So this is going to be a bit of a long post...
I wouldn't know about the measurements or any of that, but I wouldn't go with any bigger than 17" wheels for two reasons 1). Your turn radius is affected & 2). The bigger the wheels the heavier they are, affecting not only fuel economy but also your speed sensor which would need to be calibrated for the new size. I wouldnt wanna bother with all that.
I know you're just trying to help, but you are making a lot of assumptions here.
First, turn radius has nothing to do with the diameter of your wheel. The WIDTH of your tires can have an affect, but that's only a very small part of it unless we're working in extremes. A 1" width difference will be minuscule.
Next, generally larger wheels are heavier but that's not always the case. I have a few sets of 18" wheels and tires that are lighter than stock 16" wheels and tires. You need to take into account the weight of both wheel and tire to make a claim that larger diameter wheels are less efficient. I think what you're referring to is the fact that moving that weight further from the center point of the wheel requires more work, and that can hurt fuel efficiency.
That brings me to the next point, the diameter of the wheel has NOTHING to do with your speed sensor, that is affected by the outside diameter of your tires, not your wheels.
Actually, I just checked their site again and the only size they have in 4x108 bolt pattern is 17x8, but it is offered in 35 or 42 offset.
The number you will want is directly related to the suspension you have, how much camber front and rear you have, and what size tire you wish to run.
Does anyone know how wide of a wheel I can fit or if I can find a tire that will fit that wide of a wheel?
Should I just get the narrowest wheel and then install home wheel spacers?
Anyone ever taken any measurements similar to what I am looking for, e.g. from hub mounting surface to fender?
The width of wheel you can fit is again directly dependent upon suspension set up.
Narrow with spacers is one way to do it, but quality spacers aren't cheap and they add more weight than a wheel at the proper width and offset.
The measurements you're talking about have already been done, sort of. The wheels width, offset, and backspace will tell you exactly where the wheel will sit on your car in relation to the hub.
My ST3 has 18's & the turn radius is worse than my dad's F-450
That's because you have a performance car with a progressive rate steering rack. Any car that is going to have a responsive steering wheel will have a poor turning radius. Don't believe me? Drive a Ferrari or a Porsche Turbo or anything like that. The standard focus Titanium suffers from poor turning radius because ford installed hub spacers and stops to make it so drivers don't make contact with the suspension components with the ridiculously high offset stock wheels.
Trucks have poor turning radius because of their wheel base. The longer the distance between the front amd rear wheel the poorer the radius. A focus SE would out turn that full size truck any day.
I actually made that thread to get a more direct answer because I have a couple questions in this one. I don't know what the backspacing is, but they are available in +15 to +35 offset. They are watercooledIND cc10's. I was thinking about getting the +15 offest.
Don't do +15, you'll never get them to fit.
15 offset would be nuts, you'd be better off with 35. Remember the lower the number the more the wheel sticks out. Stock wheels are et52 to 49. I run 18x7.5 et45 on my first gen. they sit nearly flush.
Focus MK1 RS wheels are
18x8 et42 they require fender work to fit on a 1st gen focus that's lowered.
Here is a set on a stock SVT suspension.
Here is a set on a slammed focus.
Here is that same wheel on a slammed Mk2.
I fixed the wheel size, its 18x8 not 18x9.
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