tonydt1g3r

I was wondering what is the height difference from the stocks to 20's height wise including the tire. I want to get a picture in my head of how much the gap is filled and how much lower the car will need to be dropped.

2fast4u

20" rim is 2" taller than our stock 18". We need a new lower profile tire. Use the website below to calculate your tire size.
http://www.miata.net/garage/tirecalcold.html

rominl

iTrader: (4)

if you use 245/35/20 and/or 285/30/20, the overall height is about 1" over spec. if you are dare to use 245/30/20 and 285/35/20 (rubber band) you are pretty much with original spec

tonydt1g3r

why wouldnt you use 35's all around

Neo

iTrader: (3)

Well, if you are going with a staggered setup, 35s all around will make the front wheel diameter smaller than the rear. With cars not setup for different wheel diameters, it is optimal to try to retain the same size (like OEM).

Remember this number is an aspect ratio to determine the sidewall height. It is a percentage of the tire width (245, 285 in this case). As you can see, 35% of 245 < 35% of 285.

tonydt1g3r

I am sorry for being retarded, but if you had 35's all around wouldnt the diameter be the same. What is the stock tire set up? are you telling me the stock tires dont have the same size front and rear and thats why you would want 35's up front and 30's in the back.

Neo

iTrader: (3)

rominl alluded to a staggered setup and my statement started with "if you are going with a staggered setup".

The OEM setup is not staggered. The OEM rims are 18x8 all around. If you get the same rims all around (non-staggered - for example 20x8.5), then you would only be using 245/35 tires all around.

If you do staggered (for example 20x8.5 front and 20x10 rear), then you'd have to use different series tires with the sizes above as an example.

rominl

iTrader: (4)

hah that's why i said and/or

tonydt1g3r

Ok I think I get it now, I always thought staggered set up was just different width tires up front and in the back, IE 245's up front and 285's in the rear. I didnt think the height of the tires had to deal with the staggered setup IE 35's up front and 30's in the rear I thought it could be the same size. Thanks for the clarification

Neo

iTrader: (3)

Well, you are right that it has to do with different widths the way you described it. The way tire specs are setup, though, is that the sidewall height (and ultimately the overall height/diameter) is based on the ratio of the first and second number.

For our cars, you WANT to keep the front and rear diameters the same. This is why you have to play with the numbers to get the specs right.

rominl

iTrader: (4)

yup that's correct. our car is not g35, z, nsx, or vette, so we need and should maintain same overall wheel diameter everywhere

tonydt1g3r

AHH I see the light. So 35 for a 245 width tire isnt the same height as a 35 for a 285 width tire. And since that is the case its harder to maintain the same diameter for front and back. Or maintain the raition of width and height of a tire. What is the ratio supose to be?

rominl

iTrader: (4)

hahah that is the ratio!

for 245/35, the sidewall is 245x0.35 = 85.75mm
for 285/30, the sidewall is 285x0.30 = 85.50mm
for 285/35, the sidewall is 285x0.35 = 99.75mm (a lot more)

see the difference now?

camillian

So Henry, if we are using 19x9f and 19x10r on an sc. We go with 245/35(85.75mm) in the front, but why do we go with 275/30(82.50) in the rear. Thats off by 3.25 mm. Shouldn't we go with 285/30(85.50mm) or is that to wide for the car? I know it is only 3mm difference in height, but to have the 3mm shorter in the back is funny. If it was 3mm shorter in the front then atleast the car would sit right

Neo

iTrader: (3)

I like the 245/285 combo. (I think Henry does too. ) It depends if your rear wheels is set up right so that the extra width from the 285 does not rub. 275 is just "safer" for rubbing (or not rubbing if you want to look at it that way) purposes.