topdown-z

Just a little info for those of you who are getting new tires/wheels. I just put a set of ADR M-Sports 18X8.5 (f) 18X9.5 (r) with 245-45 & 275-40 Toyo Proxes T1S tires on my 04 Roadster. After pulling out of the tire shop, I took a very mild turn and my "slip" indicator light came on and my car began to slow down very rapidly. Needless to say, it was a very strange experience. After the same thing happened several more times I remembered that I had read on this forum about tire staggers that could cause this problem. And by-the-way, it was the tire shop that suggested I go with the 45/front and 40/rear combo. Anyway, the shop was cool about it and put 40's on the front and the problem has been fixed. Sorry to ramble on but I just thought this my help some unsuspecting new Z owner looking for wheels and tires. P.S. My roadster is awesome, "hats off" to Nissan. I was driving a 3.2 Acura TL and wish I had bought my Z sooner.

Type R Boy

edit I should learn to read the whole post first :P

Todd@ProDyno

this is why I push the fact that you need to keep the stagger over and over on this board. This is why I let everyone know what Nissan USA and I suggest. You now have a combo where your front tire is taller (not much) than your rear 26.68f vs 26.66 rear. You needed to have the 245-40-18 front 25.72 in order to have a near correct stagger. This problem will haunt you until you change it. The car simply needs a stagger, period.

Blue Liquid

Well put, DiscountTireDirect. People are willing to cause potential problems with ABS , TC, and VDC simply to save a few bucks or get some set-up that looks cool. Nobody wants to hear that they can't run whatever tire size combo they want. Topdown-Z, i'm not implying that's what you did, but I've seen it many times on these boards. The real problem is that the current major tire manufacturers simply don't make the tire sizes the Z needs (yet). I've been proactive and have written Yokohama, Kumho, Pirlelli, Michelin, and Toyo to explain to them that there is a need for tire sizes that will acommodate one of the best selling sports cars in America. No doubt, they'll be listening.

Todd@ProDyno

A lot of times its an inexperienced shop. Its a relatively new car, and some shops simply dont have access to the correct information. This is part of the reason I am here...to help you guys out in situations like this.

WashUJon

This must get frustrating for ya, Todd...

All these guys just have to do a little bit of homework first! I'm horrible with math and even I can get the computation done.

For a shop to not know that the rear tire/wheel combo they've suggested is smaller in diameter than the front seems pretty bone-headed to me, especially if they are experienced. I don't know. Like I said, the computation isn't hard...

jackwhale

I just discovered that my rear tires are smaller than the front tires. The VDC/TCS SLIP doesn't activate unless I lose grip while pushing it cornering and accelerating tight turns.

I wanted to order 255/40/18 for the rear but they were back ordered a couple of months. So impatient me ordered the 265s

From previous posts I realized that the rear tire is one size over that recommended for 8.5" wheels. When these tires wear out I will replace the rears with 255/40 because of this.

TIRE CIRCUMF REVOLUTIONS
225/45/18 (stock) 81.6” 777/mile
235/40/18 (SO-3) 79.8” 794/mile
245/45/18 (stock) 83.8” 756/mile
265/35/18 (SO-3) 79.5” 797/mile

Now I'm wondering why I don't get the SLIP that others have noticed.

jackwhale

Sorry the columns don't line up in the previous post. I hope that it is still understandable.

I have come to appreciate the complexity of electronics on this car. and it seems like every minor change we make probably has a major effect on the electronics. Its way beyond my understanding of ECU's.

I recall changing my exhaust. The hp and torque initially increased and then after two weeks settled back down where it was before with the stock exhaust.

Blue Liquid

Very interesting...is this based on before and after dyno pulls? Or before and after butt-dyno pulls?

jackwhale

I had never heard of 'butt dynos' before joining this forum. Clearly this is just another word for subjective impressions.


I have a friend who has a muffler company who paid for the development and the dynos. [4 different y-pipes, straight pipe, several different mufflers] The process was indeed interesting and frustrating. After consulting with other ECU gurus in the area, the consensus was that the computer was 'relearning'. Others have posted here about resetting the computer to make the hp gains re-appear but we didn't do much more with it.

The muffler shop put a similar exhaust (y-pipe, straight pipe, single exhaust) on another 350Z and 10 hp gain was maintained over a two week period. He autocrosses locally (SF region) and does very well. [race wheels, tires and a much more experienced and motivated driver].

Todd@ProDyno

D'oh! Nevermind. I re-read. Yes...im suprised you dont see SLIP more. Mind you, it probably takes a pretty agressive corner to do this...but still, its not right

jackwhale

Todd: Sometimes ignorance is bliss! lol

The SLIP light only appears momentarily when I lose traction. As long as I have traction, no light. Nothing like others where they rapidly lose speed. I'd really worry about that.

Blue Liquid

Thanks jackwhale. BTW, your hyposthesis is correct. Some people install 'xyz brand' cold air intake, which actually reduces horsepower, but beause it's bright chrome, cost them $200, and makes a loud noise under acceleration, they swear their car is now much faster than before (even though actual dyno testing shows the car lost hp or tq). Now the real significance of your statement is that this now brings into question the performance gains of many such naturally aspirated mods. Am I to assume then that this may be the case with many other mods (forced induction excluded)? Well, cams may be exempt as well. I'm thinking CAI and exhaust. Items which the ECU has a chance to learn from and modulate. This is scary.

jackwhale

I guess that I'm more of a skeptic than before and I don't have the background to assess the situation.

On the 510 it's much easier. No ECU. Basically tune on the dyno by changing the size of the jets on the Mikuni carbs.

topdown-z

Thanks for the comments regarding my lack of a tire stagger on my roadster. The whole thing started when I decided to get some aftermarket wheels and tires. I read most of the posts on this site and saw that many of the people here had put the same size (35/35, 40/40, etc...) on their cars. However, I also saw that some people had (35/40, 40/45 combos) also. Then I asked a friend of mine with a BMW M-3 Coupe what his tires were. He was running the stock set-up of 45 fronts and 40 rears. So.......when the tire "guru" at the tire shop told me that I needed a 245/45 front and a 275/40 rear, it sounded right. I should have been a little suspicious when the new fronts were actually about an 1/8 inch taller than the rears. My original "stock" fronts were about 3/4ths of an inch shorter than the rears. "Thus the stagger" DUH........ Well they always say that hindsight is always 20/20... After they changed the fronts to 40 series, life was like a bowl of cherries. On a techinical note, the "SLIP" light ONLY came on when I entered a sweeping turn (like an on-ramp) at 55-60 MPH nothing really out of the ordinary. It would NOT come on when I really pushed it hard into a tight turn. That kind of surprised me. Thanks again for your attention. In closing....is there any kind of a club or group of Z coupe/roadster owners in the S.F. Bay Area? I'd love to share the joy of ownership.............

jackwhale

Your description of the SLIP light is basically what I have noticed. I'd always considered that was the way it was supposed to operate. People who described not being able to accelerate or even maintain speed definitely have a problem IMO.

I hope that someone will be able to develop alternative electronics for the VDC/TCS--have the operation be more subtle. There are situations when I've been very relieved to have it--unexpectedly finding water, leaves, frost while exiting a somewhat blind corner.

There are 4-5 350s that appear at SCCA SFR autocross events, held on rotating basis at Candlestick, Coliseum and Golden Gate Fields in Albany.

I've never been able to attend but there are also 'rides' that are announced on this site. Mt Hamilton, Diablo, hwy 92. ZONC (Z owners of northern calif) is a very active club with all generations of Zs.