Wheels: How Big Is Too Big..?

[MilesSpeed]

It's obvious that 15-inch wheels aren't ideal for grip, and that larger diameter wheels paired with better technology in the tires can help keep sidewall flex down without loosing compliance.

Where is the line? When does the lack of side wall flex cause loss of traction?

I am looking to get together information to help advise people so they aren't shocked with their $3,000 20s don't handle as well as their 17s.

Does anyone have any input? Any cool diagrams showing sidewall flex? Personal stories about this first-hand?

Any input is appreciated!

[Vegas69]

17's are probably the best if you still want to fit good brakes.

['JustDreamin']

It's obvious that 15-inch wheels aren't ideal for grip

I wouldn't immediately jump to that conclusion, since there are alot of race cars running 15" wheels. Some of that is mandated, some of that is by design. There are probably many vehicles out there that perform best with 13" wheels or smaller (say Formula SAE or something along that lines).

The biggest problem with 15" wheels on a typical musclecar is the lack of space for adequate brakes for the weight of the average vehicle (at least IMO).

It strikes me that every vehicle is a different compromise, depending upon the owner's desire, and that the answer is different for every car. But, I'd say 17 or 18 is the top end of the window. Beyond that, the gains in rotational inertia are just too great. 22's are funny to look at, and much tougher to start and stop. I think a comparison of the physics involved would be interesting (say an Excel spreadsheet) and it would be great to have somebody do some testing to verify that the math works. Has the possibility of being a neat magazine article (IMO).

The ceramic 15.5" front rotors on the '09 ZR1 are really neat and cutting edge, but I wonder what they weigh & cost. And the 19" rims that are required to fit over those rotors (and calipers) certainly put alot of aluminum an awful long way from the center of the spindle. I would be interested as to how a similar, yet smaller sized set of rotors (and wheels) would work on the ZR1.

[fastback]

Wheels:How Big is Too Big..?

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[brownz]

^^ HAHA what a idiot

[Mr.VENGEANCE]

and i wouldnt say the 20s are out of the ballpark so fast yet either..

but yea.. it all depends on your suspension setup...

[TonyL]

There's plenty of threads here already on the subject Liz, but to paraphrase them, it comes down really to brake clearance and rotating mass issues. There's a fine line, right at the 18" mark where the rotating mass of the wheels becomes a bigger detriment to performance than the gain of the lower sidewall, and resistance to flex. Plus, you have to take into account the lack of good R compound tires available for wheels in excess of 18" They just don't exist.

[Vegas69]

Not true....19's are available now.

[TonyL]

I stand corrected. However, I'm sure that extra inch of rotating mass costs more than any performance gained.

[1969CamaroRS]

17s I think is where the sweet spot is. Just big enough to clear big brakes and get modern tires. Anything else is just adding rotating mass. Unless you are going monster brakes that won't fit 17s, no performance reason to go bigger, aesthetics aside.

I do see what some people say about 18"s fitting the wheel wells on our classic cars better, but to me I think a little bit more sidewall looks better than a slightly bigger wheel, imho.

[ProdigyCustoms]

Besides the Moment of Inertia issue with larger wheels / tires. There is the issue with not being able to get enough sidewall on a 20 and get it under many cars. Take a Camaro for example, the most tire you will get under it if you lower the car is a 27" tire. Which is only 3.5" sidewall. Go to a 19 and 27" tire and a 4" sidewall which is much better. Still a greater Moment of Inertia, but better none the less in all ways then the 20.

But with that said the new Vipers and ZR1 Corvette come with 25 series tires on 20" wheels

[MrQuick]

I'd go with 18's max....20's are just silly.

As long as they are light I don't see any other problems.

[Young Gun]

For a while I was planning on running 20s in the back and 19s up front. I started looking through wheels and the difference between 20s and 19s as opposed to 18s all around was close to 600 bucks for the wheels alone and I don't even want to think about the difference in the cost of tires... When it comes down to it, I think I definitely benefit front the larger sidewall as well as the greater selection of tires available. I can still fit large breaks behind 18s and I do not lose any of the aesthetic appeal the wheels offer. The best part? I do not have to hear my stupid friends saying I am riding on "dubs"

[Roadbuster]

The rule of thumb is to have the wheel diameter just large enough to clear the brakes and suspension. I went with 18s vs 17s since I could get a taller tire, and could clear more of my front suspension. The extra inch in diameter did not help me clear the shock mounts in the rear over the 17s but it did let me get a tire that really filled out the rear wheel well.

To sum it up: don't go any larger with the wheels than you have to.

Jon

[WILWAXU]

On a true corner carving muscle car, 18's are probably max, mostly limited by suspension design.

Once you jump above 18's you need a suspension specifically design to use them, i.e. new Vette's, super cars, etc.

[chicane67]

Largest practicle ?? 18"

But it is true... 17's do have a sweet spot with a first gen's wheel base.

[Sparky67]

The ceramic 15.5" front rotors on the '09 ZR1 are really neat and cutting edge, but I wonder what they weigh & cost.

Here is a post on how much the new Carbon Ceramic Brakes cost.
http://www.leftlanenews.com/brembo-announcement-could-lead-to-more-affordable-carbon-ceramic-disc-brakes.html

Jeff

[MilesSpeed]

thanks for all the great input guys, can anyone tell me why NASCAR runs small wheels still?

[MilesSpeed]

https://static1.pt-content.com/images/noimg.gif


That is REALLY too big, and even worse, 3 spoke!

[TonyL]

because they work. It's one of those "if it aint broke dont fix it" things.

Rapid changes in sidewall deflection don't happen when you are constantly turning left.

[Damn True]

The bigger tire volume also gives them the ability to tune the rate of each corner to enhance the jacking that is needed to get a car to corner well on an oval. Not a feature you'd want in a road-race/auto-x application.

[MilesSpeed]

so what happens when nascar goes to sears point?

[buickfunnycar.com]

so what happens when nascar goes to sears point?

They turn left and right...?:lmao:

Sorry Liz,just couldn't resist...

[TitoJones]

so what happens when nascar goes to sears point?

From my understanding the road race NASCAR chassis is different from the oval racing chassis. They also still use Truck arm rear suspension; not because it rocks balls either. They just seem to keep it the way it is.

I would not put any wheel over 18 inch diameter on any car I build. For road racing, if you can put a 17" over your brakes and still clear, they still rock the most. Problem is getting a 14" setup stuffed into a 17" diameter.

Tyler

[Damn True]

so what happens when nascar goes to sears point?

They go slower than they would with a different package.

The corner weights on an oval setup are widely dissparate. This in intentional to manipulate turn-in and the ability to plant power on corner exit. Since the tire is essentially just another spring, it's pressures are used, like springs, to manipulate the corner weights.

Now in a road race application, even in something as slow and light as a Miata tire heat will be different as well, but subtly so. If we start with equal pressures we will have usually a 2-3psi delta at T-Hill (hotter and higher on the right). So we start with the pressures a touch higher on the left-side to equalize things. With greater volume, such as in the 15" NASCAR setup, the impact of even small changes would be greater and tougher to manage.

It's impossible to make a lap time comparison at Sears Pt. because NASCAR is the only group that runs the sissy layout.

But if you look at Watkins Glen where the layout is the same there is a nearly 4sec difference in lap times between the NASCAR record and a Rolex DP car. The NASCAR vehicle has a huuuuuge power advantage (250-300hp difference) yet is way slower.

[WILWAXU]

thanks for all the great input guys, can anyone tell me why NASCAR runs small wheels still?It's completely because of the rules. Many of the teams have petitioning NASCAR to change the size, (mostly do to wanting to use bigger brakes). NASCAR says it would cost too much $$$$ for all the teams to switch over and won't consider it for anytime in the near future.

Like someone else said, NASCAR sees it as a "if the racing isn't broken, then why fix it" situation.

[Roadbuster]

so what happens when nascar goes to sears point?

They have a hell of time braking! The truck arm rear suspension is prone to some serious wheel hop under braking.

Jon

[parsonsj]

We've been over and over this subject here. Previous conclusions:
1. No suspension design can overcome the performance disadvantages of larger wheels. Those late model Vette, Viper, and whatever wheels are costing their owners performance. It's simple: larger wheels look better to most people, so they show up on these cars. But they aren't there to increase performance.
2. It's all about the MOI (moment of inertia) and while weight matters, diameter matters a lot more. The smallest wheels to fit your brakes are the best for performance.
3. I found a Mazda racing spreadsheet once that attempted to turn the MOI differences into something understandable. It calculated the wheel differences into virtual weight. I no longer have that, but I remember it's conclusions: each inch of wheel diameter cost about 50 lbs in virtual weight. That's per wheel. So a car that has 17 inch wheels has something like a 200 lb advantage over an identical car with 18 inch wheels.

jp

[GBodyGMachine]

https://static1.pt-content.com/images/noimg.gif
Had to post a pic of a regal.

[Damn True]

We've been over and over this subject here. Previous conclusions:
1. No suspension design can overcome the performance disadvantages of larger wheels. Those late model Vette, Viper, and whatever wheels are costing their owners performance. It's simple: larger wheels look better to most people, so they show up on these cars. But they aren't there to increase performance.
2. It's all about the MOI (moment of inertia) and while weight matters, diameter matters a lot more. The smallest wheels to fit your brakes are the best for performance.
3. I found a Mazda racing spreadsheet once that attempted to turn the MOI differences into something understandable. It calculated the wheel differences into virtual weight. I no longer have that, but I remember it's conclusions: each inch of wheel diameter cost about 50 lbs in virtual weight. That's per wheel. So a car that has 17 inch wheels has something like a 200 lb advantage over an identical car with 18 inch wheels.

jp

Bingo.

The car that won the 25hrs of Thunderhill this year was a highly modified ex-MX5 cup car. Just for kicks they decided to run tires and wheels from the Porsche Cup car that the shop also owns.

They admit that it was a mistake to do so as it probably cost them 5-7mph at the end of the straights with no measurable difference in corner speeds. The drivers did feel like they had more grip, but the corner speeds don't reflect that and the car was not fast enough to exploit it.

Further data point. Huge tires/wheels on a Viper Comp Coupe right? A Viper absolutely cannot pull away from a 105hp Miata between turn 1 and turn 6 at Thunderhill.

[Vegas69]

Bigger wheels just means more horsepower.:1st:

[Damn True]

Bigger wheels just means more horsepower.:1st:.....that you won't be able to exploit.

[Vegas69]

I like the idea of a spare set for the track anyway. Be nice to have a set of R rated tires mounted up and ready to go for track days. Then you can have your desired looks on the street. That is my plan anyway.

[XLexusTech]

Not to Hijack but on a related note what are the best brakes that will fit in a 17 wheel? I know it dpends on the Rim but as a general question what brake and 17 wheel combos are folks using.
And in relation to Liz's initial ? isnt the tire options better for 17" wheels?
And areent thier more race tires available in 17 as well

[Damn True]

Why don't you break that out into another thread? Once you do I'll delete your post.

[slowcamaro]

I understand the the argument of the lighter, smaller diameter wheels and I agree. The smaller the better given they cover your brakes and good rubber is available.

So whats the market like for scuffs in 17's? 18" Cup car scuffs can be had for $200-250 a set, is there a similar market in 17" rubber?

Price vs Performance vs Track Time. How do these things add up? Is it worth sacrificing a bit of potential performance at the expense of affordable race rubber? Of course I'm talking about open tracking or HPDE events otherwise why consider used tires. Is it potentially a feasible to want 18" wheels for a track wheels?

18x10.5 c5 wheels aren't "that" heavy. How light is considered light by 18" standards?

[Damn True]

17" BFG R1's are pretty dang affordable. Within a couple bucks of Kumho and Hoosier.

Check Tire Rack.com

The R888 is a great tire too and quite a bit more appropriate for street use.

[MilesSpeed]

thanks for all the great input guys! You've helped a lot! Have a happy holidays!

[Hellbound]

Had to post a pic of a regal.


Now those would be great on me golf cart ...hehehehe

not!

[Damn True]

thanks for all the great input guys! You've helped a lot! Have a happy holidays!

We expect a footnote.

[carguy502]

I'd go with 18's max....20's are just silly.
IMO 17s are the best look for most 60s and 70s muscle. As far as building an all around car, I perfer the extra sidewall typical of 17s versus 18s given a fixed tire height. Unless your suspension is built with larger wheels in mind (see Parson's II Much suspension artical in PHR or several Vipers, Ferraris, and the ZR1), going larger will simply add to the unsprung weight, rattle teeth to one extent or another, and limit performance tire selection. 20s are just silly.

[Vegas69]

While I agree with the unsprung weight, my car rides really nice with 18/19 combo. Of course the DSE sub and G Bar make the difference and the shock valving adjustment. Now on stock supspension absolutely. Apples vs Oranges here.

[MilesSpeed]

I've plugged you guys several times :) Ask Larry !

[CarlC]

Been there, done that in Camaro Performers about 6 years ago. 17's work the best on my car. The less sidewall there is, the less signal you will get before traction is lost. It was no fun driving a car that would give little warning before the back end of the car wanted to pass the front.

[MilesSpeed]

The less sidewall there is, the less signal you will get before traction is lost. It was no fun driving a car that would give little warning before the back end of the car wanted to pass the front.


I was JUST writing about that part of it. Get out of my brain!

[StRacerDuke]

19's are perfect for any performace use. There is a reason why Porsche hasn't stepped up to 20" wheels yet. You don't need to carry the extra weight and can fit massive brakes under 19's.
https://static1.pt-content.com/images/pt/2008/12/763621932_0e5ba61a17_o-1.jpg

20's just look cool though...
https://static1.pt-content.com/images/noimg.gif

[StRacerDuke]

PS, if you are writing about wheels don't forget to include the new light weight options...

www.dymag.com
http://www.hrewheels.com/monoblok/

[Procharmo]

19's are perfect for any performance use. There is a reason why Porsche hasn't stepped up to 20" wheels yet. You don't need to carry the extra weight and can fit massive brakes under 19's.
https://static1.pt-content.com/images/pt/2008/12/763621932_0e5ba61a17_o-1.jpg

20's just look cool though...
https://static1.pt-content.com/images/noimg.gif
Porsche 911 997 pictured above came with 18"s and 19"s optional.
Porsche 911 996 came with 17"s and 18" optional. I run 19"s on my 996 and I believe the shape of a cars wheel arches and body proportions have more effect on the aesthetics some of us seek when discussing wheel size.
https://static1.pt-content.com/images/noimg.gif (http://imageshack.us)

[Throttle]

I think for most GM Muscle Cars the brakes I have on my car are good to stop any of them.. I have the 13.5 inch 2008 C6 Z51 Front brakes and SSBC 12 inch rear disc brakes and I run 17's all the way around..

I have never been a fan of anything over 18's until I bought the wheels for my truck that a friend was damn near giving away.. They just look good.. :D

https://static1.pt-content.com/images/pt/2008/12/238825216_25e06bd859-1.jpg

[thedude327]

Liz,
After reading this thread from start to finish, I'm left wondering if you are getting ready to upgrade your camaros wheels, brakes and tires from what you are using now? How about posting back with some results if you do.........

Paul

[Mr.VENGEANCE]

https://static1.pt-content.com/images/pt/2008/12/inspector_gadget-1.jpg

[GregInAtl]

Liz, To be fair comparison, it has to be comparable wheels on the same car in the same conditions. I have been close to this, but not exactly.
I had a car w/ 17", 18",19" and 20" wheels at different times all 8" width. The 17" were OEM, 18" BBS RS-GTs (Forged multi piece) 19" RoJas, and 20" TSW Kylami. With all 4 sets of wheels, the car had Tokico 5 ways, H&R race springs and H&R sway bars.
To no ones surprise, the 18" were the lightest, and yielded the best 1/4 time and best handling. Strangely the 20" were next in handling 3rd in the 1/4. The OEM were the second in the 1/4 and last in handling. The 19s were obv the slowest when accelerating but handled well.
(btw, All wheels ran BFG tires, KDW when available.)
Being on a turbo car w/ a smaller motor it was more obvious when a wheel is heavy , the lag seemed to be exaggerated.
In the end, I came to realize my faves were the 20", they looked cool (not chrome btw) handled well and were way out of the box. The 18"s that conquered all, got lost at the car show and in the parking lot, they looked too "almost hot". At $850 a wheel, that was not ok w/ me.
In the end its all what YOU want. I care more about a functioning form, but more form than function. I'll give up a tenth every fri night for more radical look in traffic everyday.....and watch peoples draw drop like mine did when I bolted them up...but that's just me. If you live and die by a stop watch, consider two sets, because lets be real, tires and drivers win more races than wheels lose you, so you may be majoring in a minor.
Finally, when was the last time you weighed a tire? Many tires the exact same size have VERY different weights. Also, those giant discs people cant live w/o may be over kill, and add the weight your smaller forged wheel saved. In many forums I get flamed loving the Foose big wheel look, and it kills me how the same people only want to debate wheels. (Got dynamat, A/C, leather, electric windows, etc etc?! All that is weight that a stop watch guy can shed....but that rarely gets mentioned.)
Its so much bigger than just the wheel diameter.
I subscribe to PHR, its clearly my home, as is the pro-touring style, but there has been yet not a single article written on this subject that actually addresses the full picture. What I mean by this is where the diam of the wheel is only a minor aspect in the overall performance of any vehicle, yet the first to be named and blamed. As soon as someone steps up, does more homework than they really want to, the general public will be left in the ignorant dark thinking big wheels equal lost performance period.
btw, am I the only one who gets frustrated w/ the dude on drag lites and skinnies who rag larger wheels for perf loss, yet can't get them to try and follow me thru curves?!! Remember Performance has many definitions.

Sorry for the length of the post,
GC

[Damn True]

By reading your post I am led to believe that the car in question is your VW Passat Wagon. I'm wondering if you did any actual timed evaluation of the various setups (auto-x? road course?) or is this information gained via the seat of the pants on an I-85 off-ramp?

[GregInAtl]

By reading your post I am led to believe that the car in question is your VW Passat Wagon. I'm wondering if you did any actual timed evaluation of the various setups (auto-x? road course?) or is this information gained via the seat of the pants on an I-85 off-ramp?
Nope, not racing the wifes wagon, and not on the street either! :P I didn't post car because many people have a preconceived notion that if you drive "x" car you are less a car guy than them, or have less experience or knowledge. That's the only reason, but I'll risk it and admit it was a 2003 Jetta 1.8t w/ all the basic bolt ons and a chip set to run 20 psi on stock snail w/ 93 octane. No race car, but an excellent daily commuter that surprised many including a few at the F body shoot out in "x" class. I know, not RWD, or high tq and HP, but w/ less it actually showed far easier the effect of the set ups.
I had time slips for all 4 sets in the 1/4 from Reynolds in middle GA, and dyno sheets for 2 sets only. Road Atlanta was the track I had the chance to run on, but never full timed laps truthfully....if you were at 06 Year One experience, I could be seen making laps w/ the Year One cars a few times.(they slowly pull in the straight, I'd reel em in REAL fast in the curves and esses.
http://public.fotki.com/AllstarGN/my-previous-cars/21.html