Positive offset rims vs. Negative

[hat_man]

I have been mulling about the idea of finding different rims for the truck. Just in my mind for now but that's where all my ideas have started.

My stock rims weigh approx. 15 lbs. each and I have seen some from a Mazda 929 that have the same bolt pattern and weigh approx 12 lbs. each. I know this would be beneficial with the weight savings ( approx. 12 lbs. static weight and 45 lbs. rotational weight) but they might be considered "air blenders".

My stock rims have a negative offset and the Mazda ones have a positive offset. I'm not sure of how much of a difference it is but I do know the Mazda rims would move the wheels/tires inboard maybe an inch or two. In my mind I would think I could counter the "air blender" effect in the rear with full skirts. The inboard shift would create the clearance to make this possible. With the inboard shift in the front maybe a "bubbled" front skirt could be accomplished that would allow full wheel travel side to side.

What the real question is.....how would the positive offset rims affect the alignment of the truck? I'm sure the new alignment racks would compensate for the inboard shift and could keep the tires square to each other to prevent pulling or "crabbing" but what about toe-in or toe-out, etc?

This is all conjecture at this point and I may never do this anyhow, but if I play it in my mind and ask questions then I can at least learn something along the way. And if it could be a good idea then I might someday pursue it.

Thanks.

[niky]

If the offset difference isn't too huge, you can probably compensate some with spacers (just be sure you have enough thread left to lock the wheels onto the studs tight).

Also mind the load capacity of the wheels. If they're 12 lbs, I can't imagine they'd be built for heavy loads.

[hat_man]

I had thought about the load ratings a bit but in my case (disclaimer***your results may vary***) I don't haul anything of any size anymore or tow anything at all. The curb weights seem about the same for both vehicles. My truck is a bit lighter than listed being a shortbed and stepside. It has fiberglass body panels for the bed.

And would the spacers be necessary? That is part of what I am wondering. If you used them with no spacers how bad would that throw off the alignment and would it make it harder to align in the future?

[AntiochOG]

It doesn't seem to me like changing your wheel offset would affect your alignment at all.

[aardvarcus]

One thing to check is your clearances between your wheels and your wheel wells and engine components. Changing the wheel offset will change the tire’s location with respect to the axis of steering rotation, so not only will it move the location of the tire inward, it will also vary the amount the tire travels forward and backwards when you cut the wheels all the way. I would suggest you check the clearances with your wheels cut all the way. This is probably less of an issue with stock size tires, but if you are pairing this change with oversize tires it could be a bigger problem. My Celica with 26.5” tires (stock is 24”) will rub at a full lock because the offset of the tire swings the tire into the back of the wheel well, thus I can only turn the wheel 90% of the way.

As far as the rims being “Air Blenders” there are always pizza pans until you can get your wheel skirts built.

[rmay635703]

Originally Posted by AntiochOG

It doesn't seem to me like changing your wheel offset would affect your alignment at all.

Very wrong, it can have a large affect depending on the type of suspension.

[hat_man]

Not saying you are wrong or right rmay, just trying to learn. Can you eloborate more?

[rmay635703]

Originally Posted by hat_man

Not saying you are wrong or right rmay, just trying to learn. Can you eloborate more?

On my cars if the rim sticks out further it affects toe in/out.

Not impossible to fix though.

[bestclimb]

Originally Posted by AntiochOG

It doesn't seem to me like changing your wheel offset would affect your alignment at all.

You may be surprised. Changes in offset alter the lever arm of the rearward forces of the tire (scrub radius). The little bit of give in the steering rods will cause slight changes in toe. Moving wheels farther out can cause toe out moving wheels in can cause toe in. If the steering components are worn the effect can be significant, with parts that are in good shape the effect is pretty small, though enough to adversely affect tire wear and mileage.

If you get the scrub radius very far from zero it can cause a very significant steering input if a tie rod fails. If that input loads (negative scrub radius causes a turn away from failed tie rod) the tire with a failed tie rod the wheel you still control is unlikely to have enough traction to make a controllable stop possible.

[AntiochOG]

Thanks for elaborating bestclimb. I am aware of the relationship between scrub radius and wheel offset. However, wouldn't the effect of this only be seen in a dynamic driving situation and not when the car is stationary, i.e. on the alignment rack. The face of the wheel should be parallel to the hub regardless of how much or little it is offset.