Wheels question
Thread Starter
Burning Brakes
Joined: Jan 2010
Posts: 884
Likes: 84
From: New Boston, NH
Wheels question
Hi all,
So I have been looking at wheels lately and after reading many posts and learning about bolt patterns, backspace, offset and such, I am still confused about something. I am looking at the Ridler 650 and 695 in 18x9.5 and 18x8, with the specs below.
18x9.5 +6 offset 5.5 backspace
18x9.5 0 offset 5.25 backspace
18x8 0 offset 4.5 backspace
It seems to me that the wheels listed above were measured, backspace, based upon the width of the wheel with the lip factored in. Question is, is the factory 8 in wheel with 4 in backspace measured the same way? Seems like, if so, it should really be 4.5, or if not, maybe 3.5 backspace. I am having a hard time reconciling this and figure that there is something that I am missing. I am appreciative of any and all information the forum can provide.
Thanks,
Bryan (BEJ)
So I have been looking at wheels lately and after reading many posts and learning about bolt patterns, backspace, offset and such, I am still confused about something. I am looking at the Ridler 650 and 695 in 18x9.5 and 18x8, with the specs below.
18x9.5 +6 offset 5.5 backspace
18x9.5 0 offset 5.25 backspace
18x8 0 offset 4.5 backspace
It seems to me that the wheels listed above were measured, backspace, based upon the width of the wheel with the lip factored in. Question is, is the factory 8 in wheel with 4 in backspace measured the same way? Seems like, if so, it should really be 4.5, or if not, maybe 3.5 backspace. I am having a hard time reconciling this and figure that there is something that I am missing. I am appreciative of any and all information the forum can provide.
Thanks,
Bryan (BEJ)
Race Director
Joined: May 2006
Posts: 18,734
Likes: 2,582
The factory wheel 8" number is inner to outer tire mounting bead, the wheel is about 9" from inner to outer edges. It has 4" backspace so about 12.7 mm offset.
All wheels are measured that way.
All wheels are measured that way.
Last edited by MelWff; Sep 26, 2020 at 08:08 PM.
Thread Starter
Burning Brakes
Joined: Jan 2010
Posts: 884
Likes: 84
From: New Boston, NH
So, 12.7mm is about .5in. Backspace then is measured from mounting surface to the outer edge of the wheel (including the mounting bead)? Correct? So a 9.5in wheel is actually 10.5in wide, with 0 offset, 5.25 backspace is measured mounting surface to outer edge, leaving 5.25 from mounting surface to the front edge of the wheel. That wheel would be .25in further out than the stock wheel?
Race Director
Joined: May 2006
Posts: 18,734
Likes: 2,582
So, 12.7mm is about .5in. YES.
Backspace then is measured from mounting surface to the outer edge of the wheel (including the mounting bead)? Correct? YES.
So a 9.5in wheel is actually 10.5in wide, with 0 offset, 5.25 backspace is measured mounting surface to outer edge, leaving 5.25 from mounting surface to the front edge of the wheel. That wheel would be .25in further out than the stock wheel? YES.
Backspace then is measured from mounting surface to the outer edge of the wheel (including the mounting bead)? Correct? YES.
So a 9.5in wheel is actually 10.5in wide, with 0 offset, 5.25 backspace is measured mounting surface to outer edge, leaving 5.25 from mounting surface to the front edge of the wheel. That wheel would be .25in further out than the stock wheel? YES.
Last edited by MelWff; Sep 27, 2020 at 01:29 PM.
Le Mans Master
Joined: Jan 2001
Posts: 6,741
Likes: 1,383
