Mechanical Advantage (Gearing)
02-16-2008, 05:16 PM
#41
Wouldn't the 10% extra gear multiply torque throughout the usable rpm range? That might help acceleration a little. Drag limited top speed still is a function of hp. So, with more gear you still get up to 187 mph on a long straight, but you get there perhaps a tenth quicker.
Hey we can fix that by putting in a gear (or rpm) rule to keep competition close and "save money"! Ever notice how well the "saving money" thing works?
I believe Cup teams can choose from 2 or perhaps 3 rear end ratios for the Datona 500. The difference between a 3.54 and a 3.70 is about 400 rpm. Which would you, as a crew chief, choose for the 500? Why?
Jon
Hey we can fix that by putting in a gear (or rpm) rule to keep competition close and "save money"! Ever notice how well the "saving money" thing works?
I believe Cup teams can choose from 2 or perhaps 3 rear end ratios for the Datona 500. The difference between a 3.54 and a 3.70 is about 400 rpm. Which would you, as a crew chief, choose for the 500? Why?
Jon
I guess it is just a guess because you really don't know how it will end, GWC or do you have a good 5 laps to make up the speed.
I would personally make the engine make as much power as possible after the restrictor takes effect and run the 3.54. This will let my driver have the option of going faster if the opportunity arrives.
02-19-2008, 02:49 PM
#42
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Nothing is that simple.
A car and motorcycle with the same power:weight. Bike has far less drag (1/5th the frontal area). From a 50mph roll, car wins. Drag effects the p/w more harshly on the bike than the car
A car and motorcycle with the same power:weight. Bike has far less drag (1/5th the frontal area). From a 50mph roll, car wins. Drag effects the p/w more harshly on the bike than the car
02-20-2008, 10:21 PM
#43
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I don't think you understood me.
Torque isn't what moves a car the fastest. Its power.
If you know and understand that the next step is to realise that power is the same at the wheel regardless of gear ratio. (power = torque * angular speed) Torque changes by n/1 where gear ratio is n and angular speed changes by 1/n
What moves a car down the track absoulutely the fastest is which ever gear combination that keeps the engine at RPM which it makes the most power the most amount of time.
Torque isn't what moves a car the fastest. Its power.
If you know and understand that the next step is to realise that power is the same at the wheel regardless of gear ratio. (power = torque * angular speed) Torque changes by n/1 where gear ratio is n and angular speed changes by 1/n
What moves a car down the track absoulutely the fastest is which ever gear combination that keeps the engine at RPM which it makes the most power the most amount of time.
02-21-2008, 10:04 AM
#44
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I appreciate it DanO.
Admittedly, I've gotten much more into trucks and off-roading in recent years, and less into drag racing. I got used to looking at wheel torque (using engine torque and gearing) because you NEED as much of that as possible to turn huge meats against thick mud that tries to hold the tires still. or for rock crawling. a 500 CI big block purpose-built for mostly low end torque might only make 200whp like a modded honda civic, but that civic won't come close to turning 44" boggers in the slop. much less 4 of them at a time with front and rear lockers engaged. it might with REALLY LOOWWW gears, but then you can't get enough wheel speed to do you any good.
I just figured it worked the same way with acceleration... not anymore.
Admittedly, I've gotten much more into trucks and off-roading in recent years, and less into drag racing. I got used to looking at wheel torque (using engine torque and gearing) because you NEED as much of that as possible to turn huge meats against thick mud that tries to hold the tires still. or for rock crawling. a 500 CI big block purpose-built for mostly low end torque might only make 200whp like a modded honda civic, but that civic won't come close to turning 44" boggers in the slop. much less 4 of them at a time with front and rear lockers engaged. it might with REALLY LOOWWW gears, but then you can't get enough wheel speed to do you any good.
I just figured it worked the same way with acceleration... not anymore.
02-21-2008, 02:14 PM
#46
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It's a shame you need a full ME degree course to understand the course but...
you know that course that relates electrical energy (current, voltage, resistance, capacitors etc) to mechanical stuff (pressure, force, velocity, springs, flywheels, mass, flow rate, etc)- that course makes the whole "hp vs torque" topic very clear.
It's not an art. It's not a debate. It's not based on experience. It's not an opinion. It's fact.
I'd to repeat that, because it seems like gear-heads dont get it(ironically called gear heads):
It's not opinion. It's fact.
Power can get you wheel speed or "wheel torque" (torque after gearing). More power, whether at 1,500rpm or 15,000rpm will get you more wheel speed AND more torque. That's the whole point of measuring power.
you know that course that relates electrical energy (current, voltage, resistance, capacitors etc) to mechanical stuff (pressure, force, velocity, springs, flywheels, mass, flow rate, etc)- that course makes the whole "hp vs torque" topic very clear.
It's not an art. It's not a debate. It's not based on experience. It's not an opinion. It's fact.
I'd to repeat that, because it seems like gear-heads dont get it(ironically called gear heads):
It's not opinion. It's fact.
Power can get you wheel speed or "wheel torque" (torque after gearing). More power, whether at 1,500rpm or 15,000rpm will get you more wheel speed AND more torque. That's the whole point of measuring power.
02-21-2008, 10:56 PM
#47
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02-21-2008, 11:28 PM
#48
How the hell can a stupid thread that can be answered with an EXTREMELY simple math equation have gone on for 3 pages? This isn't complex fluid dynamics or harmonic pressure wave math, it's just gearing! After reading this thread, I have to go add 2+2 just to feel smarter. That does still equal 4, right?
02-22-2008, 02:17 AM
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I fully intended to stay out of this, but now I'm more curious with those last replies... let's put acceleration and the drag strip aside for a minute.
Why are the off-road peeps (mud bog, tough truck, rock crawlers, etc) obsessed with LARGE gear ratios and BIG displacement to make the MOST torque at moderately low rpm? 99% of the time we don't care about acceleration, you don't find us running to dynos, and in most cases more wheel speed than necessary is a bad thing. And we really don't care about "high" rpm... strokers and bigger engine swaps there are as common as head and cam packages are here. And total drive line reduction calculations there are about as common as cam questions here.
What if I'm stuck in a hole with the tires in deep thick mud, and if my drive line rpm is zero, wouldn't that mean that the most torque available would be necessary to get the tires turning again? I bring this up because I've seen many instances were guys would throw on big tires then go charging into holes banging off the rev limiter, just to get in there and have the engine strain way down to the mid range rpm (around the torque peak) and either hold it there or come to a complete stop (can't turn the tires at all). Even a high rpm clutch dump in gear can't get those tires going again... and sometimes with hilarious results. So, it's either gear that baby down with a higher ratio axle gear set or transfer case, or go with a bigger engine or forced induction to turn those big tires.
Is the "wheel torque" analysis still wrong for this? I'm not trying to be cantankerous, just want to see it from that perspective...
Why are the off-road peeps (mud bog, tough truck, rock crawlers, etc) obsessed with LARGE gear ratios and BIG displacement to make the MOST torque at moderately low rpm? 99% of the time we don't care about acceleration, you don't find us running to dynos, and in most cases more wheel speed than necessary is a bad thing. And we really don't care about "high" rpm... strokers and bigger engine swaps there are as common as head and cam packages are here. And total drive line reduction calculations there are about as common as cam questions here.
What if I'm stuck in a hole with the tires in deep thick mud, and if my drive line rpm is zero, wouldn't that mean that the most torque available would be necessary to get the tires turning again? I bring this up because I've seen many instances were guys would throw on big tires then go charging into holes banging off the rev limiter, just to get in there and have the engine strain way down to the mid range rpm (around the torque peak) and either hold it there or come to a complete stop (can't turn the tires at all). Even a high rpm clutch dump in gear can't get those tires going again... and sometimes with hilarious results. So, it's either gear that baby down with a higher ratio axle gear set or transfer case, or go with a bigger engine or forced induction to turn those big tires.
Is the "wheel torque" analysis still wrong for this? I'm not trying to be cantankerous, just want to see it from that perspective...
How the hell can a stupid thread that can be answered with an EXTREMELY simple math equation have gone on for 3 pages? This isn't complex fluid dynamics or harmonic pressure wave math, it's just gearing! After reading this thread, I have to go add 2+2 just to feel smarter. That does still equal 4, right?
In all honesty- if you refuse to (or simply can't) understand it- just accept it.
02-22-2008, 12:56 PM
#50
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so your question becomes.. would you rather have 40lb ft or 10 lb ft more at 1300rpm..
This is REALLY simple guys. You always want more power no matter what condition you can throw at it. because more power = more ability to apply mechanical advantage (gearing)
Power is energy and energy is what moves things..
02-23-2008, 02:47 AM
#51
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My last post in here...
It's obvious my way of thinking needed correction. That is why I challenge most things I don't understand, or only have a moderate understanding of. Otherwise, how do you learn without having YOUR specific issues addressed? Reading words on a screen is one thing, the meaning of those words when read by different eyes can be something completely different. And it's the biggest reason why I hate the internet. While you can read words, you can't read emotions. And nothing is more disruptive than trying to learn something while seemingly in the face of hostility.
I'm still grasping the concept, and getting more comfortable with applying it to different situations. Just have to remind my self of "torque times rpm" every time my mind tries to wonder back to the other way.
DanO, you have much respect from me. Professionalism is hard to find nowadays, and you taking the time to clear it up in a way I can understand shows this well.
Trey:
It's hard for me to "just accept" some things. I hunger for knowledge, to understand as well as accept. Most, if not all gear heads, are fascinated by Mech. Eng. theory and application, but not everyone would be happy being an M.E. day in and day out. I don't see where "shame" fits in with being something other than an M.E.
I'm just a little O.C.D. if you can't tell. I was sick with the flu last week when this thread blew up (my fault, entirely). I don't post much anymore because of it; and you see why in this thread... I can obsess about things with little control. I do take medication for it, but couldn't last week.
Peace
It's obvious my way of thinking needed correction. That is why I challenge most things I don't understand, or only have a moderate understanding of. Otherwise, how do you learn without having YOUR specific issues addressed? Reading words on a screen is one thing, the meaning of those words when read by different eyes can be something completely different. And it's the biggest reason why I hate the internet. While you can read words, you can't read emotions. And nothing is more disruptive than trying to learn something while seemingly in the face of hostility.
I'm still grasping the concept, and getting more comfortable with applying it to different situations. Just have to remind my self of "torque times rpm" every time my mind tries to wonder back to the other way.
DanO, you have much respect from me. Professionalism is hard to find nowadays, and you taking the time to clear it up in a way I can understand shows this well.
Trey:
It's hard for me to "just accept" some things. I hunger for knowledge, to understand as well as accept. Most, if not all gear heads, are fascinated by Mech. Eng. theory and application, but not everyone would be happy being an M.E. day in and day out. I don't see where "shame" fits in with being something other than an M.E.
I'm just a little O.C.D. if you can't tell. I was sick with the flu last week when this thread blew up (my fault, entirely). I don't post much anymore because of it; and you see why in this thread... I can obsess about things with little control. I do take medication for it, but couldn't last week.
Peace
I did say that if you can't understand it, just accept it. If you dont "get it" just accept it and use the darned formula. Misguided intuition is terrible thing for an engineer. I've seen people, first hand, use their intuition when they thought a formula/principal was wrong and it never ends in anything more than a clusterfuck.
Sorry to be so cold; it's the way it is. It isn't a personal attack, but physics isn't accommodating. Tq is irrelevant. It's all about HP. It's not an opinion or discussion. It's simply fact. HP is king.
02-29-2008, 02:03 AM
#52
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I haven't looked at this thread for awhile and haven't really spent the time to really read into all of the posts but I think I might have a simple way to look at it that you don't even need an ME to understand:
Don't forget that the 5252 is just a unit conversion so throwing out the unit conversion you got a really simple formula: HP=Torque*RPM
(this would also make HP always higher than Torque on a graph, which would mean there would be more HP at Torque peak, I think the unit conversion causes half of the confusion for most people)
Torque and HP are very similiar things just that the HP has a time value (RPM) added in and Torque is static.
When people talk about how fast their car is it is how their car moves over a period of time, it isn't static.
So logically HP is more important than Torque in making your car "fast".
Gearing is just a way of trading the torque and RPM values around because when you are moving slower you need more Torque over less movement of the wheels. The HP is the thing that stays constant and can't be changed through gearing.
The wheel's higher Torque value at a given wheel RPM will be at the engine's HP peak, not the engine's Torque peak if you used different gearing to convert the wheel RPM value to be equal on both. Because of basic math principles, from the equation above, you can't take away from one side of the formula (hp) and add to the other (torque) while keeping the RPM the same, the formula wouldn't equal anymore.
Don't forget that the 5252 is just a unit conversion so throwing out the unit conversion you got a really simple formula: HP=Torque*RPM
(this would also make HP always higher than Torque on a graph, which would mean there would be more HP at Torque peak, I think the unit conversion causes half of the confusion for most people)
Torque and HP are very similiar things just that the HP has a time value (RPM) added in and Torque is static.
When people talk about how fast their car is it is how their car moves over a period of time, it isn't static.
So logically HP is more important than Torque in making your car "fast".
Gearing is just a way of trading the torque and RPM values around because when you are moving slower you need more Torque over less movement of the wheels. The HP is the thing that stays constant and can't be changed through gearing.
The wheel's higher Torque value at a given wheel RPM will be at the engine's HP peak, not the engine's Torque peak if you used different gearing to convert the wheel RPM value to be equal on both. Because of basic math principles, from the equation above, you can't take away from one side of the formula (hp) and add to the other (torque) while keeping the RPM the same, the formula wouldn't equal anymore.
