Hey everybody,

ok, here is the scoop, I have an 06, and I recently purchased the OEM 19in rays wheels that are offered on the newer model G35. These wheels are about 5 pounds lighter than my stockies. Although the rim is bigger, the size of the rim+tire combo is almost identical due to a smaller Aspect ratio on the 19's.
i know some about unsprung weight, but after searching through this forum, i realized that its all about where the mass is located, the further away, the worse the conditions, and all the weight loss does not matter even on a lighter rim that is larger than stock (i.e a 20" as opposed to the stock 18")

So, my question for all you guru's is, the entire tire+rim combo is lighter, will I receive a neglible effect on my car, even though the wheel size is the same??
Maybe it has something to do with the tires?

I think that I should receive a positive feedback( better braking, handling, etc.) because the wheel size is the same even though the rims are larger.

I hope you understood what Im asking

Thank you, sorry for the long post

 

I'd like to know this too about 18" OEM touring wheels compared to Nismo 19" wheels.

 

In general, the lighter the wheel/tire combo, the better your acceleration, braking, and gas mileage. But you are correct in stating that the larger the wheel, the farther from the center of the hub the weight shifts. A 5lb per corner drop is nothing to sneeze at, that's significant. I'd say you're close to a wash though because of going up 1" in size. It's really hard to say withot getting into pretty detailed physics calculations. Just stick with as light as you can get in the sizes you desire. And I'd say that 19" is the biggest that look normal on a 350Z, I prefer 18's.

 

All the factors that you mentioned are valid. Whether or not you can “feel” the difference is debatable.

One thing that you will notice from lighter wheels is improved stopping distance. I cannot comprehend a member adding fat-*** 20-inch chrome wheels, and keeping the OEM brakes.

 

Not to mention that your new larger tires will weigh more than your old ones, probably negating any weight loss from the wheels.

 

Very true, those 'pretty' 295/30 19's weigh a lot that many members here feel the *need* to run.

 

I guess the mathematical way to do it is to get the WR^2 (rotational inertia, or mass moment of inertia) of the wheel/tire combo of your stockers and the new setup and see which one is lower. As one guy mentioned this is the figure that represents how the mass is distributed from the centerline of the wheel (the axle). The problem is that I doubt you will find Nissan / Infiniti or tire manufacturers' WR^2 figures published anywhere for general consumer use. Maybe they would provide it if you called and asked but even then it might be proprietary info that they won't hand out.

I went through the same thing last year when I bought 19" wheels and tires as an 'upgrade' from the 18" 2006 stockers. I put them both on the scale and as far as my bathroom scale goes the weight differences were negligible. However, the 18" stockers have pretty thick spokes all the way out from the center, while my 19's have much thinner spokes and a wider rim, so my guess is that the weight is shifted farther towards the OD of my 19's than it is on my 18's. Farther out weight distribution means higher rotational inertia means more power absorption to get them up to speed (i.e. slower acceleration given no improvements to the drive train performance). Luckily the butt dyno didn't notice any real decrease in acceleration so that's really all it takes to make me happy.

 

The 19's are lighter because the weight is pushed out. Does nissan advertise different fuel mpg for the G with 19's no because they made the rims light to counter the size diference.

 

I went from the stock 18" wheels to 19" Volk LE37Ts. The stock wheels/tires were about 53/57 lbs whereas my Volks are 44/48lbs. Obviously, I dropped some unsprung weight. The rotational inertia was a wash - I did some rough calculations and while the weight dropped, it is farther from the axis.

Tire weights vary greatly, you can easily find 19" wide tires that weigh less than the OEM Potenzas - I'm on Michelin PS2.

One thing that most people never think about is a little thing called "rolling resistance". Big, wide tires have more rolling resistance than narrow ones. You will see a drop in gas mileage because of that. You also get a lot more grip so it just depends on what you're looking for overall.

As for feeling any difference - it's hard to tell. The car definitely handles differently - mainly from the greatly increased grip of wider and better tires. Ride quality hasn't suffered nor has performance from what I can tell.

 

Thanks for all the feedback guys, but I think you misunderstood me. I purchased the Stock OEM 19in Rays that are 19x8.0 front and 19X8.5 Rear.

Front tires are 225/40 and Rears are 245/40 as opposed to the stock 225/45 and 245/45 respectively.

I know from fact that the Rays are each approximately 5 pounds lighter than the 18's. Also as stated previously, the diameter (including rim+tire) is almost identical, so is the tire and rim width. So I just dont see all this extra weight coming from the tires. They are in fact smaller! due to the aspect ratio and smaller sidewall.

Hope I clear up some confusion.

So is all the weight still pushed on the outside?? It seems to me that given all these facts, the 19in forged wheels should give positive feedback, even though i plus sized??

Thank you

 

Overall weight is more significant than wheel diameter. After all, tire diameter remains the same.

 

I went from stock 17's to SSR Comp-H17's. IIRC the stock 17's were 24lbs ea. and the SSR's are +/-16lbs each. The test and tune track we used recorded almost a full second drop on a 40+ sec course. (part of that was 20mm extra rubber on the rear, but the fronts stayed the same size.)

The main thing I could "feel" was the steering. It just felt like the car was more willing to do what I asked of it.

BTW: My overall wheel/tire diameter has been reduced by about 3% from stock also. (275/40 17 and 255/40 17)

 

When the Q45 was launched in 1989. The T package came with rear toe variable HICAS steer and FORGED 15" wheel vs cast 15" and fixed rear toe for standard............there was only a 6 pound difference per wheel tire.

These rare ugly wheels make a dramatic feelable difference when used on a standard 4,000 pound Q............the turnin is crisper, the braking is 6 feet shorter. Acceleration test were inconclusive probably was the 0.1 second improvement recorded in testing.

This was only a 5% reduction in unsprung weight - 123 vs 117 pounds on front.

As wheel/tires/rotors have gotten heavier the engineers have been forced to more and more aluminum suspension parts and arms to try to minimize upsprung.......even the wheels are weaker and don't last [bend] for 15 years unlike earlier versions.

 

I think only the manufacturer has the weight distribution on the wheel, and it will not likely give you that information

 

you can actually perform a test of the rotational inertia of the tire/rim combo very simply.

you can set up two workhorses, one at a higher height than the other, and then suspend to rails spaced apart running perpendicular to the horses, then put a rod through the center of the rim (remove the center cap) and roll the tire/rim combo down the rails, timing it.

whichever one is faster is the better combination. this shows the rotational resistance cause the longer it takes, the harder it is for the setup to start moving. I think they call it polar moment of inertia or something.

you can probably find a better walk through with like, angles for the rails to be set at or something. but yeah, even if the combo is lighter, if the weight is all pushed out farther than the other setup, it will be harder for the engine to turn the wheel over.

 

not that the test measures exactly what you all are talking about.

 

Ok, just making sure that we are on the same page. Also, I do not see how the weight distribution could have shifted that drastically either.

On a side note, they are on the car, and it does feel more responsive , maybe its just all in my head

Thanks for all the help guys!

 

don't mean to thread jack, but i kind of have the same question. i went from 18" stock touring wheels (6 spoke) to 19" axis shine, wheel weights are about the same if not less 1 pound. but how much difference would the tires make going from factory 225/45/18 to 245/35/19 for fronts and from 245/45/18 to 275/35/19. once again i don't mean to thread jack, but i feel like my question is very similar (just more simple) to these questions here. like is there any difference i should feel or actually is that would show on track times? thanks!

 

EDIT: woops double post!

 

Friend has the 03 G w/18s, while I have the 05 w/19s.

Not that it's conclusive, but 0-60, he's got me by 3/4+ cars. We're both 6spds, but then again, he's got more tourque than I do. I've been sold on the fact that the lower tourque AND wheels are to blame, and not my shoddy driving , but I would never go lower on the diameter, as anything lower than 18 on the G looks too small.