I've been reading that some people have 235/40/18 and some that have 225/40/18.

I'd like to get some opinions on which to get. I have an 01 CL-S with Comptech Springs.

Please help.

 

235s would be best

 

235's are pretty much equal diameter as stock 17's

 

a 235 tire has nothing to do with the stock tire, and the "235" size has nothing to do with diamater to begin with!

the 235 is the width of the tire, and for a 18x8" rim 235 is perfectly fine. I've heard of people putting 235 tires on the stock 17x7 wheel but that's really pushing it on the stock wheel. for safety sake i'd only go as high as 225 on the stock 17x7 wheel.

for the 18x8 wheel u could go with a 235/40/18 or 235/45/18 depending on what you want. you'll feel a smoother ride if you go with the 45 tire.

fyi, 215/50/17 is the normal stock tire size, not 235.

 

i think the above replies were assuming a 40 height ratio. just guessing.

 

he was saying that the 235/40-17 is a close match in OD to the stock 215/50-17.


but thanks anyway, tire genius.

 

no, he was saying the 235/40-18 is a close match to 215/50-17:P

 

oops. yeah, that's what i meant to say. :o

 

but why would you wanna put a 18" diameter tire on a 17" diameter rim? is that what you are saying? i'm just curious?

 

this conversation is assuming an upgrade from stock 17" to 18" wheels and tires. we're comparing the outside diameter of the tires. it has been noted that the 235/40-18 is a close match to the OD of stock tire size. got it?

 

Actually, 235 has a great deal to do with the diameter.

The outside diameter (OD) of the tire is equal to the rim diameter plus 2 x the sidewall height. The sidewall height is equal to the tire width (235 in this case) multiplied by the Aspect Ratio (40 in this case).

For a stock size tire of 215/50/17 we have:

OD = Wheel Diameter + ( 2 x ( Tire Width x Aspect Ratio ) )
OD = 17 inches + ( 2 x ( 215 mm x 0.50 ) )
OD = 17 inches + ( 215 mm )
OD = 17 inches + ( 215 mm * ( 1 inch / 25.4 mm ) )
OD = 17 inches + 8.46 inches
OD = 25.46 inches

For a 235/40/18 tire:

OD = 18 inches + ( 2 x ( 235 mm x 0.40 ) )
OD = 18 inches + ( 188 mm * ( 1 inch / 25.4 mm ) )
OD = 18 inches + 7.40 inches
OD = 25.40 inches

So a 235/40/18 tire gives a speedometer error of only:

ABS ( 1 - ( 25.40 / 25.46 ) ) * 100 = 0.24% Too Fast

 

I always found this one helpful.

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

 

Um, I'll skip the math and the reading comprehension test and simply say I use 225/40/18's with Comptech springs...No rubbing, either...

 

I know the math of the whole thing, but I was looking for opinions on the look. Y'all are some geeks

J/K

Thanks for the replies.

 

i wouldn't go with 40 series tires with a comptech drop, it'll just produce a bigger tire gap, i'd go with 45's, a tiny bit smaller than the stock tires but since u have 18's it'll be good. and your car will ride smooth too, with 40's u'll start to feel the pebbles in the road lol

 

i've got 235/40/18's dropped with H&R sports...which sits about 0.5" lower than the comptech.

PICS Here

 

Tire compound has a bunch to do with ride quality also...but that's a different discussion...

 

See the math from my previous post. A 40 series tire will not produce a different gap than stock if you go with a 235/40/18 tire on an 18" wheel. The gap would be almost identical to stock.

And the 45's are not smaller than stock on a 235/45/18 or even a 225/45/18. These tires are actually larger than stock and are more likely to rub. The 225/45/18s are a 1/2 inch larger in diameter than stock, and the 235/45/18s are 8/10 inch larger than stock.

 

That looks clean Rocket. I think I'll put one of each on and see what it looks like. 225/40/18 & 235/40/18

I want to stay away from 45's

I'll send pics after I get it done today.

BTW...

My new comptech springs feel awesome.

 

I have 235/40/18 and my tires rub against the outer side wall of the car when I go over bumps alittle fast. Also they stick out alittle more then stock tires.

 

What kind of suspension Mods & wheels are you running ???

 

i have 225/40/18 and they're perfect on my 18x7.5" rims

 

I have 225/40/18 and they need to be replaced next summer.
I checked into getting 235/40/18 and the tire place recommended sticking with 225.
I know mathematically 235 looks better, but they said they couldn’t guarantee no rubbing because all tires are built different.
Especially if I switch tire BRANDS like I plan to do.

Shawn S

 

I have 2 235/40 18 Nitto 555's that are brand new that i'll sell you CHEAP if you are interested!

 

WTF? Um, while the Nittos seem to give more of a "feel" for the road, my other Maxxis tires--which were also 225/40/18--rode better than the stocks ever did, and certainly, did not have any "pebble feeling" qualities...I also have very little gap in the front at all and 45 series would definitely rub with my wheel set up...

 

235/40/18 is the closest diameter as stock 215/50/17