SWAT81

iTrader: (14)

I'm looking for tires to put on 17'' ~ 18'' rims but I want the ones that are thinner then the regular tires. The ones that have less gap between the rim and to the ground.

weaklink

you are talking about low profile tires. What you are concerned with is aspect ratio. http://www.tirerack.com/tires/tiretech/tiretech.htm

try starting there...

jimlab

Here's a crash course on P-metric tire sizing...

P275/40-17 (P-metric tire size information)

275 - Width in mm (cross section, not the tread)
40 - "Series" or "aspect ratio". Basically, the sidewall height is 40% of the width in mm
17 - Wheel diameter in inches

1. To select the right tire for your wheels, make sure it matches the diameter of your wheels, 17" in this case.

2. Divide the width of the tire (275mm in this case) by 25.4 (1 inch), and you get a cross section of roughly ~10.8 inches. Ideally, this tire should be installed on a 9.5" or 10" wide wheel.

3. To get the "look" you want, the lower the aspect ratio (40, 35, 30, etc.) the shorter the sidewall, on average. Increasing the width of the tire will somewhat offset a smaller aspect ratio, though.

P275/40-17
275mm * 0.40 = 110mm sidewalls

P285/40-17 (a little wider tire)
285mm * 0.40 = 114mm sidewalls

P285/30-18 (larger wheel, lower aspect ratio)
285mm * 0.30 = 85.5mm sidewalls

Hope that helps.

SWAT81

iTrader: (14)

Thank you so much!

jimlab

No problem.

You can figure out the nominal (tires compress with weight, obviously, so they're not a perfect circle when installed on a car) height of the wheel and tire by taking the sidewall height in mm, multiplying by 2, dividing by 25.4, and adding the wheel diameter.

275mm * 0.40 = 110mm
110mm x 2 = 220mm
220mm / 25.4 = 8.66"
8.66" + 17" = 25.66" tall

If you figure out how tall your stock combination was (for the FD, P225/50-16s were about 24.9" tall), then you can keep approximately the same height by subtracting the diameter of your new wheel size, dividing by 2, and then multiplying by 25.4 to get the sidewall height you need to keep the height the same.

24.9" - 17" = 7.9"
7.9" / 2 = 3.95"
3.95" * 25.4 = ~100mm sidewall height

To find a tire that fits that bill, you just divide the sidewall height you found by a smaller aspect ratio than the stock aspect ratio, and you'll get the rough width of a tire that has about the same height as the stock tires.

100mm / 0.4 = ~250.8mm = P255/40-17

You can double check by doing the math...

255mm * 0.40 = 102mm
102mm * 2 = 204mm
204mm / 25.4 = ~8"
8" + 17" = 25", or about 0.1" taller than stock.

If a P255 is too narrow for your tastes, then you can decrease the aspect ratio further and try again.

100mm / 0.35 = ~285.7mm

Therefore a P285/35-17 would also be about the same height as stock. However, sometimes the ideal tire size doesn't exist or isn't available in the brand or style you want, so you can go a little wider or a little narrower and live with a little taller or shorter tire.

The reason you want to stay close to the same diameter as stock is to avoid throwing off the accuracy of your speedometer, and to ensure that you'll have minimal problems with tires rubbing.

Again, hope that helps.

FDNewbie

iTrader: (10)

Jimlab...DAMN. lol...that was great man. Someone should def. make this a sticky for us...=)

Thanks a lot