Might be buying wheels and tires or my H3 base model in the next day or two and am wanting to find out what is the offset range - + I need to stay within, the 18" wheels Im looking at are Discount Tires, Razor (in chrome) 18X8.5 or 18X10, Im looking for a deeper dish kinda look but not sure of the offset I should go with.

Thanks in advance
Davyo

 

Davyo-

You do not want to exceed the backspace that the factory wheels have; the stockers have a 38mm offset which translates to a 5.75" backspace on those 16x7.5 wheels.
[ul][*]backspace = (wheel width +1)/2 + wheel offset/25.4, where wheel width is in inches and wheel offset is in mm[/ul]
In some cases, (like the wheels I've recently ordered) the wheel's design will require even less backspace due to possible interference with the brake calipers. Sometimes going with a larger diameter wheel will help this situation, sometimes not (my 17 x 8.5 wheels will require a maximum 5.5 inch backspace to clear the brake calipers). Check with the wheel manufacturer or your local wheel shop that will guarantee a proper fit without interference. You can sometimes get around this problem by using wheel spacers, but there are several potential issues involved with using them that you should investigate and understand first.

Also, you will need to consider the amount of inner tire "bulge" thatcanalso contribute to rubbing issues. Tire bulge is the amount that the widest part of the tire protrudes from the wheel edge. Smaller wheel widths tend to result in higher tire bulges; larger wheel widths result in lower tire bulge. I can get into that in another post if needed.

Considering only the wheel backspace limitation of5.75", the following wheel widths should never have an offset that exceeds these limits (on an H3):
8" width : 32 mm offset max
8.5" width: 25mm offset max
9" width : 19mm offset max
10" width : 6 mm offset max

When considering a wheel width (you obviously have a limited selection for a given wheel design), make sure you take into account that every tire manufacturer specifies an acceptable wheel width range. If you always plan to run at a relatively low air pressure (for instance, on a dedicated offroad vehicle where your maximum speeds are well below highway speeds) you can run any width in that acceptable range.

However, if you plan to run the tires at highway speeds, you'll need to ensure that the tires have the proper inflation to guaranteeat least the same load carrying capacity as the stock tires (which is ~2200 lbsfrom what I recall). Tires heat up and fail when underinflated, especially at highway speeds. In most cases the minimum inflation would work out to be 37-40psi for most 285/70R17 or 33x12.5R17(both load D) tires; have your local installer determine the minimum inflation for your specific tire size and load rating. Fine tune that tire pressure by using the chalk on the tire test to verify that you are wearing the tires evenly.

So you may ask: What does tire pressure have to do with wheel width? Well, when you inflate a tire with more pressure, the outside tread tends to lift off the pavement when you have wheels sized at the smaller end of the tire's acceptable wheel width range. (Larger wheel widths tend to pin the entire tread to the ground, regardless of inflation psi.) In general, if you're driving highways, your research should show that you're better off using a tire with a wheel width between the middle to largest of the acceptable wheel width range. By doing so, you will be laying down a flat (and larger) footprint that will ensure maximum traction under all conditions (think safety) and will also maximize the life of your tires (think $).

Also consider that with today's ~$4/gal fuel, wider tires will reduce your gas mileage due to higher rolling resistance and more tire weight. The heavier tires will also limit your acceleration and braking performance; they're also more prone to hydroplaning on pavement. In general, aftermarket tires will be either 285 (~11.5 inch), 305 (~12 inch), or 315 mm (~12.5 inch) in width. Wide tires look cool, but don't rule out the narrower tires if you are looking for an