Yeah I'm definitely overthinking this to a factor of 100000x. I've watched Kai's (Tinkerer's Adventure) video at least five times. But because I'm already driving myself insane, here's some more info that's partially vehicle related, partially an insight into my life, and partially justification and reasoning for some decisions that I'm hoping you all can verify. Bear with me, this is going to be a lot as I basically vomit out what's on my mind here to try and make sense of it all.
Background time. There's a lot of reasons I am pursuing changing up the wheel/tire package on my GX, which buckets into one project goal to either get a more aggressive or taller tire while minimizing any extra unsprung weight at each corner and without creating a situation in which I have to find a speciality shop for an alignment and/or cut and trim extensively. I'll go into more detail later as to why these are important. It's a lot of juggling to make this "happy medium" happen.
Let's say I'm going with the 255/80/17 tire. The wheel sizes and offsets being considered to pair with this are:
- 17x8, 20mm
- 17x8, -6mm
- 17x8.5, 0mm
An 8.5" wide wheel technically works as per the tire manufacturer, but blowing the tire off the bead when airing down to ~15 PSI will always be in the back of my mind, and peace of mind is huge off-road. This rules out an 8.5" wide wheel for this tire size. So then the options are 17x8 20mm and 17x8 -6mm. As far as which is better for this application, here's how I'm deciphering things:
- The -6mm offset wheel sticks out further from the vehicle, but has a longer scrub radius. This means that there's a higher likelihood (in concept) of hitting the body mount, which with this tire size isn't too likely, but can't be ruled out. [Someone correct me if I'm wrong]. It's likely that caster will have to be maxed out for -6 to work.
- The 20mm offset wheel tucks in further, and will likely clear without issue, but running too wide of a tire on this offset can mean rubbing the UCA. In essence, this is 26mm tighter to the suspension than the -6mm wheel, which translates to 1.02" closer-- or it can be looked at as the -6 being 1.02" further out from the hub.
View attachment 3901779
For the hell of it though, let's say I were to do 285/75/17. This opens up the option of a 17x8.5" 0 offset wheel. Here's how it compares to the 17x8 -6 offset wheel:
View attachment 3901783
And here's how it compares to the 17x8 20mm offset wheel:
View attachment 3901784
Math tells me that with 285/75/17 being 33.9x11.3" and 255/80/17 being 33.1x10.0", the 285/75 is .8" taller, which is really only .4" more tire per side. This alone shouldn't be an issue fitting my GX (which has a BMC and Ironman bumper) as far as I can tell. But the 285/75 is 1.3" wider, which is over a half inch more per side. There's also a 17x8.5 -10mm offset wheel that's an option, but I understand that brings an even higher likelihood of needing to trim/cut/align in a specific way. In any capacity, the benefit of picking the 8.5" wide wheel even with 0 offset is to run a 34-35" tire, which goes back to the need to trim/cut and do a maximum-caster alignment.
I honestly can't say I trust any of the shops near me to with anything beyond a standard alignment. Definitely nowhere in my immediate vicinity that I trust to do so at least. Additionally, and here's where things get even more complex and possibly stop the 34-35" show in its tracks for the time being: I have a toddler, a newborn, and work 2 jobs. Extra time, effort, and/or money to get a tire to fit properly without any rubbing is just not in the cards right now. I keep trying to tell myself that it is, and that I can find the time to make it all work, but I'm acknowledging my free time is minimal as-is and I can't devote any of it to fighting for tire clearance. Call it adulting or maturing, but it is what it is.
All of this brings me back to the 255/80/17, which I'm not particularly excited about being shorter in diameter than would be ideal (some of the trails we run are really geared towards 35" tires) and than my current 34x10.5" tires (which measure 32.5" tall overall mounted on 17x8" wheels on the GX) but it makes for the fewest outright headaches at least for the time being.
So coming full circle, the decision again comes down to whether I should go -6mm or 20mm offset for a 17x8" wheel.