >
> > > I've seen
195/45x15 on H*ondahs - IMHO they look damn silly, 195/50
are
> >
also
> > > popular on 1600/180B but they are much smaller than the
stock tyres
rpm
> > > wise, they are very similar to running one
diff ratio lower. 195/55
> series
> > > are close to perfect
for a 1600/180B but for some reason only the exy
> top
> > >
end stuff make that size where as the cheapies come in 50 series
to
get
> > the
> > > H*ndahs & Excels, 195/65 or
205/60 are about right for 200B/Bluey.
Also
> > I've
> >
> found the 50 series 15" tyres are off the comfort scale to but 55
are
> very
> > > nice and handle just about as well.
>
> >
> > > regards
> > > Terry
> >
>
> > >
> > >
> > > -----Original
Message-----
> > > From:
[EMAIL PROTECTED]
> > > [mailto:[EMAIL PROTECTED]]On
Behalf Of Adam Jackson
> > > Sent: Sunday, 24 March 2002 9:20
PM
> > > To: [EMAIL PROTECTED]
> > >
Subject: Re: TRX Wheels
> > >
> > >
> > >
how much were these tyres?
> > >
> > > while on the
topic of TRX rims. What is the lowest profile you can go
> to?
>
> I
> > > just bought some trx rims last week and would like some
nice neat low
> > > profile tyres on them.
> > >
>
> > cheers,
> > > Adam
> > >
> > >
----- Original Message -----
> > > From: "Ben"
<[EMAIL PROTECTED]>
> > > To:
<[EMAIL PROTECTED]>
> > > Sent: Monday, March 25,
2002 12:18 PM
> > > Subject: Re: TRX Wheels
> >
>
> > >
> > > > a539s are beautiful, i have them
on my car, they stick like glue.
> > > >
> > > >
----- Original Message -----
> > > > From: "Paul Stanley"
<[EMAIL PROTECTED]>
> > > > To: "OZDAT Mailing
list" <[EMAIL PROTECTED]>
> > > > Sent:
Saturday, March 23, 2002 5:40 PM
> > > > Subject: TRX
Wheels
> > > >
> > > >
> > > > >
I bought some 15" TRX mags the other day for my 200B. I want
to
put
> > 205
> > > > on
> > > > >
the rear and 195 on the front, but I'm open to suggestions. I am
not
>
> > going
> > > > > to spare any expense on tyres, I'm
after a quiet comfortable ride.
> > > > >
> > >
> > I'm wondering what the highest profile I can go with the above
>
widths
> > on
> > > > the
> > > > >
live axle 200B with stock suspension, and what would be the
correct
>
> > > profiles
> > > > > so the speedo would have a
correct reading?
> > > > >
> > > > > I did
ask this before and James recommended Yokohama A539.
> > > >
>
> > > > >
> > > > > From: Paul
Stanley
> > > > > [EMAIL PROTECTED]
> > > >
> [EMAIL PROTECTED]
> > > > >
[EMAIL PROTECTED]
> > > > >
> > > >
>
> > > >
> > >
> > >
> >
>
> >
>
>
>
>
>
>
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