Thumper Club Forum
Club House => Chatter => Topic started by: Propellor on January 28, 2016, 05:53:51 PM
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Watched an old episode of top gear last night. In it jezza tested two fast cars (can't remember what they were). He told us that they had near as dammit the same power and near as dammit the same weight. But the engine characteristics were a lot different. One had more cylinders and revved higher. The one he thought would stomp all over the other in a sprint was the one with the most engine torque. I thought the times across the line ought to be near identical.
Turns out the times were near identical. He was a little puzzled by this, wondering what happened to the extra "80 odd torques" (as he puts it).
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several reasons probably, no matter how much power and torque you have, your performance in a car a bike or any wheel driven motor is all going to be down to the tyres gripping and putting it on the road, hence, loads of power or loads of torque makes no odds if the tyres you use have a certain limit as to how much they will hold. plus, if the cars had engine management systems, its possible that they might have been detecting wheelspin and limiting power or torque to help traction, thus narrowing the gap between the claimed outputs of both vehicles. lets say that a tyre can cope with 250 hp before it lets go, so two of them can handle 500bhp, 4 of them could put down 1000 bhp if you had 4 wheel drive. but if your engine management detects that the 700bhp you are trying to use is making the tyres lose grip, so you might well only be putting down 500bhp with your boot to the floor. now elevated bhp figures that can overcome grip at heavy footed moments, might only show an advantage over a lower powered car at higher speeds when it has to overcome wind resistance, (oh, yes, aerodynamics might also slow down a car compared to another) and finally, you assume that if a car maker says it makes 500bhp that it actually is, manufacturers have been known to be very sparing with the facts with regards to power and torque, sometimes measuring at the ncrank rather than the wheels, and sometimes telling porkies.
so if 2 cars have similar wind resistance and weight but have the same performance over a standing quarter or half mile, then perhaps the performance difference might only become apparent at higher speeds.
oh, and clarkson is a dick, i woldnt accept anything he said on tv as being related to reality in any way.
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Yep, failure of a single component, the nut behind the wheel.
Andy
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Ha ha ha...yeah very well put Andy. That bloke is a deek heed.
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several reasons probably, no matter how much power and torque you have, your performance in a car a bike or any wheel driven motor is all going to be down to the tyres gripping and putting it on the road, hence, loads of power or loads of torque makes no odds if the tyres you use have a certain limit as to how much they will hold. plus, if the cars had engine management systems, its possible that they might have been detecting wheelspin and limiting power or torque to help traction, thus narrowing the gap between the claimed outputs of both vehicles. lets say that a tyre can cope with 250 hp before it lets go, so two of them can handle 500bhp, 4 of them could put down 1000 bhp if you had 4 wheel drive. but if your engine management detects that the 700bhp you are trying to use is making the tyres lose grip, so you might well only be putting down 500bhp with your boot to the floor. now elevated bhp figures that can overcome grip at heavy footed moments, might only show an advantage over a lower powered car at higher speeds when it has to overcome wind resistance, (oh, yes, aerodynamics might also slow down a car compared to another) and finally, you assume that if a car maker says it makes 500bhp that it actually is, manufacturers have been known to be very sparing with the facts with regards to power and torque, sometimes measuring at the ncrank rather than the wheels, and sometimes telling porkies.
so if 2 cars have similar wind resistance and weight but have the same performance over a standing quarter or half mile, then perhaps the performance difference might only become apparent at higher speeds.
oh, and clarkson is a dick, i woldnt accept anything he said on tv as being related to reality in any way.
Good points John. Well put. Any one of those points could easily have been the "equalizing" factor. Then again it could just simply have been that the cars had (near as dammit) equal power and weight. Surely the most important factor in a 1/4 mile dash? Assuming there was nothing silly in the way of gear ratios, pro rata, we could expect equal torque where it matters.
I agree on what you say about aero drag, but the two cars concerned were of the same ilk, so probably very very similar in that respect anyway.
Cheers
I personally feel that Clarkson is amusing. In the past he has been downright hilarious. One gets the feeling his ego got the better of him.
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Sorry Prop, he's a dick. I have this on good authority, as my bro-in-law works in F1, and lived in Chipping Norton, where Mr Clarkson lives. Their sons played rugby together, so he met him frequently at local events. And he says he's a dick. He should know, cause he's a dick too :D
Well, actually that's not true.He's an arrogant twat!
Plus Clarkson is part of the Rebecca Brooks/David Cameron set, that all live in that very small exclusive area of Oxfordshire :-\
Don't start me ;)
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Sorry Prop, he's a dick. I have this on good authority, as my bro-in-law works in F1, and lived in Chipping Norton, where Mr Clarkson lives. Their sons played rugby together, so he met him frequently at local events. And he says he's a dick. He should know, cause he's a dick too :D
Well, actually that's not true.He's an arrogant *******!
Plus Clarkson is part of the Rebecca Brooks/David Cameron set, that all live in that very small exclusive area of Oxfordshire :-\
Don't start me ;)
I never said I liked him. ;) What I said about him doesn't change any of the stuff you said.
Maybe time to nip orf over to the rant section and go for it? ;D
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Johnr is right, there are too many other factors that might come into play for me to assume that equal power to weight should automatically translate into equal acceleration.
My main point was that I'm not surprised that the vehicle with the higher revving engine is able to match the lower revving, higher torque one, in terms of acceleration (and also top speed). It probably would have fewer cc's as well, not that that should matter. Actually, that makes for an interesting topic of its own. How should we judge a vehicle, in terms of achieving a certain performance level? Is it simply power to weight and the rate of fuel consumption? cubic capacity is irrelevant?
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Capacity is irrelevant. I called in the RAF museum in the summer. They have rotary piston engines, hundred year old designs. 9 cylinder, 9 litre, fuel use in gallons an hour, leave a trail of castor oil thick enough to keep the pilots regular, strip down after a few hours running, 80 HP. My 1990's BMWs beat that in every way ( except running three times faster, so must have a gearbox ) and were lighter. Mostly a case of modern materials.
HP, weight, torque vs RPM describe a piston engine.
Andy
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Hi Propellor, I love this thread, and thoroughly " get " all of the variations put forward. One more variation in the mix must surely be the length of the "course" involved. Or, just where we are expecting our torque and horse power to be delivered, and how many constraints we are putting on them..... This puts me in mind of a rather "explosive" little CCM I owned a decade ago. One massively oversquare piston, 4 valves, 39mm carb, 400cc, and 42 horses catapulting you everywhere.... All in a machine ( FT35S), weighing about as much as a bag of crisps...!! A good friend on a Bandit 1250 S, used to stay behind me, most of the time..... I could always leave him from standing starts, outbrake him at the first corner, run rings around him on every bend.... you get the drift .... But, lead him onto a dual carriageway, or a long enough straight, and he could use every one of his horses, making me feel like I was stopped... He also relished the opportunity to "downsize" and never refused a chance to ride my little "hand grenade" ..... As the old saying goes.... It's horses for courses.... or, Whatever floats your boat. Regards, Tony
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Hi Propellor, I love this thread, and thoroughly " get " all of the variations put forward. One more variation in the mix must surely be the length of the "course" involved. Or, just where we are expecting our torque and horse power to be delivered, and how many constraints we are putting on them..... This puts me in mind of a rather "explosive" little CCM I owned a decade ago. One massively oversquare piston, 4 valves, 39mm carb, 400cc, and 42 horses catapulting you everywhere.... All in a machine ( FT35S), weighing about as much as a bag of crisps...!! A good friend on a Bandit 1250 S, used to stay behind me, most of the time..... I could always leave him from standing starts, outbrake him at the first corner, run rings around him on every bend.... you get the drift .... But, lead him onto a dual carriageway, or a long enough straight, and he could use every one of his horses, making me feel like I was stopped... He also relished the opportunity to "downsize" and never refused a chance to ride my little "hand grenade" ..... As the old saying goes.... It's horses for courses.... or, Whatever floats your boat. Regards, Tony
Ha ha. What a great reply.
Sounds bl**dy great fun.
I'm a great believer that fun doesn't necessarily need hp. Quite often the opposite. Besides, fun is subjective and only one aspect of biking.
Cheers.
Andy.
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Yes I couldn't agree more, well put Tony. Yes like you and Andy say fun is about just that, having FUN not necessarily exhilaration which is usually what you get with big hp figures and lots of power. Quite often exhilaration is/can be mistaken for fun. Please don't misunderstand me both are brilliant feelings to have on a bike at any given time but both quite different....cheers ..Michael
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and the thing with torque and bhp isnt just how much you have, but where it is and how well its spread, in a standing start quarter mile sprint, i will take the engine with its power and torque at the bottom or middle of the rev range over the high power screamer with a knife edge power band every time. as someone raised on two strokes in the pre power valve (and other exhaust port closure devices were available) i daily experienced the razor sharp power delivery of a motor tuned only for max bhp, and whilst it was fun in short bursts (usually very short before it nipped) it got a bit wearing when you just needed to get to work in the rain. it aint what youve got, its where youve got it,,,,,,,,
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Refraining from commenting on clarkson, the basic equations of motion tell us that acceleration = force divided by mass. Torque is a measure of force applied at the road surface (if for example we have 50 ft-lbs applied through a wheel with radius 1 foot then there would be a force of 50 lb at the road); power is the rate at which that force is delivered. If an engine had an absolutely flat torque curve then power would increase linearly as the engine speed increased - if it was 50 bhp at 2,500 rpm it would be 100 bhp at 5,000 rpm. But of course internal combustion engines aren't quite like that.
Again, if we had a CV transmission (like the old DAF cars) we could set it so that it maintained the engine at its maximum torque figure and then we would get linear acceleration.
None of which answers the question of course, and all the above conspicuously fails to take into account aerodynamic and frictional drag....
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..... power is the rate at which that force is delivered. ....
None of which answers the question of course, ......
This bit answers the question. It is the main point I was hinting at.
To look at it from another angle, could we (dare to) say that you can ignore the engine torque and concentrate on the power available (I realise they're connected). With the correct use of ratios this one figure is pretty much all you need to know when comparing. How much power available to put to the road surface at any given road speed.
The beautiful thing about motorcycle engines in particular (because there is surely a more direct "connection" with the operator than in a car) is that this power comes in all sorts of sizes and varieties. Pretty much spoilt for choice these days.
Perfect example from my own experience. Zx6 and z1000, both gave near as dammit the same power, but one did it on 600cc the other on 1000cc. The zx6, which the press described as gutless, ridden back to back felt like it pulled stronger than the z1000. It was a lot lighter. Yet a look at the engine torque figures and it was obvious which had the higher figure.
It goes without saying that the character and feel you get will drastically change. A lot of people simply don't like the sensation of multi cylinder, higher rpm motors. Fair enough.
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Clarkson never did think much. "Torques" are just turning effort without a time factor. The glorious artworks of the Caterpillar Tractor Company have bags of torque but shockingly little horsepower. They don't need it. Dragsters, on the other hand have monstrous power but bugger-all torque.
I stopped watching Clarkson's show years ago because there awe enough ar**holes already; I don't need to sit in front of a TV watching them.
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I do have to agree with the Clarkeson comments, my cousin lives in the same village... and reckons its them & us, the brookes/clarkeson/Cameron set, and the locals... who hate the lot of them.
several years ago I tried to register a URL (website name) of 'jeremyclarkesonsaprat' ... strangely... it got turned down ;D