shelby gt500 12.48@110

[broeli]

Fourcam, I'm kind of surprised by your disbelief in tire resistance making a difference in et's. Go run your Cobra with low air pressures in the front, then make another pass with it inflated high..you WILL see a difference. It's done by many, including Evan Smith, when he tries to extract the maximum times out of a car.

 

[Yellow Horse]

Not a shot at you....but LMAO. I see people shoving 50psi into their stock front tires at the track all the time, ****ing hillarious. :lol:



In a car with any real power (say one that can light them up in 4th gear on a non prepped track like most are) that deflated slick is also still going to be transmitting all of it to the ground vs. a street radial.



Again, the only benefits to running skinnies are less overall weight and weight transfer. I guess you could throw smaller frontal area (wind resistance) in there too.



Accepted as fact to you. Most of "facts" that you read on the net are BS, for instance the 4v head tick being a coolant flow problem--it's actually a guide issue. I've also been drag racing for some time. What I've posted is a collaboration of what I've personally experienced along with guys that make hundreds of passes per year. :beer:

Bottom line. If you follow the same launch procedure you always have when switching to a real tire then you will lose mph. You have to reoptimize your setup when making any significant change. Once that happens your traps will increase. I've seen it happen more times than I can count.

I bought a set of 3 1/2 x 24 Weld Pro Stars and MT Front Runners for my 03 and they didn't make hardly any difference. I forgot the weight savings, maybe 50 at the most. The one thing they did do was make the car more stable and take the wobble out of the ass from the ET Streets on the rear.

 

[TERMN8U]

Geez, I should have went to the shootout. How did the black Cobra vert do? He is a buddy of mine.

Hey man. You wouldn't be talking about me would you?

 

[broeli]

In the United States, vehicle manufacturers are required to maintain an average fuel economy for the "fleet" of new vehicles they sell each year. Currently, the government Corporate Average Fuel Economy (CAFE) mandate is 27.5 miles per gallon (mpg) for cars and 20.7 mpg for light trucks (includes minivans, vans, and most pickup trucks and Sport Utility Vehicles). However because it's an "average" fuel economy, in order to sell large cars or trucks (that use more fuel), the vehicle manufacturer must also sell small cars and trucks (that are fuel efficient). The vehicle manufacturer can be fined if their annual vehicle "fleet" uses too much fuel, and can earn "credits" towards future years if their fleet's average fuel economy is better than the government mandated level.

A tire's rolling resistance does affect fuel economy. For that matter, CAFE is so important to most vehicle manufacturers that they demand their suppliers develop low rolling resistance tires to be used as Original Equipment on their new vehicles. In order to meet these demands, these tires are often designed with a priority on reducing weight and rolling resistance and are molded with slightly thinner sidewalls, shallower tread depths and use low rolling resistance constructions and tread compounds.

However, in order to understand CAFE tests and the roll that tires play, it is important to recognize that CAFE tests are conducted in a laboratory and not on the highway. Many aspects that affect fuel economy in the real world are reduced to "constants" incorporated into the formulas specified.

A vehicle's fuel economy is the direct result of its total resistance to movement. This includes overcoming inertia (Newton's Law), driveline friction, road grades, tire rolling resistance and air drag. In order to offer the same level of performance, heavy vehicles require more power (and more fuel) than light vehicles. All-wheel and four-wheel drive vehicles require more power than two-wheel drive vehicles; and boxy vehicles require more power than low drag aerodynamic vehicles.

But how much influence does each of these elements have and when are their influences felt? The relative percent of influence that these factors represent during stop-and-go city driving are very different then during steady, state highway driving.

During stop-and-go city driving, it's estimated that overcoming inertia is responsible for about 35% of the vehicle's resistance. Driveline friction is about 45%; air drag is about 5% and tire rolling resistance is about 15%.

Overcoming inertia no longer plays an appreciable role in the vehicle's resistance during steady speed highway driving. For those conditions it is estimated that driveline friction is about 15%; air drag is about 60% and tire rolling resistance represent about 25%.

Now, lets explore a scenario where a High Performance replacement radial tire has a whopping 20% increase in rolling resistance over a low rolling resistance Original Equipment standard passenger radial. To calculate the potential change in mpg resulting from using the High Performance tires in place of the Original Equipment tires, we would multiply the tire's percentage of influence in the vehicle's overall resistance (15% in the city and 25% on the highway) times the High Performance tires' 20% increase in rolling resistance.

If the vehicle equipped with standard Original Equipment low rolling resistance passenger tires normally provided 25 mpg in the city and 30 mpg on the highway, installing tires with 20% greater rolling resistance would only drop fuel mileage by a calculated 3% (to 24.25 mpg) in the city, and a calculated 5% (to 28.5 mpg) on the highway. While this is a measurable difference, it probably isn't much more of an influence on real world fuel economy than being stuck in rush hour traffic a couple of times a week or being stopped at every red light instead of continuing through a string of green lights.

Additionally, the easiest way to reduce rolling resistance to enhance fuel economy is to make certain that the tires are properly inflated. A vehicle that requires its tires to be inflated to 35 psi (based on the vehicle's tire placard) will have an increase in rolling resistance of approximately 12.5% if the tires are allowed to become underinflated to just 28 psi. Therefore, maintaining the vehicle manufacturer's pressure recommended for light load and heavy load conditions may almost be as important as the tires being used.

 

[Ace5Oh]

i am going to flash the comp back to stock for a few passes...but I can only run 1/8th mile around here...our 1/4 mile track is too dangerous to run on.

Will you be running at Irwindale?

 

[Fourcam330]

I can't believe something that is common knowledge and so simple is being debated here. Go try to push a car with the tires half flat..then go and push it with them aired up. You will find it MUCH easier to push the car with high inflated tires. The same goes for tire width. Not only do skinny tires weigh less they also have less rolling resisitance due to less contact patch. A tire with more contact patch will have a higher roll resistance. The contact patch becomes less when they are overinflated. That's is why many people will overinflate the fronts at the drag strip and turn slightly better times. All simple, well known, tricks of the trade.
A slick or Et Street type tire will expand when the car accelerates creating less resistance than it would if it was pushed at a slow pace..but there is still some increased roll resistance. The air inside will expand causing higher tire pressure during the run but it won't be anymore than about 5psi.

I'm talking about a difference (front tires) of 10psi, 40psi to 50psi. Not 10psi to 50psi. I agree about the 5psi difference bewteen an ET Drag/Street at the start and at the end. That's exactly what I've found 4-5psi.

 

[Purvis]

Not a shot at you....but LMAO. I see people shoving 50psi into their stock front tires at the track all the time, ****ing hillarious. :lol:

Because it works..
Go try riding a tenspeed with the tires half inflated, and see if it gets herder or easier to peddle. Same concept.

Is someone posting in place of the normal Fourcam??:shrug:

 

[Fourcam330]

In the United States, vehicle manufacturers are required to maintain an average fuel economy for the "fleet" of new vehicles they sell each year. Currently, the government Corporate Average Fuel Economy (CAFE) mandate is 27.5 miles per gallon (mpg) for cars and 20.7 mpg for light trucks (includes minivans, vans, and most pickup trucks and Sport Utility Vehicles). However because it's an "average" fuel economy, in order to sell large cars or trucks (that use more fuel), the vehicle manufacturer must also sell small cars and trucks (that are fuel efficient). The vehicle manufacturer can be fined if their annual vehicle "fleet" uses too much fuel, and can earn "credits" towards future years if their fleet's average fuel economy is better than the government mandated level.

A tire's rolling resistance does affect fuel economy. For that matter, CAFE is so important to most vehicle manufacturers that they demand their suppliers develop low rolling resistance tires to be used as Original Equipment on their new vehicles. In order to meet these demands, these tires are often designed with a priority on reducing weight and rolling resistance and are molded with slightly thinner sidewalls, shallower tread depths and use low rolling resistance constructions and tread compounds.

However, in order to understand CAFE tests and the roll that tires play, it is important to recognize that CAFE tests are conducted in a laboratory and not on the highway. Many aspects that affect fuel economy in the real world are reduced to "constants" incorporated into the formulas specified.

A vehicle's fuel economy is the direct result of its total resistance to movement. This includes overcoming inertia (Newton's Law), driveline friction, road grades, tire rolling resistance and air drag. In order to offer the same level of performance, heavy vehicles require more power (and more fuel) than light vehicles. All-wheel and four-wheel drive vehicles require more power than two-wheel drive vehicles; and boxy vehicles require more power than low drag aerodynamic vehicles.

But how much influence does each of these elements have and when are their influences felt? The relative percent of influence that these factors represent during stop-and-go city driving are very different then during steady, state highway driving.

During stop-and-go city driving, it's estimated that overcoming inertia is responsible for about 35% of the vehicle's resistance. Driveline friction is about 45%; air drag is about 5% and tire rolling resistance is about 15%.

Overcoming inertia no longer plays an appreciable role in the vehicle's resistance during steady speed highway driving. For those conditions it is estimated that driveline friction is about 15%; air drag is about 60% and tire rolling resistance represent about 25%.

Now, lets explore a scenario where a High Performance replacement radial tire has a whopping 20% increase in rolling resistance over a low rolling resistance Original Equipment standard passenger radial. To calculate the potential change in mpg resulting from using the High Performance tires in place of the Original Equipment tires, we would multiply the tire's percentage of influence in the vehicle's overall resistance (15% in the city and 25% on the highway) times the High Performance tires' 20% increase in rolling resistance.

If the vehicle equipped with standard Original Equipment low rolling resistance passenger tires normally provided 25 mpg in the city and 30 mpg on the highway, installing tires with 20% greater rolling resistance would only drop fuel mileage by a calculated 3% (to 24.25 mpg) in the city, and a calculated 5% (to 28.5 mpg) on the highway. While this is a measurable difference, it probably isn't much more of an influence on real world fuel economy than being stuck in rush hour traffic a couple of times a week or being stopped at every red light instead of continuing through a string of green lights.

Additionally, the easiest way to reduce rolling resistance to enhance fuel economy is to make certain that the tires are properly inflated. A vehicle that requires its tires to be inflated to 35 psi (based on the vehicle's tire placard) will have an increase in rolling resistance of approximately 12.5% if the tires are allowed to become underinflated to just 28 psi. Therefore, maintaining the vehicle manufacturer's pressure recommended for light load and heavy load conditions may almost be as important as the tires being used.

That's a neat study and all but we're talking about accelerating WOT down a quarter mile track vs. constant steady state driving down the highway.

 

[Fourcam330]

Because it works..
Go try riding a tenspeed with the tires half inflated, and see if it gets herder or easier to peddle. Same concept.

Is someone posting in place of the normal Fourcam??:shrug:

I don't know anyone that drives around with 25psi in their front tires on a regular basis. In fact I always kept 40-42psi in them. Changing to 50psi didn't make a damn bit of difference at all with regard to ET/Traps same track, same day.

 

[bad360rt]

if you are talking about this one, it was determined to be a fake (?). really ran a 13.46. i don't think that famoso would have helped too much, might have even run slower there

http://www.svtperformance.com/forums/showthread.php?t=314693&page=3

Nope, I believe he was referring to this one:

http://www.300cforums.com/forums/sr...1-50-mph-bone-stock.html?highlight=stock+12's

12.5@111, stock, great air at a great track. I think that given the same conditions, a well driven GT-500 could see low 12's, maybe better.

 

[P49Y-CY]

:beer:

 

[ON D BIT]

so what you are saying is that a radial will have statistically significant less rolling mass at 50lbs of pressure than at 40lbs of pressure?

is anyone going to answer this question?

 

[ac427cobra]

Temps in the 40's!! :dw: That is some mighty dense air right there!

 

[broeli]

That's a neat study and all but we're talking about accelerating WOT down a quarter mile track vs. constant steady state driving down the highway.

It still applies. In this study there was a 12.5% increase in rolling resistance with a difference of only 7psi of tire pressure. That resistance will be present under all driving conditions. The Et Street will create even more resistance due to the added width, less air (less than 7 psi difference from stock), more contact patch (related to both width and tire pressure), and overall design. This also shows that the front tires will have a significant drop in rolling resistance by nothing more than adding tire pressure. T12.5% from 7psi. Imagine the difference if someone was rolling around with 35psi..then inflated to nearly 50psi for a 1/4 mile pass. It would probably equate to something more in the range of 20%+ less rolling resistance. You don't think that's make a difference?

 

[Fourcam330]

It still applies. In this study there was a 12.5% increase in rolling resistance with a difference of only 7psi of tire pressure. That resistance will be present under all driving conditions. The Et Street will create even more resistance due to the added width, less air (less than 7 psi difference from stock), more contact patch (related to both width and tire pressure), and overall design. This also shows that the front tires will have a significant drop in rolling resistance by nothing more than adding tire pressure. T12.5% from 7psi. Imagine the difference if someone was rolling around with 35psi..then inflated to nearly 50psi for a 1/4 mile pass. It would probably equate to something more in the range of 20%+ less rolling resistance. You don't think that's make a difference?

Front tires: You're assuming that delta P is static, is it going from 43-50psi vs. a lower pressure like 35 to 42psi? Regardless you're still talking about a minute difference when at WOT not coasting/steady driving. Will it knock a hundredth off your ET, maybe, but who gives a shit?

Rear tires: Again, any car with any decent power is still going to be able to spin a radial street tire in 4th gear at the track. Real life example: Years ago my stock longblock 4.6 N/A Cobra ran 12.7s@107 on Nitto DRs (mid 1.80 shor times) launching at 6k with a slip. Same car on 26x10" ET Drags with a 7k dump runs 12.3s@110+ (1.62-1.64 60'), same shift points and everything else.
It's all in the launch, you just can't let the car bog at all--which it is if you're losing trap when going to a stickier tire. What's gained in a proper/optimized launch with ET Streets/Drags can easily overcome the minute difference over inflating your front tires will net you.

 

[ON D BIT]

Bottom line. If you follow the same launch procedure you always have when switching to a real tire then you will lose mph. You have to reoptimize your setup when making any significant change. Once that happens your traps will increase. I've seen it happen more times than I can count.

:read: :idea: :beer: epper:

im going with fourcam on this one. here is why:

- Ranger -
'06 Z06 red 33 passes; launch not dialed-in
Bone Stock Stock Tires.11.31 127.52 1.90 60' Details
Bone Stock DRs...........11.20 127.55 1.84 60' Details
'02 Z06 sold C5Z06 Launch Techniques
Bone Stock Stock Tires.11.81 117.26 1.78 60' Details
w/Halltech CAI & DRs...11.52 120.21 1.64 60' Details

06 z, the same mph with drag radials as with stock tires? yes

02 z, 3 mph increase with drag radials and intake as with stock tires? yes

from where i sit, the majority of local drag racers do not know how to optimize launch with different sets of tires, hence the loss of trap speed. when a drivers changes technique to compensate for these different conditions speed over the course of the 1/4 is not loss.epper: have a good day.

 

[bad360rt]

Temps in the 40's!! :dw: That is some mighty dense air right there!

Yup :-D Combine that with great track prep and that's why we see a lot of great times from Atco, along with a lot of records (fastest stock C5, 350Z, SRT-8, just to name a few that I know of). That's why I want to see a GT-500 run there this fall, I think it will show the true potential of this car. A lot of people need to keep in mind that the guys that are getting them to the track right now aren't racing in the best of conditions, and have had minimal seat time in the car.

FWIW, I love the GT-500, beautiful car, love the engine and what it's capable of. I finally saw one in person on Sat, red w/white stripes coupe at the local cruise in. Only thing I didn't like were the horrible vinyl stripes (they were actually cut and overlapped on the front bumper around the license plate frame, made me want to cry), other than that it's perfect (aside from personal taste, I think it needs to be a couple inches lower and a new set of wheels, but that's just my taste). :thumbsup:

 

[broeli]

Front tires: You're assuming that delta P is static, is it going from 43-50psi vs. a lower pressure like 35 to 42psi? Regardless you're still talking about a minute difference when at WOT not coasting/steady driving. Will it knock a hundredth off your ET, maybe, but who gives a shit?

Rear tires: Again, any car with any decent power is still going to be able to spin a radial street tire in 4th gear at the track. Real life example: Years ago my stock longblock 4.6 N/A Cobra ran 12.7s@107 on Nitto DRs (mid 1.80 shor times) launching at 6k with a slip. Same car on 26x10" ET Drags with a 7k dump runs 12.3s@110+ (1.62-1.64 60'), same shift points and everything else.
It's all in the launch, you just can't let the car bog at all--which it is if you're losing trap when going to a stickier tire. What's gained in a proper/optimized launch with ET Streets/Drags can easily overcome the minute difference over inflating your front tires will net you.

I agree with what you say here. I guess I was trying to get the point across that rolling resistance does matter for et's when it comes to the front tires. The advantage slicks have over-rides the minute addition of rolling resistance they create. You will knock time off your et's by using skinny fronts or making your contact patch less...that's what I was trying to say. I'm not arguing about losing mph due to slicks. It is definitely in the launch but gearing plays a huge role in how beneficial the slick is as a whole. Your mph will suffer with a bog...and a bog can't always be avaoided by a reline dump if you don't have the gearing.

 

[ON D BIT]

You will knock time off your et's by using skinny fronts or making your contact patch less...that's what I was trying to say.

i think its less than you believe. is it statistically significant is the real question?

throw some skinnies on with proper width and inflation that weigh the same as stock front wheels and tires. run the car 10 times. let it cool down then run the same car 10 times with stock front wheels tires at proper inflation and see what you get.

i will believe you would save much more time by dropping wieght off the front than dropping rolling resistance.:rockon:

 

[Fourcam330]

I agree with what you say here. I guess I was trying to get the point across that rolling resistance does matter for et's when it comes to the front tires. The advantage slicks have over-rides the minute addition of rolling resistance they create. You will knock time off your et's by using skinny fronts or making your contact patch less...that's what I was trying to say. I'm not arguing about losing mph due to slicks. It is definitely in the launch but gearing plays a huge role in how beneficial the slick is as a whole. Your mph will suffer with a bog...and a bog can't always be avaoided by a reline dump if you don't have the gearing.

Correct. Sometimes a raised launch rpm alone won't do the trick, like I said in past posts in this thread, gearing/suspension are also very critical. :beer: