The slower show! (2 Viewers)

[ironpony]

well that begs the question, what would they be running without the rule changes over the years. Of course that would also lead to how many more accidents due to out performing equipment, tracks and such

I am sure someone could figure out the perfect pass mathematically within a few percent. rpm, gear ratio, tire growth, zero tire slippage. If I get some time I might give it a shot.

What numbers can we agree to use?
rpm limit
gear ratio
tire growth, diameter

 

[Jeff]

I am sure someone could figure out the perfect pass mathematically within a few percent. rpm, gear ratio, tire growth, zero tire slippage. If I get some time I might give it a shot.

What numbers can we agree to use?
rpm limit
gear ratio
tire growth, diameter

Yup, except its not diameter but really radius from the axle center to the ground. Those of us with laser sensors under the axle center know that every 1/100th second of the run. I run a very low growth slick on my wife's top dragster and the car picks up almost 2" on a smooth track (rough track gets more rear wing and it is noticeable to tire growth ... in fact rough tracks are why I spent the $1k on that Racepak channel).

If they were to make a new tire, I think they will leave the tread width of the tire the same (to allow them to accelerate hard down low) but limit the section width (the gut) of the tire to keep them from standing up under centripetal force. The radial guys have both a tire that doesn't grow and a tire with very limited give in the sidewall. Seeing them go fast is truly watching a magic act.

Oh yeah, and in a fuel car I'm pretty certain there is no point in the 1000 ft run where there is zero tire slippage (I've got another Racepak channel that helps me understand that .... to avoid shake (e.g. too little slippage)).

 

[I was NITRO BREATH]

new track prep is giving us good competitive races in the short run. tuners will overcome it as they always do and high buck teams will go faster and dominate the semi's and finals. Is having wilk and terry mc and blake advancing up the ladder caused by track prep or are teams getting a handle on their tune ups ??? who cares. i just like seeing them winning rounds

 

[none]

Yup, except its not diameter but really radius from the axle center to the ground. Those of us with laser sensors under the axle center know that every 1/100th second of the run. I run a very low growth slick on my wife's top dragster and the car picks up almost 2" on a smooth track (rough track gets more rear wing and it is noticeable to tire growth ... in fact rough tracks are why I spent the $1k on that Racepak channel).

If they were to make a new tire, I think they will leave the tread width of the tire the same (to allow them to accelerate hard down low) but limit the section width (the gut) of the tire to keep them from standing up under centripetal force. The radial guys have both a tire that doesn't grow and a tire with very limited give in the sidewall. Seeing them go fast is truly watching a magic act.

Oh yeah, and in a fuel car I'm pretty certain there is no point in the 1000 ft run where there is zero tire slippage (I've got another Racepak channel that helps me understand that .... to avoid shake (e.g. too little slippage)).

Jeff is exactly right, diameter isn't a accurate way to measure because at speed the top of the tire is much farther from the axle than the bottom, just look at a picture of a car in the lights, the bottom and back of the tire are flat, the top and front are round, but you could figure it out with the ride height measurement. He is also correct about the slippage, they are spinning all the way to the stripe, here's the wheel speed graph from Leah's 3.640 in Brainerd last year (at the time the quickest run in history) the red line is rear wheel speed, the yellow is front wheel speed. You can even see that it was trying to pick up the front wheels going to lock up just after 2 seconds into the run.

Alan

 

[TooTall999]

new track prep is giving us good competitive races in the short run. tuners will overcome it as they always do and high buck teams will go faster and dominate the semi's and finals. Is having wilk and terry mc and blake advancing up the ladder caused by track prep or are teams getting a handle on their tune ups ??? who cares. i just like seeing them winning rounds

Tuners can only overcome so much, it's the track that's the limiting factor. You can only give it a certain amount of power before reaching the limit.

 

[ironpony]

Jeff is exactly right, diameter isn't a accurate way to measure because at speed the top of the tire is much farther from the axle than the bottom, just look at a picture of a car in the lights, the bottom and back of the tire are flat, the top and front are round, but you could figure it out with the ride height measurement. He is also correct about the slippage, they are spinning all the way to the stripe, here's the wheel speed graph from Leah's 3.640 in Brainerd last year (at the time the quickest run in history) the red line is rear wheel speed, the yellow is front wheel speed. You can even see that it was trying to pick up the front wheels going to lock up just after 2 seconds into the run.

Alan

View attachment 4670

I understand all this, the original assumption was the perfect fastest run possible, highest rpm x axle ratio x tire circumference x no loss of traction.

is it possible no, but it would be the fastest they could possibly go under the existing rules.

How far off is it from the fastest run now ??

it is going to take some math to figure out, then it can be compared to the existing fastest run.

 

[ironpony]

OK so this is what I came up with

7900 rpm
1:1 trans ratio
3.42 reared ratio
tire radius, loaded, 28 inches

384.4 MPH

what numbers do you want to try ?? how far off am I ?

 

[Jeff]

Fuel tire static diameter is 36" ... So starting radius is 18" ... you are presuming a downtrack increase of 10"?

Based on my experience (a world apart from this extreme of the nitro sport) I would have guessed half the radius growth.

tire rotations per minute 7900 / 3.42

effective tire rollout max in inches 2 x 3.1416 x 23 (e.g. 2 x pi x radius)

convert to feet / 12

convert to miles / 5280

convert to hours x 60 = 316

so clearly my 1/2 guess of 5" was wrong! Haha!


But now you see the basis for my argument that if you want to limit MPH, the thing you have to limit after RPM and rear gear is the tire's ability to achieve a higher MPH than you want the car to go.

 

[Dragracer]

I have been racing since the late 50's and the great mathematical minds have been trying, without much luck, to predict what the fastest/quickest a drag car can run. There are way too many variables for anything accurate to be predicted, and let's not forget tract prep, weather, altitude, and a whole lot of other variables. If all the computers the team's use could truly predict a run then your run would be the absolute quickest and fastest the car could run. Oops, let's not forget what the engine is going to do and nobody knows that.
I think the new track prep rule is the best and least expensive method to slow the cars down and still have great runs. The big $$ team's are always going to have some advantage but this is going to reduce that advantage some.

 

[Stan]

Let remember that what is being calculated is an instantaneous speed whereas the speed on the time slip is an average through the time trap.

7900 rpm
1:1 trans ratio
3.42 reared ratio

Radius MPH
23-------316
23.5-------323
24-------330
24.5-------336.7
25-------343.6
25.5-------350.7
26--------357.3

Stan

 

[none]

OK so this is what I came up with

7900 rpm
1:1 trans ratio
3.42 reared ratio
tire radius, loaded, 28 inches

384.4 MPH

what numbers do you want to try ?? how far off am I ?

Ken,

The rear end ratio is 3.20
In optimum conditions I have seen 299 mph at the eighth, picking up 85 mph down the back seems like a stretch. The faster you go the harder it is to go faster so picking up 40 from 660 to 1000 is considerably easier than getting 40 more from 1000 to 1320.

I think most people don't realize what it takes to make gains once you get this far, an injected nitro car can run 280 with 3500 ish HP the extra 50 mph that you get in Top Fuel takes close to 3X that much power. Where 100 HP in a Pro Stock car would increase speed 2.5 MPH you would need at least 500 HP to get a couple more in Top Fuel.

Fun Discussion,
Alan

 

[Dennis]

Ken,

I think most people don't realize what it takes to make gains once you get this far, an injected nitro car can run 280 with 3500 ish HP the extra 50 mph that you get in Top Fuel takes close to 3X that much power. Where 100 HP in a Pro Stock car would increase speed 2.5 MPH you would need at least 500 HP to get a couple more in Top Fuel.

This is a great point. And to throw yet another set of numbers into the discussion to state it another way - AFD can run 80% of the speed with only 30% of the horsepower.

 

[Stan]

7900 rpm
1:1 trans ratio
3.2 reared ratio

____tire_radius____MPH
____21.00000_____308.59
____21.25000_____312.27
____21.50000_____315.94
____21.75000_____319.61
____22.00000_____323.29
____22.25000_____326.96
____22.50000_____330.64
____22.75000_____334.31
____23.00000_____337.98
____23.25000_____341.66
____23.50000_____345.33
____23.75000_____349
____24.00000_____352.68
____24.25000_____356.35
____24.50000_____360.03
____24.75000_____363.7
____25.00000_____367.37

Stan

 

[none]

Great chart Stan, and I'm sure that there's a math equation for this, but I'm certainly not smart enough to figure it out.
As the tire grows you obviously go faster, but as you go faster the wing exerts more force to squash the tire so that would add to the diminishing return. There would have to be a point where the tire squash would mean you were making more wheel speed but losing mph.

Alan

 

[Stan]

Alan,
That is more complex that I can handle.

Do not know if this will help or just confuse.

It show different mph with the range of tire radius and what the rpm is.

Stan

Varying_mph__From_305__To_355__By_5

***_7-15-2018_--_11:14:51_***

Varying_tire_radius__From_21__To_25__By_0.25
___tire_radius____rpm
_mph_--->_305
____21.00000_____7808
____21.25000_____7716.1
____21.50000_____7626.4
____21.75000_____7538.8
____22.00000_____7453.1
____22.25000_____7369.3
____22.50000_____7287.5
____22.75000_____7207.4
____23.00000_____7129
____23.25000_____7052.4
____23.50000_____6977.4
____23.75000_____6903.9
____24.00000_____6832
____24.25000_____6761.6
____24.50000_____6692.6
____24.75000_____6625
____25.00000_____6558.7
_mph_--->_310
____21.00000_____7936
____21.25000_____7842.6
____21.50000_____7751.4
____21.75000_____7662.3
____22.00000_____7575.3
____22.25000_____7490.2
____22.50000_____7406.9
____22.75000_____7325.5
____23.00000_____7245.9
____23.25000_____7168
____23.50000_____7091.7
____23.75000_____7017.1
____24.00000_____6944
____24.25000_____6872.4
____24.50000_____6802.3
____24.75000_____6733.6
____25.00000_____6666.2
_mph_--->_315
____21.00000_____8064
____21.25000_____7969.1
____21.50000_____7876.5
____21.75000_____7785.9
____22.00000_____7697.5
____22.25000_____7611
____22.50000_____7526.4
____22.75000_____7443.7
____23.00000_____7362.8
____23.25000_____7283.6
____23.50000_____7206.1
____23.75000_____7130.3
____24.00000_____7056
____24.25000_____6983.3
____24.50000_____6912
____24.75000_____6842.2
____25.00000_____6773.8
_mph_--->_320
____21.00000_____8192
____21.25000_____8095.6
____21.50000_____8001.5
____21.75000_____7909.5
____22.00000_____7819.6
____22.25000_____7731.8
____22.50000_____7645.9
____22.75000_____7561.8
____23.00000_____7479.7
____23.25000_____7399.2
____23.50000_____7320.5
____23.75000_____7243.5
____24.00000_____7168
____24.25000_____7094.1
____24.50000_____7021.7
____24.75000_____6950.8
____25.00000_____6881.3
_mph_--->_325
____21.00000_____8320
____21.25000_____8222.1
____21.50000_____8126.5
____21.75000_____8033.1
____22.00000_____7941.8
____22.25000_____7852.6
____22.50000_____7765.3
____22.75000_____7680
____23.00000_____7596.5
____23.25000_____7514.8
____23.50000_____7434.9
____23.75000_____7356.6
____24.00000_____7280
____24.25000_____7204.9
____24.50000_____7131.4
____24.75000_____7059.4
____25.00000_____6988.8
_mph_--->_330
____21.00000_____8448
____21.25000_____8348.6
____21.50000_____8251.5
____21.75000_____8156.7
____22.00000_____8064
____22.25000_____7973.4
____22.50000_____7884.8
____22.75000_____7798.2
____23.00000_____7713.4
____23.25000_____7630.5
____23.50000_____7549.3
____23.75000_____7469.8
____24.00000_____7392
____24.25000_____7315.8
____24.50000_____7241.1
____24.75000_____7168
____25.00000_____7096.3
_mph_--->_335
____21.00000_____8576
____21.25000_____8475.1
____21.50000_____8376.6
____21.75000_____8280.3
____22.00000_____8186.2
____22.25000_____8094.2
____22.50000_____8004.3
____22.75000_____7916.3
____23.00000_____7830.3
____23.25000_____7746.1
____23.50000_____7663.7
____23.75000_____7583
____24.00000_____7504
____24.25000_____7426.6
____24.50000_____7350.9
____24.75000_____7276.6
____25.00000_____7203.8
_mph_--->_340
____21.00000_____8704
____21.25000_____8601.6
____21.50000_____8501.6
____21.75000_____8403.9
____22.00000_____8308.4
____22.25000_____8215
____22.50000_____8123.7
____22.75000_____8034.5
____23.00000_____7947.1
____23.25000_____7861.7
____23.50000_____7778
____23.75000_____7696.2
____24.00000_____7616
____24.25000_____7537.5
____24.50000_____7460.6
____24.75000_____7385.2
____25.00000_____7311.4
_mph_--->_345
____21.00000_____8832
____21.25000_____8728.1
____21.50000_____8626.6
____21.75000_____8527.4
____22.00000_____8430.5
____22.25000_____8335.8
____22.50000_____8243.2
____22.75000_____8152.6
____23.00000_____8064
____23.25000_____7977.3
____23.50000_____7892.4
____23.75000_____7809.3
____24.00000_____7728
____24.25000_____7648.3
____24.50000_____7570.3
____24.75000_____7493.8
____25.00000_____7418.9
_mph_--->_350
____21.00000_____8960
____21.25000_____8854.6
____21.50000_____8751.6
____21.75000_____8651
____22.00000_____8552.7
____22.25000_____8456.6
____22.50000_____8362.7
____22.75000_____8270.8
____23.00000_____8180.9
____23.25000_____8092.9
____23.50000_____8006.8
____23.75000_____7922.5
____24.00000_____7840
____24.25000_____7759.2
____24.50000_____7680
____24.75000_____7602.4
____25.00000_____7526.4
_mph_--->_355
____21.00000_____9088
____21.25000_____8981.1
____21.50000_____8876.7
____21.75000_____8774.6
____22.00000_____8674.9
____22.25000_____8577.4
____22.50000_____8482.1
____22.75000_____8388.9
____23.00000_____8297.7
____23.25000_____8208.5
____23.50000_____8121.2
____23.75000_____8035.7
____24.00000_____7952
____24.25000_____7870
____24.50000_____7789.7
____24.75000_____7711
____25.00000_____7633.9

 

[ironpony]

Ken,

The rear end ratio is 3.20
In optimum conditions I have seen 299 mph at the eighth, picking up 85 mph down the back seems like a stretch. The faster you go the harder it is to go faster so picking up 40 from 660 to 1000 is considerably easier than getting 40 more from 1000 to 1320.

I think most people don't realize what it takes to make gains once you get this far, an injected nitro car can run 280 with 3500 ish HP the extra 50 mph that you get in Top Fuel takes close to 3X that much power. Where 100 HP in a Pro Stock car would increase speed 2.5 MPH you would need at least 500 HP to get a couple more in Top Fuel.

Fun Discussion,
Alan

again, I do understand all of this, my background is in aircraft. This started as a "perfect" world discussion. What if everything was perfect. A TF car at 12,000 hp has the HP to overcome the drag created, they lack the traction at this point in time.
As far as the calculation it is

(0.00595) * (RPM * r) / (R1 * R2) = vehicle speed in miles/hour
where:
RPM = engine speed, in revolutions/minute
r = loaded tire radius (wheel center to pavement), in inches
R1 = transmission gear ratio
R2 = rear axle ratio

 

[ironpony]

So, does anyone know the tire radius on a TF car at the top end ?????

 

[Cliff]

Just wanna throw this out. The ET's cars run are accurate, but speed is not. Some years ago, NHRA changed the finish line clocks for MPH. Clocks used to be located (I think) 120 ft before the finish line & 120 ft after, so the MPH reading you got was exactly as the car crossed the finish line. The speed clocks are now located before the finish line and at the finish line, so the speed that is registered is not what the car is running at the finish line (or the 660', etc). When Alan said he has seen T/F run 299 at the 1/8, the speed was probably 301. That also means Robert Height did run over 340, maybe 341 on the 339 run. I really wish the clocks would go back to true speed, but I think we're stuck with them as they are. I think the reason NHRA gave was that racers would run the car "out the back door" for MPH, so they were taking longer to shut off and less room to stop.

 

[ironpony]

Just wanna throw this out. The ET's cars run are accurate, but speed is not. Some years ago, NHRA changed the finish line clocks for MPH. Clocks used to be located (I think) 120 ft before the finish line & 120 ft after, so the MPH reading you got was exactly as the car crossed the finish line. The speed clocks are now located before the finish line and at the finish line, so the speed that is registered is not what the car is running at the finish line (or the 660', etc). When Alan said he has seen T/F run 299 at the 1/8, the speed was probably 301. That also means Robert Height did run over 340, maybe 341 on the 339 run. I really wish the clocks would go back to true speed, but I think we're stuck with them as they are. I think the reason NHRA gave was that racers would run the car "out the back door" for MPH, so they were taking longer to shut off and less room to stop.

IIRC it was 60' before and 60' after, because I used to run my car out the back to see what I could get out of it.

 

[ironpony]

So, just for fun I figured how many HP it would take to run 400 MPH.

Used the following stats

coefficient of drag .5 which is fairly high, a muscle car
frontal area of 30 SQFT fairly large
weight 2850 race car weight

HP required
6553 HP to overcome air drag plus 40 to overcome rolling resistance for a total of

6593 HP to run 400 MPH