Wheel backspacing explanation.
Thread Starter
Melting Slicks
Joined: May 2001
Posts: 2,812
Likes: 4
From: Gig Harbor Wa
Wheel backspacing explanation.
People get so wrapped around the axle with the whole backspacing thing. Its not about the backspacing. Its about total tire width.
What you need to do is find the total width of your tire. For example:
255/60/15 has a total width right around 10.5"
Now this is mounted on an 8" rim with neutral offset or 4" backspacing. Everyone knows that the 255 fits excellent and looks great.
Now lets say you want to run a 275/40/17. Total width 10.9" on a 9.5" rim. At first you might think that since you are adding 1.5" to the wheel, you need 5.5" backspacing. Well this is not true at all. The tires are essentially the same width so we want to place them in the same position relative to the body to get the right look. This means we need a wheel with a neutral offset just like the 255's which leads us to a 9.5" rim with 4.75" backspacing. Just like WA 2 FST has on his car. In theory, you should be able to run the 275/40/17 on stock TA's.
What you need to do is find the total width of your tire. For example:
255/60/15 has a total width right around 10.5"
Now this is mounted on an 8" rim with neutral offset or 4" backspacing. Everyone knows that the 255 fits excellent and looks great.
Now lets say you want to run a 275/40/17. Total width 10.9" on a 9.5" rim. At first you might think that since you are adding 1.5" to the wheel, you need 5.5" backspacing. Well this is not true at all. The tires are essentially the same width so we want to place them in the same position relative to the body to get the right look. This means we need a wheel with a neutral offset just like the 255's which leads us to a 9.5" rim with 4.75" backspacing. Just like WA 2 FST has on his car. In theory, you should be able to run the 275/40/17 on stock TA's.
Safety Car
Joined: Oct 2000
Posts: 4,080
Likes: 565
From: Allen TX
Re: Wheel backspacing explanation. (70 LS1)
People get so wrapped around the axle with the whole backspacing thing. Its not about the backspacing. Its about total tire width.
What you need to do is find the total width of your tire. For example:
255/60/15 has a total width right around 10.5"
Now this is mounted on an 8" rim with neutral offset or 4" backspacing. Everyone knows that the 255 fits excellent and looks great.
Now lets say you want to run a 275/40/17. Total width 10.9" on a 9.5" rim. At first you might think that since you are adding 1.5" to the wheel, you need 5.5" backspacing. Well this is not true at all. The tires are essentially the same width so we want to place them in the same position relative to the body to get the right look. This means we need a wheel with a neutral offset just like the 255's which leads us to a 9.5" rim with 4.75" backspacing. Just like WA 2 FST has on his car. In theory, you should be able to run the 275/40/17 on stock TA's.
What you need to do is find the total width of your tire. For example:
255/60/15 has a total width right around 10.5"
Now this is mounted on an 8" rim with neutral offset or 4" backspacing. Everyone knows that the 255 fits excellent and looks great.
Now lets say you want to run a 275/40/17. Total width 10.9" on a 9.5" rim. At first you might think that since you are adding 1.5" to the wheel, you need 5.5" backspacing. Well this is not true at all. The tires are essentially the same width so we want to place them in the same position relative to the body to get the right look. This means we need a wheel with a neutral offset just like the 255's which leads us to a 9.5" rim with 4.75" backspacing. Just like WA 2 FST has on his car. In theory, you should be able to run the 275/40/17 on stock TA's.
As you are well aware to keep the _outside_ wheel/tire profile the same as current, you have to add any width to the inside. I think this is why people (including myself) ask a lot of questions about it.
I can tell you right now there is no way my new rear wheels/tires would have fit with the stock TA's had I not at least relocated the e-brake bracket, and quite honestly I don't believe _on my car_ they would have fit even if I'd done that. I sat under the car for a long time, measured 3-4 different times (to try and give myself a fresh perspective each time I measured) and came to the conclusion that unless I ran 4-4.5" BS maximum I could not have fit the new combo under there without interference. Since I knew I wanted at least 4.75" BS, I decided to go ahead and get the offset TA's. Knowing what I know now, I could have run 5" BS with no problems, but it all looks good, and my wheel bearings will thank me for using a neutral offset. :)
Also, I'm sure you're aware of this too, but it is good to check each manufacturer's measurements for the _same_ size tire. They do differ slightly. It isn't going to make a huge difference, but nevertheless its good to check. Tire Rack's website allows you to compare and contrast a number of different brands/sizes.
