???

Yes it is a good indicator of your speed even if you coast or slow down. The way the speed is calculated doesnt change.

Trap length / Time to get from beginning of trap to the finish line

I'm guessing what you are trying to say is that if you coast or slow down its not a good measurement of your max mph. But you cant say the mph is way off because its not. It cant be. Traps are measured at the end of the track, that is your trap speed.

 

have you spent much time at the dragstrip watching cars run and watching cars let off?

a friend of mine runs 10.80's at 126. last year at the fbody vs. ford shootout in darlington sc he ran the time above. on the next run he let out just before the end and went 10.90 at 118.

how do you explain that? common sense tells you he was going fast than 118 because there is no way he can lose 8 mph in 50 to 100 ft.

 

Try doing some math.

Going 1 hundredth of a second slower in the traps will cut 2-3 mph off your speed and it EXPONENTIALLY grows as you get faster.

.30 seconds in the traps is 150 mph

.35 seconds in the traps will net a 128.6 mph

.37 seconds will give a 121.6 mph

who would have guessed that .07 seconds makes a 30 mph difference

If you are wondering how this is figured out....

66 ft = 20.1688 m

20.1688 m / time through traps = Trap speed in m/s

Convert to mph and voila.

Your buddy probably goes through the traps in ~ 0.357 seconds to trap 126 if that slows to ~0.380 then hes down to 118 mph.


Math doesn't lie sorry. It's common sense.

 

Wouldn't it make since that your MPH go up the more you spin?


Since if your spinning and and your already at high RPMS and your car shifts and the tires catch the tires are already traveling at that speed you would be going that much faster.

Like if you spin and you go 60 ft and tires catch and at that time its already in 2nd gear at ----- RPMS that means that tires already traveling fast enough to be going lets say 40 MPH

But if you catch and you dont spin the tires and you reach the 60ft at a lower gear and or RPMS then your tires arnt traveling as fast you didn't spin but you get better traction so there for you get lower E.T.s

So by spinning you make more time/space for your tires to accelarate to a higher speed and when they catch it trys to ppush the car up to that speed even faster.

I beleive that is the point in launching a car at 3k or so so when you dump the clutch the tires will be turning at whatever speed 3k is in 1st gear thus making the car go faster in a shorter distance and lower e.t's but if you dont hook and you spin you go a shorter distance but your tires are more faster in that shorter distance then they would if you hooked.

Does anyone get what im saying or am i completely wrong?

 

No, if you are spinning, you are wasting energy, and time that could be used accelerating. Just cause the speedo is going 150mph doesnt mean the car is moving 150mph. It doesn't work like how you say

Dumping the clutch is so you have the car immediately in the powerband, not what you said.

So yes, you are wrong

 

yea in the power band so you accelarate faster right..?

and i know that because the speedo is going 105 doesnt mean the car is but if the tires catch at 105 and you spun all the way thru a gear or so and the gear is higher the tires are going to be moving faster which means it will want to make the car more that speed also.

so if you hook and it takes 100 feet to reach XX MPH then if you spin 50Ft and the car is in 2nd gear and the tires are set to move that much faster due to the wheel rotation/per engine rotation of the gear it is going to try move the car to that speed as fast as it can faster then it would normally side the tires are already.

What i meant by the reving to 3k and dumping the clutch is so that the car is in its power band and as soon as the clutch catchs its going to TRY to spin the tires at that speed and IF they hook its going to be going 30 mph in a shorter distance then it would if you didn't launch the car. So in the end the car is going to catch up to the wheels sooner or later.

lol i think i got it figured out in my head its just to hard to put down into words but its kinda complicated. Even tho i could be still wrong. but o well this is my last try at it

 

what i said earlier, i didnt explain right...but i cant remember the correct reasoning behind it...but anyway, when u drop the clutch at 3k, the rpms most likely wont stay at 3k, unless you are spinning...the rpms will fall as the tires hook

 

It alls comes down to gearing and engine output....the more power a engine makes if it hooks it most likley will mph better..If it spins its not accellarating (shortens the track) mph will be lower..Now lets go to other extreme.. a lets say slighlty modified stock engine...car sticks bogs because power isnt so great et and mph suffer...saem car with wheel spin car doesnt bog (unless just totally blows the tires off) but gets over the hump if you will the bog it would have had ..If it would have hooked a lower power car with slight wheel spin most likley will mph better than if it would have stuck...now gearing lets compare. we'll use 3.23's vs. 4.11's car with 3.23's hooks mph's lower, spins mph's higher (helps car get moving from lack of torque)..;same car 4.11's hooks gearing helps over come loss of torque engine doesnt make ,car mph's more..car spins now car has wasting rpm and movement forward..so now winding harder on other end to point car cant accelerate any further than engine will let it..lays over if you will, mph falls..

lots of reasons why mph isnt tell all,we're not even factoring driver ,shift points etc.. Its alot of things

proper gearing to compliment the engines output is what affects mph,...MPH will be different anyone of those things are not optimized..

wheelspin will help somewhat a low torque engine vs. hurt a good torque engine

higher gear will help a low torque engine vs. hurt a good torque engine

no wheelspin will hurt a low torque engine vs help a good torque engine

lower gear (if properly chosen ) will help a good torque engine)
vs. hurt a low torque engine..

It gets confusing but alot of variables determine if traction or lack there of would increase or decrease mph.. there is no such thing as x-hp=x-mph unless your taking everything mention down to the driver and shift points was taken for granted were ideal...

 

why i said it would TRY to

 

As mentioned already, it can go both ways. This past weekend I had a friend at the track with a turbo prelude. on street tires he went a best of 14.1@111mph. Bolted on the slicks and went 12.5@115mph.

 

im pretty sure that is for measuring a constant speed, not accelerating or decelerating.

 

Serene i think your confused with the argument here, were talking about trap speed, not ET. What your saying is true, it is stime wasted not acellerating, but if your only goal is Trap its kinda time well spent (if its minimal).

Let me do a massive simplification here which might help alot of the pple who dont quite see why spinning could help ET and Trap Speed. (theres a sweet spot though of course).

Suppose car A is spinning a tad.
Suppose car B isn't spinning.
Lets say the Race is 10meters. (sorry folks im canadian eh)
Sweet Spot = The point where more power would cause slipping, less would mean your not making optinal accelleration.
Sweet spot is measured in Ft/lbs of torque.
Car A and B have the same sweet spot.

X = Ft/Lbs of torque of the Engine.
Y = Rotating mass of Drive train components

Car A Spins .1 seconds before catching traction. When it does, it catches its sweet spot. Car A's "Sweet Spot" = X(Engine Power) + Y(Drivetrain momentum).

Car B Hooks right up, at it's at its"Sweet Spot" too. Car B's
"Sweet Spot" = X + Y as well.

Only thing is that Y (Drivetrain Momentum) would be slightly lower in car B because the parts aren't already flying in motion like in A. Also X (the engine) would need to be slightly higher at this sweet spot than A to compensate for that.

This means Car A, will have a bit of extra power to give from the engine when accellerating after the Sweet spot.

Car B will need to make up for that tiny loss of power advantage Car A recieved from its "Y factor"

At 10m, Car A should be going faster than Car B
(Theoretical instance of trap speed at the end). Whether its ahead of Car B is another matter. That depends on if the Momentum of the Y stuff was enough to give Car A enough power to compensate for the time it lost spinning.

It is ALSO true though, that car A has used more energy than car B. But car B was probably much more efficienant than Car A at getting from start to finish. But the most efficient car doesnt always mean its going to win based on this example.


Ok This is a huge oversimplification, but I think it demonstrates how trap speed "can" be improved by spinning the tires.

Finally, Car A will always hit that sweet spot as it catches. Car B might not always hit that sweet spot of aquiring traction before slipping. --->I think that this is probably the biggest factor when arguing spinning vs not spinning <---
Which is why A will likely have more speed at the trap.

Err hope this helps.. plz jump in if you want to correct any mistakes i've made

 

why don't we just ask the ricers why they think the trap speed would be up or down with traction? let's see what they say...