18inc rims

[JMortensen]

Sorry I worded that all wrong. That's what I was trying to say, if you just slam your car your just making it handle like crap. To get a true suspension setup you have to put the car on scales and everything and adjust accordingly. I remember seeing it done at Richard Petty Driving Experience but I was to young to understand it. What I meant was there is no reason to just slam a car to look cool. You should set your height accordingly to what preforms the best for whatever sort of driving you are doing. If that be daily, road racing, drifting, auto cross, or whatever you may do, ice racing for all I care, that's what you lower/raise a car for, and yes there is lots more than just height to change handling but height is one of them.

I have no idea what you are talking about. Scaling a car is about getting the cross weights as even as possible. Setting the height 1" higher or lower doesn't change the cross weights. Setting the right front 1/4" higher than the left front will.

 

unless you have a race prepped car or a die hard track car, if all you worry about is your cars performance than you will have a nice car, but in the end there is absolutely no reason why you cant have a nice balance of form and function, and if you slam your car right with the correct set-ups and modifications it will handle great. Dont automatically asume that it will handle crappy. and disregard 90% of the things the NasDumb school taught you.

 

anyway, In my not so experienced or humble opinion very few z cars can pull off anything larger than 17's.

NASCAR is the most boring racing there is. The cars are not built stupidly or by stupid people though, and if you think that they are then I suggest you do some research and maybe read a good magazine on the subject like Stock Car Engineering. You might find out you're really very very extremely wrong.

 

The problem with large diameter wheels, and I've said this many times here before so I'll state it briefly and then let you guys search for more if you want to know and ignore me if you don't, is that they don't "look right" when you just stick the wheels on. You have to make the gap between the fender and the wheel very small to get the look right, and THAT is where the problem lies. Lower the car far enough and the bumpsteer gets scary. I know because I had a car that would do emergency lane change type manuevers without any input on the steering wheel due to bumpsteer on my very lowered Z car. It's true that you CAN modify the suspension to handle well, but I've only ever seen a handful of people do that. The rest just slam it and drive around thinking it looks cool and they've improved the handling. I'm biased against big wheels, because I hate putting more weight on the car, and I hate it most when that weight is rotating weight. It makes the car slower, and makes the brakes less effective, and the suspension work harder.

 

If you don't want to take my word for it on the slammed z thing, take it from johnc who has built one of the fastest Z cars on the west coast and ran it a lot higher than your typical slammed Z and has repeatedly told people that if they want to go faster they should raise the car up. Take it from blueovalz who went to great lengths to fix the rear roll center issues on his car. Or don't.

 

Here's mine which was too low for the mods at the time this picture was taken:

[B00STDZ]

 

The problem with large diameter wheels, and I've said this many times here before so I'll state it briefly and then let you guys search for more if you want to know and ignore me if you don't, is that they don't "look right" when you just stick the wheels on. You have to make the gap between the fender and the wheel very small to get the look right, and THAT is where the problem lies. Lower the car far enough and the bumpsteer gets scary. I know because I had a car that would do emergency lane change type manuevers without any input on the steering wheel due to bumpsteer on my very lowered Z car. It's true that you CAN modify the suspension to handle well, but I've only ever seen a handful of people do that. The rest just slam it and drive around thinking it looks cool and they've improved the handling. I'm biased against big wheels, because I hate putting more weight on the car, and I hate it most when that weight is rotating weight. It makes the car slower, and makes the brakes less effective, and the suspension work harder.

 

There are alot of lightweight racing rims that are 18"...

[Daeron]

There are alot of lightweight racing rims that are 18"...

But the vast majority of the weight is STILL 17-18 inches from the center of the wheel, as opposed to a 13 inch libra, which comes in at around nine pounds, (and those are the aluminums.. the magnesium wheels are REALLY light!!) and most of THAT weight is 12-13 inches from the center of rotation.

 

It is called "polar moment of inertia;" Check it out sometime. Get in a swiveling computer chair, and get in the center of a nice clear room. spin around, and while spinning, extend your knees fully. You slow down. Now draw them in. You speed back up.

 

18 inch wheels rob power, in a sense... IN ADDITION to all that Jon had to say above. Besides, the car was designed in an era of 13 or 14 inch wheels; putting these huge dubs on it with overpriced, 35 series tires just looks goofy... But then I guess you can go put some nice blacked out, bolted on flares on your fender to get the visual wheel/negative space/fender proportions correct.

[Bartman]

Well I guess all the newer cars out there got it wrong. Daeron, you need to share your wisdom about 'polar moment of inertia' with them so they can start upgrading to smaller diameter wheels. The reality is that many of the sport models or sport options on certain models include larger diameter wheels than the non-sport models. If smaller diameter wheels have all the advantages, then why are tire makers stoping production of smaller diameter tires and why do manufacturers keep upgrading to larger diameter wheels?

[johnc]

But the vast majority of the weight is STILL 17-18 inches from the center of the wheel,

 

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.

 

I built a SM2 autocross 240Z for a customer and it was designed from the ground up to run a 18 x 10 wheel with 285/30-18s on all 4 corners. The wheel and tire combo (Kodiak wheels, Kumho V710s) weighed around 45 lbs each. That's actually pretty light given the size. As a comparison, a trophy winning CSP Miata wheel and tire combo (15 x 10 with Hoosier 275/35/15s) weighed in at 39 lbs.

[ModernS30]

I have no idea what you are talking about. Scaling a car is about getting the cross weights as even as possible. Setting the height 1" higher or lower doesn't change the cross weights. Setting the right front 1/4" higher than the left front will.

 

 

 

 

 

I didn't mean just for lowering the car, I meant for suspension setup. Plus I did say I really don't know what I am talking about never done it before. I just know there is a lot more to setting up a car than turning a few nobs and slamming it.

[Sketch_hs]

Geez, those big rims look all wrong for the car. I would never go over 16"

[JMortensen]

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.

Are you positive on that? I haven't dissected a rim to measure, but I think the majority of the rim weight is the outer part from the drop center out, not the spokes and hub. I'm going to assume that the tire is 1/2 or more of the total wheel assembly, and again I haven't cut up a tire to measure the tread vs sidewall weights, but I would guess the majority of that being the tread which is the OD, I think this is more likely to be true on an 18 with a short sidewall. So there is a lot of mass right out at the OD. I would expect if the diameter is 25.5 or 26 the center of mass would be more in the 11" range. On a 23" tall tire with a taller sidewall, maybe 9". That's pure SWAG, so it would be interesting to see actual calculations if you have them.

 

I built a SM2 autocross 240Z for a customer and it was designed from the ground up to run a 18 x 10 wheel with 285/30-18s on all 4 corners. The wheel and tire combo (Kodiak wheels, Kumho V710s) weighed around 45 lbs each. That's actually pretty light given the size. As a comparison, a trophy winning CSP Miata wheel and tire combo (15 x 10 with Hoosier 275/35/15s) weighed in at 39 lbs.

That is pretty light. Still even an equal weight with a higher PMOI is going to be harder to speed up or slow down. I understand that car hauls ass and I'm not trying to say it doesn't, only that it might haul more measurably more ass with the Hoosiers on it.

[johnc]

Are you positive on that?

 

Yup. An 18" OD rim generally has the rim itself 9" out from the center.

[JMortensen]

Yup. An 18" OD rim generally has the rim itself 9" out from the center.

You must be running those helium infused tires then. We were talking about the center of mass of the tire and wheel, right?

Edited March 4, 2010 by JMortensen

[19762802+2]

why do manufacturers keep upgrading to larger diameter wheels?

because of this,

Consumer demand, since all the SUVs are getting bigger rims lots of people decided it "looks cool" so they want that for their cars. Not a lot of people today like the old school smaller rims, for example all the ricers getting larger rims for their Honda's. Most people don't car about performance just looks and to car manufacturers that means money.

[johnc]

You must be running those helium infused tires then. We were talking about the center of mass of the tire and wheel, right?

 

No. I was replying to this statement earlier:

 

But the vast majority of the weight is STILL 17-18 inches from the center of the wheel,

 

The vast majority of the wheel weight is 9" from the center of an 18" OD wheel. You know, the radius of an 18" diameter circle is 9".

[JMortensen]

No. I was replying to this statement earlier:

 

But the vast majority of the weight is STILL 17-18 inches from the center of the wheel,

 

The vast majority of the wheel weight is 9" from the center of an 18" OD wheel. You know, the radius of an 18" diameter circle is 9".

I get you. He made a blantant error substituting diameter for radius, but the tire diameter is still 24.8 for a 285/30/18 as an example, and the Kuhmo that you referenced weighs 25 lbs, so that is more than half of the tire/wheel weight. I'd expect the center of mass to be out at the 11-11.5 inch mark.

[JustinOlson]

With a large diameter tire you need to do lots of suspension changes to get a Z low. PITA really. Here's my 18x12 with a 345/35-18. This tire will not fit properly with a stock inner fender well. Its just too wide even with these YZ fenders. In these picture the tire is pushed all the way in against the inner fender wall and all the way up against the top. I want to lower the car more and have a bit of compression travel from static so its a all new inner fender and suspension.

 

 

Edited March 4, 2010 by JustinOlson

[Bartman]

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.

[JMortensen]

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.

 

From your link:

Advantages of Plus Fitments: 1. Improved levels of traction & cornering grip. The level of improvement will depend on the new tyre size & pattern chosen. Increasing the levels of traction available will decrease braking distances and therefore improve vehicle safety. 2. Improved aesthetics. Fitting wider tyres & rims nearly always improves a vehicle's looks. 3. Improved steering response. The level of improvement will depend on the new tyre size & pattern chosen. The vehicle should be more stable & responsive when attempting lane changes and other similar vehicle manoeuvres. 4. Larger diameter wheels allows the fitment of larger diameter disc brake rotors. This is one reason why the trend for O.E. manufacturers is for larger diameter wheels with low & ultra low-profile tyres. Increasing brake rotor diameter considerably improves braking system power & efficiency.

 

1. There is SOME truth to the idea that a larger diameter wheel has a longer contact patch and will therefore accelerate and stop better. I say some because inflating the tire to a higher pressure reduces the size of the contact patch and the smaller sidewall hinders the ability of the tire to conform to the road, and the lower the profile of the tire, the higher the pressure needs to be and the less flexible the tire is.

 

2. This is the real reason for people running bigger rims on their Z cars. You've said so yourself in the past.

 

3. Assumes plus sizing, where you run a shorter sidewall to get the same OD. If you run a lower profile tire on the smaller tire, then 3 is not necessarily true.

 

4. The Ferrari has 14" rotors, hence the larger rims. If you think that Ferrari doesn't put 20's on the back for style points, I can't help you.

Edited March 4, 2010 by JMortensen

[johnc]

The 18" wheel example I posted above weighed about 45 lbs - 25 lbs tire, 19 lbs wheel, and 1 lb lug nuts, valve stem, and wheel weights. In a wheel like that most of the weight is the center but the mass center could be 9 to 11" out from the center of the wheel, I never did the math and it really wouldn't matter anyway. Having done testing on Toby's DSP 325is we found that the car was quicker to the first corner from a standing start ProSolo launch running 285/30-18s then 245/40-17s. It was also quicker through the course by about 3% with the larger tires. I thought the 245s would be quicker and argued against the 285s to the point that I arranged and paid for the testing setup. I was wrong.

 

We don't have a definitive reason why it was quicker to 50 mph. Toby felt he could launch the car harder and wheelspin was easier to control.

[JMortensen]

The 18" wheel example I posted above weighed about 45 lbs - 25 lbs tire, 19 lbs wheel, and 1 lb lug nuts, valve stem, and wheel weights. In a wheel like that most of the weight is the center but the mass center could be 9 to 11" out from the center of the wheel, I never did the math and it really wouldn't matter anyway. Having done testing on Toby's DSP 325is we found that the car was quicker to the first corner from a standing start ProSolo launch running 285/30-18s then 245/40-17s. It was also quicker through the course by about 3% with the larger tires. I thought the 245s would be quicker and argued against the 285s to the point that I arranged and paid for the testing setup. I was wrong.

 

We don't have a definitive reason why it was quicker to 50 mph. Toby felt he could launch the car harder and wheelspin was easier to control.

Faster on an autox because the extra 160mm tread width. Faster to 50 probably because it was overgeared prior to the wheel swap. I can't think of another reason a heavier wheel with a higher PMOI would make you faster.

[EvilC]

18s look so stupid!

 

Give me a break. If you have enough HP, diameter of the wheel will go out the window. If you are worried about handling and retaining stock body lines then size does matter. I am speaking of a street car here.

 

Really, if I was worried about a second or so on the track....maybe I would spend the time to "down size" my wheels to 16s if it was worth it. Again, I would have to have the knowledge to know what I gain as far as rotating mass, I don't lose in "grip" while conering. I know there are more componets than just wheel size here at play.

 

I just can't believe I see statments saying 18s and 19s are just wrong on a Z and look horrible.

[Slammed68]

17's are where it's at IMO.

 

For the things I do, an 18 would be retarded, and anything under a 17 would look, well, lamesauce. All I do with my junk is daily drive it, and planning on taking it to the track once the new rear end/turbo setup is wrapped up..

 

And big wheels slowing you down? True, but when you have enough power going to those that it doesn't really make a difference anymore, it will be just fine.

 

And your Ferrari/Lamborghini/Veyron, nobody would buy them unless they had fitting wheels - hence the 19's/20's, do you think a 15" wheel would look attractive on a Z06? Nope. I'd rather lose 1mph trap, than look like a homeboy on my 15" daytons with truck tires.

 

 

 

A fitting wheel on a daily driver, is awesome. What some fail to realize is that 90% of people on this website don't hardcore track their car, and although I understand bumpsteer and roll center can get to degrees of just being dangerous, I have seen more than enough people stay away from this site, just because of the harsh attitudes on "car setup".