View Full Version : Double Check My Math on Backspacing?

03-25-2010, 09:10 PM
So with the winter season almost over, I am about ready to get a new set of wheels for the cruiser, leaving the snow tires on the OEM rims. As it seems finding sets of cruiser rims is a bit tricky, I started looking at the early 00's Tundra Rims.

Am I correct in that backspacing doesn't really matter too much in this instance? Its the offset that makes the difference? (Realize they are both tied together) Seems like the tire/wheel moves more than .6 inches of side to side just from the lift and not adjusted panhard. Plus the narrower rim would "narrow" up the tire a bit? (So maybe only shifting the tire .5" inwards?) Also seems like you could end up with .6" difference in just manufacture's variance. End goal is to run 285's without dealing with spacers.

I've got these specs so far:

OEM 80 Series Wheel: 0 offset, 4.5" backspacing, 16x8, 108 bore size.
Tundra Wheel: 15mm offset, 4.6" backspacing, 16x7, unconfirmed bore size of 106 or 110)

Centerline of tire moves inwards: 15mm/.6 inches
Inside of rim moves in: 2mm
Outside of rim moves in: 28mm

Did some searching on mud but couldn't find anyone running the Tundra alloy's, just the steelies:confused: And lots of folks were arguing that you needed 1.5" spacers. I don't understand that when the tire only shifts by .6 inches inwards? I guess to compound this the early Tundra Alloy's came in both acorn and shank style lugs? Am I correct in that a hubcentric/shank style wheel would require the hub and bore to be a perfect match so that the lugs are not taking a bulk of the up/down force?

Suppose another path would be to mount the summer/dirt tires on the Cruiser rims and mount the snow tires on the Tundra wheels, since they'd see less articulation when going skiing rather than desert travels?

Am I on the right path?

03-25-2010, 09:56 PM
I don't know what offset is, but the backspacing looks right. remember more backspacing=tires closer to the inside of the wheel wells.

I think you've got a good point that it won't matter much- with your lift you could run 33x12.50 tires and not have issues, so your comparatively skinny 285's shifting a little be here or there isn't likely going to lead to any rubbing.

My experience with the hub centric/shank wheels is all the load is still on the lugs. The hub gets is close, but there's always a little shift when I run that first lug down inside the rim. However when removing the lugs, the rim does kind of stay in place doesn't it.. On back of my Taco, I have to smack those with a BFH to get them to pop free after all the lug nuts are off, but on the 80 everything just falls off.

But regardless, you can run either style rim as long as you've got lugs to go with them. IOW I don't think there's a stronger side load lug out there for conical rims.

03-25-2010, 10:11 PM
Cool thanks for the info. I'm still a newb at this, but from my understanding offset is the +/- distance from the mounting surface on the wheel to the wheel centerline. People on 'mud had me a bit worried sayin' you need 1.5" spacers to run these....