Thread: Tire question: Understanding tire specs

I thought this might best fit in suspension stuff, but mods please move it if I'm incorrect...

I am looking at getting new tires and want to make sure I am understanding the tire specs correctly. I am going to get Falken Ziex 512s again, but I'm not sure which size. I have a 15" rim and was going to get 205/50's because it should have the greatest contact patch, but now I'm not so sure. Here are the important specs from Falken's website of the three sizes I'm considering:

Size...............Section Width..............Tread Width...........Weight
195/50R15 .................7.7 ......................... 6.9 ................... 16.8
195/55R15................. 7.7 ..........................6.9 ....................19.2
205/50R15..................8.1............................6.9......................17.9

Based on my understanding of those numbers, each of the those three tires will give me exactly the same contact patch size on the road (equal amount of tread on the road given same psi). Is that correct? And the section width is essentially how wide the tire actually is (the fender-rubbing measurement)?

It seems to me based on these numbers that getting the 195/50 size is a no-brainer as it will be the lightest, tied for most aerodynamic (lower section width= less drag= better fuel economy), and has the exact same size contact patch. Oh, and the 195/50 size will best match the OEM diameter, so my speedo will almost be perfect. This flies in the face of my previous understanding that a 205-sized tire will always give a bigger contact patch than a 195 tire. Am I missing something completely here?!?

The 205/50 will give you the most contact patch over the 195/50 because;

a) 10mm more tire as a whole, from sidewall to sidewall
b) same % sidewall as the 195, so there will be more rubber in between sidewalls
c) The 205/50 will look amazing on the car.

Yes, according to the stats I posted, sidewall to sidewall the 205 would be larger than the 195. However, if the tread width numbers are straight-up measurements (rather than a proportion or ratio), then there is no difference in the actual contact patch size, so there is no more grip.

The 195/50 would have a shorter sidewall than the 205/50, which should improve handling.

I would be dropping 1lb of unsprung weight per tire, which is good for everything. Plus, the smaller section width will reduce drag, which would improve fuel economy. I do love the look of the 205's I currently have on my car, but they rub the fender in the back (38 offset rims), so I think the 195/50's are winners in everything but looks.

What suspension and what wheels are causing rub in the rear?

Suspension: Hyperco Gen 2's with Koni Reds
Rims: Rota Circuit 8's.

This is on a B13. According to the Khumo website, the 205/50/15 Khumo Ecsta ASX tires have a section width of 8.4 inches, which is .2 inches wider than even the RT-615's in the same size. This tire just runs too wide. And is crappy. Crappy crappy crappy crappy.

I see.

With all of my questions lately regarding the treadwear and overall "stickiness" quality, and other (your thread included) questions pertaining to overall tire sizes, I am hoping to start a "Definitive Tire Thread".

Look for it shortly.