BigRed12
Proven Member
- 62
- 1
- Jan 23, 2013
-
Smithfield,
Virginia
I have plans to go with a much wider tire and wheel and am looking at going with an 18" wheel. But determining a proper offset has been a bit of a pain. Overall my height wont really change going from a 225/45-17 to a 255/35-18. But, I think I have found a calculation that makes sense.
Tire Dimensions:
Old 225 wide, 634.3 overall height
New 255 wide, 635.4 overall height
with a difference of 1.1mm, I am not at all worried about height differences
So, Currently I have a 17x7" wheel with a +45 offset and converted I get these numbers:
Width - 7 x 25.4 = 177.8mm
Centerline - 177.8 / 2 = 88.9mm
Hub surface - 88.9 + 45= 133.9mm
With the dimensions and math from the old wheels we can continue to the new 18x9.5" wheels
Width - 9.5 x 25.4 = 241.3mm
Centerline - 241.3 / 2 = 120.65mm
Now, we know the old wheels fit so we can determine that the hub surface needs to be about 134mm from the inside of the wheel.
New offset - 133.9 - 120.65 = 13.25mm
So with this math, we can determine a wheel sized at 18x9.5 with an offset of +15 will be ideal.
Does this make sense to anybody else? Are there an major flaws in my math or how this would work?
Also, I do know that there will be clearance issues at the fender, but I will be going with either flares or full custom fenders. So, I am not worried about fender clearance, just Knuckle clearance.
I could also use the tire width and used the same math and that might make a bit more sense.
But what do you guys think?
Tire Dimensions:
Old 225 wide, 634.3 overall height
New 255 wide, 635.4 overall height
with a difference of 1.1mm, I am not at all worried about height differences
So, Currently I have a 17x7" wheel with a +45 offset and converted I get these numbers:
Width - 7 x 25.4 = 177.8mm
Centerline - 177.8 / 2 = 88.9mm
Hub surface - 88.9 + 45= 133.9mm
With the dimensions and math from the old wheels we can continue to the new 18x9.5" wheels
Width - 9.5 x 25.4 = 241.3mm
Centerline - 241.3 / 2 = 120.65mm
Now, we know the old wheels fit so we can determine that the hub surface needs to be about 134mm from the inside of the wheel.
New offset - 133.9 - 120.65 = 13.25mm
So with this math, we can determine a wheel sized at 18x9.5 with an offset of +15 will be ideal.
Does this make sense to anybody else? Are there an major flaws in my math or how this would work?
Also, I do know that there will be clearance issues at the fender, but I will be going with either flares or full custom fenders. So, I am not worried about fender clearance, just Knuckle clearance.
I could also use the tire width and used the same math and that might make a bit more sense.
But what do you guys think?