wheel E.T question

[rockit]

i want to fit new 19in rims to my boxster s trouble is the wheels i want are E.T47 front the guy rekons ill have trouble gettin them on with the red calipers i have ,will i be able to use spacers to fit
thanks in advance

[diver944]

You need to know the width and offset of your current wheel, as well as the width and offset of the new wheel. Then enter them all into this handy calculator to let you know the new positions of the inner and outer edges of the rim

www.1010tires.com/WheelOffsetCalculator.asp

[rockit]

cheers driver944 that was a great help mate now im sorted,,bring on the 19in rims

[Davi]

diver944 said:

You need to know the width and offset of your current wheel, as well as the width and offset of the new wheel. Then enter them all into this handy calculator to let you know the new positions of the inner and outer edges of the rim

www.1010tires.com/WheelOffsetCalculator.asp

OK, I'm confused by that site. I was always told offset was measured from the centreline to the back edge of the centre boss of the wheel, so, if you have a 7" 35mm offset, and go to an 8" 35mm offset, it will make no difference at all as the offset from the centreline to the inner edge of the boss is still 35mm, but the calculator is saying it's 13mm less obviously missing something simple here - if anyone could be so kind as to point out what!

[Gaity]

Could it be that if you maintained a 35mm offset, half of the extra width of the rim (1/2" or 13mm) would sit towards the car and possibly foul the inner body, so the reduced offset sets it back out again to maintain the original wheel/body spacing?

[Merritt]

Davi said:

diver944 said:

You need to know the width and offset of your current wheel, as well as the width and offset of the new wheel. Then enter them all into this handy calculator to let you know the new positions of the inner and outer edges of the rim

www.1010tires.com/WheelOffsetCalculator.asp

OK, I'm confused by that site. I was always told offset was measured from the centreline to the back edge of the centre boss of the wheel, so, if you have a 7" 35mm offset, and go to an 8" 35mm offset, it will make no difference at all as the offset from the centreline to the inner edge of the boss is still 35mm, but the calculator is saying it's 13mm less obviously missing something simple here - if anyone could be so kind as to point out what!

Offset is the distance from the centreline of the wheel to the hub mating surface...

These sites explain it quite well:

www.tirerack.com/wheels/tech/techpage.jsp?techid=101

and

www.yokohamatire.com/utcustom.asp

So with this in mind, if you increase the width of the rim (remember you are now changing the centre line fo the wheel) whilst maintaining the offset, you are changing the position of the wheel.

Steve

[Merritt]

Think of it another way...

8" in mm is 25.4 * 8 = 203.2mm (total wheel width)
7" in mm is 25.4 * 7 = 177.8mm (total wheel width)

so centre line is :

203.2 / 2 = 101.6mm (for 8" wheel)
177.8 / 2 = 88.9mm (for 7"wheel)

difference between centre lines of wheels = 101.6 - 88.9

= 12.7mm which is 13mm as near as matters..

Steve

[Davi]

Cheers guys, reading that I see the mistake I was making - I thought the upper of the two figures on the original website posted was the change in position of the inner surface in relation to the hub & brake ass (probably due to the original posters question specifically mentioning this) whereas as you say, it actually refers to the clearance of the upright which the inner wheel may foul against as the size increases.