LVDell

Easy up on the caffeine before you break the ! key on your computer.

doubleurx

LV Dell is correct. You need to check the manufacturer's actual size. TireRack is great for this as they list all the specs for each tire they carry. You will see there are variations between different manufacturers for the same size tire.

BTW 315's fit fine on an 11" rim. I have Kumho XS in that size and the rim range is 10.5-12"

LVDell

But wait, he found a couple tires that confirmed his calculator were almost spot on so it must be right.

doubleurx

Provided to me from Joe Weinstein who opened my eyes to the calculator theory:

225-40-18 tires:
Hoosier A6 - 24.8"
Bridgestone expedia S-01 - 24.9"
...
Michelin Pilot Sport - 25.3"
Dunlop Sp Sport 01 - 25.5"

LVDell

How dare you provide more data points to the sample

doubleurx

Sorry I am getting used to arguing with Dock!

Also I was mistaken on rim size. The Kumho XS 315/30/18 has a recommended range of 10.5-11.5. The specs they list were mounted on an 11" - the same as the rear TT.

LVDell

I run the 315 on both 11" and 11.5" wheels. Fits perfectly.

doubleurx

What tires do you run street/track?

LVDell

Street:
Hankook Ventus 225/40 F 295/30 R

Track:
Nitto NT01 225/40 F 315/30 R

doubleurx

Great choices. So far I am happy with the XS on the street - other than the days we are still getting with snow, including today.

I'm looking forward to getting them on track soon.

Kevinmacd

Spoken like true engineers! I guess I have to conceed to the self proclaimed experts that can't understand how manufacturers model. Since you mentioned Tire Rack, maybe you guys should go do some reading before trying to contradict a statement that really is accurate. Try this thread from Tire Rack and read tires aspect ratio! http://www.tirerack.com/tires/tirete....jsp?techid=46, oh gee that must be false also they actually do calcualtions!

LVDell

Kevin, you have just become irrelevant in this thread with that thickheaded attitude. Back off the overuse of the ! and have an intelligent conversation and just maybe you will understand the basis for the thread. Kevin, you seem to infer that by law a tire manufacturer must adhere to an exact formula spitting out a perfect diameter that lines up with the algorithm for diameter computation.

Cliff Notes:
1. Use the calculator as a guide to give you a good approximation of the diameter of a tire size.
2. Find the manufacturer specs for the tire size you selected
3. Verify that diameter is within the tolerance allowed for the car
4. Install
5. Drive
6. Enjoy

LVDell

Snow? Holy, what the.......

We are high 90s today

nick49

In a nutshell,

the only accurate true measurement on a tire is diameter, 17, 18, 19 etc.

the widths 225, 235, 295, 305 etc are approximations and generally are only helpful in determining what rim wdith should be used.

the aspect ratios 25, 30, 35, 40 are approximations of height to width ratios

Tire manufacturers have the freedom to label a tire with a certain size designation and vary substantially in the actual manufactured measurable dimensions.

Measure a mounted and properly inflated tire on rim used is the most accurate way to determin actual size, followed by manufacture tech sheet listing actual sizing. I have found this to vary somewhat based on rim sizing and running pressures.

LVDell

Bingo!