These are the numbers I measured for my Sedan rear wheelhouse:

* Wheel mount face to Leaf Spring: 140 mm
* Wheel mount face to Inner Fender: 73 mm Right
* Wheel mount face to Inner Fender: 86 mm Left

So on a stock sedan the rear wheelwell has an internal usable width of 213 to 226 mm. The rear axle normally shifts to one side or another, but we can take the minimum distance.




Allowing for 4mm clearance to the Leafs, and 2mm to the fender lip, adding e=mc3, I get:

* Wheel hub is offset -30 mm from centerline. So +30 offset wheels (as with the stock wheels) will be perfectly centered inside the fender.

* Optimum offset: +30 for tires up to 175-wide front, 195-wide rear

* No Body Mods SEDAN REAR
Tire size Min. Max. Offset
155/80R12 6 58
165/70R12 7 56
165/55R12 12 52
175/70R13 16 48
185/60R13 21 43
195/60R13 26 38

* With Rolled Guards SEDAN REAR
Tire size Min. Max. Offset
205/45R16 23 29
205/60R13 24 27

* With 1" Flares SEDAN REAR
Tire size Min. Max. Offset
205/55R14 2 25
215/50R14 5 22
225/50R15 8 18
235/45R17 10 17

that works for stock width wheels... any change in wheel width will drastically change the offset requird

and i'm guesing no one will put 235s on a 4.5 inch wide rim!

I sure hope not. 235s require more like an 8"-wide rim.

But within the range of rim size recommended by the tire manufacturer, with any rim you use, the offset needed is still the same. The tire is what matters most as they are wider than the rims and the tire will hit the spring or the fender before the wheel. It will be different a bit with stretched tyres, but the offsets still hold true.

Say with 175/70R13, use can use any appropriate wheel (4.5" to 6" wide) with offset from +16 to +48 and still fit under the body. By contrast, a zero offset will position the tyre where it will not be totally inside the fender lip.

i think you are not correct there

an offset of +30 on a 6 inch wide rim is different to +30 on a 7 inch wide rim, this is because the offset is measured from the centre of the wheel

this means that the backspace is changing, the ider the rim gets the lower the positive offset you need to maintain the same backspace (or distance from tire/wheel to the leaf/strut)

this website demonstrates what i mean, go to the link and click "calculate" you can see the example has different offset on different rim widths to achieve the same "inner space"
offset calculator

you've also got to factor in how much leaf springs allow the rear axle to move laterally under hard cornering (which would surprise most people!) and for the axle to pivot about the centre of the axle in single wheel bump travel. Both of which means you need alot more clearance to the inner gaurd than you've allowed for. Give it an inch more if you have reasonably firm rear suspension. You'll probably still get some minor scrubbing on the inner arch though.

A panhard would help a little but they move the axle one way or the other depending on which way you're turning. A Watts link would help maintain clearance both sides.

Quote:

yeah, but if tyre width remains the same, the clearance is not affected much at all if the offset remains the same, as long as the wheel fits in there. Obviously there's a limit to how much wider wheel you can fit, but DD's example of the 175/70 on a 4.5 to 6" rim is on the money. Clearance is not affected.

i have used this page heaps already and even used it when i was getting rims made up for my ute, enter the stock rim and tyre dimentions then the new ones your looking at or even use it to give you the info your looking for

http://www.willtheyfit.com

Steve

Quote:

So true. Many have reported using 205s on the rear but along the lines of your comment I would not recommend it but leave a little more room than they are running. So I listed 195-width tyres as the max. If you keep the tire diameter down, it's less of a problem body-side. Many 1200 owners are running their tyres right on the edge of the body lip with occasional rubbing.


Anyways, here's how Offset affects where the tires are located
(not entirely to scale, but fairly representative of the rear of a Sedan)




0 offset will hit the body lip. You can roll it to gain the needed clearance, but it's not enough.



Any more offset than this and they hit the leaf spring



And of course with any Negative offset, the tyres will stick out -- regardless of the wheel width. But the deep lip rims do look beautiful.

I'd go along with that. I had 205/60x13s on a 1200 sedan (my first car actually). Scrubbed inside and out. They were on 13x6 Cheviot Raiders, nfi what offset they were.

Now about WIDE tires

235/45R17 requires a wheel width of 7.5 to 9"

235/45R17 might work fine with +10 offset and 1" flares?



You could also go with Zero offset and larger flares. Zero offset will space the tire farther outboard.




This is also a fairly tall tire (about the same height as 185R14). So the rear should be at stock height and fenders need to be flared out, or cut away a bit with overfender flares.