Driven

First off, forget my earlier post...I must have been half asleep (actually, my wife could kill me...but I often stalk this board until 2AM....!)

Anyway, here is what you all are asking about: Lets talk about rear wheels first. Luke set up the Brembo car with 11" wheels and a 44+ offset, right? And Skiddazzle has his with 9.5" and 24+ offset, right? This means Skiddazzle's outer rim sits 1mm closer to the fender lip. Other popular wheel widths with the same "fender distance to the wheel" as the Brembo car would be as follows:
8.5" = 12+
9" = 19+
9.5" = 25+
10" = 31+
10.5" = 38+

Earlier numbers were close...but these are much more accurate...AND remember these offsets ONLY address the "LOOK" you are asking about!

I don't recall what Luke set the Brembo car with up front, but since I can't imagine anyone wanting more than a 9" up front, the comparable offset to what Skiddazzle has would be:

8.5" = 27+
9" = 33+

I don't understand all the jargon about ackerman angles and the such...and although I completely understand you can't keep the stock offsets when you want to stuff a seriously fat tire in the same well if you don't want to take a torch to your fenders...but if everything is suppossed to be running with the "centerline" of the tire (regardless of width) the same distance from the mounting surface....well then everything "should" have a 33+ offset just like the stock. If you stuff a 10" wheel on....an extra inch will stick further out and the other inch will sit further in....that simple. There must be more to all this geometry than I understand.

z461

I believe Luke DOES have a vested interest, just because he doesn't sell the wheels that we've been buying so far, because he wants us to wait for tirerack's offerings. BTW, they started developing wheels for the 350Z over 2-3 months before the car even came to America while it was in Japan. I know that Nissan went to Volk when Volk was developing their track wheel for the Z, and Volk also took measurements to make their own aftermarket wheels. Therefore whatever they are selling are in the proper offsets.

Luke@tirerack

the 245/45-18 rear tire size is the widest I would recommend. However the 255/45-18 will fir an 8.5" wheel but the diameter is a little over 27" tall and that would hurt the acceleration by effectively changing the final gear ratio so, I can not recommend that size. The 265/40-18 needs a minimum of a 90." wide wheel so that won't work either so, stay with the 245/45-18 tire size.

Driven

Luke,

Regarding final gear ratio/acceleration:

I agree that in essance you are messing with the gear ratio when going with any tire size other than stock...but how can you say it will certainly "HURT" acceleration? (I'm only asking...not attacking ) Are you assuming Nissan hit it "EXACTLY" on the head for maximum acceleration? If you have enough torque on the low revs to break traction you obviously are geared low enough...wouldn't a slightly larger tire not only minimize excessive wheel spin, but allow higher speeds at the same revs to allow a higher speed in any gear prior to shifting? In other words...if you were lined up with another car and weren't going to break a certain speed (either out of road or safety) and you only had to shift once rather than twice to get to that final speed...wouldn't this possibly be an advantage??

Monkey Man

This is a very good point. Since Rays Engineering developed the Track wheels for Nissan, wouldn't they know exactly what would fit the car? I would certainly hope so. We have had ZERO fitment issues with any of the Volks we have ever sold. All the fitments are always tested thoroughly before we get our sizing list. I will continue to sell the wheels to my customers because I have faith in the information I am given. Another thing to point out, that Skidazzle touched on, is usage. Not many people buy 3K dollar wheels to race on at the track. Wouldn't the track be the only situation where the slight variation from perfect a scrub radius, etc. comes into play??

Luke@tirerack

it will slow down acceleration but increase top speed much as a 3.73 gear ratio as opposed to a 4.11 gear ratio ... the 4.11 will accelerate faster due to a lower load on the engine and the 3.73 will have a higher top speed (if everything else was equal) that's providing you have enough grip from the tires. With a higher gear ratio the engine will spin up faster because of the lower load that the engine is overcoming which will allow you into 2nd, 3rd, 4th etc. sooner meaning you would be accelerating faster .... When you compare both in 4th gear at 3500rpm the taller gear would be physically going slower than the lower gear

Driven

Makes sense...thanks.

MonkeyMan; another point of topic would be tire wear which certainly comes into consideration not only on the track...but for everyday use. I expect to loss dollars fast at the track when talking about tire expenses...but not for daily driving.

Luke@tirerack

and since offset issues will alter scrub radius and ackerman it will increase tire wear ... and the handling issues can alter the street driving characteristics of a car as well not just on the track ... as previously described in many other posts not to mention the additional torsional forces on other parts and what that will cause in the long run

Driven

Luke,

Since you seem to be around this morning...could you explain:

If the car had a stock setup of 30mm+ (front) and 33mm+ (rear) then exactly how does any combination other than that, when changing to different tire widths, "keep things the same"? Do you understand what I am asking? Since the offset is the distance to the center of the wheel only the same offset keeps the center of the wheel the same distance from bearings etc.....or are you saying just to keep the offsets as close to stock as possible as you go fatter? In other words: if it "fit" would you put that 11" on a 33mm+ offset???

roberto350z

SANDERMAN:


Using 255/45 will change the accuracy by 1.3%. This results in a speedo discrepancy of .8mph. If I were you, I would ask TXSTYLE how he feels his acceleration has changed, because his new wheels have a 1.8% difference or somthing like that.

I think the speedo change and acceleration change are acceptable if changing to 255's. Think about this, the 17" stock tires and the 18" stock tires on the Z differ by 1.6%. Nissan obviously thinks that this much of a difference is OK. Once again, if you have any questions, ask TXSTYLE, as his tires selection differed by the amounts Im talking about.

Luke@tirerack

..

Sanderman

I don't really want to go to a larger diameter. I'd be curious of using a 255-40-18 instead as that would actually be a slightly smaller diameter than the stock rears (26.1 inches vs. 26.7 inches) and that would in fact slightly help acceleration. Just wonder if that would fit the 8.5 inch rim. Maybe match that with 245-40-18s in front as that would be within 1/2 inch of the stock 225 fronts assuming you could put those on 8 inch rims. That would also help overcome the understeer as well by getting the fronts closer to the rears in width. But will this combo fit the stock Track rims?

joe

Driven

Joe,

Absolutely no problem doing what you suggest. Nissan has already put there stamp of approval on the 245 on an 8" wheel by doing it on the Performance and Touring model (rears) And as far as a 255 on the rears...well, you already have an additional 12.7mm more (8.5" compared to the 8") than the Performance or Touring rear which is more than the 10mm you want to bump up to. So, yes, you will actually have the extra 2.7mm more in wheel rim width with the 255 wheel than the others running 245's on their 8" wheels.

Make sense....or was that confusing?

sdpearso

First, the Ackerman angle and Scrub radius only apply to steering wheels. Ther rear wheels are not affected by these.

Second, changing offsets in either direction will change the Ackerman angle and Scrub radius. Both affecting wear and handling.

It seems to me that if I am going to change my offset and increase wear on the tires, I'm going to go with a lower offset so that I can at lease get better performance out of it.

Now I'm not saying that you can go to 0 offset and improve performance. But if I have the choice of going +25 or +35 in the front (stock being +30) and neither offset will cause rubbing, then I will chose the +25. I know that this increases stress on the bearings. However 5 mm is not much and when I increase the tire width by 12.5 mm, this offsets the issue.

roberto350z

AHA!!! Sanderman, I think you have the *money* idea of 255/40. Check it out and see if you can follow...

17" stock wheels and rubber measure 26.3"
18" stock wheels and rubber measure 26.7"
the difference between these two is .4, yah?

NOW, 255/40/18 has a diameter of 26.0"
the difference now from the 17" is .3" So we have a closer match. Also, this makes the tire "smaller" only by .8%. If you REALLY think that these differences in sizes will be significant in any way, then youll be getting BETTER acceleration.

Now heres my dilemma. How can Nissan have two tire sizes so completely different?!?! How did they calibrate the odometer? For the 18"s or the 17"s? Either way, they are seriously off. Do you really think that the odometer gearing is different for each model? *Probably* not. So whatever gear they chose, it should be a compromise between the two. If this is the case, then the gearing should be ideal for a 26.5" diameter. Choosing the 255/40 will put you at 26" and 255/45 will give you 27". Either way you will have an error only slightly greater than Nissans allowable error, assuming the speedo gearing is a compromise and fixed between all models. As far acceleration, I think that the point is moot.

phew...end transmission

2003z

iTrader: (7)

I think the calibration is different for each model. Its just a simple parameter in the computer. I had a blazer, and they hypertech programmer let you input your tire diameter for different than stock. I don't know why Nissan wouldn't calibrate them differently.

roberto350z

does a computer control the analog speedo?

SKiDaZZLe

are you serious? of course the computer controls it... this is the 21st century...

did you think the digital speedo and analog speedo get signals from different places?

they all come from the VSS (vehicle speed sensor). this is a pulsed input, which both the digital and analog speedos interpret.

m

Z33Fan

ok, answer this: My Z's analog speedo consistently registers 1-2mph lower than the digital reading. Why would this be? Could it be that the speedos are calibrated based on the 18" wheel and tire setup, and that anyone with 17's has the difference in calibration between the digital and analog speedos?

If they both come from the VSS, then why would one read differently than the other? I'm not trying to flame, just curious.

SKiDaZZLe

all Z's have this problem... mine is off by 1-2mph from the digital readout. with either my 18"s or 19"s

this because one converts the pulses straight into a digital readout. this is going to be pretty much dead on. the analog one has many more factors, like the D-A conversion, and the sweeping motion. notice it does not move like a second hand. it moves more fluidly, as this is how most people would like to see it. if you were going 20mph and slammed on the brakes, the digital readout would get to 0 before the analog speedo. there could be other reasons like parallax errors and such, but those would be very small.

speedometers have been off since cars have been made. we are spoiled to have a digital readout, and so we can complain about the "off-ness" with the analog speedo. i wouldnt worry about it too much.