Front Wheel Offset With 20's

oops, i meant 45mm maz2low.

i got 20's on my mazda, Boss 326's with a +42 offset 8.5 wide, i'm using aim drop spindles and my upper control arms are modified, the wheels wheels hit the fenders when i go up so we spaced the upper control arms, but try and get some +45s they will work the best, but u can get +42 to work

i'm also usings 4x4 fenders

Kinda off the subject but man them Boss's you want are pimp as fuck! They were one of my first choices when I bought my 20's but the backspacing wouldn't cut it on my Taco. This is good info though, I'm gonna buy me another Mazda pretty soon (had my first one bagged back in 97) and this thread just got me stoked enough to sell some shit on ebay to help fund it. Hope you get the answers you need. Show some pics when she's rollin' large.

Originally posted by FlamedS10



i got 20's on my mazda, Boss 326's with a +42 offset 8.5 wide, i'm using aim drop spindles and my upper control arms are modified, the wheels wheels hit the fenders when i go up so we spaced the upper control arms, but try and get some +45s they will work the best, but u can get +42 to work

Are you sure yours are 42++ Offset I thought at putting those on mine and they were only 40+++ Offset

they'll fit but the upper control arms need to besectioned 1/4" shorter or put a1/4" shim between the cross shaft and frame mounting point

positive they r +42

ok i checkd the boss site there is not a 326 style wheel with over +40 so whats up, are YOU 120% they are +42 did you special order or are they 40+

not to be a dick but biggest amount of backspace is 6.263" aka +40 is this sufficent with arm mods to tuck on a mazda?

I will tell you now. An 8.5 with +40 or +42 (come on, seriously, 2 mm is like a 16th of an inch) will NEVER TUCK with drop spindles and 2wd sheetmetal. It will also BARELY tuck without drop spindles and with 2wd sheetmetal, and only in the front, the back will chew up fenders.


in order to know offset you have to know width. The two go hand in hand, as I'll explain. Without knowing width, you could run ito trouble just basing your wheel buying on offset alone. For example, IF (hypothetically, not having anything to do with mazdas or any specific truck) IF a 7 inch wide wheel with +20 barely tucked, an 8.5 inch wide wheel with +20 will stick out almost an inch. Same offset, different fit. Here is how to figure it:



Figuring backspace from offset and vice vera is EASY. You need to know width.

step one: add an inch to the width. A 7 inch wide wheel is actually 8 inches wide lip to lip because of the half inch bead on either side. adding an inch allows you to know the exact centerline.

step two: divide by two. This is the centerline of the wheel. Any offset quote is given FROM THIS IMAGINARY LINE. Thats what offset means, "the wheel mounting surface is OFFSET from the center by + or - XX mm. A + offset means the mounting surface is offset to the front side of the wheel (FWD cars are high + offset) a - offset means the mounting surface is offset to the inside of the rim (you have seen wheels that really stick out, thats - offset)

step three: convert the mm to inches. 25.4 mm = 1 inch, so divide your offset number by 25.4. If you want an easy way, go to google.com and type in "XX mm in inches" (where XX is your offset number) and it will convert for you.

step four: If it was + offset, add the offset in inches you got in step three to the wheel centerline measurement you got in step two. If it was negative offset, subtract the offset from the centerline. This is your backspace.

Recap: Add an inch to the stated width. Divide this number by two and record. Convert mm offset to inches. Add (or subtract) this number from half the width. = backspace.

SO lets use what we know: +42 on an 8.5 inch wide wheel.

8.5 + 1 = 9.5

9.5 / 2 = 4.75

42mm / 25.4 mm = 1.65

1.65 + 4.75 = 6.4 inches of backspace.

to go the other direction, converting backspace to offset, is easy too.

add an inch to the width

divide by two

sutract this result from the stated backspace

convert the result to mm by multiplying by 25.4mm

So, 6.4 backspace on 8.5

8.5 + 1 = 9.5

9.5 / 2 = 4.75

6.4 - 4.75 = 1.65

1.65 * 25.4 = 42mm offset.


Back to mazdas. No way will a +42 fit with 2wd sheetmetal unless you do as said and narrow the upper arm. It absolutely will not fit the back, ever, unless you shorten the axle or go to a courier rear. The guy who has them also neglected to mention he is running an RX7 rear end, which will camber in like the front. For 2wd sheetmetal, 7 inches of backspace on a 8.5 inch wide wheel would be

8.5 + 1 = 9.5

9.5 / 2 = 4.75

7- 4.75 = 2.25

2.25 * 25.4 = 57mm offset. Which is moot, because they dont make anything that high offset in 6 lug.

Switch to five lug. the toyota rear end will give you some extra tuck in the back, and you can buy 20x7 with +40 offset in a 5 on 4.5 pattern, which will tuck great on a maz.