tire size, whats the proper conversion?

[Rogmok]

Factory 15's have tires that are: 205/65/15

i have 17's, whats the proper tire size? i had 215-40-17, should it be more of a 215/45... or 225/45?

Thanks

[537]

The aspect ratio is a percentage of your tread width. A formula below is a guideline to stick to:

(tire width) X (aspect ratio) = (Sidewall height from the rim )

Since you're always going to include the entire diameter of the wheel + tire when calculating what your plus-size configuration will be, it follows that your (Tire Width X Aspect Ratio) + Rim size should be as close to, if not identical, to the factory specifications as possible. Remember that 'Tire Width' is measured in millimeters, and roughly 25.4 millimeters make an inch.

This formula should be worked out in respect to the factory wheel + tire combination first to figure out what you need when plus-sizing your wheels. With your situation above, the factory wheel + tire combo works out to:

(205 X .65)/25.4 = 5.25 inches of sidewall X 2, + 15" rims = 25.5 inches total Wheel + Tire

Now plug in the numbers for Tire Width and Aspect Ratio. Divide by 25.4 then multiply by 2 and add this to the rim size you are gravitating towards. Whatever comes closest or equal to the 25.5 figure is your magic wheel + tire combo.

Now, plugging in the numbers for your proposed tire packages you can determine what size tire you need for 17"s. Or 18"s. Or for extra bling you can throw some 20"s on there.



Here's the short version:

(215 X .40)/25.4 = 3.4 inches.
(215 X .45)/25.4 = 3.81 inches.
(225 X .45)/25.4 = 3.97 inches. (X2 + 17 = 24.97)
(235 X .45)/25.4 = 4.16 inches. (X2 + 17 = 25.32)

So, when coupled with 17" rims, the 235/45 tire combination would in fact be the preferred one.


edit: I got my original metric translations screwed up. ren28 showed me the light! It's fixed now.

[ren28]

Here is a site with more than you wanted to know about wheels.

http://www.chris-longhurst.com/carbibles/

There is also a tire calculator on that site which is super handy-dandy.

If you have an 8" width rim and if the car can fit it w/o rubbing the fender or suspension, I'd choose a 235/45/17 size tire.

[TB4000]

And here I always thought it was just the number next to the R on the tire...me and my oversimplification.

[mrazntre]

2 of you guys and no one mention of offset.

[Rogmok]

well, i'm not replacing the rims, so offset shouldn't affect the tiresize.. right?

[mrazntre]

for you no, but for general info yes since this has become more of a tire thread.

[Rogmok]

ia ctually got lucky.. i didn't even know about offset when i bought my rims.

but luckily the offset looks ok on my car..

[mrazntre]

ia ctually got lucky.. i didn't even know about offset when i bought my rims.

but luckily the offset looks ok on my car..

just because it fits doesn't mean it's the correct offset for the car. you have wheel bearing issues if the offset is too way off (other than having the rim hit the strut, caliper or fender).

[deez nuts]

The aspect ratio is a percentage of your tread width. A formula below is a guideline to stick to:

(tire width) X (aspect ratio) = (Sidewall height from the rim )

Since you're always going to include the entire diameter of the wheel + tire when calculating what your plus-size configuration will be, it follows that your (Tire Width X Aspect Ratio) + Rim size should be as close to, if not identical, to the factory specifications as possible. Remember that 'Tire Width' is measured in millimeters, and roughly 25.4 millimeters make an inch.

This formula should be worked out in respect to the factory wheel + tire combination first to figure out what you need when plus-sizing your wheels. With your situation above, the factory wheel + tire combo works out to:

(205 X .65)/25.4 = 5.25 inches of sidewall X 2, + 15" rims = 25.5 inches total Wheel + Tire

Now plug in the numbers for Tire Width and Aspect Ratio. Divide by 25.4 then multiply by 2 and add this to the rim size you are gravitating towards. Whatever comes closest or equal to the 25.5 figure is your magic wheel + tire combo.

Now, plugging in the numbers for your proposed tire packages you can determine what size tire you need for 17"s. Or 18"s. Or for extra bling you can throw some 20"s on there.



Here's the short version:

(215 X .40)/25.4 = 3.4 inches.
(215 X .45)/25.4 = 3.81 inches.
(225 X .45)/25.4 = 3.97 inches. (X2 + 17 = 24.97)
(235 X .45)/25.4 = 4.16 inches. (X2 + 17 = 25.32)

So, when coupled with 17" rims, the 235/45 tire combination would in fact be the preferred one.


edit: I got my original metric translations screwed up. ren28 showed me the light! It's fixed now.

whoa dizzy.

[mrazntre]

just think of it as a saline drip. you need the right amount per patient.

[Beat180]

225/45/17 will still give you a 2% error in your reading, fortunately it'll be reading a number higher than you're actually going over stock. The 215's will yield a 3.4% error.