I'll explain what tire sizes mean so you can figure it out for any size....the aspect ratio or profile is a percentage of the section width...therefore the sidewall of a 60 series tire is 60 % of the width ,in your case 185mm which means the height is 185 x .60 = 111 sidewall height times 2 (because there are two sidewalls plus the height of the rim size(not needed as a factor in your case since you aren't changing rim size..if you were you would need to convert one or the other measurement to metric or standard) the tires you are looking at are 205x.50 = 102.5 and 205 x .55 = 112.75 ...the first tire will be a little shorter that may result in your speedometer reading slightly faster but the second choice is a very little bigger and the difference from stock would probably not be noticeable.