New to forum.....
I have a new 19 magnetic RWD SCREW with the 265/60/18 tire, when I got the truck I wanted the argent grey 6 spoke 20 inch wheel.
The 275/55/20 tire is really close but not the same height, the 265/60/18 and the 295/45/20 match height prefect, of course the 295 is wider...…
I have found a new 6 spoke set. looking to see if anyone is running a 295/45/20 tire and if there are any issues? Rubbing?
I don't want the speed meter to be off....

 

I haven't read about anybody with that size tire.
It sure will be a thin sidewall though.
A quick search returned a handful of tires in that size but they were all highway oriented, that I saw. Didn't dig deep though.

Not sure at all what your style is or what you are looking for with appearance but that tire will look very small on the back. Front not so much.
I had 305/50-20 on a different truck. It was 'alright' in the front but man it look tiny in the rear. Your tire is going to be about 1.5" smaller than what I referenced. I think these 4x4's have more fender gap than my 2003 did.

I can't imagine that tire rubbing though, to get back to your question.

My truck is supposed to have 275/55-20 but has 275/65-18 (same size). Adding less than an inch wider wouldn't give me any rub points, at the same diameter.

Good luck.

 

I thought this would be the best place to ask but looks like the lower truck section may have been a better place to ask.
im going for a sport truck look.

 

If you stay within 2" or so there isn't enough difference to matter. My current tires are 2" taller than factory and when my speedometer shows 70, I'm actually doing 73. Below 60 mph and I'm within 1 mph. Unless you're changing by 3-5" it isn't something to worry about.

And your speedometer is changing all the time anyway. Most truck tires have 1/2" to 3/4" of tread on them when new. As the tire wears down they will be about 1" to 1 1/2" smaller than when they were new. When you replace a set of worn out tires they will be about 1 size smaller than they were when new. Your speedometer and odometer will almost always be off by a small amount even if you stay with the same size tire.

 

Speedometer / odometer display is always off by the percent change of tire.
If you change tire size by 6%, speed/odo is off by 6%. Regardless of the speed, it's always 6%.
Two inches of change is about 6% which is similar to marshallr, however you'll just need to determine the difference once you get your final size.

Gotcha on the overall sizing -the tires seemed best suited for road use, and the size seemed like a lowered (or at least lowered rear end) truck.
However, if you lower the front end, I can't speak to a 305 fitment on a lowered vehicle if you go that route.