Is there a relationship between horsepower and Torque, like a direct link. Im asking as I was watching an old 5th Gear and they had a Unimog on with 220BHP and over 1000Nm of Torques. So how is torque generated and is there a reason for low power high torques and vice versa ?
Horsepower And Torque Whats The Deal
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Doovde
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Bazmcc
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Nope, might be worth another read through. bhp is power. Brake horse'power'.
Torque and RPM are calculated to give a power figure.
Torque and RPM are calculated to give a power figure.
Doovde
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Put it like this, in the offroad world, torque is king
See why is it better than BHP doovde for the muddy stuff ?
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Its the torque that will turn the big wheel though mud, glar and up hills. But in 4x4 its all in relation to gearing as well. You take an engine that produces 200ft/lb in 3rd high and put into into 3rd low, it'll be considerably more. Half the idea behind having a low range is to massively increase the pulling power of the engine as well as slowing the lot down to make it more finely controllable.
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There is a relationship. The calculation is HP = Torque x RPM/5252.
So on my wagon:
At 4000rpm I get my peak of 220lbft of torque which works out at 168bhp, but at 4750rpm I get my peak horsies at 190bhp however that only gives me 211lbft of torque. Seems to give me a nice smooth curve of torque & bhp.
In essence then something like a VTEC or motorbike that gets max bhp at high revs gets low torque and something like your unimog that gets huge torque at low rpm is going to have relatively low bhp.
Confused? I am
So on my wagon:
At 4000rpm I get my peak of 220lbft of torque which works out at 168bhp, but at 4750rpm I get my peak horsies at 190bhp however that only gives me 211lbft of torque. Seems to give me a nice smooth curve of torque & bhp.
In essence then something like a VTEC or motorbike that gets max bhp at high revs gets low torque and something like your unimog that gets huge torque at low rpm is going to have relatively low bhp.
Confused? I am
Torques all well and good but its how many rpm it lasts . For eg you hear all these mad figures from diesels but that's s torque spike that only lasts a few hundred rpm then runs out of puff at low revs. And lastly from bitter experience torque breaks stuff lol !
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Andy044
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I heard that,
Understeer is when you hit the wall with the front of the car
Oversteer is when you hit the wall with the back of the car
Hp is how fast you were going when you hit the wall and
Torque is how far you took the wall with you
Coog sums it up pretty well
However Power (kW) = Torque * RPM
Horsepower = Power (kW) * 1.341
Best explanation I know of paul, written by Michael Daniel from SCN
Q. Is it power or torque that defines acceleration and top speed?
A. Yes.
That's usually the full depth of explanation folks are given……
In reality (switch on memory now) it is the torque that reaches the drivewheels that dictates both acceleration AND max speed. This figure is comprised of engine torque and gearing. That's it. Simple. Nothing more.
Higher engine torque = higher torque at the wheels = higher acceleration.
Lower gearing = higher torque at the wheels = higher acceleration.
Remember that TORQUE is the only engine output a driver feels. Power is a kind of esoteric measure that is simply calculated from Torque and Engine Speed. If we are talking “BHP” and “lbs.ft” then the equation is:-
Power= (Torque x rpm)/5252
So that's you then……thanks for listening.
But wait a minute. If Torque is all that matters, why is power always considered so important?
Because (re-engage your memory banks again) “power dictates how much advantage you can make of gearing”……which is where it all gets a little bit complex…and folks start switching off…but come back…it's not that difficult!
I've seen a few analogies before, but the best one I've thought of now is YOU. Well, you on a bike actually – we can all relate to that (yeah?).
Torque is what your legs generate. As stated above ~ If you press harder on the pedals you'll accelerate harder…..simple! You use the gears on your bike to multiply the torque your legs generate. In 1st gear the bike wheel may only rotate once for every 5 times you spin the pedals. In this gear you can zip up a hill (or accelerate really quickly), ‘cos this gearing has the effect of multiplying your leg power by 5.
If you maintain a steady force on the pedals, the bike accelerates at a steady rate. The torque you are generating stays constant, but the faster you spin your legs the more power you muster. Eventually you discover that you run out of “RPM” – your coordination goes, and you can't really get any force into your leg strokes. This is like your engine going upto and beyond its' peak power point.
Higher gears allow you to move along quickly whilst your legs go round at a comfortable pace. Nice one. Try to pull away from a standstill in the same gear however and (without enormous multiplication of your leg strength) it'll take you significantly longer to get up to speed.
Lets invent two characters:-. Arnie and Splinter. These guys epitomise two extremes of engine genre. Arnie has whopping leg muscles…thighs thicker than Tara-Palmer-Tomkinson. He is however a little clumsy and uncoordinated, so whilst he can REALLY “pump dem pedals”, he can only manage slow rotations. Anything else is too much for his feeble mind and coordination. (whisper…he's the turbodiesel).
Splinter conversely has spindly “twiggy legs” - He can barely stand up from his seat when his cup of Horlicks is full to the brim. Splinter however has been surgically enhanced with “VAJ” (variable-ankle-jeometry) that endows him with an uncanny ability to “spin da cog”. Although he can only manage a feeble push, he can maintain the coordination needed to rotate the pedals at…oh god knows how many rpm…it's so fast I can't count. You'd really need to see this guy. (whisper again….he's the VTEC)
We line them up on the drag strip and Whooaa! Arnie storms into the lead, his rear tyre barely able to contain the thrust created by those burly legs. But…oh dear….his coordination is going, and he's quickly forced to change up into second, then third…and look at this! Splinter is staging a comeback, still in first with his legs flailing like ….a flaily thing. Whilst Arnie is producing major leg thrust, he's currently using 3rd gear, which only doubles the torque his legs generate before it reaches the rear wheel. Splinter is still in first, so his weedy leg strength continues to be subject to 5-times multiplication…and he's reeling Arnie in!
It's a similar story when they are up to maximum speed. By enormous coincidence they appear to have an identical flat-out pace. Arnie is pumping his top gear firmly and steadily ~ wind resistance and friction conspire against him – he can go no faster. Splinter is right up there with him, but he's still in 3rd - legs whizzing round.
If we assume they have the same drag coefficient & weight etc, they are both producing the same POWER at this point. Arnie via high leg torque and low rpm, Splinter via low leg torque and high rpm. Their two power outputs are equal, and each calculation is valid.
It's exactly the same story when you look at the torque arriving at the rear wheel of the bike ~ Arnie is making high leg torque, but it's being blunted by the high gearing he has to use. Splinter uses low gearing to maintain the multiplication of his leg muscles and provide an identical torque at the rear wheel.
Back to the world of cars. You should now be able to understand why TDI's are often quoted as having “massive in-gear thrust”, whilst it's acknowledged that they suck fat ones when it comes to both “0-60” and top speed. Most TDI's barely get to 60 in third (let alone second), so in addition to requiring an extra gear change over most petrol models, they pass “the magic 60” in 3rd ~ which is by definition higher geared than 2nd, so the prodigious torque is multiplied to a lesser extent before it get's the chance to arrive at the drivewheel and “do the business”.
As diesels operate using compression ignition they don't require spark plugs. This omission unfortunately makes advancing the spark somewhat difficult ~ the main cause of their high rpm torque defecit. Lack of power (torque at high rpm) alone blunts their maximum velocity potential, but the coup-de-grace is that (with a rev ceiling around 4,500rpm) they have to use higher gearing ~ which again reduces the torque reaching the wheels. These two traditional performance metrics are therefore unreflective of the “real world” performance of a modern TD…it's low-rev torque very noticeable on the road, but fairly irrelevant in the two above circumstances.
A VTEC engine with 140lbs.ft max torque CANNOT punch as hard as a TDI with 200lbs.ft. In a VTEC however you will choose to accelerate with a lower gear than the TD, so the torque it does have is multiplied to a greater extent before it reaches the wheels. A TDI might feel impressive in 4th~ certainly more impressive than a VTEC in 4th, but the VTEC driver would undoubtedly pop it into 3rd (or even 2nd) to make better progress. The TDI has no such option.
Real Life Example – for the average TDI, gearing multiplies engine torque by a factor of approximately 12 in 1st gear, but only 2.5times in 5th gear. A TDI with 200lbs/ft will therefore produce a peak of 500lbs.ft at the drivewheels in 5th.
A VTEC shares pretty similar gearing in 1st, but its' lower top gear multiplies engine torque by a far higher 3.7times(approx) in 5th. Its' 140lbs.ft engine torque peak therefore equates to a peak at the drivewheels of 518lbs.ft in top.
Assuming they are the same weight etc and each car is at peak-torque rpm, you can see that the VTEC will accelerate marginally harder in top than the TDI - despite its apparent torque deficit.
As a rule - lower gearing makes better use of what torque you have available, but leads to unfashionably (and often uncomfortably) high-rev cruising. If you like that – fine. If you don't. what do I care? Your decision ~ there is no “best”.
Just out of interest – lets look at a (current) F1 car example-
Assume 800hp at 18000rpm. Using the equation in the 1st paragraph, we can see that it is only producing 233lbs.ft at this point. Not a lot really….a 1.9TDI VAG unit produces up to 235lbs.ft in el-boggo-standard form.
However…..if we want it to do 210mph, then our mega-revvy F1 engine only needs a top gear pulling 12mph per 1000rpm…..which is barely higher than 2nd gear in most road cars. Hence the “torque multiplier” from the gearing is massive, and you can still spin those fat rear slicks in top gear. Massive power allows vast exploitation of gearing. (I would guess gearing ratio in top is approx 6.5:1….so the engines' 233lbs.ft becomes 1500+ lbs.ft to be shared between the rear wheels).
What if you could extend the rev range further? Okeydokey - let's double it to 36000rpm. With this, the same car could use gearing of only 6mph per 1000rpm (about the same as 1st in a road car) and still manage 210mph. All 800 horses are still required (and produced), although only 116.5 lbs.ft torque is required to create it at this astronomical engine speed. Has the torque arriving at the wheels changed? (No). You can see why F1 engineers love engines that rev.
It aint simple….but then the best things never are. When this all clicks home in your noggin it's as satisfying as your first clean heel&toe downshift, and you'll never look at engines in the same way again.
Knowledge is power as they say. Or should that be “torque x rpm”?
Q. Is it power or torque that defines acceleration and top speed?
A. Yes.
That's usually the full depth of explanation folks are given……
In reality (switch on memory now) it is the torque that reaches the drivewheels that dictates both acceleration AND max speed. This figure is comprised of engine torque and gearing. That's it. Simple. Nothing more.
Higher engine torque = higher torque at the wheels = higher acceleration.
Lower gearing = higher torque at the wheels = higher acceleration.
Remember that TORQUE is the only engine output a driver feels. Power is a kind of esoteric measure that is simply calculated from Torque and Engine Speed. If we are talking “BHP” and “lbs.ft” then the equation is:-
Power= (Torque x rpm)/5252
So that's you then……thanks for listening.
But wait a minute. If Torque is all that matters, why is power always considered so important?
Because (re-engage your memory banks again) “power dictates how much advantage you can make of gearing”……which is where it all gets a little bit complex…and folks start switching off…but come back…it's not that difficult!
I've seen a few analogies before, but the best one I've thought of now is YOU. Well, you on a bike actually – we can all relate to that (yeah?).
Torque is what your legs generate. As stated above ~ If you press harder on the pedals you'll accelerate harder…..simple! You use the gears on your bike to multiply the torque your legs generate. In 1st gear the bike wheel may only rotate once for every 5 times you spin the pedals. In this gear you can zip up a hill (or accelerate really quickly), ‘cos this gearing has the effect of multiplying your leg power by 5.
If you maintain a steady force on the pedals, the bike accelerates at a steady rate. The torque you are generating stays constant, but the faster you spin your legs the more power you muster. Eventually you discover that you run out of “RPM” – your coordination goes, and you can't really get any force into your leg strokes. This is like your engine going upto and beyond its' peak power point.
Higher gears allow you to move along quickly whilst your legs go round at a comfortable pace. Nice one. Try to pull away from a standstill in the same gear however and (without enormous multiplication of your leg strength) it'll take you significantly longer to get up to speed.
Lets invent two characters:-. Arnie and Splinter. These guys epitomise two extremes of engine genre. Arnie has whopping leg muscles…thighs thicker than Tara-Palmer-Tomkinson. He is however a little clumsy and uncoordinated, so whilst he can REALLY “pump dem pedals”, he can only manage slow rotations. Anything else is too much for his feeble mind and coordination. (whisper…he's the turbodiesel).
Splinter conversely has spindly “twiggy legs” - He can barely stand up from his seat when his cup of Horlicks is full to the brim. Splinter however has been surgically enhanced with “VAJ” (variable-ankle-jeometry) that endows him with an uncanny ability to “spin da cog”. Although he can only manage a feeble push, he can maintain the coordination needed to rotate the pedals at…oh god knows how many rpm…it's so fast I can't count. You'd really need to see this guy. (whisper again….he's the VTEC)
We line them up on the drag strip and Whooaa! Arnie storms into the lead, his rear tyre barely able to contain the thrust created by those burly legs. But…oh dear….his coordination is going, and he's quickly forced to change up into second, then third…and look at this! Splinter is staging a comeback, still in first with his legs flailing like ….a flaily thing. Whilst Arnie is producing major leg thrust, he's currently using 3rd gear, which only doubles the torque his legs generate before it reaches the rear wheel. Splinter is still in first, so his weedy leg strength continues to be subject to 5-times multiplication…and he's reeling Arnie in!
It's a similar story when they are up to maximum speed. By enormous coincidence they appear to have an identical flat-out pace. Arnie is pumping his top gear firmly and steadily ~ wind resistance and friction conspire against him – he can go no faster. Splinter is right up there with him, but he's still in 3rd - legs whizzing round.
If we assume they have the same drag coefficient & weight etc, they are both producing the same POWER at this point. Arnie via high leg torque and low rpm, Splinter via low leg torque and high rpm. Their two power outputs are equal, and each calculation is valid.
It's exactly the same story when you look at the torque arriving at the rear wheel of the bike ~ Arnie is making high leg torque, but it's being blunted by the high gearing he has to use. Splinter uses low gearing to maintain the multiplication of his leg muscles and provide an identical torque at the rear wheel.
Back to the world of cars. You should now be able to understand why TDI's are often quoted as having “massive in-gear thrust”, whilst it's acknowledged that they suck fat ones when it comes to both “0-60” and top speed. Most TDI's barely get to 60 in third (let alone second), so in addition to requiring an extra gear change over most petrol models, they pass “the magic 60” in 3rd ~ which is by definition higher geared than 2nd, so the prodigious torque is multiplied to a lesser extent before it get's the chance to arrive at the drivewheel and “do the business”.
As diesels operate using compression ignition they don't require spark plugs. This omission unfortunately makes advancing the spark somewhat difficult ~ the main cause of their high rpm torque defecit. Lack of power (torque at high rpm) alone blunts their maximum velocity potential, but the coup-de-grace is that (with a rev ceiling around 4,500rpm) they have to use higher gearing ~ which again reduces the torque reaching the wheels. These two traditional performance metrics are therefore unreflective of the “real world” performance of a modern TD…it's low-rev torque very noticeable on the road, but fairly irrelevant in the two above circumstances.
A VTEC engine with 140lbs.ft max torque CANNOT punch as hard as a TDI with 200lbs.ft. In a VTEC however you will choose to accelerate with a lower gear than the TD, so the torque it does have is multiplied to a greater extent before it reaches the wheels. A TDI might feel impressive in 4th~ certainly more impressive than a VTEC in 4th, but the VTEC driver would undoubtedly pop it into 3rd (or even 2nd) to make better progress. The TDI has no such option.
Real Life Example – for the average TDI, gearing multiplies engine torque by a factor of approximately 12 in 1st gear, but only 2.5times in 5th gear. A TDI with 200lbs/ft will therefore produce a peak of 500lbs.ft at the drivewheels in 5th.
A VTEC shares pretty similar gearing in 1st, but its' lower top gear multiplies engine torque by a far higher 3.7times(approx) in 5th. Its' 140lbs.ft engine torque peak therefore equates to a peak at the drivewheels of 518lbs.ft in top.
Assuming they are the same weight etc and each car is at peak-torque rpm, you can see that the VTEC will accelerate marginally harder in top than the TDI - despite its apparent torque deficit.
As a rule - lower gearing makes better use of what torque you have available, but leads to unfashionably (and often uncomfortably) high-rev cruising. If you like that – fine. If you don't. what do I care? Your decision ~ there is no “best”.
Just out of interest – lets look at a (current) F1 car example-
Assume 800hp at 18000rpm. Using the equation in the 1st paragraph, we can see that it is only producing 233lbs.ft at this point. Not a lot really….a 1.9TDI VAG unit produces up to 235lbs.ft in el-boggo-standard form.
However…..if we want it to do 210mph, then our mega-revvy F1 engine only needs a top gear pulling 12mph per 1000rpm…..which is barely higher than 2nd gear in most road cars. Hence the “torque multiplier” from the gearing is massive, and you can still spin those fat rear slicks in top gear. Massive power allows vast exploitation of gearing. (I would guess gearing ratio in top is approx 6.5:1….so the engines' 233lbs.ft becomes 1500+ lbs.ft to be shared between the rear wheels).
What if you could extend the rev range further? Okeydokey - let's double it to 36000rpm. With this, the same car could use gearing of only 6mph per 1000rpm (about the same as 1st in a road car) and still manage 210mph. All 800 horses are still required (and produced), although only 116.5 lbs.ft torque is required to create it at this astronomical engine speed. Has the torque arriving at the wheels changed? (No). You can see why F1 engineers love engines that rev.
It aint simple….but then the best things never are. When this all clicks home in your noggin it's as satisfying as your first clean heel&toe downshift, and you'll never look at engines in the same way again.
Knowledge is power as they say. Or should that be “torque x rpm”?
Last bit
Note1: In an attempt to keep things simple (honest) I ignored the fact that one aspect of your overall gearing comes from the total diameter of the wheel/tyre combination. If you “max da Nova” with 19” rims, then (even using 25 series tyres) the overall diameter will increase. Which raises your overall gearing (and incidentally knocks your speedo calibration out). Does this make it faster then? …..errr….nope.
Note2: Above detail also explains a question that haunted me for years: I could never fathom that I was able to strain on a torque wrench and tighten a front hub nut to approx 160lbs.ft without the wheel spinning, whilst a fwd hot-hatch with 160lbs.ft torque struggled for traction…..despite that figure being shared between both front wheels (????)
I now realise that in 1st gear, 160lbs.ft at the engine becomes approx 2000lbs.ft at the drivewheels due to your gearing. 1000lbs.ft per wheel = I can smell rubber.
I'm off again…..lets call this note 3: It's interesting to compare this with the F1 car example above ~ which achieves 75% of this “torque at the wheels” figure…but in top gear. Now since it weighs less than half of the hot hatch…if it weren't for horrendous aerodynamic drag it would shove you back in your seat in top gear with over 50% MORE force than the hot hatch could in first! Hmmmmmm.
are this with the F1 car example above ~ which achieves 75% of this “torque at the wheels” figure…but in top gear. Now since it weighs less than half of the hot hatch…if it weren't for horrendous aerodynamic drag it would shove you back in your seat in top gear with over 50% MORE force than the hot hatch could in first! Hmmmmmm.
Note1: In an attempt to keep things simple (honest) I ignored the fact that one aspect of your overall gearing comes from the total diameter of the wheel/tyre combination. If you “max da Nova” with 19” rims, then (even using 25 series tyres) the overall diameter will increase. Which raises your overall gearing (and incidentally knocks your speedo calibration out). Does this make it faster then? …..errr….nope.
Note2: Above detail also explains a question that haunted me for years: I could never fathom that I was able to strain on a torque wrench and tighten a front hub nut to approx 160lbs.ft without the wheel spinning, whilst a fwd hot-hatch with 160lbs.ft torque struggled for traction…..despite that figure being shared between both front wheels (????)
I now realise that in 1st gear, 160lbs.ft at the engine becomes approx 2000lbs.ft at the drivewheels due to your gearing. 1000lbs.ft per wheel = I can smell rubber.
I'm off again…..lets call this note 3: It's interesting to compare this with the F1 car example above ~ which achieves 75% of this “torque at the wheels” figure…but in top gear. Now since it weighs less than half of the hot hatch…if it weren't for horrendous aerodynamic drag it would shove you back in your seat in top gear with over 50% MORE force than the hot hatch could in first! Hmmmmmm.
are this with the F1 car example above ~ which achieves 75% of this “torque at the wheels” figure…but in top gear. Now since it weighs less than half of the hot hatch…if it weren't for horrendous aerodynamic drag it would shove you back in your seat in top gear with over 50% MORE force than the hot hatch could in first! Hmmmmmm.
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Is there anything left
Cheeky coont Ill have to check with coog how the points system works on the new forum
Home now so ill have to give these thread replies a proper read through
Coog
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Aye because that's probably because it's what most people understand.
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