[MINIAC]

 
     WHEEL           SIZE      ET      LB       KG
---------------     ------     --     ----     ----
SSR Competition     15x7       42      9.6     4.36
OZ Superleggera     15x7       37     10.7     4.86     [N/A]
Kosei K1 Racing     15x7       38     13.5     6.14

SSR Competition     16x7       42     11.3     5.14
OZ Superleggera     16x7       37     14.3     6.50
Kosei K1 Racing     16x7.5     43     15.0     6.82

SSR Competition     17x7.5     42     13.0     5.91
OZ Superleggera     17x7       37     15.1     6.86
Kosei K1 Racing     17x7.5     45     16.0     7.27
BBS RK              17x7       42     17.5     7.95

Click highlighted wheels for pictures.

[Keith]

Great info.

The prices for the 17" wheels are:

SSR Comopetition: $375
OZ Superlegerra: $280
Kosei K1 Racing: $199 (listed as a special price)
BBS RK: $289

That's a big price jump to save the last two pounds.

May be a dumb question: what is ET and what is a good value for it?

[rambo]

Quote:

Originally posted by Keith
May be a dumb question: what is ET and what is a good value for it? [/b]

that's the offset in millimeters, in this case positive.
what's the best-i'd say following the stock measurements of 48mm on the r85/r90 of 50mm/48mm on 7 inch wheels.the question is what that means when you want to buy 7.5 inch wheels. the extra 0.5 inch is equal to 6.35mm so does it mean you need to go for 42mm (48mm-6mm)?

i read in a car (tuner) magazine (2002) that a 1 lb wheel reduction is equal to 1.5 lb reduction in vehicle weight and with tires it's 2 lbs.

[DaveNagy]

I'm thinking you'd want to "split the difference", offset-wise. If you go with a wheel that's (say) 6mm wider than stock, wouldn't you want your offset to be 3mm less than stock? That way, you'd be splitting the 6mm of "extra" width between the inboard and outboard sides of the wheel.

So, if 48mm is the "perfect" offset for a 7" wide wheel, perhaps 44mm would be about right for a 7.5" wheel.

(I'm just making this up as I go, so somebody slap me down if I'm spreading misinformation.)

-Dave

[Keith]

It looks like rambo has split the differece - 6.35mm is actually 1/4".

It sounds as though the OZ wheel would be 11mm closer to the center of the car than standard. Am I getting this right?

I am trying to understand what this offset is. The car has a physical offset between the mounting plate for the wheel and where the center of the tire is expected it be. If this was the offset specified in the wheels then it would not change as the rim widths changed. This suggests an offset from one edge of the rim to the mounting plate. Measuring from the outside of the wheel would give an offset that you would make larger instead of smaller when you went for a wider wheel. That leaves an offset from the inside egde of the wheel to the mounting plate but the values do not seem large enough.

... so, what does the offset measure?

Now for the next dumb question: how did an offset get to be called ET?

[MINIAC]

The FAQs on wheels have quite a few embedded links explaining related terminology ... one of these is for offset

[rambo]

Quote:

Originally posted by Keith
It looks like rambo has split the differece - 6.35mm is actually 1/4".

It sounds as though the OZ wheel would be 11mm closer to the center of the car than standard. Am I getting this right?

I am trying to understand what this offset is. The car has a physical offset between the mounting plate for the wheel and where the center of the tire is expected it be. If this was the offset specified in the wheels then it would not change as the rim widths changed. This suggests an offset from one edge of the rim to the mounting plate. Measuring from the outside of the wheel would give an offset that you would make larger instead of smaller when you went for a wider wheel. That leaves an offset from the inside egde of the wheel to the mounting plate but the values do not seem large enough.

... so, what does the offset measure?

Now for the next dumb question: how did an offset get to be called ET?

from my research:

the offset a) is measured from the centerline of the wheel b) can either be positive or negative

i'm a newbee myself so i'm in no better shape than you-but yes, i did split the difference of the increased half-inch of the wheel and subtracted it from the std offset : this basically spreads the the tire width increase evenly on both sides of the wheel (1/4") in the "HOPE" that
1)this achieves the closest wheel mass distribution spec as the mfr wanted on the car
2)by doing so, the increased 1/4" on both sides DO NOT
a)make the inner wheel side hit the strut or b) make the outer wheel side hit the fender.

i think we need an expert here-plus we're missing clearance measurements between the stock wheels and the strut (and possibly the fender).

[Keith]

Yes - an expert would be good. We will have to guess until one jumps in this thread...

I am now wondering why you would want a different offset for different rim widths. If the offset is from the wheel centerline to the mounting plate, then two wheels with the same offset will have the same centerline on the car regardless of their rim widths. If you are putting the same tire on a 7" or 7.5" rim, only the centerline affects the side clearances as it is the edge of the tire, not the rim that matters. My guess is you should keep the offset the same when the rim width changes. But that is just a guess.

I would also like to know is the impact the 11mm offset change between the Oz and stock wheels. It sounds very significant.

questions, questions, questions... help, we need an expert!

[DaveNagy]

I believe the reason we need to change the offset when changing the width of the wheel is simply because there is only a tiny bit of clearance between the inside of the (front) wheel and the strut, and we want to try to preserve this clearance. (Without making it any bigger than necessary.)

If you install a 1" wider wheel that still has the stock 48mm offset, it will stick an extra 1/2" inch inwards, and an extra 1/2" outwards. The outward part is no problem, but I believe you would risk the tire rubbing against the strut. So, what do you do? You buy a wheel with "less" (positive?) offset. This "pulls" the centerline of the wheel outwards, closer to the mounting plane. This frees up some extra space inboard, but brings the outer edge of the tire even closer to the fender lip. There's a limit how far this strategy can be followed. (That 37mm offset would push the wheel out a bunch, and I'd worry about fender clearance and extra stress on the wheel hubs. Maybe it's no big deal. No idea.)

Offset is the distance between the centerline of the wheel, and the plane where the hub and wheel actually touch. In the MINI, and most other FWD cars I think it is called a "positive" offset. In any event, it means that the lugnuts are outboard of the wheel's centerline. On the other hand, a deepdish wheel would have its lugnuts way back "behind" the centerline, and thus would have a negative offset of some sort.

A zero offset wheel would still be more deepdish than the stock MINI wheels. They'd stick way out of the fender wells. Think low-rider. To save money, you could hire the Incredible Hulk to manually add positive offset to these wheels by having him grab the mounted wheel and shove it violently towards the car. <screeeech> The center portion of the wheel would appear to come thrusting outwards as the centerline of the rim was shoved back behind it, opening up a measurable gap between those two planes. Once that gap reached 48mm, you'd want the Hulk to stop pushing. (This is always the most difficult part, in my experiance!)

As Hulk would say, "Less offset make wheel stick out more."

(All of the above may be wrong, but I think I'm pretty close.)

-Dave

[Keith]

Thanks - this is starting to make sense...
This suggests having too large an offset can be fixed with wheel spacers but you can end up screwed if you get wheels that have the offset too small.

[BruceK]

Some of this discussion about offset seems to be fixating on the clearance of the wheel and or how a wheel looks on the car, but my understanding is the real reason for sticking to the manufacturer's specific wheel offset is to maintain the suspension geometry that has been engineered into the vehicle.

Quoting from the TireRack site that MINIAC referenced above in the FAQs:

"If the offset of the wheel is not correct for the car, the handling can be adversely affected."

[MINIAC]

DaveNagy is correct ... the lower the offset, the more the wheel (tire) is pushed toward the fender.

Rather than considering the width of the wheel, you should be concerned about the width of the tire (in conjunction with the offset).

Of the factory wheel/tire combos, the 205/45 tires on 17" ET50 R85 wheels puts the edge of a tire closest to the struts (and also to the fender). As far as aftermarket goes, I've read about someone running 215/40 tires on 17" ET37 BBS RZ wheels, but they also reported slight rubbing in certain situations. The new Panasport 16" wheel is ET35 and is supposed to work fine with 205/50 tires (3mm farther away from fender than 215/40 tires on 17" ET37 wheels).

The above fitments seem to define a "comfort zone" between 70.5mm outside the mounting face of the wheel hub to 152.5mm inside.

Two things to bear in mind:

1. Lowering the suspension will undoubtedly change this "comfort zone".

2. Specified tire width doesn't necessarily mean actual tire width.


A couple of questions:

1. Anyone running 17" ET37 OZ Superleggera - what tire dimensions?

2. Anyone running wider than 215 tires - what wheel offset and tire dimensions?