I just recently put an order for Work XD9 now I'm looking for tires. My friend suggested 245/40 and 275/35. He said you want it to be the same diameter. Can someone explain this to me pls. It seems that mostly everyone is running the same profile front and back.

 

need more info..... rim size, offset, are you dropped, are your fenders rolled....

I have 275/35/19 and 245/35/19 if that helps

 

i have the same wheels. i used to have 245/40 and 275/35. It didn't handle the way I wanted to, but it fit nice. I bought 265/35/18 and 275/35/18 the 2nd time around and they fit just as good, and they handle much better.
What your friend means by the 'same diameter' is the rolling diameter of the tire. The rolling diameter should be (size of rim) + 2*(profile)*(width of tire)*(1cm/10mm)*(1inch/2.54cm). The last part is just a conversion from mm to cm.

 

they're size 18 wheels +20f and +18r ...I will be drop with tanabe gf this weekend my fenders aren't rolled

 

i was thinking that same set up too but here is what Motormouth gave it to me. check this out girl

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

it help.

 

How wide (front width and rear width) are your 18" diameter wheels?

--Spike

 

Since you have a Touring, then you have TCS/VDC. Therefore, you don't want the tires to have the same OD, the fronts need to be shorter by at least ½". 245/35/19 and 275/35/19 are pretty much the standard, if you have 18" wheels, then 245/40/18 and 275/40/18 would be the correct size.

 

What do you think a nice-moderately stretched size would be for a 19" rim to keep the cpu happy front and back???

 

245/40 and 275/40 is the correct size but looks like *** and could handle better. On the XD9's which are 18x9 and 18x10 I would at least do a 245/40 and 285/35.... Mich closer diameter than the 275/35. And if you really want meat do a 275/35 295/35 setup. All depends how aggressive you want to get and how much meat you want on the road, which goes with your driving style.

Either:
245/40 & 275/40 <--- Lager rear tire diameter looks goofy.
245/40 & 285/35 <--- Very close good looking diameter front to rear.
265/35 & 285/35 <--- What im going to be running this summer.
275/35 & 295/35 <--- Might have to roll the fenders, very meaty setup.

 

Thank you I will look into this.

 

You will absolutely need to roll fenders for anything bigger than 265 in the rear. I didnt know you have VDC, so I don't know what to suggest anymore .. I liked the square setup the best, but if you don't autoX on them, 245/40 and 275/35/18 works great, and looks nice

 

It looks like Im going with 245/40 and 285/35. Thanks!

245/40
sidewall: 3.9 in
radius: 12.9 in
diameter: 25.7 in
circumf: 80.8 in

285/35
sidewall: 3.9 in
radius: 12.9 in
diameter: 25.9 in
circumf: 81.2 in

 

Are you sure I need to roll my fenders!?

 

you might have to. Like if you follow your plan for install tanabe Gf

 

You have a Touring model, and thus you have VDC. With that setup you need to respect the diameter for stock tires to keep VDC working as it is intended.

The stock diameter for rear wheels is 26.7 inches. The Z’s rear fenders are designed to look best with this tire diameter, and that’s true even with a conservative (1/2 inch) drop.

The 285/35-18” tires at the 25.9” diameter you report are too short. This size (undersize) works most of the time under casual driving with VDC; but if you push it hard, you will see some erratic results with VDC running an undersized tire.

I would go with 275/40-18” on the rear. It will look better, won’t carry any risk of rubbing, and works perfectly with your car’s VDC since it is the correct overall diameter.

Visually and performance-wise, the difference between a tire width of 285mm or 275mm is insignificant (about one third of an inch). It would be foolish to risk VDC malfunction or fender rubbing to go wider with no significant gain. The best tire sizes for your setup are front 245/40-18” and rear 275/40-18”.

--Spike

 

+1

 

sigh... and with 275/40 I wont require to have my fenders rolled correct?

 

I have 285's in the rear without any rubbing problems and no rolled fenders. You can't go just by the tire width, it's a function of width, wheel offset and how lowered the car is.

 

OMG I'm confused.....

 

You will not understand 100% untill you try them on.
or you can test drive other member's Z

-Here is answer ( from PM )
i orderd mine from tirerack, but they don't have stock in around my area so i have to wait few more days.

You can call them check with them see if they have in stock.

245/40/18 275/40/18 this is size that i ordered.