Understanding trap speed/gear ratio
03-19-2010, 10:28 AM
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Understanding trap speed/gear ratio This may seem like a basic or stupid question to some but bear with me.
How does trap speed relate to gear ratio?
This might be a crude, exaggerated example but here we go.
For example, lets say we have two cars drag racing. They have the exact same transmission/clutch/ rear end gear ratio/ tire size, but one car has more overall power than the other.
In this imaginary drag race both cars run the exact same ET. BUT...the car with more power the traps at 135 mph. The less powerful car passes the traps at 115.
(Obviously, the car with higher trap speed got a horrible launch but then its power made up the difference. Where the car with the lower trap speed got a good launch off the line, but has less power overall...resulting in the same ET).
The question is:
Did the car with the faster trap speed actually use MORE gear in order to cover the same distance, since his speed was faster(mph)?
In other words, did he possibly have to shift into the next forward transmission gear?
I know this is probably simple but I cannot get my mind wrapped around this.
MPH is directly related to gearing, right? ...Since a given MPH will always net the same RPM in the same gear, right?
So will you always travel the same amount of distance (feet) in a given gear/rpm/speed?...Regardless of the launch?
This is a lesson in physics and i need to get my *** back in a classroom!
How does trap speed relate to gear ratio?
This might be a crude, exaggerated example but here we go.
For example, lets say we have two cars drag racing. They have the exact same transmission/clutch/ rear end gear ratio/ tire size, but one car has more overall power than the other.
In this imaginary drag race both cars run the exact same ET. BUT...the car with more power the traps at 135 mph. The less powerful car passes the traps at 115.
(Obviously, the car with higher trap speed got a horrible launch but then its power made up the difference. Where the car with the lower trap speed got a good launch off the line, but has less power overall...resulting in the same ET).
The question is:
Did the car with the faster trap speed actually use MORE gear in order to cover the same distance, since his speed was faster(mph)?
In other words, did he possibly have to shift into the next forward transmission gear?
I know this is probably simple but I cannot get my mind wrapped around this.
MPH is directly related to gearing, right? ...Since a given MPH will always net the same RPM in the same gear, right?
So will you always travel the same amount of distance (feet) in a given gear/rpm/speed?...Regardless of the launch?
This is a lesson in physics and i need to get my *** back in a classroom!
Last edited by feelnlo; 03-19-2010 at 06:21 PM.
03-19-2010, 06:06 PM
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I think I get it now. I'm gonna try to explain and answer my own question.
Tell me if I'm right or way off.
This is assuming you have 100% traction--
If you have more power (vs the car with lesser power/ same final gearing), you will rev thru the gears more quickly (accelerate more quickly), thus spending less actual time in each gear. This means you will be traveling at an increased mph, yet you will actually be covering less distance (feet) per gear. You will have an increased mph in less distance vs the other car. It will require less time to attain the given mph, require less distance to attain the given mph, but require more mechanical gearing due to the way you revved thru the gear so much more quickly (vs the other car). You will be required to shift sooner, and it will seem like the gearing is shorter than the other car. In reality you just used your gear more quickly by accelerating at an increased rate through the rpms. Your engine has more power and this is why you are able to do this.
For example:
If you eased on the throttle all the way through 1st gear until reaching the redline, you could eventually achieve the same actual speed as the other car did at the top of first at redline. BUT the other car was accelerating thru 1st with his foot on the floor...reaching the same mph at redline much more quickly with less distance traveled. It would take you a longer amount of time to reach the top of first while easing on the throttle, and would require a longer overall distance covered. Keep doing this in every gear and I'll bet you wont use many gears until you reach the end of the 1/4 mile track.
So its safe to say that top speed in each gear IS limited respectively by the gear ratio and redline. However, the actual distance required to reach this speed is variable-- dependent upon the rate of acceleration.
Did I get this right or am I still a dumb redneck?
Go on and flame me
Tell me if I'm right or way off.
This is assuming you have 100% traction--
If you have more power (vs the car with lesser power/ same final gearing), you will rev thru the gears more quickly (accelerate more quickly), thus spending less actual time in each gear. This means you will be traveling at an increased mph, yet you will actually be covering less distance (feet) per gear. You will have an increased mph in less distance vs the other car. It will require less time to attain the given mph, require less distance to attain the given mph, but require more mechanical gearing due to the way you revved thru the gear so much more quickly (vs the other car). You will be required to shift sooner, and it will seem like the gearing is shorter than the other car. In reality you just used your gear more quickly by accelerating at an increased rate through the rpms. Your engine has more power and this is why you are able to do this.
For example:
If you eased on the throttle all the way through 1st gear until reaching the redline, you could eventually achieve the same actual speed as the other car did at the top of first at redline. BUT the other car was accelerating thru 1st with his foot on the floor...reaching the same mph at redline much more quickly with less distance traveled. It would take you a longer amount of time to reach the top of first while easing on the throttle, and would require a longer overall distance covered. Keep doing this in every gear and I'll bet you wont use many gears until you reach the end of the 1/4 mile track.
So its safe to say that top speed in each gear IS limited respectively by the gear ratio and redline. However, the actual distance required to reach this speed is variable-- dependent upon the rate of acceleration.
Did I get this right or am I still a dumb redneck?
Go on and flame me Last edited by feelnlo; 03-19-2010 at 06:36 PM.
03-19-2010, 07:56 PM
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I think I get it now. I'm gonna try to explain and answer my own question.
Tell me if I'm right or way off.
This is assuming you have 100% traction--
If you have more power (vs the car with lesser power/ same final gearing), you will rev thru the gears more quickly (accelerate more quickly), thus spending less actual time in each gear. This means you will be traveling at an increased mph, yet you will actually be covering less distance (feet) per gear. You will have an increased mph in less distance vs the other car. It will require less time to attain the given mph, require less distance to attain the given mph, but require more mechanical gearing due to the way you revved thru the gear so much more quickly (vs the other car). You will be required to shift sooner, and it will seem like the gearing is shorter than the other car. In reality you just used your gear more quickly by accelerating at an increased rate through the rpms. Your engine has more power and this is why you are able to do this.
For example:
If you eased on the throttle all the way through 1st gear until reaching the redline, you could eventually achieve the same actual speed as the other car did at the top of first at redline. BUT the other car was accelerating thru 1st with his foot on the floor...reaching the same mph at redline much more quickly with less distance traveled. It would take you a longer amount of time to reach the top of first while easing on the throttle, and would require a longer overall distance covered. Keep doing this in every gear and I'll bet you wont use many gears until you reach the end of the 1/4 mile track.
So its safe to say that top speed in each gear IS limited respectively by the gear ratio and redline. However, the actual distance required to reach this speed is variable-- dependent upon the rate of acceleration.
Did I get this right or am I still a dumb redneck? Go on and flame me
Tell me if I'm right or way off.
This is assuming you have 100% traction--
If you have more power (vs the car with lesser power/ same final gearing), you will rev thru the gears more quickly (accelerate more quickly), thus spending less actual time in each gear. This means you will be traveling at an increased mph, yet you will actually be covering less distance (feet) per gear. You will have an increased mph in less distance vs the other car. It will require less time to attain the given mph, require less distance to attain the given mph, but require more mechanical gearing due to the way you revved thru the gear so much more quickly (vs the other car). You will be required to shift sooner, and it will seem like the gearing is shorter than the other car. In reality you just used your gear more quickly by accelerating at an increased rate through the rpms. Your engine has more power and this is why you are able to do this.
For example:
If you eased on the throttle all the way through 1st gear until reaching the redline, you could eventually achieve the same actual speed as the other car did at the top of first at redline. BUT the other car was accelerating thru 1st with his foot on the floor...reaching the same mph at redline much more quickly with less distance traveled. It would take you a longer amount of time to reach the top of first while easing on the throttle, and would require a longer overall distance covered. Keep doing this in every gear and I'll bet you wont use many gears until you reach the end of the 1/4 mile track.
So its safe to say that top speed in each gear IS limited respectively by the gear ratio and redline. However, the actual distance required to reach this speed is variable-- dependent upon the rate of acceleration.
Did I get this right or am I still a dumb redneck?
Go on and flame meeach gear in the trans will reach a lower speed and therefore cover less distance until you get to the top gear which you would want to be able to cross the finish line at the max usable rpm.
there are variables though:
weather
DA
real altitude
track prep
suspension
tires
either of those can change your overall distance and speed in each gear.
this would be something interesting to see a datalog of.
to simply answer your question, the car that ran the 135 used the same "amount" of gear it just took longer to get there because of short shifting.
03-22-2010, 10:05 AM
#6
It is a pointless question, and you are wasting valuable brain energy on a non-existent hypothetical situation that could be better spent staring out the window!
Sometimes a more powerful car will spin and get the same ET as a slower car with maybe 5-7 extra MPH, not 20!
There have been too many of these same questions lately. Figure it out at the track, in practice, instead of theory!
Al
Sometimes a more powerful car will spin and get the same ET as a slower car with maybe 5-7 extra MPH, not 20!
There have been too many of these same questions lately. Figure it out at the track, in practice, instead of theory!
Al
03-22-2010, 10:10 AM
#7
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Thanks for your smart *** contribution. It was hypothetical and exaggerated purposefully. Find somewhere else to waste your time besides wasting mine with it, as you post in my thread.
