How to determine proper offset??
#1
How to determine proper offset??
Ive been checking craigslist for rims every now and then and just came across some really cool looking boss motorsports 340s. There 20x8.5 with a +14 offset and a 5 on 4.5 bolt pattern. Will these fit right on my car? and does anyone know much about these rims? i googled but couldnt find much about them
#2
I cant say for certain that those will fit your car, but the 18" FRPP Bullitts I just put on ours were 18" x 8.5" with a 50mm offset. The stockers were 16" x 7"? and a 39mm offset.
14 mm seem pretty deep dish and may put the rims/tires outside of the fenders, but you will prob get better info from others on here!!!
14 mm seem pretty deep dish and may put the rims/tires outside of the fenders, but you will prob get better info from others on here!!!
#4
Sounds like they're for the earlier cars that came with wheels more like +22 mm.
The outer flange surface will sit almost 1.38" further out than the 18 x 8.5 OE wheels. Measure the clearances that you have now carefully, and keep in mind that if your choice in 20" tires is either wider than 235 or taller than 27" overall that you'll lose a little more clearance. Up front, check also with the wheels steered.
FWIW, cars tend to drive better, can be less "nervous" or "darty" under hard braking, and have a better "feel" at the steering wheel when the offset doesn't differ too much from OE.
Norm
The outer flange surface will sit almost 1.38" further out than the 18 x 8.5 OE wheels. Measure the clearances that you have now carefully, and keep in mind that if your choice in 20" tires is either wider than 235 or taller than 27" overall that you'll lose a little more clearance. Up front, check also with the wheels steered.
FWIW, cars tend to drive better, can be less "nervous" or "darty" under hard braking, and have a better "feel" at the steering wheel when the offset doesn't differ too much from OE.
Norm
Last edited by Norm Peterson; 05-12-2010 at 07:00 PM.
#5
+14 isn't enough offset, the lip of the wheels will be poking out.
this link helps you figure out offsets...
http://www.1010tires.com/WheelOffsetCalculator.asp
I found a better one at one point but it's bookmarked on my other computer.
this link helps you figure out offsets...
http://www.1010tires.com/WheelOffsetCalculator.asp
I found a better one at one point but it's bookmarked on my other computer.
#7
Backspacing is the value you want to compare.
It does not depend on the rim width where as offset
has a direct relationship with the width.
If the rims are the same width as stock, the offset applies.
If the rims have a different width that OEM, then the
offset # goes out the window unless you compensate for
the differences in rim widths.
Backspacing does not care about the rim width.
Offset does....
16x7 39mm offset
17x8 45mm offset
18x8.5 50mm offset
Three different OEM rims with different widths
and different offsets but all stick under the fenders
the same on the S197.
It does not depend on the rim width where as offset
has a direct relationship with the width.
If the rims are the same width as stock, the offset applies.
If the rims have a different width that OEM, then the
offset # goes out the window unless you compensate for
the differences in rim widths.
Backspacing does not care about the rim width.
Offset does....
16x7 39mm offset
17x8 45mm offset
18x8.5 50mm offset
Three different OEM rims with different widths
and different offsets but all stick under the fenders
the same on the S197.
#8
You really need both numbers as well as the width.
Backspacing is a quick way of estimating clearance on the inside only.
Offset is a little better at estimating fender-side clearances, and is the number that means more with respect to how the car will end up "feeling" when you drive it.
But you can calculate backspacing from offset (and vice versa) close enough in most cases. The 1" is approximately the total of the two flange thicknesses for alloy wheels.
Offset = Backspacing - [Advertised Width + 1"] ÷ 2
Backspacing = Offset + [Advertised Width + 1"] ÷ 2
Norm
Backspacing is a quick way of estimating clearance on the inside only.
Offset is a little better at estimating fender-side clearances, and is the number that means more with respect to how the car will end up "feeling" when you drive it.
But you can calculate backspacing from offset (and vice versa) close enough in most cases. The 1" is approximately the total of the two flange thicknesses for alloy wheels.
Offset = Backspacing - [Advertised Width + 1"] ÷ 2
Backspacing = Offset + [Advertised Width + 1"] ÷ 2
Norm