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Old 06-26-2003, 12:33 AM   #1
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Default How to read tire sizes

Okay, this might seem like a minor league question but I'm asking only because I need to settle an argument with my friend.

Say I want to move up to a larger tire, where, when looking at that tire straight on, from alongside the car, it just looks larger in the wheel well from top to bottom or side to side? I'm not refering to a wider "treadprint" size which you can easily make out when you look at the exposed lower portion of a tire from front, rear, or when the front wheels are turned and you could see the tread designs.

What number in the specified tire sizing (example: P225/60R16) would represent that tire, higher and larger simply from top to bottom?

The reason is because my 1992 SE came with unusually smaller tires, P215/60R15, and I don't plan on spending the money on larger rims just larger tires. I'm trying to find a size that was slightly larger without altering the speedometer all that much to where I'll be getting tickets each and every other weekend! I want to stick with the 15" rims.
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Old 06-26-2003, 12:58 AM   #2
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15" rims on a 92? Odd.

Anyway the first number is the width, second is the ratio (usually has to do with sidewall hieght) and the third is rim size. I believe if you went with something like 225/70/16 that would be alot taller of a tire compared to 225/60/16.
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Old 06-26-2003, 01:09 AM   #3
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Yeah. I thought it was real odd too! And I'm not comfortable with the ride all that much to be honest. Always felt that smaller tires/rims gave off a lot of tire hum!

But that'* what the car came with and that'* what is specicifed on the label inside the front drivers door - direct from GM. My sisters 1995 Olds Cutlass has bigger tires for Christ'* sake!

I won't be getting new tires until sometime next summer, but maybe by then I'll just go and get some new 16" rims. Just wanted to see what I can get away with using the stock 15" rims.
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Old 06-26-2003, 06:06 AM   #4
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I never heard of that tire size before. I have 235-55-16'* on my car
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Old 06-27-2003, 01:45 PM   #5
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Default Re: How to read tire sizes

It'* easy, let me explain how to read tyre'* markings.

First number represents tyre'* width, in millimeters. After the slash, second number says profile'* hight, in per cents of tyre'* width. The letter "R" says the tyre has Radial cord structure (this is not a tyre inner radius, as many think!). Next, tyre'* inner diameter in inches. For example, 255/45ZR16 tyre has following parameters:

width: 255 mm (~10 inches)
profile hight: 45% from 255m, 115 mm (~4.5 inches)
has radial cord structure
Rim diameter: 16 inches

So, if you need wheels of larger diameter, you could increase tyre width, or profile hight, or both. But increasing profile hight will lead to worse handling (the lower profile, the better cornering). Also, make note that if want to stick with your current rims, you should check their width. Too wide tyres won't feet them.

To calculate your new tyres size, there'* extremely nice site, I used many times.
Here it is:
http://www.miata.net/garage/tirecalc.html

With best regards,
Yuri.
Moscow, Russia
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Old 06-28-2003, 12:15 AM   #6
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Hey I got 225/60/R16 now what about if I go with 225/50/R16 would the car be lower one inch or two. What do you guys think about that. Should i do It. I ll already have two tires ready. Put them on front and keep the back ones 225/60/R16 or change all four two 225/50/R16
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Old 06-28-2003, 06:50 AM   #7
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I'd advise do not install those 225/50R16 tires. Let me explain.

First, if you keep 225/60R16 on back, and install 225/50R16 on front, it'* very likely that anti-lock braking system would go offline every time you gain certain speed. I believe it would happen if you get to speeds between 40 to 60 mph'*. Those tires have 6.7% difference in outer diameter, so front wheels will rotate 6.7% faster than rear ones.

Modern ABS systems permanently measure every wheel'* rotation speed, and if the system decides that one wheel rotates faster than others, it should consider some of its sensors fail. So, after the "failure" detection it should switch off.

To avoid this problem, you should use the tires of equivalent dimensions or at least with the same outer diameter. For example, 225/60R16 on front and 245/55R16 on back; or 225/60R16 on front and 245/50R17 on back. But, you also should check if 245 tires fit your car. Wider tyres may not fit...

Next, the smaller wheels, the lower car. In your case, it should lower by one inch.

And the last, your speedo will read faster (6.7 per cent faster, to be specific).

Anyway, I'd use only stock tires that listed in vehicle operation manual or at the factory sticker somewhere on the car (on BMW'*, it located under the door'* lock bolt of driver'* door). Those tires tires listed there are designed to fit your car, others could possibly affect car'* handling or suspension reliability or cause things I listed above.

With best regards,
Yuri,
Moscow, Russia
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Old 06-28-2003, 09:11 AM   #8
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This is I site I found for the Techinfo Section awhile back (yes, we have alot of great stuff available at this site).

http://www.c5-corvette.com/tirecalc.htm

You can compare two different tires for overall size and speedometer difference or specify how close you want to be to your current tire height and it will give you available sizes.

Jay
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