Wheels: How Big Is Too Big..?

[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...?

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]

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.

[Damn True]

Bigger wheels just means more horsepower.

.....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.