Wheel fitment question

[WildBillyT]

Bear with me here, I'd really appreciate your input.

So I was all set to sell off my TTD's because they don't fit the car with only 3.75" of backspacing. Well, on a hunch I measured my 9" rear- and it comes out to 58.125" vs the 12 bolt's width of 60".

So I got out some measuring tools and went to town.

First, I laid the rim and tire flat on the ground and measured the distance from the ground upward to the wheel mounting surface, and it came out to 6.625". So the distance from the mounting surface to the outer edge of the wheel is that number.

Then I taped a plumb bob to the inside of the quarter panel wheel lip so that it dropped down right in front of the axle. When I measured from the axle flange to the plumb bob string, I got a distance of 6" even. So I have 6" of space between the flange and the body lip.

Based on this it's obvious why they don't fit- I need 6.625" of space and I only have 6".

But on the 9", the flange is .9375 of an inch closer to the centerline of the car, so I would have 6.9375" of space with that rear installed if my logic works- and then I'd have roughly a third of an inch between the outer edge of the tire and the quarter panel lip.


Does this make sense to you guys? It seems to make sense to me.

Executive summary:

Will a rear that's 2" narrower make the wheels act like they have 1" more of backspacing (each)?

[sweetbmxrider]

i would think yes. will you run into issues with the inside of the wheel now?

[WildBillyT]

Originally Posted by sweetbmxrider

i would think yes. will you run into issues with the inside of the wheel now?

I don't think so. I think it wouldn't change anything except move the entire wheel in 1", offsetting the fact that it's out 1" too far...

[sweetbmxrider]

yeah the entire rim will be 1 inch closer to your inner fender, correct? there is probably a good amount of room there though. what is the difference in the brake setups between the 9inch and 12 bolt?

[WildBillyT]

Originally Posted by sweetbmxrider

yeah the entire rim will be 1 inch closer to your inner fender, correct? there is probably a good amount of room there though. what is the difference in the brake setups between the 9inch and 12 bolt?

Yes, it will be 1" closer. But like I said- the rim itself is 1" out farther than stock.

The 12 bolt has drums on it, so I figure that's 1/8" that the rim is further outward. The 9" has no brakes on it at all. It will get disc brakes, and I'm hoping that the rotor hat will be 1/4" or 3/16" thick.

[SRGN]

Originally Posted by WildBillyT

Executive summary:

Will a rear that's 2" narrower make the wheels act like they have 1" more of backspacing (each)?

Simple answer. The wheels will tuck in nearly an inch more on each side.

[Pampered-Z]

Not sure how to expalin myself here:

Don't forget to account for the disk caliper. Some rims have a short inside offset they do not have enough area to clear the caliper as it extends beyond the outer edge of the rotor.

Also, a 1/3" between the tire and fender lip seems tight to me? You really need to check that body roll or squat don't cause any contact.

How much clearance do you have between tire and inner fender?

[WildBillyT]

I think I'm going to end up biting the bullet and buying the Percy's wheel gauge from Summit.