Todd@ProDyno

Gator...re-read this thread a bit. Its not the speedo we are worried about either. Yes, you want the speedo to be as correct as possible as it also effects your mileage and gearing but the issue is...

ABS and Traction control. As stated above Nissan programmed your ECU to know exactly how many more times it needed to pulse the front brakes, compared to the back based on the revolutions per mile when in an ABS Braking situation. Also, it will mess with traction control, but not as big of an issue.

And your other question about people buying rims & tires...well, when they buy both they are usually upgrading 17 to 18, 18 to 19 etc. When they do so we are able to match them up with the correct size and height tires front to rear.

I find it odd...jspec...that your dealer told you that. When we 1st had a 350 here for test fitment we spoke with Nissan USA regrading this stagger fitment and they pushed its importance on us regarding the above stated issues.

GATORZ

iTrader: (17)

By the way GATORZ, the 40 series tires in the back, if they handle OK, will look funny in those wheel wells.

If they are a tad bigger diameter won't they look the same. If I'm being stupid here feel free to let me know.

jackwhale

DisTirDir: Its after the fact because I have already upgraded my tires to SO3s (track wheels)

the sizes I planned to purchase were one size up:
235/40/18 and 255/40/18. The 255s were back ordered a couple of months from Bridgestone so I bought 265/35/18 for the rear.

I attended my first track day shortly afterward and really appreciated that the car no longer had the pronounced understeer and was very neutral in the corners. Since I had not driven on the track with the original tires, I have no comparison.

One thing I did notice was how easy it was to engage the ABS during high speed braking....120mph down to 40mph. I attributed this to applying too much pedal pressure since I was not used to braking at such high speeds. My previous experience at the track had been in a '70 510 which requires heavy pedal pressure to slow from 90 mph to 40 mph.

Now I'm wondering whether the ABS clicked in because the tire circumference is mismatched. I don't think that there is any way to test this other than putting on the old tires.

The difference in circumference is:
diam circum rev/mile difference
front
26.0” 81.6” 777/mile stock tire
25.4” 79.8” 794/mile -2.2%
Rear
26.7” 83.8” 756/mile stock tire
25.3” 79.5” 797/mile -5.2%

The front difference is within the .75" that you suggest but the difference in the rear is 1.3"

GATORZ

iTrader: (17)

This has turned out to be way more info than I thought possible for replacing my tires. I'm having them put on in about 2 hours. I'm going to look at them closely to see if they will look funny in the wheel well. If they do I will not put them on and I will look at something different. If the look is good I'm going for it. Worst case I get a year or so out of them and they mess with the abs, handling and I get something different. This thread should come in handy since a lot of us will be coming up on the new tire buying experience.

Todd@ProDyno

I think that some of you has misunderstood. For example...Jack, its not the % youve changed your fronts, and the % youve changed your rears...its the % difference between front and rear tires. 225-45-18 25.97 245-45-18 26.68 .71" difference stock, front to rear.

lowrider

iTrader: (3)

GATORZ, No, the rears will be smaller in diameter, not bigger! That's why they will look funny.

Lou

GATORZ

iTrader: (17)

Stockers
Front was 225/45/18 25.9 Dia (can't find the exact)
Rear was 245/45/18 26.7 Dia (can't find the exact)
New
Front is 245/40/18 25.67 Dia
Rear is 255/45/18 26.97 Dia

Verdict - Old tire stagger was .8
New tire stagger is 1.3
Bottom line is .5 more stagger.
Looked at fronts and rears compared on and off the rim and the difference is so minimal that I just can't imagine having a hard time sleeping. 35 MPH was 2750 RPM and it still is. It just happens that it is raining like hell. Did everything I could to have a problem with traction and braking to no avail. So this doesn't make it right or to Nissans specs but is it wrong? I don't think so.
The rears are a little bigger (higher) sidewall and fill the wheel well better than the stockers did (not that it's enough to make you think twice). The fronts are just flat out the same look.

I say that within reason.......buy what you like. To h*ll with Nissan and there dumb a*s tire size and sh*tty potenza's.

IMHO, Dan
GUYS THANKS AGAIN FOR ALL THE INPUT. I NEVER WOULD HAVE GIVEN ALL THIS A SECOND THOUGHT.

WAIT I KNOW WHAT IT IS. THE ECU HAS TO LEARN THEN EVERYTHING WILL CHANGE.

Jspec350z

iTrader: (3)

To clear up what I said. My dealer didn't have a clue. They gave me the line about the ABS and Traction control. I can Nissan customer service. I talked to one of the 350z guys. And he basically said they don't suggest it, but it shouldn't affect anything. Maybe I am messing up my car. Who knows. You can ask nissan in 3 years when they get it back!

lowrider

iTrader: (3)

Uh GATORZ, you did the right thing. I think that's the sizes I recommended.
Good Luck with your new tires.

Lou

slaponte

iTrader: (2)

You lowered the front wall by 3.25mm (removed 6.50mm of the diameter), raised the back wall by 4.5mm (9mm more diameter)... humm... you probably can't see this from a helicopter...

Good job.

D'oh

Actually, what I said was that Discount Tire did not have much available in the 255/45-18 (at least in my area - maybe it would be different if I picked other areas). All I can find on their web page are the Mischelin Pilot Sports, and I'm not ready to spend $255 per tire....

I just checked some other locations at Discount Tire, and they have more options in that size, so that's probably why I'm not seeing much.

Anyhow, I think the 255/45-18 with 245/40-18 would be fine.

-D'oh!

jackwhale

DiscountTireDirect: Thanks for the response. I hadn't really thought through how the TCS receives and responds to information. I had been thinking more along the lines of the info the speedo responds to because there will be a 5.2% difference.

And best of all the difference is still within your suggested parameters.

I agree with GatorD. This thread is great. It's very helpful to hear how more experienced car guys think about technical aspects of their cars.

gooters

so is 265/45-18 on the rear just too damn big for Perf rims? Heh, hope I'm not pouring oil on hot embers or anything.

I am also considering using some high quality 1" wheel spacers from a racing shop as well as upgrading to the largest tire I can fit. I happen to like the look of my rims.

Does anyone know about wheel spacers? Is the 265 rear just totally off limits? I WOULD like to play with my car at the track.

jackwhale

The 265/35/18 work well on my track rims (8.5" wide). I think performance rear rims are 8" wide.

gooters

yes, 8" wide all the way around.

baron

iTrader: (2)

I read that changing the tire size (diameter) could affect the speedo/odometer reading from the ABS sensors. Does the car calculate the speed using the front or rear wheels?

Is there anyway to recalibrate the speedo for a different sized tire?

Thanks,
Baron

Z-Noob

I need to know the sizes for front and rear that will no screw up my ABS. I'm about to replace the stock track tires. I would prefer not to go with the original size since it doesn't seem to fill up the wheel well as much. I don't intend to lower my car since it's my daily driver. Please let me know which sizes will fill the gap better and not screw up my ABS. Just post the sizes that will work front and rear. My head is spinning from all the sizes I've read on this thread.

karmstro

That tire selection should make your car understeer more then even the stock sizing. To reduce understeer you need to make the fronts close to the rear's width. That just doesn't make any sense.....