RE: Mark Hales on Technique: Shifting the weight about
Discussion
Gemaeden said:
Braking does just one major thing, it slows the wheels down. This has a number of effects.
It slows the speed of the contact patch of the tyre, so the tyre sidewalls distort by being stretched from their ''normal' profile as the rest of the mass of the car wants to continue at a higher speed. This is what is generally known as weight transfer.
This weight transfer means that when the car is steered the front tyre sidewalls are less stiff and therefore less able to transfer steering input to the contact patch.
This will inevitably result in understeer as the wheels now need to turn through a larger angle to change the direction of the contact patch
However, as the car is now slowed down, the tyres need to generate less cornering force to follow a certain radius corner than they would at the previously higher speed.
The increased cornering force that comes from lower speed exceeds the lowering of cornering force due to tyre distortion, so the car can corner on a tighter radius.
Weight transfer improving turn in is unfortunately a red herring in this article's explanation.
That being said, in the world of driver training, as long as the driver improves, their understanding doesn't have to be pedantically correct.
What separates highly skilled drivers such as Mark from me, and probably most of the rest of us on Pistonheads, is their ability to sense the difference between, and closeness to the limit of, the front and rear slip angles.
Tyres do not behave in a linear fashion. Weight transfer reducing understeer is most definitely not a red herring, but it can also increase oversteer... it depends on the load sensitive characteristics of the vehicle and especially the tyres. It slows the speed of the contact patch of the tyre, so the tyre sidewalls distort by being stretched from their ''normal' profile as the rest of the mass of the car wants to continue at a higher speed. This is what is generally known as weight transfer.
This weight transfer means that when the car is steered the front tyre sidewalls are less stiff and therefore less able to transfer steering input to the contact patch.
This will inevitably result in understeer as the wheels now need to turn through a larger angle to change the direction of the contact patch
However, as the car is now slowed down, the tyres need to generate less cornering force to follow a certain radius corner than they would at the previously higher speed.
The increased cornering force that comes from lower speed exceeds the lowering of cornering force due to tyre distortion, so the car can corner on a tighter radius.
Weight transfer improving turn in is unfortunately a red herring in this article's explanation.
That being said, in the world of driver training, as long as the driver improves, their understanding doesn't have to be pedantically correct.
What separates highly skilled drivers such as Mark from me, and probably most of the rest of us on Pistonheads, is their ability to sense the difference between, and closeness to the limit of, the front and rear slip angles.
Edited by Gemaeden on Saturday 15th July 17:49
griffgrog said:
I think you're getting questioned because your asserting that Mark's article about weight transfer improving turn is incorrect - or a red herring as you put it.
In racing, the effect of braking on cars like the Formula Ford referred to in the article has a dramatic effect on how the car changes direction. Even small amounts of braking and or acceleration can change the steering angle of the car. You have probably heard the phrase 'steering on the throttle'? Or perhaps - 'lift off oversteer'. What you're asserting is that both of these are due to tyre wall distortion and not weight transfer.
Braking during turn in, effectively rotating the car as the grip is at the front rather than the back is exactly how Caterham racers and many other cars without slicks and wings attack corners in their cars.
Whilst I'm sure your correct that tyre distortion due to weight transfer has some effect, it's unlikely to have anything like the difference that weight transfer has, especially in very light cars such as the ones mentioned in the article.
If Mark had written what I have, turning most peoples beliefs on their head, and I had suggested some of what he had written was a misunderstanding I'm sure most people would choose to believe Mark rather than me as he is well known race driver and instructor and therefore seen as authoritative.In racing, the effect of braking on cars like the Formula Ford referred to in the article has a dramatic effect on how the car changes direction. Even small amounts of braking and or acceleration can change the steering angle of the car. You have probably heard the phrase 'steering on the throttle'? Or perhaps - 'lift off oversteer'. What you're asserting is that both of these are due to tyre wall distortion and not weight transfer.
Braking during turn in, effectively rotating the car as the grip is at the front rather than the back is exactly how Caterham racers and many other cars without slicks and wings attack corners in their cars.
Whilst I'm sure your correct that tyre distortion due to weight transfer has some effect, it's unlikely to have anything like the difference that weight transfer has, especially in very light cars such as the ones mentioned in the article.
However, if I can bring some respected research from another authoritative source into my argument perhaps it might help people to understand where I am coming from.
Here is data extracted from Milliken and Milliken's "Race Car Vehicle Dynamics"
Vertical load(lbf) 900 Fy/Fz max 1.10 Slip Angle degrees 5.6
Vertical load(lbf) 1350 Fy/Fz max 1.08 Slip Angle degrees 6.0
Vertical load(lbf) 1800 Fy/Fz max 0.97 Slip Angle degrees 6.7
Basically Fy/Fz indicates that the load sensitivity (of most real tires in their typical operating range) is such that the coefficient of friction decreases as the vertical load, Fz, increases. i.e. forward weight transfer reduces grip, not only that but the amount of steering input required to generate the maximum lateral force increases.
Of course we are probably all aware how braking during turn in has a dramatic effect on how the car changes direction. But that is due to a car's turn radius being proportional to the square of its speed.
Let's take the instance where you are cornering at 1g at 72.5 mph. Your turn radius is about 108.6 metres. Decrease the speed to 70 mph and the radius decreases to 101.2 metres. That's over 24 feet tighter for a decrease of 2.5 mph. Increase it by the same 2.5 mph to 75 mph and it goes a bit further the other way to 116.2 metres.
You refer to "Steering on the throttle". What happens when we do this is that that acceleration in a rear wheel drive car causes the rear tyre sidewalls to deform due to weight transfer. This sidewall deformation then allows the chassis to move laterally toward the outside of the corner at the rear relative to the contact patch. At the same time weight transfer off of the front tyres causes their sidewalls to stiffen, resulting in a smaller slip angle between wheel and tyre contact patch. If the steering is held constant, these combine to be experienced as an increase in yaw or improved turn in.
"Lift off oversteer" occurs because as the driver lifts off the throttle the car slows down. Physics once again takes over and the car starts following a tighter radius. It could just as well be titled "Slow driver steering reaction to speed reduction"
If having more weight transferred to the front improved turn in I'm sure some smart designer would have incorporated a dumb-bell shaped fuel tank along the length of the car, which would allow weight transfer of the fuel load to the front under braking, and shift it rearwards under acceleration.
This doesn't mean that I believe what Mark is teaching people to do is incorrect, far from it. The proof of the success of his instruction in increasing peoples corner speeds is myriad. My point was simply some detail about the reasons for his technique being useful.
Gemaeden said:
If Mark had written what I have, turning most peoples beliefs on their head, and I had suggested some of what he had written was a misunderstanding I'm sure most people would choose to believe Mark rather than me as he is well known race driver and instructor and therefore seen as authoritative.
However, if I can bring some respected research from another authoritative source into my argument perhaps it might help people to understand where I am coming from.
Here is data extracted from Milliken and Milliken's "Race Car Vehicle Dynamics"
Vertical load(lbf) 900 Fy/Fz max 1.10 Slip Angle degrees 5.6
Vertical load(lbf) 1350 Fy/Fz max 1.08 Slip Angle degrees 6.0
Vertical load(lbf) 1800 Fy/Fz max 0.97 Slip Angle degrees 6.7
Basically Fy/Fz indicates that the load sensitivity (of most real tires in their typical operating range) is such that the coefficient of friction decreases as the vertical load, Fz, increases. i.e. forward weight transfer reduces grip, not only that but the amount of steering input required to generate the maximum lateral force increases.
Of course we are probably all aware how braking during turn in has a dramatic effect on how the car changes direction. But that is due to a car's turn radius being proportional to the square of its speed.
Let's take the instance where you are cornering at 1g at 72.5 mph. Your turn radius is about 108.6 metres. Decrease the speed to 70 mph and the radius decreases to 101.2 metres. That's over 24 feet tighter for a decrease of 2.5 mph. Increase it by the same 2.5 mph to 75 mph and it goes a bit further the other way to 116.2 metres.
You refer to "Steering on the throttle". What happens when we do this is that that acceleration in a rear wheel drive car causes the rear tyre sidewalls to deform due to weight transfer. This sidewall deformation then allows the chassis to move laterally toward the outside of the corner at the rear relative to the contact patch. At the same time weight transfer off of the front tyres causes their sidewalls to stiffen, resulting in a smaller slip angle between wheel and tyre contact patch. If the steering is held constant, these combine to be experienced as an increase in yaw or improved turn in.
"Lift off oversteer" occurs because as the driver lifts off the throttle the car slows down. Physics once again takes over and the car starts following a tighter radius. It could just as well be titled "Slow driver steering reaction to speed reduction"
If having more weight transferred to the front improved turn in I'm sure some smart designer would have incorporated a dumb-bell shaped fuel tank along the length of the car, which would allow weight transfer of the fuel load to the front under braking, and shift it rearwards under acceleration.
This doesn't mean that I believe what Mark is teaching people to do is incorrect, far from it. The proof of the success of his instruction in increasing peoples corner speeds is myriad. My point was simply some detail about the reasons for his technique being useful.
very strange couple of posts. to say the least. i think you're teasing.However, if I can bring some respected research from another authoritative source into my argument perhaps it might help people to understand where I am coming from.
Here is data extracted from Milliken and Milliken's "Race Car Vehicle Dynamics"
Vertical load(lbf) 900 Fy/Fz max 1.10 Slip Angle degrees 5.6
Vertical load(lbf) 1350 Fy/Fz max 1.08 Slip Angle degrees 6.0
Vertical load(lbf) 1800 Fy/Fz max 0.97 Slip Angle degrees 6.7
Basically Fy/Fz indicates that the load sensitivity (of most real tires in their typical operating range) is such that the coefficient of friction decreases as the vertical load, Fz, increases. i.e. forward weight transfer reduces grip, not only that but the amount of steering input required to generate the maximum lateral force increases.
Of course we are probably all aware how braking during turn in has a dramatic effect on how the car changes direction. But that is due to a car's turn radius being proportional to the square of its speed.
Let's take the instance where you are cornering at 1g at 72.5 mph. Your turn radius is about 108.6 metres. Decrease the speed to 70 mph and the radius decreases to 101.2 metres. That's over 24 feet tighter for a decrease of 2.5 mph. Increase it by the same 2.5 mph to 75 mph and it goes a bit further the other way to 116.2 metres.
You refer to "Steering on the throttle". What happens when we do this is that that acceleration in a rear wheel drive car causes the rear tyre sidewalls to deform due to weight transfer. This sidewall deformation then allows the chassis to move laterally toward the outside of the corner at the rear relative to the contact patch. At the same time weight transfer off of the front tyres causes their sidewalls to stiffen, resulting in a smaller slip angle between wheel and tyre contact patch. If the steering is held constant, these combine to be experienced as an increase in yaw or improved turn in.
"Lift off oversteer" occurs because as the driver lifts off the throttle the car slows down. Physics once again takes over and the car starts following a tighter radius. It could just as well be titled "Slow driver steering reaction to speed reduction"
If having more weight transferred to the front improved turn in I'm sure some smart designer would have incorporated a dumb-bell shaped fuel tank along the length of the car, which would allow weight transfer of the fuel load to the front under braking, and shift it rearwards under acceleration.
This doesn't mean that I believe what Mark is teaching people to do is incorrect, far from it. The proof of the success of his instruction in increasing peoples corner speeds is myriad. My point was simply some detail about the reasons for his technique being useful.
Anyway. I won't engage in the physics, not my forte and others will be along no doubt. However, i will ask where are Ff and N in your formulae?
If you load up the front the friction coef may decrease but your friction force will increase. that's useful as you now asking the front tyres to do 2 things, the rears less.
As for a the dumb-bell fuel tank, well that's got a couple of obvious flaws that lead me to think you're trolling again.
Nice try, better quality than most around here.
Thanks, I enjoyed this article and look forward to more.
It's a shame that any attempt to discuss physics on a forum brings out the quacks, but I hope that doesn't put PH off bringing us this sort of in-depth expert writing - thanks!
It's a shame that any attempt to discuss physics on a forum brings out the quacks, but I hope that doesn't put PH off bringing us this sort of in-depth expert writing - thanks!
simonrockman said:
Videos too please.
http://www.markhales.com/publications/howtodrive.htmlGemaeden said:
griffgrog said:
I think you're getting questioned because your asserting that Mark's article about weight transfer improving turn is incorrect - or a red herring as you put it.
In racing, the effect of braking on cars like the Formula Ford referred to in the article has a dramatic effect on how the car changes direction. Even small amounts of braking and or acceleration can change the steering angle of the car. You have probably heard the phrase 'steering on the throttle'? Or perhaps - 'lift off oversteer'. What you're asserting is that both of these are due to tyre wall distortion and not weight transfer.
Braking during turn in, effectively rotating the car as the grip is at the front rather than the back is exactly how Caterham racers and many other cars without slicks and wings attack corners in their cars.
Whilst I'm sure your correct that tyre distortion due to weight transfer has some effect, it's unlikely to have anything like the difference that weight transfer has, especially in very light cars such as the ones mentioned in the article.
If Mark had written what I have, turning most peoples beliefs on their head, and I had suggested some of what he had written was a misunderstanding I'm sure most people would choose to believe Mark rather than me as he is well known race driver and instructor and therefore seen as authoritative.In racing, the effect of braking on cars like the Formula Ford referred to in the article has a dramatic effect on how the car changes direction. Even small amounts of braking and or acceleration can change the steering angle of the car. You have probably heard the phrase 'steering on the throttle'? Or perhaps - 'lift off oversteer'. What you're asserting is that both of these are due to tyre wall distortion and not weight transfer.
Braking during turn in, effectively rotating the car as the grip is at the front rather than the back is exactly how Caterham racers and many other cars without slicks and wings attack corners in their cars.
Whilst I'm sure your correct that tyre distortion due to weight transfer has some effect, it's unlikely to have anything like the difference that weight transfer has, especially in very light cars such as the ones mentioned in the article.
However, if I can bring some respected research from another authoritative source into my argument perhaps it might help people to understand where I am coming from.
Here is data extracted from Milliken and Milliken's "Race Car Vehicle Dynamics"
Vertical load(lbf) 900 Fy/Fz max 1.10 Slip Angle degrees 5.6
Vertical load(lbf) 1350 Fy/Fz max 1.08 Slip Angle degrees 6.0
Vertical load(lbf) 1800 Fy/Fz max 0.97 Slip Angle degrees 6.7
Basically Fy/Fz indicates that the load sensitivity (of most real tires in their typical operating range) is such that the coefficient of friction decreases as the vertical load, Fz, increases. i.e. forward weight transfer reduces grip, not only that but the amount of steering input required to generate the maximum lateral force increases.
Of course we are probably all aware how braking during turn in has a dramatic effect on how the car changes direction. But that is due to a car's turn radius being proportional to the square of its speed.
Let's take the instance where you are cornering at 1g at 72.5 mph. Your turn radius is about 108.6 metres. Decrease the speed to 70 mph and the radius decreases to 101.2 metres. That's over 24 feet tighter for a decrease of 2.5 mph. Increase it by the same 2.5 mph to 75 mph and it goes a bit further the other way to 116.2 metres.
You refer to "Steering on the throttle". What happens when we do this is that that acceleration in a rear wheel drive car causes the rear tyre sidewalls to deform due to weight transfer. This sidewall deformation then allows the chassis to move laterally toward the outside of the corner at the rear relative to the contact patch. At the same time weight transfer off of the front tyres causes their sidewalls to stiffen, resulting in a smaller slip angle between wheel and tyre contact patch. If the steering is held constant, these combine to be experienced as an increase in yaw or improved turn in.
"Lift off oversteer" occurs because as the driver lifts off the throttle the car slows down. Physics once again takes over and the car starts following a tighter radius. It could just as well be titled "Slow driver steering reaction to speed reduction"
If having more weight transferred to the front improved turn in I'm sure some smart designer would have incorporated a dumb-bell shaped fuel tank along the length of the car, which would allow weight transfer of the fuel load to the front under braking, and shift it rearwards under acceleration.
This doesn't mean that I believe what Mark is teaching people to do is incorrect, far from it. The proof of the success of his instruction in increasing peoples corner speeds is myriad. My point was simply some detail about the reasons for his technique being useful.
Gemaeden said:
If Mark had written what I have, turning most peoples beliefs on their head, and I had suggested some of what he had written was a misunderstanding I'm sure most people would choose to believe Mark rather than me as he is well known race driver and instructor and therefore seen as authoritative.
However, if I can bring some respected research from another authoritative source into my argument perhaps it might help people to understand where I am coming from.
Here is data extracted from Milliken and Milliken's "Race Car Vehicle Dynamics"
Vertical load(lbf) 900 Fy/Fz max 1.10 Slip Angle degrees 5.6
Vertical load(lbf) 1350 Fy/Fz max 1.08 Slip Angle degrees 6.0
Vertical load(lbf) 1800 Fy/Fz max 0.97 Slip Angle degrees 6.7
Basically Fy/Fz indicates that the load sensitivity (of most real tires in their typical operating range) is such that the coefficient of friction decreases as the vertical load, Fz, increases. i.e. forward weight transfer reduces grip, not only that but the amount of steering input required to generate the maximum lateral force increases.
Of course we are probably all aware how braking during turn in has a dramatic effect on how the car changes direction. But that is due to a car's turn radius being proportional to the square of its speed.
Let's take the instance where you are cornering at 1g at 72.5 mph. Your turn radius is about 108.6 metres. Decrease the speed to 70 mph and the radius decreases to 101.2 metres. That's over 24 feet tighter for a decrease of 2.5 mph. Increase it by the same 2.5 mph to 75 mph and it goes a bit further the other way to 116.2 metres.
You refer to "Steering on the throttle". What happens when we do this is that that acceleration in a rear wheel drive car causes the rear tyre sidewalls to deform due to weight transfer. This sidewall deformation then allows the chassis to move laterally toward the outside of the corner at the rear relative to the contact patch. At the same time weight transfer off of the front tyres causes their sidewalls to stiffen, resulting in a smaller slip angle between wheel and tyre contact patch. If the steering is held constant, these combine to be experienced as an increase in yaw or improved turn in.
"Lift off oversteer" occurs because as the driver lifts off the throttle the car slows down. Physics once again takes over and the car starts following a tighter radius. It could just as well be titled "Slow driver steering reaction to speed reduction"
If having more weight transferred to the front improved turn in I'm sure some smart designer would have incorporated a dumb-bell shaped fuel tank along the length of the car, which would allow weight transfer of the fuel load to the front under braking, and shift it rearwards under acceleration.
This doesn't mean that I believe what Mark is teaching people to do is incorrect, far from it. The proof of the success of his instruction in increasing peoples corner speeds is myriad. My point was simply some detail about the reasons for his technique being useful.
There's always one, and you're being 'ridiculed' because it's a load of nonsense and selective 'facts' to support a weakly reasoned belief that weight transfer is nonsense. Usually from someone who can't separate weight (which is a colloquial shorthand really), and mass. If everyone thinks you're talking nonsense, there are two possibilities - maybe it really *IS* a conspiracy, or just maybe you're the one that's missing the point However, if I can bring some respected research from another authoritative source into my argument perhaps it might help people to understand where I am coming from.
Here is data extracted from Milliken and Milliken's "Race Car Vehicle Dynamics"
Vertical load(lbf) 900 Fy/Fz max 1.10 Slip Angle degrees 5.6
Vertical load(lbf) 1350 Fy/Fz max 1.08 Slip Angle degrees 6.0
Vertical load(lbf) 1800 Fy/Fz max 0.97 Slip Angle degrees 6.7
Basically Fy/Fz indicates that the load sensitivity (of most real tires in their typical operating range) is such that the coefficient of friction decreases as the vertical load, Fz, increases. i.e. forward weight transfer reduces grip, not only that but the amount of steering input required to generate the maximum lateral force increases.
Of course we are probably all aware how braking during turn in has a dramatic effect on how the car changes direction. But that is due to a car's turn radius being proportional to the square of its speed.
Let's take the instance where you are cornering at 1g at 72.5 mph. Your turn radius is about 108.6 metres. Decrease the speed to 70 mph and the radius decreases to 101.2 metres. That's over 24 feet tighter for a decrease of 2.5 mph. Increase it by the same 2.5 mph to 75 mph and it goes a bit further the other way to 116.2 metres.
You refer to "Steering on the throttle". What happens when we do this is that that acceleration in a rear wheel drive car causes the rear tyre sidewalls to deform due to weight transfer. This sidewall deformation then allows the chassis to move laterally toward the outside of the corner at the rear relative to the contact patch. At the same time weight transfer off of the front tyres causes their sidewalls to stiffen, resulting in a smaller slip angle between wheel and tyre contact patch. If the steering is held constant, these combine to be experienced as an increase in yaw or improved turn in.
"Lift off oversteer" occurs because as the driver lifts off the throttle the car slows down. Physics once again takes over and the car starts following a tighter radius. It could just as well be titled "Slow driver steering reaction to speed reduction"
If having more weight transferred to the front improved turn in I'm sure some smart designer would have incorporated a dumb-bell shaped fuel tank along the length of the car, which would allow weight transfer of the fuel load to the front under braking, and shift it rearwards under acceleration.
This doesn't mean that I believe what Mark is teaching people to do is incorrect, far from it. The proof of the success of his instruction in increasing peoples corner speeds is myriad. My point was simply some detail about the reasons for his technique being useful.
I would say however that 'weight' is a bad term in this case really - it's a shorthand for the acceleration of a mass, usually due to gravity, but in this case the mass does not have any significant movement relative to the frame of reference (the vehicle). Download is probably a better term - what matters is moving the download, or more particularly redistributing the 'weight' of the vehicle, which always must total mass x accel due to gravity in order to keep it from flying or sinking through the floor. Extreme example - a motorbike braking so hard the rear wheel is lifting... If it weighs 250kg, then all 250kg is on the front, and 0 on the back - 100% 'weight' transfer.
So...
sure - the increase in grip with download is not linear, so the coefficient of friction lowers. *GRIP* however is mu*R - coef of friction times reaction force (aka download). Front grip does not reduce - It's still outweighed (sorry
) by the increase in download. .97 with 1800 download is more grip than 1.1 and 900, even allowing for a partial and context-free quote from miliken.Your moving fuel tank demostrates entirely that you've not grasped the difference between mass and download ('weight'). The shaped fuel tank would transfer mass. That would not help at all, the increased download so gained would also mean an increased force requirement from the front tyres (Force = mass x acceleration bites..)
Because deceleration is in the ground plane, and the cog is somewhat above the ground plane, the longtitudinal couple has to be resisted by the front tyres via increased reaction. mu*R gives you more grip (even if mu decreases slightly), while the mass stays precisely where it is (baring a tiny amount of dive and roll which is mostly insignificant). Meantime the reverse happens at the rear.
Also, if you think lift off oversteer is just tightening due to slowing you've obviously not stepped off the throttle mid corner on the limit - I can promise it is a lot more dynamic and dramatic than that.. The rest of the deflection and blah is second order at best..
Me too - an excellent magazine.QBee said:
I had a memorable instruction session from Mark in my TVR a few weeks ago around Blyton Park.
I asked him to teach me to get out of corners faster, and he taught me where to look.
And I came out of the corners faster and on the right line.
Never a murmer of complaint from him, as this inexpert threw the car around at speed while trying to follow his instructions.
Top man, and this is a most interesting read.
Same here in my Cerbera, and also at Blyton! Yes, he has a fantastic poker face when others would be yelling either fury or terror.I asked him to teach me to get out of corners faster, and he taught me where to look.
And I came out of the corners faster and on the right line.
Never a murmer of complaint from him, as this inexpert threw the car around at speed while trying to follow his instructions.
Top man, and this is a most interesting read.
upsidedownmark said:
There's always one, and you're being 'ridiculed' because it's a load of nonsense and selective 'facts' to support a weakly reasoned belief that weight transfer is nonsense. Usually from someone who can't separate weight (which is a colloquial shorthand really), and mass. If everyone thinks you're talking nonsense, there are two possibilities - maybe it really *IS* a conspiracy, or just maybe you're the one that's missing the point
I would say however that 'weight' is a bad term in this case really - it's a shorthand for the acceleration of a mass, usually due to gravity, but in this case the mass does not have any significant movement relative to the frame of reference (the vehicle). Download is probably a better term - what matters is moving the download, or more particularly redistributing the 'weight' of the vehicle, which always must total mass x accel due to gravity in order to keep it from flying or sinking through the floor. Extreme example - a motorbike braking so hard the rear wheel is lifting... If it weighs 250kg, then all 250kg is on the front, and 0 on the back - 100% 'weight' transfer.
So...
sure - the increase in grip with download is not linear, so the coefficient of friction lowers. *GRIP* however is mu*R - coef of friction times reaction force (aka download). Front grip does not reduce - It's still outweighed (sorry ) by the increase in download. .97 with 1800 download is more grip than 1.1 and 900, even allowing for a partial and context-free quote from miliken.
Your moving fuel tank demostrates entirely that you've not grasped the difference between mass and download ('weight'). The shaped fuel tank would transfer mass. That would not help at all, the increased download so gained would also mean an increased force requirement from the front tyres (Force = mass x acceleration bites..)
Because deceleration is in the ground plane, and the cog is somewhat above the ground plane, the longtitudinal couple has to be resisted by the front tyres via increased reaction. mu*R gives you more grip (even if mu decreases slightly), while the mass stays precisely where it is (baring a tiny amount of dive and roll which is mostly insignificant). Meantime the reverse happens at the rear.
Also, if you think lift off oversteer is just tightening due to slowing you've obviously not stepped off the throttle mid corner on the limit - I can promise it is a lot more dynamic and dramatic than that.. The rest of the deflection and blah is second order at best..
Good post, and good article PH - look forward to the next one. I would say however that 'weight' is a bad term in this case really - it's a shorthand for the acceleration of a mass, usually due to gravity, but in this case the mass does not have any significant movement relative to the frame of reference (the vehicle). Download is probably a better term - what matters is moving the download, or more particularly redistributing the 'weight' of the vehicle, which always must total mass x accel due to gravity in order to keep it from flying or sinking through the floor. Extreme example - a motorbike braking so hard the rear wheel is lifting... If it weighs 250kg, then all 250kg is on the front, and 0 on the back - 100% 'weight' transfer.
So...
sure - the increase in grip with download is not linear, so the coefficient of friction lowers. *GRIP* however is mu*R - coef of friction times reaction force (aka download). Front grip does not reduce - It's still outweighed (sorry
) by the increase in download. .97 with 1800 download is more grip than 1.1 and 900, even allowing for a partial and context-free quote from miliken.Your moving fuel tank demostrates entirely that you've not grasped the difference between mass and download ('weight'). The shaped fuel tank would transfer mass. That would not help at all, the increased download so gained would also mean an increased force requirement from the front tyres (Force = mass x acceleration bites..)
Because deceleration is in the ground plane, and the cog is somewhat above the ground plane, the longtitudinal couple has to be resisted by the front tyres via increased reaction. mu*R gives you more grip (even if mu decreases slightly), while the mass stays precisely where it is (baring a tiny amount of dive and roll which is mostly insignificant). Meantime the reverse happens at the rear.
Also, if you think lift off oversteer is just tightening due to slowing you've obviously not stepped off the throttle mid corner on the limit - I can promise it is a lot more dynamic and dramatic than that.. The rest of the deflection and blah is second order at best..
Debaser said:
I think a post got deleted - I'm sure there were a couple of good and reasonably long posts above mine but I can only see one now.
That was my post, sorry. I love explaining physics, but sadly I hate getting into online arguments and what I wrote disagreed with the poster earlier (cause he was wrong!). The best way to ensure an argument didn't ensue was to delete my post.Gassing Station | General Gassing | Top of Page | What's New | My Stuff