Tire Stickout and Backspacing

[TJ's-TJ]

We have been looking into wheels and tires quite a bit and am concerned with stickout due to the new MA state inspection process. I think we could get away with maybe 1" of stick out, but much more than that may cause issues. We have Sahara flares (wider than stock, same as the Rubicon flares). I never realized that 15" wheel backspacing was so limited. Almost all are at 3.75". 16" wheels seem to have standardized on 4.5" BS.

So based on this pic of Chris' old rubicon (285/75R16 with 16" Moab's, 5" BS):

I came up with the following table (also used that fact that he said this combo just barely touched the front control arms at full lock):

Based on this, we are leaning towards 16" wheels and tire, even though they are D&E rated, so that they are tucked better... Unless someone can point me to some 15" wheel options with 4.5" BS and maybe some 11.5-12" tire options in 15"...

If anyone sees any problems with my math, please let me know.

 

[Rob5589]

BS on alloy wheels does seem to be limited. I found some basic black steelies that were in the 4.5-5 range while searching for wheels a while back. There is always a 33x10.50 that would tuck better. Unfortunately not many tire manu have picked up on this popular size.

 

[Mr. Bills]

The only real problem I see with your math is that the numbers are largely hypothetical because tire width varies from tire model to tire model, the particular tire pressure used, and a myriad of other factors which renders it unlikely that a chart calculated to 0.01" or even .1" would translate to the real world.

I think you need to focus on which wheel/tire attribute is most important to you: (1) escaping negative scrutiny by Massachusetts state vehicle inspectors or law enforcement personnel because your tires aren't fully covered by your fender flares (which can be easily solved with wider flares that are removed and replaced with your stock flares after the inspection if you choose), or (2) tires you like that fit on the wheels you like that don't rub where you don't want them to rub.

Some things to keep in mind when you choose tires:

1. When you air down for offroading the tread footprint of a radial tire gets longer more than it gets wider, which means that "metric 33's" (285/75) or "metric 35's" (315/75) which are typically a bit narrower than flotation sizes (33x12.50 and 35x12.50) may work just as well for you on the trail.

2. C, D and E load ratings are just that - load ratings. It does not mean that there are more plies in the tread or sidewall as one moves through the alphabet. Load ratings are not a measurement of sidewall stiffness. Also, P load rated tires are rated at 35 psi while C, D and E rated tires are typically rated at 50, 65 and 80 psi respectively. If one evaluates the load ratings published by the Tire and Rim Association for each letter rating at 24-28 psi instead (typical street pressure used for TJ's and LJ's with oversize tires) you will find that the load ratings for each letter at the lower pressure aren't that much different. The bottom line is that a C load rated tire is a better match on paper for a vehicle the weight of a TJ at the published rating pressures, but at actual street and trail pressures the difference in may not be as pronounced as you might think. Tires also vary in "stiffness" from brand to brand and model to model even at the same load rating.

3. Tire attributes that are important for a "Southern California Fair Weather Rockcrawler" (I love that term, I wish I could remember who on this forum coined it) may be less important to someone who regularly wheels in the forests of the Pacific Northwest or New England and vice versa. Overlanders may have different priorities altogether. Choose tires that work best for how you use your jeep where you use it.