Offset Question

[benny]

Does anyone know if a

 

16x7 +24 (fronts)

 

and

 

16x8 +26 (rears) will fit on a zed??

 

Thanks,

 

Ben

[luvemfast]

 

Does anyone know

No, I don't. thanks for asking

 

Call Benzed, he should know.

 

[Roberto]

You will find that they will be too close to the spring perch and probably hit it at the rear.  If you use 15-25mm wheel adapters / spacers, then you should be ok depending on tyre width.

 

Aim for a lower offest of zero to +15 (max) for rims of that width.

[benny]

sorry i shouldve mentioned i didnt want responses from ZX owners ;D

 

I thought that would be the case roberto just for some reason i thought the orig z offset was around +20

[Zeddophile]

Does anyone know if a

 

16x7 +24 (fronts)

 

and

 

16x8 +26 (rears) will fit on a zed??

 

Thanks,

 

Ben

 

Its been asked a few times, and the big factor in it all is what struts does your car have?  There are 3? different struts, all of which have different limitations on rim size.  There is more information on the struts and which widths/offsets will clear in the big sticky thread at the top of this section (240Z & 260Z Wheel/Tyre Options, Offset, Backspace).

 

sorry i shouldve mentioned i didnt want responses from ZX owners ;D

 

I thought that would be the case roberto just for some reason i thought the orig z offset was around +20

 

Original offset may well be +20, but remember this (I think you may be getting confused with backspace, more on that at the bottom):

Offset is a measurement which specifies the location of the mounting face of the wheel (the part in contact with the hub when you fit the wheel) with respect to the centreline of the wheel.  Positive offset means the mounting face is outboard of the wheel centreline (effectively pushing the rim's edges inwards to the centre of the car), and negative offset obviously means the mounting face is inboard of the centreline (rim edges move outwards).

 

With that in mind, assume you have a 14x6 with +25 offset, and a 14x10 with +25 offset.  In this situation, your rim now sticks out an extra 2 inches either side (as in, the outer face is now 2 inches closer to the outside of the car, and the inner face is also 2 inches closer to the centre of the car.  If you now change the 14x10 to have 0 offset (approx 1 inch less), you now have a rim that sticks out 3 inches more on the outside of the car, and 1 inch more on the inside of the car (compared to the 14x6 we started with).

 

Getting the right offset is a juggling act which involves change in rim width, clearance to the strut and body on the inside, and guard clearance on the outside.  When you start playing with rim widths, original offsets have no use other than as a reference point to calculate where the new wheel will end up from what you currently have on the car.

 

Backspace, however, is somewhat more useful in respect to zeds.  It specifies the distance of the mounting face away from the BACK EDGE of the rim.

Lets pretend now that we have a 14x6 with a backspace of 4 inches, and a 14x10 also with a backspace of 4 inches.  The back edge of the rim stays in exactly the same place with respect to the car (the hub that the wheel bolts to hasn't moved, has it!), and all the 4 inches of extra rim width protrudes toward the outside of the car.  For the sake of completeness, let's now change the 14x10 to have 6 inches of backspace.  Now your rim sticks out 2 inches to the outside of the car, and 2 inches to the inside.

 

Clear as mud?

[benny]

Thanks for that zeddophile... just cleared all that up :D

[Zeddophile]

Thanks for that zeddophile... just cleared all that up :D

 

I just added a bit more while you were reading it - the last paragraph is new, it explains backspace which I suspect you may have been confusing with offset.

 

Incidentally, given any two out of backspace, width and offset, you can work out the other, if you wanted.  Probably only useful if looking at American wheels though, as they seem to be the only ones who still use backspace instead of offset.

[benny]

i prefer backspace now!! any idea of what the backspace should be at a maximum??

[Zeddophile]

i prefer backspace now!! any idea of what the backspace should be at a maximum??

 

Again, depends on your struts (and possibly your tyre size, depending on where the clearance issue is).  And don't forget, backspace still won't tell you how much clearance you have to the guard at the outside edge of the wheel 

 

Personally, I see no reason to use backspace over offset for calculating your theoretical clearance, the important thing is to understand what the two measurements mean, how they differ to each other, and what effect increasing rim width will have with relation to them.  And the ultimate test is to actually try and fit the wheel you've selected.  Rim widths are not usually measured to the very outside edge of the rim, they measure to the outside of the vertical surfaces at the edge of the rim (the part the tyre pushes against the back of when inflated).  The horizontal lips can be different sizes depending on manufacturer and style, likewise two tyres of the same size from different manufacturers can actually be different sizes.

 

Hmmm.... I wonder if anyone has written a calculator like the Miata.net tyre calculator, but for rim widths and offsets?

 

*edit* The answer is yes http://www.rimsntires.com/rt_specs.jsp  Gives a bunch of notes down the bottom on the effects of the wheel and tyre sizes you've chosen versus the original.  Won't let you select too wide a rim for a tyre, so if like me you are trying to enter a 195 tyre on a 10 inch rim, and wondering why it won't work properly 

[Scottz]

I am fitting Rota RB 16x7+4 offset to my 1978 260Z 2+2. I nearly bought the 16x8+4, but after a double check, and the pictures from Whittie, I changed my mind.

Outside edge of rim just clears the inner lip of the front gaurd (1mm to spare), and about 14mm clear of spring perch (2nd knuckle of pointy finger ) on the inside edge. So if you don't want to change anything, there is not much room to move. I think maximum backspace recommended is 114mm. These Rota's have 106mm backspace.

A 7" wide rim with +10 offset would be a better fit (bring the wheel in 6mm closer to the spring perch) for the front, if you can find one of your liking.

Yeah - lots of discussion has gone around about wheel and tyre size choice. There seems to be a few variations between models as the cars rolled off the production line over the years. You have to measure your setup to be sure, 'cause what one person has on their ride may not fit yours.

I'll update with rear fit once I get the pics sorted.

[Scottz]

Part 2: Rear fit.

Here are pics of the Rota RB 16x7+4 on the rear of my 1978 260Z 2+2.

Lots of clearance on the inside between strut tube and inner rim edge. Spring perch is higher up on the rear suspension.

About 18mm clear from rim outside edge to the gaurd inner lip.

So an 8" wide rim on the rear would be a better fit. But you can't always buy 2 of size A for front and 2 of size B for rear with different offsets for front and rear. Sets of 4 all the same are cheaper. Sure you can get something made, if you want to spend the big bucks.

Also if you want maximum usage of tyres, it's preferable to get all 5 the same size and rotate them properly (include spare).

Alternatively have front and rear tyres the same diameter so the spare will fit any corner.

If you aren't worried about those 2 points, then there are a lot more options.

I wanted to smarten up the look with new rims and rubber, but keep the original appearance of the car with no flares, no messing with the gaurds, no massive rubber and a spare that fits anywhere.

KISS - Therefore 5 of 16x7's with +4 to +10 offset and it doesn't attract the wrong kind of attention (blue uniforms).

Cheers,

Scottz.

[NZeder]

Original rims were 14 x 5.5 +18 if the alloys and 14 x 5 + 20 for the steel with hub caps IIRC there were some fitted with 14 x4.5 steel rims too.