why 18'' wheels more popular on track?
 

don't consider the price and weight.
Is handling better than 19''?

i have also wondered this

Umm price and weight are the only factors that matter.

1. They're lighter (being lighter is suppose to equate to better handling)
2. Tires for 18s are cheaper

:iagree:

Half the grippy tires don't come in 19s

Cheap tires=mega fun

19" is a show tire. 20" is a bigger show tire.

While going 90 mph around a corner, you don't give a f@ck what your car looks like.

18" wheel = lighter than same brand 19" wheel(it makes a big diff)

18" tire cheaper than 19" tire.

can lower car 1/2" more.

Most good tires for the 370z come in 18" wheel size.

Lol pretty much.

And even if a 19" wheel is the same weight as an 18", it's really not. Its heavier because it has 1 more inch of outer weight adding to you're rolling resistance.

If you swing a 5lbs weight in you hand in a 1 foot circle it's pretty easy and fast rpms. Swing the same weight at your max arm extension and it can pop your shoulder out of its socket trying to go to fast.

17" & 18"
 

can run tires with more rubber. Much smoother ride, also many more tires available, like for drag racing. Not a fan of big wheels & thin/little rubber if there's no reason for them. If you do some road type of driving that need very firm/hard tires then.....ok. Not a fan of spacers if the car will do some hard driving. Working with the wheel sellers/manufacturers will help get the size, right off set & look without the risk of having wheel spacers.

Maybe it's just me, but if I can get what I want without those, I'm happy. Only one pick in my home page. 17" wheels wide tires & perfect level side view. Check it out.

Also, if your tire/wheel combo actually reduces the outer diameter and ride height as mentioned above, that effectively gives you a small boost in gearing, like changing your rear end ratio.

The only flip side of a 19 vs 18 is a smaller sidewall which means less flex around a corner, which in turn would aid in track times... BUT that being said an 18 on the 370z would still use a 35-40 series profile which is still low.

For drag racing a higher sidewall in the rear may help off the line.

Overall an 18 inch would typically be lighter using the same rim comparison but a Volk CE28 in a 19 inch weighs around 19-20 pounds vs a Rota knock off weight more in an 18 inch. So this comparison must be 18 vs 19 in the same exact wheel and same tire brand combo and width.

Handling can be tweaked with the slightest adjustments like alignment, tire pressure etc.

The only real way to test if you are that specific to getting the lowest track times is testing. We all know they didn't just slap the GTR together and go "I bet she goes fast"... NOpe they continually tested at the Nurbergring track over and over and made tweaks.

-Chad

There's such a thing as too little compliance.

Smaller sidewall does not automatically mean more grip. There's plenty of folks out there that run 18's rather than 19's in order to get a slightly taller sidewall and more compliance without increasing OD.

A fun video I remember seeing years ago, using a 350z and comparing 18 v 19 inch wheel sizes:

I agree on the lines for racing and track the 18" rim has a better choice and more of a selection for what you can run for tires. You can run a better side wall for autoX and track racing in my opinion specially if your car is lowered. They also can run a few bucks cheaper, rim and tire. Then top that with the weight savings of a 18" rim over a 19" rim which i.e. the Enkei RPF1 in a 19x10 is 21.30lbs and the 18x10 is 18.45


:icon14: synolimit.... :confused: really.... That answer would fail you in Physics pertaining to the physics of a wheel. And this is were you get your participation medals thanks for trying.

He's referencing the change in MOI as the mass distribution shifts outward. The effect is right, the wording just not perfect.

:stirthepot:

What he's describing is I believe centripetal force, and not radius of gyration in the moment of inertia. As I said before that answer would fail you in physics pertaining to the physics of a wheel.

This statement by synolimit is really a waste of time. The the avarage person wouldn't think of moment of inertia, or the radius of gyration of unless they are an engineer, or have and OCD compulsion issue. It's kinda pointless, and I doubt that anyone really gives a sh!t, even about this waste of time of a post, arguing this matter.
People are going to look at style, weight, build quality, and price before they look at the actual physics of the rim and how it fuctions on their car. If that was so important way aren't people running in board brakes and small wheels on there cars.. I truth they aren't, they are running large rims i.e. the Le Mans Corvette Racing Z1 is runs 19x10 and 20x12.

The real point I'm making is that synolimit is posting something again, and I have a raging hard on for this guy, specially when he spews pointless often off basis BS that often time brings, or adds nothing to conversion, in my opinion. Here's an example. The difference of the moment of inertia of a 18" rim to a 19" rim is very small, and really as no bearing on if you should or shouldn't run a 18" or 19" rim, if that's what he was refering to. It would have more to do with the size of the tire you ran on the rim, the compound of the said tire, and it's total circumference as a whole. But that's wasn't the question, the question was why are 18" wheels more popular on the track, so lets talk about more sh!t that doesn't really matter.

In my defence I don't know sh!t from a shoe, but I do like to pick on synolimit, cause he makes it so easy. Thanks synolimit. :tiphat:

This is the tech section, not off-topic.

The physics behind the performance of tires is a valid component of why smaller wheels are used more frequently on the track. MOI is about 25-40% less on an 18 as compared to a 19 on the wheels I've examined in the past. You can check that pretty readily as a 10kg disk with a 9" diameter has an MOI about 11% lower than a disk with the same weight and a 9.5" diameter. It is a consideration for those that are using this subsection for it's intended purpose.

If you want to pick on the dude, that's between you, him, and the forum admins. But please keep it out of the tech section.

I failed physics but I know bigger is better because that's what she said :wtf2:

Exactly. I was thinking of buying some 22s for my track setup

He's not all there, just let it go. You're correct in everything though, not him.

Ps its easy for me too. The tard just made a post about average people not caring yet we're in the racing thread TALKING ABOUT RACING!! Dert dert durr!

Word, but I never said a 19 would yield better grip.. I just said could help with track times as it may help have less flex in the sidewall and possible help with cornering (less understeer type of deal)

If we are talking grip then- tire brand, tread pattern for specific event, tire pressure, alignment, suspension, sway bars etc etc.

I don't see why 370 should have traction problems-Curious had to try
 

I took my used 2012 base auto(1,200 miles) to Atco Friday night. Owned it for only 3 days but just had to find about traction/car.

My first completed run in a dry lane, 60' was 2.010 seconds & 13.137@106.12 1/4. At 1,500 rpm I let the brake go & at moderate rate stepped on the gas peddle. After that run, it looked like amateurs went into & over the watered ground & got everything right up to the stating line wet.

Even at idle or a bit more than that, my wheels chirped a bit & 60' & 1/4 times suffered. 60' 2.20's & 2.10's. I got the exact numbers in my post that I made Friday.

So if 2.00 60' can be done with stock base wheels/tires & leaving at only 1,200 to 1,500 rpm, why would I next spring have a problem doing 1.8's and better using drag radials??? It's an automatic :confused: All you need is a clean prepped dry starting lane. :confused:

:shakes head: :shakes head: :shakes head: :shakes head: :shakes head:
Let me try to explain this, for those who are still following. :icon14:

A rim, and tire is technically an annular cylinder. You could calculate the moment of inertia by calculating the annular cylinder about the symmetry axis. 1/2M(R 1over2+R 2over2) I believe is the formula, kinda hard to put it in a post like this, but hope you get the idea. You have to keep in mind, you still wouldn't be correct even then, do to the altering forces of the vehicle it's self suspesion, weight, eta. then you have different road surfaces, geometry of the road surface, that act upon the annular cylinder (AKA wheel and tire) or in other words there are real world conditions that have effects in this equation.

Red_Zed figuring out the moment of inertia of a 18" and 19" rim is great if you're in a class room, and you're solving this in a controlled environment. So in theory yes, you are correct, in caluation I would need to do the math to make sure myself to say other wise. The reason you aren't correct though is clearly you're not including the full circumference, width of the tire on either given rim, their total mass, or any of the other factors for that matter in this that play huge factors. People don't drive in class rooms, or completelly controlled environments with prefect surfaces either, not to mention there is something attached to that wheel, call a vehicle.

Red_Zed look more at the big picture, and not just one part, that's why this Bull$sh!t really has no relevance to "why 18'' wheels more popular on track?" like I said before. This is a case of people being stupid, and aguring over something that is completely superfluous to the topic.

The intertial differences are a large part of the motivation to use smaller tires, whether the average weekend warrior understands that or not is irrelevant to the physics. Regardless of whether someone can articulate that reasoning is irrelevant--it is a driving force for the use of smaller wheels on track.;)

BTW, your math would not give the "exact" moment of intertia for a real rim, as you claim. You need to take into account the mass profile. The math isn't terribly tricky but getting the right numbers is challenging. It's a lot easier to measure.

:iagree:

gentlemen, there's only one way to settle all of this argument.
:stirthepot:
:yum:
:icon17:
:bowrofl:

Now your putting words in my mouth, and I did say you have to take mass in account. It seems like your having an issue understanding this is not a disk, or a hoop. It's not just about the rim size but it's the tire size diameter and width, that will in the end dictate the moment of inertia. If your going to do it, do it right is all I'm saying.

That's a great and all, but why is it that race teams have been putting larger diameter rims on races cars, and every decade they seem to get just little bigger?

maybe you misunderstood. I measured with a photogate. Hence the "it's a lot easier to measure"

I'm pretty sure I'm not the one struggling to understand the physics involved;)


brakes.

Enough with the nerd talk, I think you guys need to race.

I was hoping for mud-wrestling.

If there's a race to be done I pick my home turf in eastern UT:
http://iliketowastemytime.com/sites/...ns_back_07.jpg

But, back on-topic as this is tech and not OT.

Loin's Back. Last time I was there. It was closed. :mad: Wanted to do it in my Power Wagon. :D

Getting back on topic - this really is the mitigating tradeoff. Smaller wheel diameter is generally going to be better for a number of reasons we've already beat to death, but at the end of the day you have to fit brakes. You need brakes big enough to do the job, and then the smallest wheels you can fit over those brakes. If there's a big gap between your front rotors and the inside of the front wheels, you're not being optimal :)

:tup:

http://i39.photobucket.com/albums/e1...ps4f551506.jpg

Tony just liked this pic, reminded me to comment. Took the wheel off the other day. A rock got caught in between the caliper and inside wheel. Cut the **** out of it all the way around the whole thing. Wheels dipped so that's an easy fix but the caliper I'm :(. At least you can't see it. I'm just worried about salt in winter time eating the powder coat off entering through the cut.

That's the issue I foresaw with my RPF1's (Thanks Mike) and my AP BBK. They were not touching but a piece of pine straw would catch when I was free spinning the wheels. That's how close mine was. So I'm running a 5mm spacer. It was that or grind down the caliper a little. It puts the wheels out there but I'm ok with it. Hopefully one day I'll run wider fenders.

You go with 18x9.5 +15? Now you have +10?

Yes. I like it. With -3.2 camber also. Not cause of rubbing issues. It clears by miles.

Good. I'll check pics. I want to switch to that wheel instead.

When I ran the brembo 6 pistons, I would get rocks caught between the barrel and the top of the caliper. I had about 1mm clearance after grinding a couple mm off of the ends of the calipers. I actually got black flagged a couple times because the noise could be so loud.