Rich Posted August 31, 2009 Report Share Posted August 31, 2009 After talking to Iain (mcwrx) the other night about the advanced drivers day he had it got me thinking about this. His car is a Honda S2000, which as we know seems to be fussy in the geometry department, with I think the rear being the main problem? I watched a video of Iain driving the car or should that be spinning it around some of the corners, yet the instructor didn't! If it was going to break away he corrected it with no problems...he also said the car handled fine for him. So, could it be the geometry is actually ok, it's just that the average road driver doesn't know how to respond when it feels like the car will spin and take control. Discuss? Quote Link to comment Share on other sites More sharing options...
Tony Posted August 31, 2009 Report Share Posted August 31, 2009 Nice topic ER... If pursued this will be a nose bleed of a read for members ... Your question knocks on the door of the darkest area of chassis/ human calibration...we have... * Chassis indexing * Chassis frequency * Human frequency * Chassis calibration Where to start...... Quote Link to comment Share on other sites More sharing options...
hms Posted August 31, 2009 Report Share Posted August 31, 2009 The driver needs to understand the physics of whats happening around him/her, be able to detect it through various inputs, visual, audible, (I nearly put Aural, the passenger screaming!) tactile through the steering wheel and seat of the pants. They also need to know the reactions of the car to their inputs. (Weight shift etc.) Finally they need to be able to decide what is the correct course of action to take and have the speed of response to take that action. (I fail on both counts!) Your average Joe driver never takes their car to the limit, only finding it when they have exceeded it and they become a passenger. Your instructor with his skill and experience is tuned in to the car and can anticipate the response of the car by feeling the inputs the car is feeding him. Time, experience and training will give the majority of people improved handling skills, being able to read the car and respond correctly. A good driver should be able to get the best fron their car regardless of the geometry set up. The better the driver the more they will be able to get from the car, a poorer driver would be losing it all over the place. h Quote Link to comment Share on other sites More sharing options...
Rich Posted August 31, 2009 Author Report Share Posted August 31, 2009 Nice topic ER... If pursued this will be a nose bleed of a read for members ... Your question knocks on the door of the darkest area of chassis/ human calibration...we have...* Chassis indexing * Chassis frequency * Human frequency * Chassis calibration Where to start...... I will probably struggle to digest it but will give it a shot...it's an interesting subject. As for starting how about number 1 in your list...Chassis indexing, what do you mean by this? The driver needs to understand the physics of whats happening around him/her, be able to detect it through various inputs, visual, audible, (I nearly put Aural, the passenger screaming!) tactile through the steering wheel and seat of the pants. They also need to know the reactions of the car to their inputs. (Weight shift etc.)Finally they need to be able to decide what is the correct course of action to take and have the speed of response to take that action. (I fail on both counts!) Your average Joe driver never takes their car to the limit, only finding it when they have exceeded it and they become a passenger. Your instructor with his skill and experience is tuned in to the car and can anticipate the response of the car by feeling the inputs the car is feeding him. Time, experience and training will give the majority of people improved handling skills, being able to read the car and respond correctly. A good driver should be able to get the best fron their car regardless of the geometry set up. The better the driver the more they will be able to get from the car, a poorer driver would be losing it all over the place. h Good post...things like weight shift are one to look into. I know the majority of the public will not push their cars to the limits, but as you say if they do end up finding it, what's going to happen? I was driving round a roundabout last week (right hand turn). I was halfway around it and started to accelerate away when I felt the car was going to oversteer (turn more than it should?). The road was a little damp though but I also feel this could be down to how my camber/caster is setup. However, my point is that I could feel it was going to happen so I got off the throttle and let the car straighten up naturally. I'm not sure if this was the correct way of doing it but it worked for me and has in the past when the back end has swung out (crap tyres!)! I'm sure there would be some drivers who would try to accelerate out of it, try and stop by braking hard or steering the opposite way...would all of these make the problem worse? Quote Link to comment Share on other sites More sharing options...
Tony Posted August 31, 2009 Report Share Posted August 31, 2009 Dynamic indexing....... Sam@ TDi summed this up perfectly in a previous post... ............................. Option one would always be to shed some weight! having a DI soo far above 1.00 can really only be caused by a mis-match in wheelbase to the mass, basically the chassis has far too much yaw inertia for the short wheelbase to influence easily. If we could take just 10% weight out of our demo car we'd have a DI of 1.39, much better! Unfortunately to take 10% weight out we'd have to seriously comprimise the car's very comfortable characteristics so for some (most) people this would defeat the object. The other option is to simply accecpt that the car will as a result of it's high DI always make poor use of it's rear axle in terms of producing lateral acceleration and then to try to work around it. A good example would be the Mitsubishi Lancer Evo-5, it's actually a car with a DI of 1.35 so this would make it pretty vectra/modeo'ish to drive... But Mitsubishi's chassis dynamics team have cunningly swerved this potential marketing disaster by employing an overly pointy geometry and suspension sollution giving the car the ability to change direction light a housefly, then in order for the average joe customer to be able to control and exploit this very odd and naturally quite unbalanced set-up they've been forced to add an active yaw control system in the form of an electronically controlled torque biasing center diff. This solution works so well that not only is the car acceptable to it's intended market it's actually now considered as one of the worlds best handling cars. Quote Link to comment Share on other sites More sharing options...
Rich Posted August 31, 2009 Author Report Share Posted August 31, 2009 Going to read that a few times and digest it overnight! Quote Link to comment Share on other sites More sharing options...
hms Posted August 31, 2009 Report Share Posted August 31, 2009 Good post...things like weight shift are one to look into. I know the majority of the public will not push their cars to the limits, but as you say if they do end up finding it, what's going to happen? I was driving round a roundabout last week (right hand turn). I was halfway around it and started to accelerate away when I felt the car was going to oversteer (turn more than it should?). The road was a little damp though but I also feel this could be down to how my camber/caster is setup. However, my point is that I could feel it was going to happen so I got off the throttle and let the car straighten up naturally. I'm not sure if this was the correct way of doing it but it worked for me and has in the past when the back end has swung out (crap tyres!)! I'm sure there would be some drivers who would try to accelerate out of it, try and stop by braking hard or steering the opposite way...would all of these make the problem worse? Still learning about this stuff, and how to react when the back end goes. A novice driver might turn into the slide and slam on the anchors, throwing the weight forward off the rear wheels, increasing the slide. Wrong thing to do, but for a novice on a circuit it may be the best thing to do rather than power into a barrier. An experienced driver will turn into the slide and keep the power on, to keep the car balanced and use the steering to drive out of the slide. The reaction for the untrained driver is to slam the brakes on, learing not to do that is very difficult, and not a skill I have achieved! Will keep trying tho'! h Quote Link to comment Share on other sites More sharing options...
Sagitar Posted August 31, 2009 Report Share Posted August 31, 2009 Controlling an unstable vehicle requires actions at rates that are too high to respond to an intellectual approach. i.e. if you have to think about what to do, you are probably too late. At the action rates required, we are dependent largely upon reflexes. Reflexes are developed and maintained by practice (think about learning to ride a bicycle) and most of us simply do not get the practice. I can think of a few winters when there have been icy conditions for long enough to develop my "slippery conditions" skills to the point where I was driving really competently. Even an hour on a skid pan will make a big difference, but if we don't practice, we lose it. A simpler example would be the balancing of clutch and accelerator when starting off. We all do it without a moment's thought, but I'll bet there are few who did it naturally from the beginning when learning to drive. Similarly, those who get the chance to drive "on the limit" for significant periods of time develop control skills that most of us do not. Understanding the physics of what is happening may help us to recognise what we ought to do, but doing it quickly enough to really be in charge demands practice. It is a perverse truth that the improvements in vehicle stability resulting from clever engineering (and the introduction of speed limits?) actually make it less likely that most road users will develop and maintain the higher skills of vehicle control. As an old man, I am certainly not complaining about it, but I doubt if I am nearly as competent at vehicle control now as I was in the days when I drove the less sophisticated vehicles of 50 years ago. Quote Link to comment Share on other sites More sharing options...
tastyweat Posted September 2, 2009 Report Share Posted September 2, 2009 One small example of car vs. driver... I went to a gravel play-area near me the other day with a friend. In a Mazda MX5. Started showing him how to drift etc and he keeps spinning out when he tries! Same thing happened to him in the snow/ice in february, causing him to have an accident. I thought things felt a bit perculiar when in the car with him driving, so had a closer look at what he was doing. He was slamming on the brakes when the car started to slide, taking his foot off the accelerator completely (ie, not left foot braking). After a bit more instruction and very expressed "Don't touch the foot brake for what we're doing here!" (was just teaching him how to kick the back end out under power... no weight shift, not even handbrake)... plus a lecture on why to never slam on the brakes when you're sliding like that (we're both physicists, heh). Talked to him about it and got the response "was i?"... he didn't even realise he was touching the brake... he said he thought it must have been instictive. I really didn't understand lol... I've never had a problem like that, my instinct is to control the car (probably due to my racing experience... although I don't remember ever having a problem like that). I think it might also have something to do with the age you first get in a car or drive something with four wheels. He had never driven anything on 4 wheels until after his 17th birthday... I, on the other hand, started driving full size cars when I was 3 (steering or pedals, lol) and started karting when I was 6, progressing to gearbox karts further down the line, along with rallying etc etc. So his instinct is to do perhaps what he was tought by his driving instructor to pass his test and was never really given a chance to push the limit of grip... the person the op is mentioning might be similar? ... just an idea Quote Link to comment Share on other sites More sharing options...
CIH Posted September 2, 2009 Report Share Posted September 2, 2009 You're oversteer instincts are probably from your karting days Quote Link to comment Share on other sites More sharing options...
tastyweat Posted September 2, 2009 Report Share Posted September 2, 2009 You're oversteer instincts are probably from your karting days Don't you mean oversteer "control" instincts? hehe You're most likely correct... have to react a lot quicker in a kart than you do in a car... hence going in to a tyre wall from 109MPH once (thankfully it was multi-layered!) Was really pushing for a good lap time & by the time the front left locked up, it was too late to correct... oopsie! Quote Link to comment Share on other sites More sharing options...
Rich Posted September 2, 2009 Author Report Share Posted September 2, 2009 Dynamic indexing....... Sam@ TDi summed this up perfectly in a previous post................................ Option one would always be to shed some weight! having a DI soo far above 1.00 can really only be caused by a mis-match in wheelbase to the mass, basically the chassis has far too much yaw inertia for the short wheelbase to influence easily. If we could take just 10% weight out of our demo car we'd have a DI of 1.39, much better! Unfortunately to take 10% weight out we'd have to seriously comprimise the car's very comfortable characteristics so for some (most) people this would defeat the object. The other option is to simply accecpt that the car will as a result of it's high DI always make poor use of it's rear axle in terms of producing lateral acceleration and then to try to work around it. A good example would be the Mitsubishi Lancer Evo-5, it's actually a car with a DI of 1.35 so this would make it pretty vectra/modeo'ish to drive... But Mitsubishi's chassis dynamics team have cunningly swerved this potential marketing disaster by employing an overly pointy geometry and suspension sollution giving the car the ability to change direction light a housefly, then in order for the average joe customer to be able to control and exploit this very odd and naturally quite unbalanced set-up they've been forced to add an active yaw control system in the form of an electronically controlled torque biasing center diff. This solution works so well that not only is the car acceptable to it's intended market it's actually now considered as one of the worlds best handling cars. For anyone who has been reading my blog will know I've got the interior stripped out at the moment. Well want can I say, the difference it has made to the handling of the car as well as acceleration has surprised me! The car feels much more responsive now. I've always been confused with what yaw inertia means, done some 'googling' and I found this...Yaw inertia is a measure of how far weight is from the centre of gravity...do you agree with this? Would the centre of gravity change for each chassis though and would it be the centre or nearer the front/rear? I have both front seats in my car at the moment but all of the rear and carpet/underlay is still out...the rear weighs quite alot on it's own, plus I only have 1/4 tank of diesel. Unfortunately as it's been raining I can't try the car properly on any corners to 'feel' the difference it has made, but the difference is noticable when driving normally. Quote Link to comment Share on other sites More sharing options...
Tony Posted September 2, 2009 Report Share Posted September 2, 2009 Depends where your noticing the change in handling.... I think it would be the polar moment of inertia rather than the yaw. Quote Link to comment Share on other sites More sharing options...
Rich Posted September 2, 2009 Author Report Share Posted September 2, 2009 Depends where your noticing the change in handling.... I think it would be the polar moment of inertia rather than the yaw. It's definitely helped with the castor issues I'm having, the front isn't as nervous now, even in the wet! I'm tempted to leave the seats out until the weekend, but put the carpet back in so I can test it some more! Quote Link to comment Share on other sites More sharing options...
Tony Posted September 2, 2009 Report Share Posted September 2, 2009 Depends where your noticing the change in handling.... I think it would be the polar moment of inertia rather than the yaw. It's definitely helped with the castor issues I'm having, the front isn't as nervous now, even in the wet! I'm tempted to leave the seats out until the weekend, but put the carpet back in so I can test it some more! I agree.... It's good to experience a change in the handling and to know why it's changed. Quote Link to comment Share on other sites More sharing options...
hms Posted September 3, 2009 Report Share Posted September 3, 2009 polar moment of inertia . Tony, can you define please? I don't understand the definitioins that come up when I google. h Quote Link to comment Share on other sites More sharing options...
tastyweat Posted September 3, 2009 Report Share Posted September 3, 2009 polar moment of inertia . Tony, can you define please? I don't understand the definitioins that come up when I google. h I'll explain in bits... and then add it all together Acceleration / braking / turning causes a torque moment... for example, when accelerating, the front of the car gets "lifted" off the ground and the rear gets pushed in to the ground... understand that bit? Torque is a tendancy for a force to cause a rotation around an axis... the axis in the case of acceleration, would be wherever the centre of mass in the car is & would be lateral (from left to right)... dependant on the exact weight distribution. So, it would pivot about a lateral line through the car. Torsion is how an object can twist due to an applied torque... ie, the metal in a car isn't strong enough to never bend under torque... when cornering/accel/braking there will normally be a little bit of warping of the chassis. A polor moment of inertia is a prediction of a certain objects ability to resist torsion. ie, it gives a rough idea of when the chassis will start to bend/twist/warp & helps predict when it will change shape so much, it actually affects the handling/behaviour of the vehicle etc Such predictions can be used to help set up a car to take in to account this warping of the chassis and do the best to compensate for it. Hope that makes sense to you bud, ask if it doesn't Quote Link to comment Share on other sites More sharing options...
Rich Posted September 3, 2009 Author Report Share Posted September 3, 2009 Makes sense to me, I've always struggled to understand it as well Quote Link to comment Share on other sites More sharing options...
Tony Posted September 3, 2009 Report Share Posted September 3, 2009 Makes sense to me, I've always struggled to understand it as well Problem is none of these predictions help after the design stage. It's the definition of the handling problem that suggests the type of correction required, or if it's an enhancement what type of materials needed to perfect the chassis past the design limitations. Your cars weight reduction proved a poor DI but in truth what manufacturer would design a sedan with a naked interior Quote Link to comment Share on other sites More sharing options...
Rich Posted September 3, 2009 Author Report Share Posted September 3, 2009 Makes sense to me, I've always struggled to understand it as well Problem is none of these predictions help after the design stage. It's the definition of the handling problem that suggests the type of correction required, or if it's an enhancement what type of materials needed to perfect the chassis past the design limitations. Your cars weight reduction proved a poor DI but in truth what manufacturer would design a sedan with a naked interior Changing even one part of the design, i.e. lowering, will throw their hard work designing the chassis out of the window then? Or if you're mazda and raise the car when it's been designed with a lower ride height that messes everything up? If I had the space I could be tempted to buy another mondeo and strip it properly to use on the track, see how it handles then Quote Link to comment Share on other sites More sharing options...
Tony Posted September 3, 2009 Report Share Posted September 3, 2009 Your spot on there mate..... An undressed Mondy would handle much better without question. Quote Link to comment Share on other sites More sharing options...
eddie Posted September 4, 2009 Report Share Posted September 4, 2009 Dynamic indexing....... Sam@ TDi summed this up perfectly in a previous post................................ Option one would always be to shed some weight! having a DI soo far above 1.00 can really only be caused by a mis-match in wheelbase to the mass, basically the chassis has far too much yaw inertia for the short wheelbase to influence easily. If we could take just 10% weight out of our demo car we'd have a DI of 1.39, much better! Unfortunately to take 10% weight out we'd have to seriously comprimise the car's very comfortable characteristics so for some (most) people this would defeat the object. The other option is to simply accecpt that the car will as a result of it's high DI always make poor use of it's rear axle in terms of producing lateral acceleration and then to try to work around it. A good example would be the Mitsubishi Lancer Evo-5, it's actually a car with a DI of 1.35 so this would make it pretty vectra/modeo'ish to drive... But Mitsubishi's chassis dynamics team have cunningly swerved this potential marketing disaster by employing an overly pointy geometry and suspension sollution giving the car the ability to change direction light a housefly, then in order for the average joe customer to be able to control and exploit this very odd and naturally quite unbalanced set-up they've been forced to add an active yaw control system in the form of an electronically controlled torque biasing center diff. This solution works so well that not only is the car acceptable to it's intended market it's actually now considered as one of the worlds best handling cars. do the competition cars not have the active yaw feature then? Quote Link to comment Share on other sites More sharing options...
Tony Posted September 4, 2009 Report Share Posted September 4, 2009 Dynamic indexing....... Sam@ TDi summed this up perfectly in a previous post................................ Option one would always be to shed some weight! having a DI soo far above 1.00 can really only be caused by a mis-match in wheelbase to the mass, basically the chassis has far too much yaw inertia for the short wheelbase to influence easily. If we could take just 10% weight out of our demo car we'd have a DI of 1.39, much better! Unfortunately to take 10% weight out we'd have to seriously comprimise the car's very comfortable characteristics so for some (most) people this would defeat the object. The other option is to simply accecpt that the car will as a result of it's high DI always make poor use of it's rear axle in terms of producing lateral acceleration and then to try to work around it. A good example would be the Mitsubishi Lancer Evo-5, it's actually a car with a DI of 1.35 so this would make it pretty vectra/modeo'ish to drive... But Mitsubishi's chassis dynamics team have cunningly swerved this potential marketing disaster by employing an overly pointy geometry and suspension sollution giving the car the ability to change direction light a housefly, then in order for the average joe customer to be able to control and exploit this very odd and naturally quite unbalanced set-up they've been forced to add an active yaw control system in the form of an electronically controlled torque biasing center diff. This solution works so well that not only is the car acceptable to it's intended market it's actually now considered as one of the worlds best handling cars. do the competition cars not have the active yaw feature then? No... not to my knowledge..... I suppose it's like saying do they have ABS?.... Most track cars are bare in the enhancements meaning the driver.. drives not the technology. Quote Link to comment Share on other sites More sharing options...
CIH Posted September 4, 2009 Report Share Posted September 4, 2009 I think the RS model, which most rally efforts are based upon, has a conventional centre diff. I imagine it's like vTec; a good compromise between everyday use-ability and high performance. Quote Link to comment Share on other sites More sharing options...
Tony Posted September 4, 2009 Report Share Posted September 4, 2009 I think the RS model, which most rally efforts are based upon, has a conventional centre diff. I imagine it's like vTec; a good compromise between everyday use-ability and high performance. Yep i have to agree mate. Quote Link to comment Share on other sites More sharing options...
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