Can someone explain tire specs for me?

[KT3]

So... I currently have 19 inch rims.
285/35/19 up front and 305/35/19 in the rear.

I want 315’s in the rear, but a lot of manufacturers only do 315/30/19, not 315/35/19...

Here’s what i’m confused about... I see people on forums running 275/35/20 up front and 315/30/20 in the rear... Wouldn’t this make the rear tire “shorter” I’m so confused.

Anyways, I really want a 315 in the rear, so I’m looking to sell my 19’s on the rear and upgrade to 20 so I can do 315/35/20... But that’s the pricey route....

Would 315/30/19 be weird on my current set up?

Thanks!

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[JCN]

The diameter of the 315/30's will be about .25 inch larger. TireSize.com is a good source for info on this, I wish I could remember what post I saw this in earlier to give credit to poster but I don't. Short lesson on tire size is the first # is section width( not tread) in mm. divide it by 25.4 (mm per inch) then take the 2nd # as a percentage of that answer and that is the sidewall . sidewall measure x2(top and bottom) plus rim size gives you your tire diameter. 315 is12.4-30 percent of that is 3.72 times 2 is 7.44 Plus 19 inch rim is 26.44 diameter. The math on your 305 is 26.2. Jim

 

[KT3]

The diameter of the 315/30's will be about .25 inch larger. TireSize.com is a good source for info on this, I wish I could remember what post I saw this in earlier to give credit to poster but I don't. Short lesson on tire size is the first # is section width( not tread) in mm. divide it by 25.4 (mm per inch) then take the 2nd # as a percentage of that answer and that is the sidewall . sidewall measure x2(top and bottom) plus rim size gives you your tire diameter. 315 is12.4-30 percent of that is 3.72 times 2 is 7.44 Plus 19 inch rim is 26.44 diameter. The math on your 305 is 26.2. Jim

Damn that’s a lot of numbers....

 

[JCN]

Damn that’s a lot of numbers....

probably explained way better on the web site

 

[shogun32]

tire rack also has LOTS of 'how we measure tires' and 'general tire information'. Go do some reading.

 

[Kong76]

I run a 275/35/20 up front and a 305/35/20 in the rear. Even though the the second number remained the same, my rear tires are a bit taller/meatier than the fronts due to the 305 width.

tire-calc.com

gives you a good visualization for different sizes and what they do to tire sidewall height.

 

[1 old racer]

I wads going to explain how to calculate exact tire size but figured I would just give you a link what will allow you to compare any size combo yourself.
https://www.americastire.com/learn/...-Hg8fSGwpQ1-CUKeqz137HaGG9ZmTzWMaAkkgEALw_wcB

 

[MidwayJ]

Damn that’s a lot of numbers....

Let's just focus on one thing. The aspect ratio ("30" or "35" in your case) means the sidewall is 30% or 35% of the width. So your 285/35 front tire has a sidewall height of 99.75 mm and your 305/35 rear has a sidewall height of 106.75 mm. A 315/30 tire has a sidewall height of 94.5 mm, so you are correct that the 315/30r19 would be shorter than the front 285/35/19.

That's all you need to get your answer since the wheels are the same diameter (19 inches) front and rear. To calculate the tire diameter in inches, you convert the sidewall from millimeters to inches, multiply by 2, and add to the 19 inch wheel diameter.

 

[KT3]

Let's just focus on one thing. The aspect ratio ("30" or "35" in your case) means the sidewall is 30% or 35% of the width. So your 285/35 front tire has a sidewall height of 99.75 mm and your 305/35 rear has a sidewall height of 106.75 mm. A 315/30 tire has a sidewall height of 94.5 mm, so you are correct that the 315/30r19 would be shorter than the front 285/35/19.

That's all you need to get your answer since the wheels are the same diameter (19 inches) front and rear. To calculate the tire diameter in inches, you convert the sidewall from millimeters to inches, multiply by 2, and add to the 19 inch wheel diameter.

I understand

 

[D Bergstrom]

So... I currently have 19 inch rims.
285/35/19 up front and 305/35/19 in the rear.

I want 315’s in the rear, but a lot of manufacturers only do 315/30/19, not 315/35/19...

Here’s what i’m confused about... I see people on forums running 275/35/20 up front and 315/30/20 in the rear... Wouldn’t this make the rear tire “shorter” I’m so confused.

Anyways, I really want a 315 in the rear, so I’m looking to sell my 19’s on the rear and upgrade to 20 so I can do 315/35/20... But that’s the pricey route....

Would 315/30/19 be weird on my current set up?

Thanks!

315/30/19’s are pretty rare also, Michelin or Falken street able race tires, or Hoosier full race tires is all I could find. If you want any type of selection in a 315 tire, you have to go to 20” wheels.

Doug

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