tire sizes??? on a BE

[02legacygt]

why specifically does me BE need 20560r15

i dont understand this whole rim thing... would a say 19560r15 fit , if i put them on all 4 tires... someone please educate me!

[Huffer]

It's your rolling diameter - if that gets out of whack, your speedo will not show an accurate speed. Whenever you go to a non-stock (factory spec) size, you throw your speedo off +/- a %. How big of a % depends on the sizing of the wheel.

Use this calculator here:

http://www.miata.net/garage/tirecalc.html

[Monkhouse]

The size breaks down by width, height, and rim. The 205 is your tread width in millimeters. The 60 is your sidewall. In this case, it's 60 percent of the tread width. Then, of course, your rim is 15 inches. Changing tire sizes may throw off your speedometer if you went with a smaller tire without increasing the sidewall percentage, you would actually be travelling slower than your speedometer says you are, and the difference will get bigger the faster you go.

Your current tire size, for example, has a circunference of just over 6.5 feet. In one mile that tire will revolve nearly 812 times. The other size you asked about has a circumference of under 6.4 feet, and will need to revolve almost 828 times to carry your car the same mile. Your car, however will think it went a mile after your tire goes around 812 times, when it really was about 102 feet short of a mile.

Long story short, you'd be closer to your original size if you went with a 195/65r15, and closer still if you went with a 185/65r15 if you can find such a thing.

I hope that helps.

[Sarra]

The size breaks down by width, height, and rim. The 205 is your tread width in millimeters. The 60 is your sidewall. In this case, it's 60 percent of the tread width. Then, of course, your rim is 15 inches. Changing tire sizes may throw off your speedometer if you went with a smaller tire without increasing the sidewall percentage, you would actually be travelling slower than your speedometer says you are, and the difference will get bigger the faster you go.

Your current tire size, for example, has a circunference of just over 6.5 feet. In one mile that tire will revolve nearly 812 times. The other size you asked about has a circumference of under 6.4 feet, and will need to revolve almost 828 times to carry your car the same mile. Your car, however will think it went a mile after your tire goes around 812 times, when it really was about 102 feet short of a mile.

Long story short, you'd be closer to your original size if you went with a 195/65r15, and closer still if you went with a 185/65r15 if you can find such a thing.

I hope that helps.

Grr, 185 65R15 tires don't have enough of a load rating for a BE/BH.

[DOOK]

my BH came with 205 55 16

[2.5GT]

same with newer BDs. I now running 215/60R16 :eek:

[02legacygt]

soooo it really shouldnt matter on the tread width as long as i stick to the same side wall size,.... like i should safely be able to go to a 19560r15, on all 4 tires or a 21560r15 on all 4???

[Monkhouse]

soooo it really shouldnt matter on the tread width as long as i stick to the same side wall size,.... like i should safely be able to go to a 19560r15, on all 4 tires or a 21560r15 on all 4???

The sidewall number is a percentage. 60 percent of 215 is bigger than 60 percent of 195. So a 215/60 tire is taller than a 195/60.

If you stay with a 60 series tire it wont hurt your car. The only real drawback to going smaller is that your speedometer and odometer will be off. You'll be going slower than the gauge says your are. If you go bigger, you'll be going faster than it says, and I can tell you from experience, you won't get out of a ticket just cause your speedometer says you were going the speed limit.

[02legacygt]

hahah, ohh man that sucks!!!

[ivwarrior]

I know it's a bit nit-picky, but the 205 part is SECTION width, not tread width. It's the measurement of the tire at its widest point. Cheap tires use a narrower tread and let the sidewalls bulge out more to get the stated width. Higher end tires tend to have wider treads and stiffer sidewalls that don't bulge as much.

[Monkhouse]

I know it's a bit nit-picky, but the 205 part is SECTION width, not tread width. It's the measurement of the tire at its widest point. Cheap tires use a narrower tread and let the sidewalls bulge out more to get the stated width. Higher end tires tend to have wider treads and stiffer sidewalls that don't bulge as much.

You're right. I forgot that. It's been more than a decade since I sold tires.

[deadlydave]

The middle number--the aspect ratio.

From TireRack.com

Sidewall Aspect Ratio
Typically following the three digits identifying the tire's Section Width in millimeters is a two-digit number that identifies the tire's profile or aspect ratio.

P225/50R16 91S

The 50 indicates that this tire size's sidewall height (from rim to tread) is 50% of its section width. The measurement is the tire's section height, and also referred to as the tire's series, profile or aspect ratio. The higher the number, the taller the sidewall; the lower the number, the lower the sidewall. We know that this tire size's section width is 225mm and that its section height is 50% of 225mm. By converting the 225mm to inches (225 / 25.4 = 8.86") and multiplying it by 50% (.50) we confirm that this tire size results in a tire section height of 4.43". If this tire were a P225/70R16 size, our calculation would confirm that the size would result in a section height of 6.20", approximately a 1.8-inch taller sidewall.

[BE-Fresh]

I went from stock 205/55/16 to 215/45/17 with the 06 LGTs then 225/45/17 with the new tires. I think my speedo is a mile an hour above than my actual speed. So it isn't much.