Wanting info/advice regarding tire aspect ratios. I currently run Cooper STT Pro’s in 295/60/20 on my 2008 Super Duty. Besides a slightly different look, and I’m not sure I can even tell the difference, would you recommend a ratio of 55, 60, or 65? I want to stay with the same tire. Just trying to understand the advantages and disadvantages of each. If there are any.

Easiest way to explain it.

The middle number is a percentage of the first. Now the sidewall height is 60% of the width(295mm). You can change many different ways but if you want same height or width or bigger or smaller it all comes into play.

In theory a 55 is shorter, 65 is taller but it’s the percentage of the width. So going skinnier to a 275 or something you may not necessarily be going taller or shorter depending on aspect ratio.

Do you feel there is a difference in ride, performance, etc between any of them given that I want to stay with a 295 20” tire? I guess I’m trying to find out if the differences are just cosmetic or not.

Going with a taller tire (295-65-20) will give you a slightly better ride. It will also be slightly softer in the corners if you don’t run the designated air pressure on the tire. Many tire shops put less air pressure in them than is needed for towing/hauling. Bottom line, going with the taller tire and correct air pressure you should be very happy.

Going shorter to the 55s will result in a worse ride and possible damage to the wheel of your truck on potholes, curbs, rocks, etc. unless you’re wanting to lower your truck for whatever reason people do that I wouldn’t go this route.

Slightly taller tires generally look better. Grossly taller tires seldom does.

If you keep the first number (295) the same, a bigger second number (55, 60, 65) will be a taller tire.

I can never remember how to do the metric sizing BS... I've found it easier to use something like this that shows you the difference via a picture. There are some others that also show the side view if you want to see width differences.

https://www.discounttire.com/learn/tire-size-calculator

I appreciate the info from everybody. Decided to go with 295/65/20.

The diameter calculation to inches is easy. 295/25.4 x aspect ratio x 2 plus rim diameter = overall diameter in inches. 295/25.4 = 11.615 x 2 = 23.23 x. 65 = 15.1 + 20" = overall diameter of 35.1". 25.4 is the number of MMs in an inch.