Discussion
nickpage said:
shame its so goddam ugly.
Broken record - It's not ugly. I think it looks good in the metal - bold and purposeful. It's obviously not gorgeous like a DB9 but that's not what it's about. BMWs were never meant to be overtly pretty. At least it doesn't look like the new XK Jag, which looks a bit limp and effeminate.
>> Edited by Top Trump on Thursday 18th May 10:11
I don't mind it actually, the whole thing grows on you. Yes there are better angles I guess, although the back is what most people see, albeit momentarily
Interesting article in Autocar pitching the M6 against the new GT3
. Wouldn't have said that was it's main competition to be honest.
As to the bike nonsense I think we have done that one to death. Mind you quoting power to weight ratios is a little over simplistic. The contact patch on the M6 is many times that of a bike. Weight actually offers advantages, particularly when putting the power down. Anyone tried slamming open the throttle on a Gixer Thou!!
And in the twisties bikes just get in the way!!
Interesting article in Autocar pitching the M6 against the new GT3
. Wouldn't have said that was it's main competition to be honest. As to the bike nonsense I think we have done that one to death. Mind you quoting power to weight ratios is a little over simplistic. The contact patch on the M6 is many times that of a bike. Weight actually offers advantages, particularly when putting the power down. Anyone tried slamming open the throttle on a Gixer Thou!!
And in the twisties bikes just get in the way!!
Laingy said:
You cannot deny the back end of the M6 is very ugly.
Okay, It's not the best and there are much nicer rears around, but so what? At least it's a bit different and distinctive. Personally, I'm not too concerned if a car isn't the prettiest around as I'm more intereseted in the complete package. I'd have the M6 (in black) over an AMG Merc SL, or AMV8, no doubt.
hunttheshunt said:
I don't mind it actually, the whole thing grows on you. Yes there are better angles I guess, although the back is what most people see, albeit momentarily
Interesting article in Autocar pitching the M6 against the new GT3
As to the bike nonsense I think we have done that one to death. Mind you quoting power to weight ratios is a little over simplistic. The contact patch on the M6 is many times that of a bike. Weight actually offers advantages, particularly when putting the power down. Anyone tried slamming open the throttle on a Gixer Thou!!
And in the twisties bikes just get in the way!!
Well, my response was aimed at this comment
"Perhaps not 0-60, but on a straight at 30mph the bike might be in a bit of trouble when the M6 deploys five hundred horsepower."
In a roll-on comparison, the bikes quoted will demolish anything short of an F1 car because the getting the power down whilst moving is much easier from 30mph. From 0-60, it would be less of a difference. My ZX12R will do 90mph in 1st gear to the red line, so to 60 I'd only be using 2/3 of the potential, with NO gear changes. So whether using DMG/SMG or whatever wouldn't help.
Also, the "five hundred horsepower" of the M6 will be about 400bhp at the wheels (so that makes it about 233bhp/tonne). The bikes are putting out more than double the equivalent torque than the M6 when taking weight into account. The drivetrain losses on a bike are much less due to much less drive train inertia losses which will extend the power/weight ratio even further.
silver993tt said:
Also, the "five hundred horsepower" of the M6 will be about 400bhp at the wheels (so that makes it about 233bhp/tonne). The bikes are putting out more than double the equivalent torque than the M6 when taking weight into account. The drivetrain losses on a bike are much less due to much less drive train inertia losses which will extend the power/weight ratio even further.
Yeah, yeah, bikes versus cars, blah blah.
Horses for courses. A quick bike is a quick bike and even the most high performance cars are pushed to keep up with them, fair enough. I'm sure this has been done to death before now. Just think of all the additional things that can be done in a car that you can't do on a bike - such as stay warm and dry.
I think the suggestion that the M6 loses 100bhp between the flywheel and the rear wheels is a bit OTT. I don't think a car that well engineered would lose a fifth of it's power just like that.
Darth Dave said:
I think the suggestion that the M6 loses 100bhp between the flywheel and the rear wheels is a bit OTT. I don't think a car that well engineered would lose a fifth of it's power just like that.
That's about par for the course with with 2WD engine at the driven end (i.e. 911s and any front wheel drie car) being the most efficient to 4WD cars being least efficient. Generally speaking. IIRC that's a range of between 17 and 25% power lost through the transmission.
Hunts is correct, I have done, I had and still own one of the fastest road bikes in the country, not just in a straight line but also round the twisties. Magazine after magazine reveiws, then the Noble, what abit of kit, used to go hunting (regularly) when bored for anything including bikes, up to 900cc were anilated on bends or straights as they couldn't lay down the power. Obviously if the rider was Chris Walker etc this could change. Hunts is saying yes the car is beautiful. I dismissed the M6 at first because of the showroom cars colour (no I'm not racist). When I saw MY M6 - the style, the performance ! Okay it cant match the Noble for performance or handling but it's more than capable of despatching most vehiches to dust. This car is comfortable, fast, flexible, stylish and still doesn't have the niggling problems of owning a high bred road car which is limited to certain tasks. The M6/M5 is a car for every man - multi tasking. For now i love it. 
I imagine if BMW wanted to design a car to deal with EVO'S & WRX STI'S, then they would have made the M6 to a size and specification similar to them, and not called it an M6.
The fact that BMW made the M6 the way they did just shows that the Evo's & Scooby's were not their target car's 'to beat'.
I imagine also that BMW are well aware of the numerous very light & powerful sports cars that would have no trouble keeping up with it to 60mph or 100mph, but again they weren't the target cars.
The M6 v superbike debate is somewhat trickier to qualify. Yes, a big bike would stuff an M6 in a straight line, although the 4 very wide, grippy tyres of the M6 mean it would makethe bike work very hard for it's victories around the twisties.
But, in all honesty, what on earth is the point of comparing a big car with a big bike and then saying that the lightweight bike will always out accelerate a car? We can all work that out anyway.
In the same way that when your powerful car is lined up against a big truck at the lights, you can be pretty certain that the truck ain't going to exactly blow you into the weeds!
I've often wondered about the whole point of the fast car v big bike debate. I will say this though. When you've got your family with you, and it's lashing down with rain and cold outside, you can bet that most people will opt for being inside the car!
The M6, like most big German cars, will only ever really come into it's natural 'zone' at very high speeds, usually above 100mph. Then it all begins to make sense.
Why then design a car you can only enjoy at 3 figure speeds? Simple-it's German, and they're allowed to go that fast, so they have to make a car that feels 'right' at those elevated speeds.
The mere fact that it may feel a little 'dead' and 'ponderous' in the land of emperor Blair's silly speed limits is probably not of great relevance to the designers in Munich, because they know the car will sell on it's headline figures.
Or, to put it another way, which company is in a very strong financial position and announcing year-on-year sales and profits increases? Then ask yourself which other company, known for producing svelte, feline cars inspired by a certain predator of the big cat family and which are nicer to drive at slower speeds, is currently in financial uncertainty, has closed one of their historic factories, and is causing Boss Man America's second biggest car producer continual headaches as to what to do with them?
The M6 is a car designed to come alive above 100mph, preferably above 130mph. It is limited to a ridiculous 155mph when it is clearly capable of breaching the 200mph barrier. There will be some owners who buy this car purely to try and have the limiter removed, fit appropiate tyres, and then head out to the Autobahn an attempt to reach the speed that a small turboprop plane cruises at.
It's the headline figures that sell, and which cause the debate, as proved by all the comments on this forum topic..
All BMW have to do is sit back and watch the orders come rolling in, which they are.
Mind you, once this car hits the second-hand market in bigger numbers, it will be the performance bargain of the century.
Whilst 1710kg may sound heavy, when you have getting on for half the power of a Mk 1 Spitfire fighter under the bonnet, somehow the weight isn't going to hold that kind of power back for very long.
Also, consider this whilst we're on the subject of power-to-weight ratios. A 1 ton car with 300bhp has 300bhp per ton. The M6 weighs 1710kg and has 507bhp, or near-as-dammit 300bhp per ton.
Both have the same power-to-weight ratio, yet the 300bhp car will run out of steam around 160mph, whereas the 500bhp car will be storming ahead in full afterburner.
Yes, the 300bhp car may have a smaller frontal area and hence less drag, but the frontal area of the M6 won't be massively bigger. The reason is this-the car cabin design is largely dictated by the shape and size of the human body, so both cabin design frontal areas will not be hugely different to an extent that requires 200 extra bhp.
Back in the 80's, a typical 150bhp per ton hot hatchback would hit 60 in around 7 seconds, and go on to reach 130mph. A similar big executive car, also with 150bhp per ton, would also manage roughly 7 seconds to 60, yet go on to hit around 145mph.
Our assessment of these cars is clouded in Britain by our 70mph speed limit, so we'll never 'legally' get to explore what they're really capable of unless you're on a racetrack.
That's why small, light, powerful sports cars predominate in Britain, and huge, absolutely monstrously powerful, massively-engined cars dominate the German driving experience, because they can legally use them to their full extent, and probably look down with slight amusement at our 'quaint' little 70mph speed limit as they speed their way legally past 200mph on a public road.
Give it 5 years when it's dropped to around £20k and I'll have one in metallic charcoal grey please with black leather interior
Just wish they'd sort out that pathetically small fuel tank though-a 150 mile range is worse than useless on a big Grand Tourer. Every time you blast past that Ford Focus TDCi Diesel, you'd have to stop for more fuel, and watch it saunter past you nonchalantly.
What was that old fable about the Hare and the Tortoise...
The fact that BMW made the M6 the way they did just shows that the Evo's & Scooby's were not their target car's 'to beat'.
I imagine also that BMW are well aware of the numerous very light & powerful sports cars that would have no trouble keeping up with it to 60mph or 100mph, but again they weren't the target cars.
The M6 v superbike debate is somewhat trickier to qualify. Yes, a big bike would stuff an M6 in a straight line, although the 4 very wide, grippy tyres of the M6 mean it would makethe bike work very hard for it's victories around the twisties.
But, in all honesty, what on earth is the point of comparing a big car with a big bike and then saying that the lightweight bike will always out accelerate a car? We can all work that out anyway.
In the same way that when your powerful car is lined up against a big truck at the lights, you can be pretty certain that the truck ain't going to exactly blow you into the weeds!
I've often wondered about the whole point of the fast car v big bike debate. I will say this though. When you've got your family with you, and it's lashing down with rain and cold outside, you can bet that most people will opt for being inside the car!
The M6, like most big German cars, will only ever really come into it's natural 'zone' at very high speeds, usually above 100mph. Then it all begins to make sense.
Why then design a car you can only enjoy at 3 figure speeds? Simple-it's German, and they're allowed to go that fast, so they have to make a car that feels 'right' at those elevated speeds.
The mere fact that it may feel a little 'dead' and 'ponderous' in the land of emperor Blair's silly speed limits is probably not of great relevance to the designers in Munich, because they know the car will sell on it's headline figures.
Or, to put it another way, which company is in a very strong financial position and announcing year-on-year sales and profits increases? Then ask yourself which other company, known for producing svelte, feline cars inspired by a certain predator of the big cat family and which are nicer to drive at slower speeds, is currently in financial uncertainty, has closed one of their historic factories, and is causing Boss Man America's second biggest car producer continual headaches as to what to do with them?
The M6 is a car designed to come alive above 100mph, preferably above 130mph. It is limited to a ridiculous 155mph when it is clearly capable of breaching the 200mph barrier. There will be some owners who buy this car purely to try and have the limiter removed, fit appropiate tyres, and then head out to the Autobahn an attempt to reach the speed that a small turboprop plane cruises at.
It's the headline figures that sell, and which cause the debate, as proved by all the comments on this forum topic..
All BMW have to do is sit back and watch the orders come rolling in, which they are.
Mind you, once this car hits the second-hand market in bigger numbers, it will be the performance bargain of the century.
Whilst 1710kg may sound heavy, when you have getting on for half the power of a Mk 1 Spitfire fighter under the bonnet, somehow the weight isn't going to hold that kind of power back for very long.
Also, consider this whilst we're on the subject of power-to-weight ratios. A 1 ton car with 300bhp has 300bhp per ton. The M6 weighs 1710kg and has 507bhp, or near-as-dammit 300bhp per ton.
Both have the same power-to-weight ratio, yet the 300bhp car will run out of steam around 160mph, whereas the 500bhp car will be storming ahead in full afterburner.
Yes, the 300bhp car may have a smaller frontal area and hence less drag, but the frontal area of the M6 won't be massively bigger. The reason is this-the car cabin design is largely dictated by the shape and size of the human body, so both cabin design frontal areas will not be hugely different to an extent that requires 200 extra bhp.
Back in the 80's, a typical 150bhp per ton hot hatchback would hit 60 in around 7 seconds, and go on to reach 130mph. A similar big executive car, also with 150bhp per ton, would also manage roughly 7 seconds to 60, yet go on to hit around 145mph.
Our assessment of these cars is clouded in Britain by our 70mph speed limit, so we'll never 'legally' get to explore what they're really capable of unless you're on a racetrack.
That's why small, light, powerful sports cars predominate in Britain, and huge, absolutely monstrously powerful, massively-engined cars dominate the German driving experience, because they can legally use them to their full extent, and probably look down with slight amusement at our 'quaint' little 70mph speed limit as they speed their way legally past 200mph on a public road.
Give it 5 years when it's dropped to around £20k and I'll have one in metallic charcoal grey please with black leather interior
Just wish they'd sort out that pathetically small fuel tank though-a 150 mile range is worse than useless on a big Grand Tourer. Every time you blast past that Ford Focus TDCi Diesel, you'd have to stop for more fuel, and watch it saunter past you nonchalantly.
What was that old fable about the Hare and the Tortoise...
Another point now-it's been suggested that the M6 may lose around 100bhp in it's drivetrain.
I am struggling a bit to visualise that the M6's transmission losses at full speed will require the full power output of a typical 1.6 litre modern engine, just to turn the gearbox cogs, the propshaft, the final drive, driveshaft CV joints, rear wheel bearings and front wheel bearings?
Transmission power losses are caused by 'stiction' and drag on the bearings, and it is, strictly speaking, torque that is lost and absorbed by bearings and lubricant viscous drag, and not revs, as there is no mechanical slippage.
When the transmission has warmed up fully, which it will have done at 155mph, the lubricants will have thinned out with the heat generated, and will impose less drag than crawling around town slowly on a cold day with stone cold transmission/bearings, and lubricant the consistency of treacle.
100bhp is a hell of a lot of power. It equates to 76.4 kW of heat, as the viscous drag will generate heat. Now 76.4 kW is a huge amount of heat-if you sat in front of a 76.4 kW electric fire for any length of time, you'd be dead in pretty short order, or very badly melted and burnt at the very least.
It's a bit risky to generalise that around '25%' of engine power is lost in the transmission.
Here's the main reason, which I put forward through hard, maybe even cold 'Germanic'logic, rather than unproven speculation.
Manufacturers fit transmissions to cope with power outputs up to certain levels. Above that they fit a heavier-duty transmission with bigger bearings and heavier gear wheels etc. So transmissions are fitted into banded torque handling capacities depending on which engine is fitted.
Lets look at 2 examples, the old 12v BMW 520i (129bhp), and 12v 525i (170bhp) from the E34 range. These 2 'small' sixes shared a similar transmission type, with only the final drive ratio being different. Same wheel bearings, same CV joints, same gearbox, same propshaft and same final drive bearing sizes.
Overall then, same transmission losses. Yet if we use the '25%' theory, then the 520i would lose around 32bhp to drive the transmission, whereas the 525i would now mysteriously lose around 42bhp to drive exactly the same transmission!
So which figure is the correct one? The answer is, we won't know unless you put them on a dyno and measured it scientifically.
Now, to complicate matters even further, this particular transmission capacity was kept when the 24v six-pot E34's came out.
Now the 525i has 192bhp and so we should now be losing 48bhp through the same transmission that we previously calculated only required 32bhp to turn it!
I hope this illustrates the danger of speculative generalisation-which inevitably leads to 'pub talk' quotes.
What it also illustrates is that it's handy to know what torque capacity your transmission has, find out which models it's fitted to, and then select the biggest engine option for that particular transmission capacity, as you'll be losing propotionately less engine torque through the transmission than a car with a smaller engine and same transmission torque capacity.
If a particular transmission requires 25bhp overall to turn it, and you select the small 129bhp engine option, you're only left with 104bhp at the wheels. Select the 192bhp engine option and you're left with a rather more healthy 167bhp at the wheels.
If you then choose the 'biggest' engine option-say the 'bix six', this will have a heavy duty transmission with greater torque loss, so you need to select the biggest engine otion here as well for the same reasons.
It's also another reason why bigger engines don't always mean much poorer fuel consumption, as less of their greater power is being wasted in transmission losses etc.
I think we could really do with some proper dyno figures for the power required to drive a car transmission.
There's another complication too...
When an engine drives the transmission, the power loss in the transmission is not the same as if the engine were disconnected from the drive train and the rear wheels were driving the transmission.
This is due to the gear wheels being cut helically in both the gearbox and final drive, and thrust forces try to move the gears forwards and backwards up against the thrust washers, and the thrust forces are not the same in both directions.
When the engine drives the car the clutch is engaged with no power loss in the thrust bearing, but if you get a dyno to rotate the driven wheels, you have to de-clutch to disconnect the engine, and then the clutch thrust bearing absorbs some power, corrupting the result slightly.
To sum up-thorny, complex topic!
I am struggling a bit to visualise that the M6's transmission losses at full speed will require the full power output of a typical 1.6 litre modern engine, just to turn the gearbox cogs, the propshaft, the final drive, driveshaft CV joints, rear wheel bearings and front wheel bearings?
Transmission power losses are caused by 'stiction' and drag on the bearings, and it is, strictly speaking, torque that is lost and absorbed by bearings and lubricant viscous drag, and not revs, as there is no mechanical slippage.
When the transmission has warmed up fully, which it will have done at 155mph, the lubricants will have thinned out with the heat generated, and will impose less drag than crawling around town slowly on a cold day with stone cold transmission/bearings, and lubricant the consistency of treacle.
100bhp is a hell of a lot of power. It equates to 76.4 kW of heat, as the viscous drag will generate heat. Now 76.4 kW is a huge amount of heat-if you sat in front of a 76.4 kW electric fire for any length of time, you'd be dead in pretty short order, or very badly melted and burnt at the very least.
It's a bit risky to generalise that around '25%' of engine power is lost in the transmission.
Here's the main reason, which I put forward through hard, maybe even cold 'Germanic'logic, rather than unproven speculation.
Manufacturers fit transmissions to cope with power outputs up to certain levels. Above that they fit a heavier-duty transmission with bigger bearings and heavier gear wheels etc. So transmissions are fitted into banded torque handling capacities depending on which engine is fitted.
Lets look at 2 examples, the old 12v BMW 520i (129bhp), and 12v 525i (170bhp) from the E34 range. These 2 'small' sixes shared a similar transmission type, with only the final drive ratio being different. Same wheel bearings, same CV joints, same gearbox, same propshaft and same final drive bearing sizes.
Overall then, same transmission losses. Yet if we use the '25%' theory, then the 520i would lose around 32bhp to drive the transmission, whereas the 525i would now mysteriously lose around 42bhp to drive exactly the same transmission!
So which figure is the correct one? The answer is, we won't know unless you put them on a dyno and measured it scientifically.
Now, to complicate matters even further, this particular transmission capacity was kept when the 24v six-pot E34's came out.
Now the 525i has 192bhp and so we should now be losing 48bhp through the same transmission that we previously calculated only required 32bhp to turn it!
I hope this illustrates the danger of speculative generalisation-which inevitably leads to 'pub talk' quotes.
What it also illustrates is that it's handy to know what torque capacity your transmission has, find out which models it's fitted to, and then select the biggest engine option for that particular transmission capacity, as you'll be losing propotionately less engine torque through the transmission than a car with a smaller engine and same transmission torque capacity.
If a particular transmission requires 25bhp overall to turn it, and you select the small 129bhp engine option, you're only left with 104bhp at the wheels. Select the 192bhp engine option and you're left with a rather more healthy 167bhp at the wheels.
If you then choose the 'biggest' engine option-say the 'bix six', this will have a heavy duty transmission with greater torque loss, so you need to select the biggest engine otion here as well for the same reasons.
It's also another reason why bigger engines don't always mean much poorer fuel consumption, as less of their greater power is being wasted in transmission losses etc.
I think we could really do with some proper dyno figures for the power required to drive a car transmission.
There's another complication too...
When an engine drives the transmission, the power loss in the transmission is not the same as if the engine were disconnected from the drive train and the rear wheels were driving the transmission.
This is due to the gear wheels being cut helically in both the gearbox and final drive, and thrust forces try to move the gears forwards and backwards up against the thrust washers, and the thrust forces are not the same in both directions.
When the engine drives the car the clutch is engaged with no power loss in the thrust bearing, but if you get a dyno to rotate the driven wheels, you have to de-clutch to disconnect the engine, and then the clutch thrust bearing absorbs some power, corrupting the result slightly.
To sum up-thorny, complex topic!
hunttheshunt said:
Fantastic piece.....have you thought of doing a weekly technical spot on Top Gear.....most informative.
Indeed. Must be along the lines of the most in depth technical post I've read in ages.
Wonderful.
I figured something similar where the transmissions are involved but there's no way I could ever describe anything as technical as that or as eloquently.
Thanks guys-glad you found it useful I've always liked reading about anything technical, and don't subscribe to a policy of closing my mind to suggestions and opinions, as there's usually something of worth to be found in everyone's argument or point of view.
I read plenty of books, brochures, handbooks etc on BMW's and sifted out the useful nuggets of information, then sat down and thought it through logically.
When I thought about losing 100bhp in the M6's transmission, I sat down and thought about it, then tried to visualise what 100bhp is actually capable of doing.
If you think about it, 100bhp is more than capable of accelerating a 1200kg car plus occupants to 60 in around 12ish seconds, as well as overcoming it's own internal transmission losses, and going on to maintain this 1.2 ton car plus occupants at around 110mph maximum.
It therefore seemed just a bit strange that the M6's transmission should require as much power to just to drive it's cogs as that required to power a full-sized family car comfortably at over 100mph.
I suspect the real transmission loss is rather less than 100bhp, and lies somewhere in the 30-70 bhp bracket depending on the transmission operating temperature and current vehicle speed.
I read somewhere once that a person can develop around 0.5 to 1bhp under heavy physical exertion. If a car required100bhp to overcome transmission losses then you'd never be able to push it!
Theresanother angle you can look at it from too. In a typical conventional manual gearbox all the cogs are in constant mesh and all rotating at the same time, giving a certain amount of torque loss to drive all the cogs.
The propshaft, final drive, CV joints and wheel bearings will also require a certain amount of torque to overcome their viscous drag. This viscous drag increases with transmission speed, if you think about it. Try stirring treacle slowly, then see how hard it is to stir treacle much faster, if you want a practical analogy!
Since power is a mathematical product of force (torque) multiplied by speed (rpm), it therefore follows that transmission power loss must increase with transmission speed, and not in a linear manner either. Double the transmission speed, and you at least double the power loss due to straightforward mathematical doubling. Then add in the fact that the viscous drag torque loss increases with speed, and it can be seen that the transmission losses will increase at a rate greater than a linear increase, as the transmission speed rises.
Now, in 1st gear, the gearbox output shaft will be rotating slowly with large torque, and the rest of the transmission will be turning slowly with large torque available to move the car.
It will therefore, proportionately speaking, not absorb very much of the available torque going to the driving wheels, as it will be sapping a small driving torque from a massive available torque, due to low viscous drag at these low transmission speeds.
Now consider what happens in top gear. The gearbox output shaft will now be rotating very fast with a much smaller output torque. As the transmission is now rotating much faster, it will now be absorbing much more torque from a much smaller available torque, as it's imposed viscous drag torque loss is much greater at these higher speeds.
It therefore follows that the transmission will absorb a larger amount of the available power when you are in a high, or top, gear, at a very high road speed.
Conversely, when you accelerate hard from a standstill in a low gear with a low transmission speed, you will lose much, much less power in the transmission.
If a transmission did absorb 25% of the engine's power, then that would literally mean that the car would not physically move forward until the engine's throttle was opened to provide at least 25% of it's maximum power!
Now as all cars will trickle along quite happily on a closed throttle at idle, and can be pushed by a half-horsepower human being at a few mph, you really need to examine everything before making a sweeping generalisation about transmission losses.
It may well that a de-restricted M6, travelling at 200mph in 7th gear, will lose a fairly large chunk of power in the transmission, but I'm not sure it would amount to 100bhp-maybe 50-70 bhp at 200mph.
I can't imagine the efficiency-obsessed Germans allowing such a wasteful transmission to corrupt the free-revving fury of their manic V10
I've always liked reading about anything technical, and don't subscribe to a policy of closing my mind to suggestions and opinions, as there's usually something of worth to be found in everyone's argument or point of view. I read plenty of books, brochures, handbooks etc on BMW's and sifted out the useful nuggets of information, then sat down and thought it through logically.
When I thought about losing 100bhp in the M6's transmission, I sat down and thought about it, then tried to visualise what 100bhp is actually capable of doing.
If you think about it, 100bhp is more than capable of accelerating a 1200kg car plus occupants to 60 in around 12ish seconds, as well as overcoming it's own internal transmission losses, and going on to maintain this 1.2 ton car plus occupants at around 110mph maximum.
It therefore seemed just a bit strange that the M6's transmission should require as much power to just to drive it's cogs as that required to power a full-sized family car comfortably at over 100mph.
I suspect the real transmission loss is rather less than 100bhp, and lies somewhere in the 30-70 bhp bracket depending on the transmission operating temperature and current vehicle speed.
I read somewhere once that a person can develop around 0.5 to 1bhp under heavy physical exertion. If a car required100bhp to overcome transmission losses then you'd never be able to push it!
Theresanother angle you can look at it from too. In a typical conventional manual gearbox all the cogs are in constant mesh and all rotating at the same time, giving a certain amount of torque loss to drive all the cogs.
The propshaft, final drive, CV joints and wheel bearings will also require a certain amount of torque to overcome their viscous drag. This viscous drag increases with transmission speed, if you think about it. Try stirring treacle slowly, then see how hard it is to stir treacle much faster, if you want a practical analogy!
Since power is a mathematical product of force (torque) multiplied by speed (rpm), it therefore follows that transmission power loss must increase with transmission speed, and not in a linear manner either. Double the transmission speed, and you at least double the power loss due to straightforward mathematical doubling. Then add in the fact that the viscous drag torque loss increases with speed, and it can be seen that the transmission losses will increase at a rate greater than a linear increase, as the transmission speed rises.
Now, in 1st gear, the gearbox output shaft will be rotating slowly with large torque, and the rest of the transmission will be turning slowly with large torque available to move the car.
It will therefore, proportionately speaking, not absorb very much of the available torque going to the driving wheels, as it will be sapping a small driving torque from a massive available torque, due to low viscous drag at these low transmission speeds.
Now consider what happens in top gear. The gearbox output shaft will now be rotating very fast with a much smaller output torque. As the transmission is now rotating much faster, it will now be absorbing much more torque from a much smaller available torque, as it's imposed viscous drag torque loss is much greater at these higher speeds.
It therefore follows that the transmission will absorb a larger amount of the available power when you are in a high, or top, gear, at a very high road speed.
Conversely, when you accelerate hard from a standstill in a low gear with a low transmission speed, you will lose much, much less power in the transmission.
If a transmission did absorb 25% of the engine's power, then that would literally mean that the car would not physically move forward until the engine's throttle was opened to provide at least 25% of it's maximum power!
Now as all cars will trickle along quite happily on a closed throttle at idle, and can be pushed by a half-horsepower human being at a few mph, you really need to examine everything before making a sweeping generalisation about transmission losses.
It may well that a de-restricted M6, travelling at 200mph in 7th gear, will lose a fairly large chunk of power in the transmission, but I'm not sure it would amount to 100bhp-maybe 50-70 bhp at 200mph.
I can't imagine the efficiency-obsessed Germans allowing such a wasteful transmission to corrupt the free-revving fury of their manic V10
Just thought I'd add another comment to this topic. Now the M6 is a damn cool car, don't get me wrong (just see the first post) but all this nonsense about cars v bikes has got to stop. In terms of pure performance, a bike will leave any car for dead on a TRACK. On a twisty road, I'd put my money on a decent car. Oz magazine Motor put a Suzuki GSXR1000 up against a 996 Turbo S on a track in a fairly recent issue. The bike won, by the slimmest of margins, but then again, the bike was piloted by an average punter, while Motor chose professional race driver Warren Luff. On any track, the bike will absolutely monster a car in acceleration, and in tight S-bends that require quick flicks from lock to lock. Any other scenario, braking, sweepers, etc, a (good, eg Porsche) car will win, on account of it's higher grip and greater contact patch with the road (most bikes have a patch of rubber roughly the size of a mobile phone actually gripping the road at any one time). The only car I can think of that will actually beat a bike in a straight line is the Veyron. Now I'm sure someone will reply "but look at the power to weight ratio" (Veyron is 1001hp over 1890kg equals 529 hp/ tonne), but that's not the whole story. The Veyron has an infinitely greater amount of grip to actually put the power to use, which is why it still accelerates from 0-60 mph in 2.5 sec, roughly on par with a modern hyperbike. Also, I'd like to see any bike in the world (Y2K aside) that will beat a Veyron to 300km/h, because once that big thing is rolling, there's not much to stop it. So, in conclusion, grip (not forgetting the small matter of 920 lb/ft torque) make bike's power/weight pale into insignificance. And don't anybody compare a Veyron and a bike on price, I am well aware of that, actually, mentioning that, in the previously mentioned Motor magazine, it turned out the whole Suzuki cost $5 less than the Porsche's ceramic brakes (!!!). I believe the most important part is that while you bike owners may boast about power/weight and all that, let's see you not wish to be inside a warm, dry, heated interior of a car on a cold, cold winter's day
. Formula 1 hits Wales! well the sound of it. Just got back from a weekend from dragon country .What roads. Saturday was dry and sunny,started off in mid wales and now the car is run in ,started playing with the twiddly knobs. After bout 70 miles things were looking good,then they got better.Fell in the middle of 50 or so bikes ,most sports,some tourers.Now after last weeks posts i read ,i thought i,d put it to the test. Picked up speed a little ,few twisties ,
bikes still champing at the bit. Select 500 bhp max EDC,mixed with shell grip on all most every corner it was goodbye bikes,
To be able to brake on the corners ,lay the power down as i'm coming out of them they did not stand a chance.By the time they got round the corners i was 3/4 the way down the straight only to repeat this time after time.
The car was dialed to the road,plus being able to keep both hands on the tiller using the SMG box, it was ausome.Only after 15 miles of these roads i stopped at some works lights.
They finally caught me up only then to give the
up to an amazing car capable of more than just a grand tourer. Remember i have ridden for many years bikes and i know there was no way in hell to catch a good car on a good road.
Only when i stopped and Grining like a chesire cat did i look round to see a rather angry wife
bo**ocking me for not stopping at the chocolate factory we were meant to go to 20 miles in the other direction. It's all well and good people laying down power to weight ratois and performance figures,but in the real world or on this particular day seeing was beleaving. God i love this car.
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