Tire sizes are confusing me!
 

Hey, I have a set of 15" rota c8s.

Now summer is almost here and I want to install some tires on them.

Does 195/55/15 fit on these rims? Or 205/55/15? I was told they both fit. If so, how is that possible?

Because I know the first number is the width of the tire in millimeters, measured from sidewall to sidewall.

If they both fit the rims, that means the 195/55/15 will be 10mms less in width? Wouldn't that make the tires unstable?

Damn, im confused!

The size of the rota is 15X6.5"

195mm = 7.7"
205mm = 8.1"

how would they fit?

They both fit...

I wouldn't do any bigger than 205...

Diameter of tire and wheel is the question you will need to look at. 205/55/15 will be larger diameter than 195/55/15. What are your stock wheels and tires?

When you say diameter, you mean the height or width?

Well I'm not sure what my stock tires are, but i'm using 185/70R14 now.

the height would be the second number and width the first...

i have the exact same rims.. i'm going with 205/50/15

i would go 205/50 because there is more tire selection in those sizes, especially performance tires and it gives alittle more rubber on the road.

I'm afraid that the second number is the aspect ratio (i.e., section height divided by section width). :wink:

Yes it is.

The first number is the width of the tire in millimeters, measured from sidewall to sidewall like I said.

With 195/55/15, the width is 195mm.

The second number is the aspect ratio like MMX stated and not the height of one side. This is a ratio of sidewall height to width. In the example above, the tire width is 195mm, multiply that by the aspect ratio to find the height of one sidewall, which is 55%. In this case, 195x0.55= 107.25mm

So the width of this tire is 195mm and the height of one side is 107.25mm.

And of course the last number is the diameter of the wheel in inches.

it's not rocket science... just simple math...
and this makes diameter calc even simpler http://www.miata.net/garage/tirecalc.html

the recommended tire width for a 15x6.5 rim is generally 205

Do no change to 195/55/R15.

Why?
cause currently at 185/70/R14
Your wheels spins 518revs/km

if you switch to 195/55/R15
Your wheels spins at 535revs/km

The closest match to your stock setup is 205/55/R15, which allows the wheels to spin at 525revs/km. Thus only affecting your speedometer slightly, and giving you much better performance out of your tire setup, with a shorter sidewall and wider contact patch.

Pick your tires wisely, some tires weigh ALOT, and will make your car feel worse than before. However there will be a whole lot of grip! :P
Personally...I prefer sharp crispy turning, so I usually pick a tire thats 10-20mm wider than stock and has a very stiff side wall, and usually lightweight. Also, keep in mind you can alter your tire contact patch and steering feel through tire inflation. Make sure you go by the tire inflation that your specific tire company recommends.

Good luck
Jonathan.

what's wrong with my tires reving more per km?

205/50/15... the best way to go.... with 15x6.5" rims