spdy0001

Ok my father and I have now argued three times about how tires are measured. I am wondering if you guys have any better ways for me to explain this to him

This is more or less a rant of me being frustrated with my father

Tried to explain it this way... 185/65/14 tire
185 = width in MM
65 = aspect ratio of sidewall (sidewall height)
14 = rim size

He won't believe me that 185 is the width no matter what the aspect ratio I tried showing him tirerack's page on tire sizing, but still nothing.

/end of rant

TSXEd05

He's probably still thinking about the old school way they used to measure tires. My dad would talk about having 60s on the back of his car that were really wide and 75s on the front which were skinny. I'm not sure how they measured but it was different back in the day!

iTimmy

I see it everyday, how tire size is achieved is probably the most misunderstood measurement on a vehicle. Most people in the biz don't even understand how they arrive at what they do.

rmpage

I'm still confused by the speed ratings. Especially considering that most of them are useless limitations that became irrelevant decades ago. It seems like you literally need to be on a track to hit the limits of any halfway decent piece of rubber these days.

iTimmy

I agree, I believe its used mostly these days as a marketing tool. The other tire myth is the UTQG rating on tires, the treadware, traction and temperature rating on the sidewall of tires, it means just this side of nothing.

Even for those who drive under 149mph sustained for a hour there are a lot of factors that impact how a tire will handle at lower speeds, and at colder temperatures that are more important to most motorists. People think the higher the speed rating the better the handling, not always true. And I love the people that feel the tread and can tell how the tire will peform, or label it has "hard" or "soft"

TSXey

This link shows some tire info using the old method of sizing tires in the U.S. http://carnut.com/specs/tires.html

I'll just add that the aspect ratio is the ratio of sidewall height to tire width; so for example, the 185/65-14 tire has a sidewall height of 185 X 0.65 = 120.25mm; overall tire diameter is two times the sidewall height plus the wheel width, e.g. 240.5mm + 14" (355.6mm) = 596.1mm = 23.47" (as you probably know, 25.4mm = 1")

TSXey

What do you expect that rating to tell you that it isn't telling you?

While it tells you very little otherwise useful information, my experience has always been consistent: if the UTQG rating is lower, the tire wears faster; and, for example, I also find that if I use a tire with a 75 rating it will last about 3/4 of what a 100 rating tire lasts. You can't put an actual milage number on that since there are too many variables, but it is a good relative comparison and everything I read "authoritative" about UTQG ratings pretty much says just that.

Have any of you guys found this not to be true in your first hand experience?

spdy0001

Well here is an update

After getting in to this debate again this weekend my father proceeded to remove one of the cheapo tires from my mom's newly acquired 94 accord. The size is 185/70/14. He then grabbed a tire that we had for another car a bridgestone 185/60/14 tire. By all modern measures these tires should be the same width, but as a slap in my face the cheapo tire on the car was about an inch skinnier.

I tried to state that sizes will vary between manufactures especially with a no name company, but at this point he had already assured himself he had won the argument. So there is no way I will ever convince him now
Maybe I will someday manage to get him in a tire shop and show him two tires from the same MFG.

iTimmy

The problem with the UTQG is every manufacturer of tires sets there own rating system, so comparing a Goodyear to a Bridgestone using the UTQG is pointless. More so with the cheap Chinese and Korean tires coming into this country they will have a UTQG 800 A A and they perform horribly in wet and wear out in 20k miles, yet a Bridgestone tire rated 600 A B will dance circles around it.