UR NZWY

how about 17 inch stockers?

ChadS

Really good info here. I get it now.
RadioMan: That tire size calculator is quite handy.

Thanks.
- Chad

Ztalker

255/45/17 rear for the stock rim is perfect. It's about an inch wider than stock 245/45/18 in an 06.

Kolia

iTrader: (2)

255 -> 245 = 10mm difference = closer to 1/2 an inch...

shinkuu

iTrader: (4)

i think going 245F/255R will also reduce some of the car's natural understeer. I currently use 255 all around and the car has noticeably less understeer than with the stock 225F/245R set up.

PS. i dont know if you consider this a deal or not but you can get 245/40/18 falken azenis rt-615 for about $150. You can sell your tires in the classifieds section.

Ztalker

LOL...it all depends on the tire manufacturer. i double checked with a measuring tape just now.
The stock bridgestone 245/45/18 treadwidth is only 7.25" wide whereas my 255/45/17Contisportcontac treadwidth measures 8.50". So it all depends LOL.

Nukiz0r

iTrader: (4)

Amazing information here, this thread should be sticky because it is so informative.

This was enough information, to actually help me understand what options I can choose. Let me see if I can coalesce it into one meaningful statement.

If Im going from 04 stock 17''s, to Gram Light 18's (18/8.5f-18/9.5r), for the best traction Id probably want 255/40f's and 275/40r . That would get me the most rubber on the ground during hard cornering. Pair those numbers up with some really good rubber (Im leaning towards BFG KDW 2s) and I will improve/maximize the cornering ability? Because Im running a 40 sidewall, I will likely have less chance of rubbing after a drop? Am I right? Is this all fairly true?

So if that statement is true why would I want to run a smaller width? For example, why would I want to have 235/40f and 255/40r's knowing that it would throw off my speedo and get less rubber to the ground during corner? Im going to take an edjumacated guess and say you would be quicker?

2nd Edit: Orrrrr, is it because the greater width increases the chance of sidewall bulge resulting in lower lateral performance? So a 245/40f -265/40r might be a good midpoint to avoid bulge but still have more rubber on the ground than stock. Or am i completely wrong in this?

Nukiz0r

iTrader: (4)

Oki.. I did some research. From what I've read, there are alot of variables to really determine what sizes would be best. I guess youd just have to test the tires after youve finished installing any aftermarket suspension products. And adjust it according to your driving style and how it feels afterwards.

Le sigh. So if anyone read my previous post, I think I can understand the 2nd edit reasons. Different widths would help against over or understeering. Unfortunately, I dont think I had enough time with my stock 04 Z to tell whether I have over or understeering problems. ( I only had a chance to drive 4 times.)
If I was to say the only time I ever pushed to car to that limit, it seemed like it had a slight case of oversteer. So I guess 245/40/18f and 275/40/18r's would be a possible solution to fix that?

Gah brain.. ... hurting. =P

JDMFairladyZ33

iTrader: (37)

Nuki, you are making this too hard. just remember this:

1) Tires that are too wide for the wheel will over hang. The sidewalls will not have the proper support during cornering. You will actually end up hurting performance with a tire that too wide then sticking with stock size.

2) The wider you go on the rears the more understeer you will have. I noticed it the minute I put on my 285s.

255/40/18s on the front according to BFG's application chart for the KDWs puts the rolling diameter at 26" and as a wheel width range of 8.5-10.

275/40/18s on the rears according to BFG's application chart for the KDWs puts the rolling diameter at 26.7" 9 -11.

Reference the stock 18"

OEM RE040 rolling diameter

F 225/45/18: 25.9"
R 245/45/18: 26.6"

So with these numbers you are dead on in your tire plus sizing in both inflated rolling diameter and wheel width application. I would go with these numbers.

Nukiz0r

iTrader: (4)

Cool, thanks Bro. When I finally make it back to dallas, the first rounds on me.

Now if I can only find a place that sells KDW's in both those sizes. Just about every place I've looked has kdw's in 275/40/18 but only KD's in 255/40/18, or something similar vice versa. =)

Im definately trying to get the most grip outta the Z that I can.


Edit: I meant kdw 2s. But it looks as if they dont make kdw 2s in 275/40 =/

JDMFairladyZ33

iTrader: (37)

Yeah I know what you mean. I think it might have to do with the fact that the KDs might be phasing out of production. BFG did the same thing when they were about to discontinue the Z rated Comp T/A models before the G-Force line came out. I'm sure you can still special order it because it is on their application charts. Go to NTB, Discount or something and see if they can order you a set from the vendor.

Kolia

iTrader: (2)

You're right. There is no specific mesurement point for the thread width. So various tires end up not being quite spot on the sidewall marking sizes.

Kolia

iTrader: (2)

Wow, you’re all excited now!

The closest plus sizing that worked using the KDW2 I find is 235/40R18 and 255/40R18. It’s overall a bit smaller than oem (76mph is actually ~75mph) but maintains the front to rear ratio. That’s what I have on mine. It looks good and also maintains the forgiving nature of the Z (slight under steer).

Going wider and people end up with 245/35R18 and 275/35R18 to keep the front to rear ratio. But as you’ve figured out, that’s not very good for under steer.

An other thing is that, in my opinion, super sticky/wide tires are boring. You get tons of grip, which is good, but until you start to get the car slightly sliding, you’re not extracting all the fun from your car. Wide tires aren’t very forgiving when they give up. I prefer to slide at a lower speed too.

As long as you’re on rails, you’re not really driving…

Nukiz0r

iTrader: (4)

LOL yeah, I am all excited. I actually learned something today by reading this thread. Every time I learn something new about my Z I feel as if Im accomplishing something.

Forgive me as I sidetrack this thread, but to me, the Z is a car that is worthy of studying and increasing your knowledge on. I guess thats what seperates the true enthusiasts from the others.

I wouldnt mind doing a little sliding now and again, I love the feeling of drifting, but I love being able to attack corners and curves fast. I guess its a matter of personal preference. =)

Is BFG phasing out KDW's and going for KDW2's?

Kolia

iTrader: (2)

I don't know about any phasing out.

Attacking curves fast? If you're not slidding a bit, I garrantee you're not going as fast as you could be And a bulging tires isn't one that will inspire confidence in transiant behaviour (going from slide to grip to slide...) so you have to keep a fair margin of safety there and drive under the maximum grip of your big wide tires...

Try all the possible combinations of availlable tires. You'll have a hard time finding different sizes that agree with both VDC and in corner balance.

spikef15

Ok, I know to most of you this is a really stupid question, but are there any drawbacks to putting the same width tires on all 4 rims and rotating them regularly? My husband keeps suggesting it, and I'm figuring there has to be a performance reason for the wider rear tires, but is it a difference I'd notice? I have stock 17s on an 05 enthusiast roadster, so I'm pretty sure I'd need new rims, but aside from that cost are there any negatives to using the same tire width on all 4? Thanks!

Kolia

iTrader: (2)

The tire width isn’t a problem with the Z. It’s the tire diameter that needs to be taken care of. The rear has to be taller.

The electronics in your Z is expecting that and will consider a condition where the rear wheels are spinning slower than the front as normal. Same size wheels front and rear will spin a t the same speed, the ECU will conclude that you’re doing a burn out and will attempt to cut the power to prevent it.

Same size wheels will also confuse the ABS and reduce its effectiveness.

ChiBlack350

iTrader: (3)

I think it only affects VDC cars. Sticky at top of this forum...

z-u-later

iTrader: (43)

^+1 I believe going with same size tire on all four corners should not affect the ABS & TCS.