Just purchased new car, has 18" rims all around wondering if it's possible to lower it 2" or so. Searched the forums and couldn't find anything on lowering it with those size tires.

 

Depends on the tire size, but if the aspect ratio is stock there's no reason why you can't. Mine is dropped 3 inches on 275/35 and 315/30 18s:



-Chris

 

The diameter of the wheel has nothing to do with tire interference when a car is lowered. The determining factors are the outside diameter of the tire, the section width of the tire, and the offset of the wheels. As noted in the post above, if you keep the tire diameter close to stock, it minimizes problems. Then the only issue you are left with is the offset of the wheels. It becomes more critical to keep the tires centered side-to-side in the wheel wells.

 

Awesome thanks for the clarification on this. Here's what I have:

Front:245/40
Rear: 275/40

 

Original tire/wheel combo was (probably) 245/50/16

245 is the tread width of the tire in millimeters (25.4 mm/inch)

50 is the percent of the tread width for the side wall height (122.5 mms)

16 is the diameter of the wheel (rim) itself..

so.. 16 + ((122.5 * .5 * 2) / 25.4) = 20.8 inches in total wheel and tire diameter..

new rear wheel/tire combo is:

18 + ((275 * .4) / 25.4) = 22.3 diameter..

so, you can see from this a 17" rim w/ a "40 aspect ratio" tire is pretty close to stock diameter.. (1 less inch of rim = 21.3 " diameter... even less on your front because of the 245 treadwidth)

Assuming your wheel offsets are close to stock, the 18" rears just lose you 1" of drop (or there abouts)...

Next time you put new "shoes" on your rear, get the 35 (or maybe 30) aspect ratio tires... (I'm not sure which, but now you can do the math... :-)

JT

JT

 

Except, don't do the math that way.

An error there - you overlooked the fact that the outside diameter of the tire includes the diameter of the wheel plus two sidewalls:

For the 245/50-16

Section width:
245 / 25.4 = 9.65"

Sidewall height:
0.50 x 9.646 = 4.825"

2 sidewalls:
2 x 4.823" = 9.65"

Outside diameter of the tire is wheel diameter plus two sidewalls:

16.0" + 9.65" = 25.65" = stock tire diameter if your car left the factory with the Z-rated tire option. If is was a V8 without the Z-rated tire option, it had 235/55-16 = 26.18" diameter.

A 275/40-18 is:

275 / 25.4 = 10.83"

.40 x 10.83 = 4.33"

2 x 4.33 = 8.66"

18.0" + 8.66" = 26.66"

A better match would be a 285/35-18 = 25.85"

All of this is covered in the FAQ. No need to do the math.

 

And the "FAQ" is stickied at the top of the Wheels and Tires forum topic listing, which is probably where this should have been posted.

 

howd you get in down 3 inches? thanks

 

Coilovers.

-Chris