kylryn

Sorry guys if this is a stupid question but I just dont get it!
I'm thinking about upgradeing to some different wheels and I'm not to sure what the offset means? it doesnt sound like its a clean fit. Can someone please explain this so the average joe understands?
Thank you.

19x10: Offset: +79mm Backspace: 8 5/8 inch

18x9.5: Offset: +50mm Backspace: 7 1/4 inch


5x4.75: 18x9.5: Offset: +40mm Backspace: 6 7/8 inch


19x10: Offset: +56mm Backspace: 8 5/8 inch

Kevin VanSlooten

backspacing is space from hub to back of wheel

kylryn

So whayt does that mean? does the tire stick out that much further? If it has a 0% ofset is that the stock look?

Thanks

steponc

Wheel Offset is the measurement from the center of the rim to the hub surface that mates to the rotor. The measurements are "plus" when the hub is to the outside of the rim center line and "minus" when the measurement is to the inside or brake side of centerline.

Back space is measured from the hub to the back edge of the rim.

Rims are considered Front Wheel Drive (FWD) when the measurement is "plus" and Rear Wheel Drive (RWD) when the measurement is minus. Not to be confused with the actual drive wheels of the car.

This was learned after making a mistake on a set of custom wheels. Very costly!!

Y2Kvert4me

This explains it pretty well.

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

C5's use positive offset wheels. Offset is always measured in millimeters, it is not a percentage. This dimension is also directly related to backspace dimension...if you know the backspace and width of wheel, you can calculate the offset. If you know the offset, you can calculate the backspace.

In more simpler terms, a higher offset dimension pushes the wheel inward more. Less offset pushes the wheel outwards. If you change the width of the wheels (ie: going from a 9.5" wheel to an 11" wheel, the ideal offset also changes.

The offset of stock C5 wheels are as follows:

C5:

Front 17x8.5 - 58mm
Rear 18x9.5 - 65mm

Z06:

Front 17x9.5 - 54mm
Rear 18x10.5 - 58mm


If you are comparing the 2 sets of wheels in your post, and those are your only choices...choose the 50mm fronts, and the 56mm rears.

Mr. Lucky

what Tom said

Seriously, here is an offset calculator that may help also.

steponc

I just looked at the calculator mentioned above. What a great tool. Put it in my favorites.

Thanks
Step-on-C

kylryn

Thanks guys!!

Darion

to the offset calc.

2kbluestreak

Back Spacing is more important and comes in handy if you're considering wider wheels for wider tires. Say you use a 3/4" thick piece of wood and it slides between the inside sidewall of the original tire and whatever non-rotaing part of the car that is closest to the tire, such as the frame, inner fender lining or Macphearson strut(other than C5). That means that you have apporximately 3/4" clearance or 19mm. A practical limit for this is probably around 9mm or .355"; therefore, you subtract 9mm from 19mm getting 10mm, which is how much more back spacing you can use with a wider wheel. Most manufactures of wider wheels will push the outside rim further out, typically 15mm, giving you a 1 inch wider wheel. This will likely push the side wall a little outside of the fender lip, but will keep the tread inside the lip. In this example, the offset has been changed by 2.5mm. If he had moved the outside of the rim 10mm, offset would have stayed the same.