18inc rims

[johnc]

I have seen more than enough people stay away from this site, just because of the harsh attitudes on "car setup".

 

That's OK with us. We are not an all inclusive site. I do understand your point but our focus here is on performance. I also agree that some of us (me included) focus a lot on track performance, sometimes a bit too much for the topic at hand.

[Slammed68]

That's OK with us. We are not an all inclusive site. I do understand your point but our focus here is on performance. I also agree that some of us (me included) focus a lot on track performance, sometimes a bit too much for the topic at hand.

 

At least you admit it There just aren't enough road courses around here to justify me needing to set up a car for a road course lol, mine is strictly for the street, and the 1/4 mile when feeling like cranking off a legal pass..

 

I didn't mean to sound like a winny or anything, I was just on LS1tech the other day and there was a few posts made by some folks that sought awful poorly of this site for said reasons. Maybe there should be a few different sections added, specifically for drag, road course, auto-x, street driving, etc, and the importances of each can be highlighted there.

 

Just a thought.

[B00STDZ]

So would you say this is the perfect rim size?

 

 

They are 15's! Less rotating mass.

[B00STDZ]

No one is still addressing my question, and it's not just looks and SUVs. Manufacturers continue to increase the diameter of wheels on performance vehicles. I did a search and found that a 2009 Ferrari 599 GTB Fiorano has 19" diameter wheels on the front and 20" diameter wheels on the back. This car is all about performance so if it would perform better with smaller diameter rims it would come with them from the factory. I'm also not talking about the aftermarket here which generally favors upgrading wheel sizes. Here's a site that talks about aftermarket reasons for getting 'plus fitments': http://www.toyo.com.au/tech_info8.htm

 

I think that as horsepower increases brake and wheel sizes can correspondingly increase as well. Since I probably have 3 or 4 times the horsepower my car had when it was stock, I think that running 18s isn't unreasonable. For those people that don't like it, I don't really care. I already have enough people that don't like that I have a Chevy V8 in my car - so get in the back of the line.

Agreed. There are MANY high performance cars with 18's from FACTORY. Look at the 350z! Look at the 370z!.. Look At the Nissan GTR.

 

Here is a local 350z

 

Im sure those 18" rims REALLY slow it down going 8 seconds in the quarter mile! Haha! They need to upgrade to some 10" rims!

[JustinOlson]

Agreed. There are MANY high performance cars with 18's from FACTORY. Look at the 350z! Look at the 370z!.. Look At the Nissan GTR.

 

Here is a local 350z

 

 

Im sure those 18" rims REALLY slow it down going 8 seconds in the quarter mile! Haha! They need to upgrade to some 10" rims!

 

That car runs 15's at the track with 28X10 tires.

 

 

http://www.turbomagazine.com/features/0803_turp_nissan_350z/index.html

Edited March 5, 2010 by JustinOlson

[B00STDZ]

Mmhmm. Alright then I stand corrected...

[B00STDZ]

The question is though how much of an impact do smaller rims really have?

I heard is something like a 8% difference... Granted the faster a car is in the quarter mile the more of a difference it would make.

But maybe a .2-.5 second disadvantage?

 

 

Also on the injected performance car... I wonder if they swap out their brake setup for smaller rotors because it APPEARS that the rotors/calipers fill up the entire space... I couldnt imagine how they could fit a 15" rim around those. Maybe wheel spacers?

[JMortensen]

Aesthetics is subjective. If you want 18's because you like the look then go for it. Just don't try to argue that there are no downsides to them or that they'll make your car faster, because in the vast majority of cases they won't. Nobody is starting "Look at these stupid ass 18's on this Z" threads. We're just responding to erroneous claims in threads about 18 inch wheels, that's all. If the OP had bothered to search before posting this thread wouldn't even exist. The topic has been beat to death here and in other threads. Let's move along, shall we?

[Bartman]

Aesthetics is subjective. If you want 18's because you like the look then go for it. Just don't try to argue that there are no downsides to them or that they'll make your car faster, because in the vast majority of cases they won't. Nobody is starting "Look at these stupid ass 18's on this Z" threads. We're just responding to erroneous claims in threads about 18 inch wheels, that's all. If the OP had bothered to search before posting this thread wouldn't even exist. The topic has been beat to death here and in other threads. Let's move along, shall we?

Yes aesthetics are subjective, but don’t continually try to argue that there are no upsides to them and that they can’t make a car faster or handle better – because they obviously can. If you don’t like them fine, but there is evidence that they do increase performance so don’t discount proof that opposes your viewpoint. John posted specific proof that indicates performance gains from larger diameter wheels, and I’m sure there are other similar results as well.

 

I think that ignoring the fact that all performance vehicles of late have larger diameter wheels, or claiming that it’s simply because of aesthetics and not performance, is just displaying an inability to accept the possibility that larger diameter wheels are a viable performance option for high horsepower vehicles – especially ones that have other performance modifications.

[B00STDZ]

18" rims really arent even considered large! You guys act like we're talking about 24" rims...

[Bartman]

I was just thinking that before I installed my 18x8.5 fronts and 18x9.5 rears I was running 17x7's all around. Too bad I sold my old wheels, but it would be interesting if I could test the diference between my 18's against 17's similar to the way John mentioned on the BMW on an autoX track.

[JMortensen]

Yes aesthetics are subjective, but don’t continually try to argue that there are no upsides to them and that they can’t make a car faster or handle better – because they obviously can. If you don’t like them fine, but there is evidence that they do increase performance so don’t discount proof that opposes your viewpoint. John posted specific proof that indicates performance gains from larger diameter wheels, and I’m sure there are other similar results as well.

 

I think that ignoring the fact that all performance vehicles of late have larger diameter wheels, or claiming that it’s simply because of aesthetics and not performance, is just displaying an inability to accept the possibility that larger diameter wheels are a viable performance option for high horsepower vehicles – especially ones that have other performance modifications.

 

Let's argue the technical bits, or stop. I know I have the tech on my side. I've been wrong and admitted it here plenty of times. Show me I'm wrong again. Please. Pretty please. I love to be proven wrong, because I learn from it. On this one I am pretty sure I'm right though. The faster to 50 mph thing has to be a gearing issue. Give me a physics based reason why a heavier wheel with higher PMOI will accelerate faster than a smaller diameter light wheel, and I'll be happy to relent and admit that I've been wrong the whole time. Don't waste too much time looking for one though. Here is my physics based reason for believing that lighter wheels with smaller PMOI accelerate faster:

 

From http://en.allexperts.com/q/Physics-1358/2009/12/Circular-motion-concepts.htm

When you do work to an object you can change the object's velocity and, therefore, the kinetic energy of the object. Since work is equal to the product of the applied force and the resulting displacement of the object, more work will be required to accelerate an object through a greater distance. Now, for a moment, consider a wheel with a radius 2R with one mass m2 located at the outer edge of the wheel at 2R, while a second, identical mass m1 is located at R.

Suppose that this wheel is spinning an some constant angular velocity. The mass M1 located at a distance R from the center of the wheel is moving with a velocity v1 while m2, located at the outer edge of the wheel, is moving with a velocity v2 which is twice the velocity of m1, v2=2*v1.

Since mass m2 at the outer edge of the wheel is moving with twice the velocity of m1, m2 has four times as much kinetic energy as m1 [KE2=4*KE1]! Since the mass m2 on the outer edge of the wheel has four times as much kinetic energy as mass m1, four times as much work would have to have been done on m2 in order to achieve the same final angular velocity!

 

The faster on the course thing is an apples to oranges comparison, because of the increased width of the tires. If you want to say that 18x12 wheels might handle better than 15x7's on an autox course, I'd happily concede that point.

 

I have no problem accepting large diameter wheels on modern performance cars, because they're generally heavier, and they have bigger brakes than our 1970's cars do. Again, that is the best reason to put large wheels on a car; to fit larger brakes. Modern cars are designed at the outset to have larger wheels so they don't have the same suspension issues that our Z's do when you put them on. You're arguing the equivalent of "Heavier sportscars are faster because modern sportscars are heavy." It's not a good logical argument. Modern sportscars may be a lot faster than 70's sportscars, but it certainly isn't because they're heavier.

[Bartman]

...

The faster to 50 mph thing has to be a gearing issue.\

...

I think it is a gearing issue – that and traction. I would think that the diameter of the drive wheels affects the performance of a vehicle the same way that changing the gears in a transmission or rear end would. So let’s just say that the gearing of a vehicle is determined based by the automotive engineers on the horsepower of that vehicle. If you add performance modifications that horsepower figure is now higher and the vehicle may be ‘over geared’. Now you add larger diameter wheels and you may be able to increase your performance by effectively bringing the gearing back down.

[leftover z]

I wouldn't think the diameter of the wheel changes anything as long as you have the appropriate tire diameter (the plus 1, plus 2 etc theory).

If the Z was designed for a 195-70 14, you go up to 205-60 15, 225-50 16, etc. As long as the outer diameter of the tire is right, it shouldn't matter if you run a 14, 17, 18 or larger wheel. It's the overall diameter of the tire that effects your gearing.

 

Just throwing my two pennies in the pot

[JMortensen]

I think it is a gearing issue – that and traction. I would think that the diameter of the drive wheels affects the performance of a vehicle the same way that changing the gears in a transmission or rear end would. So let’s just say that the gearing of a vehicle is determined based by the automotive engineers on the horsepower of that vehicle. If you add performance modifications that horsepower figure is now higher and the vehicle may be ‘over geared’. Now you add larger diameter wheels and you may be able to increase your performance by effectively bringing the gearing back down.

Which is still slower than having the smaller diameter wheels and fixing the gearing issue.

[Bartman]

Which is still slower than having the smaller diameter wheels and fixing the gearing issue.

Not necessarily, because a larger diameter profile (wheel and tire together) will have an increased contact patch which should provide better traction.

[JMortensen]

Not necessarily, because a larger diameter profile (wheel and tire together) will have an increased contact patch which should provide better traction.

Like I said before, that may or may not be true based on inflation pressures, sidewall stiffness, etc. Note the Z running 8's on the 15" rims, not the 18's.

[B00STDZ]

I see what your saying jmort... but i think bartman is talking about the increases of performance in AutoX as all that extra tire hurts performance...

[JMortensen]

I see what your saying jmort... but i think bartman is talking about the increases of performance in AutoX as all that extra tire hurts performance...

???

[Daeron]

Actually, the main mass of the wheel/tire combo on an 18" wheel is about is about 9.5" out from the wheel center if you're talking about a 285/30-18 tire on a 18 x 10 rim.

Oops.. I forgot, you can only run halfway into the forest...... So, in the sense of scale, I made a gross error, but the bones of the matter stand. The more mass that sits further from the center of the rim takes more work to accelerate and decelerate.

 

Technical/performance reasons I have a problem with 18s (and again, this is my personal taste):

 

-mass issue

-sidewall flex issue. I drove my 75 around for about a year with some BIG TALL tires on it and I have to say, it was the loosest and most enjoyable year in that can on the street.. easy to snap out of control and right back in. Everything that I liked about the way a stock Z handles, handled more like that.

 

Aesthetically, I simply point out that the direct stylistic descendant of replacing our 215-60R14s with 255/40/18s, is the instant popularity of the black, bolted on fender flare. The fenderwell is missing too much negative space (because the wheel is so big and the tire sidewall so small) so you need to go buy:

 

-expensive wheels

-expensive tires

-expensive (because they're currently all the rage) flares.

 

 

Now, I have to say that one MAJOR reason that "small wheel guys" seem so defensive about this is, my point above about tire pricing. Now that these huge wheels are all the rage, performance tires in 13, 14, and 15 inch sizes are all but gone from the market. This is something of a sore point for a lot of us, so please bear that in mind any time one of you "big-wheelers" (sorry, couldn't resist) hears one of us old fuddy-duddies* griping about your spinners.

 

*I am only 29, but my tastes are old fashioned.

Edited March 6, 2010 by Daeron