BTCC Engineering

Since 2013 the British Touring Car Championship has run to the NGTC rules. The next generation touring car concept was introduced to control the costs of competing in this form of racing that had hit multi million pound budgets under the previous S2000 rules.

The BTCC has long been one of the world's most exciting and competitive championships and has attracted manufacturers and top drivers from around the globe. It has a massive following and aside from F1, it draws the biggest crowds both at the circuit and on TV.

NGTC basically defines a lot of the running gear of the car to a kit of standardised components. Only the bodyshell, engine  and the body styling kit can change between cars/teams. The engines are turbo charged 2 litre 4 cylinder  types with equivalency rules to ensure parity of performance.

So the room for engineers to find performance is severely restricted. However because the competition is so close (often only tenths of a second covering most of the grid) small detailed improvements can make big differences to grid position.

BTCC teams range from very professional manufacturer teams to very enthusiastic amateurs with a ton of volunteer help. When you are doing any serious race car engineering work it's very important to know what you are working from.  Touring cars tend to be hand built and parts made up ad hoc as the cars come together so knowing exactly what you have can be a problem.  In F1 for example every single part will be CAD modelled allowing you a lot of possibilities for analysis and simulation.

So I think it's really important to try and understand what you have and so part of that is to build CAD models where possible in the case of my current project I've assembled CAD models of all of the standard kit components to begin with. The team have a limited budget but also practical requirements for spare parts and the desire to try and keep up with developments.

The flat floor at the front creates an aerodynamic splitter element and is one area that can be changed by the teams as it must fit an offset of the front bumper/air dam plan view silhouette. As with all race cars you are looking to reduce the weight and keep it as low as possible. This team needed spare floors and at the same time we've reduced the overall weight and made the floor area larger to the extent allowed by the regulations.  As the front air dam creates a high pressure area in the front of the car and on top of the splitter with a reduced pressure underneath you end up generating down force.  As down force comes from the pressure difference between top and bottom of the splitter multiplied by the area of the fool that that pressure acts upon, the larger the area of the flat floor the better. In this case we've added about 1300 cms Sq so hopefully that and 3kgs less weight will make for very cost effective performance improvement.

The other part of this first stage of upgrades is to redesign the body kit to further reduce weight and decrease drag and increase down force.  We don't have the budget currently to conduct wind tunnel development and whilst we have CFD capability without the budget to scan the cars shape and create CAD data for this we can't make much use of it. So we are using experience and common sense to try and make improvements in the area.

As the car is currently 3 kgs over weight and front weight balanced we are aiming to reduce the weight of the front bumper, wings etc and then if required to make up the minimum weight with ballast low down in the rear of the car. As the cars race performance is dependent on how they use and abuse the tyres, balancing the front to rear weight split to equalise tyre use is likely to be important for overall race performance.

How Autosport GP Engineering bring dinosaurs to life.

How do you take a design brief to create a realistic 3D Jurassic Park Velociraptor and produce a pair of 1m tall figures in just 4 weeks including Christmas?

Well the answer is a lot of hard work, skill and a not inconsiderable amount of advanced technology.

Equinox Products of Whitstable regularly produce fibreglass figures for Harry Levy Amusements of Broadstairs. They came to us in early December with a sketch of a new machine they had to have displayed at a games and amusements exhibition  in the 2nd week of January. Under normal circumstances you might expect this to be a 4 month project not a 4 week one, especially as across Christmas all suppliers are closed.

Normally with these projects someone will produce a 3D CAD model of the end figure, or a skilled artist might hand carve it. In order to make a realistic looking dinosaur a particularly skilled sculptor would be required and they would need plenty of time, both of which are in short supply. In order to create from scratch a 3D CAD model with such detail is a very time consuming project and requires extremely experienced CAD surfacing designers.

Once a CAD model has been produced patterns in dense foam are produced. These patterns, are essentially the finished items only split into sections so moulds can be made from them. 3 axis CNC machining centres that are computer programmed by extracting the geometry directly from the 3D CAD model, are used to produce the patterns.

Moulds are then produced in such away as they can be split apart to extract the fibreglass finished figures once they are laid up inside. In each of these processes you can see there is a lot of time spent producing items that are just links in the chain towards being able to produce a final figure, and then a production quantity of them, in this case 62 items across the first few months of 2015.

Four weeks including Christmas, made this traditional approach a total non-starter. So a new approach had to be taken. We sent out for a model toy dinosaur figure and it was optically scanned. Optical scanning is an extremely accurate (0.02mm resolution or higher) method of capturing 3D geometry. It's used for reverse engineering and for inspection because it can capture, for analysis, forms that are hard to capture by other methods.

The resulting data from the scan is in the form of a mesh of data points representing the form of the dinosaur toy. Unfortunately the original pose of the toy was not suitable for how it was required to fit on the finished machine. We used a combination of advanced software, similar to that used to produce CGI movies, to re-pose the figure, and then cover the mesh with CAD compatible surfaces that can then be used for manufacture. Some mechanical fixing elements were added in the 3D CAD model at this stage.

Finally using this CAD data we 3D printed in plastic the finished dinosaur. However being over 1 m tall our 3D printers couldn't print it in 1 piece, but, luckily the software allows us to split it into smaller parts and add socket and pin details so that it can be clipped and glue back together after.

Three were made in total two for the exhibition and a third was used to make the GRP moulds from so that a production run of 62 figures can be produced. We were thinking of creating a bit of a stir in the local press by burying some spare parts in the beach at Whitstable and seeing what the reaction was when the were uncovered!

Can we help you with a similar challenge? If so then please contact me on 01227 392840 or autosportgpengineering@gmail.com

How Marussia might be able to get on the grid for 2015

So news has hit today that the hopes of the Marussia F1 team (now Manor) have been dealt a huge blow by the veto from Force India to them using the 2014 car although it doesn't comply with 2015 regulations.

As there is reportedly over £30 million in prize money from last year at stake I can imagine how the teams backers are desperately thinking of ways to get a 2015 compliant car ready asap. I've also been thinking about how you might be able to short cut the process so they can have a car ready in time.

The apparent stumbling block is that the front bulkhead on the monocoque needs to be 50mm lower than in 2014, so you need a new monocoque design. Marussia apparently had a 2015 design complete and pictures are being circulated of a wind tunnel model. So most of the thought process for the nose and monocoque has been done, but, there isn't time to manufacture a new one.

In order to manufacture a new monocoque you first need to machine a pattern out of high density foam or aluminum from the CAD model. This is several days/weeks of machine time. After this you have to make carbon fibre moulds from the pattern, again many days work, and then you get to make an actual monocoque. So you are looking at a vast amount of time and money both of which they don't have.

However there are ways to short cut this process. They are going to have to retain as many parts as possible from the 2014 car, so I would want to choose a point along a 2014 monocoque and cut it off (figuratively) retain everything rearwards of this point, and blend the rear of the 2015 nose design they already have into this point on the 2014 monocoque. What this allows you to do is reuse most of the monocoque pattern from 2014, saving machine time, also you can cut the moulds back to this point, remould a return flange on them and then the majority of the moulds can be reused. You can then machine a small pattern which is the blend from the 2015 nose to 2014 tub, make moulds from this with return flanges that can bolt onto the main section, and away you go, you have a new set of moulds from which a 2015 tub can be made. Reducing cost and time by at least 50%.

Unfortunately for them the external shape of the monocoque is not the only problem to overcome, packaging the steering, pedals, brakes and front suspension into this new space with the minimum of new components will be an equally difficult challenge, but if they are true racers where there's a will there's a way.

It might not be a typical F1 solution, or result in a particularly attractive car, but that's the least of their worries at the moment. I'm sure we'd all like to see them on the grid however they manage it. They clearly have resolve to keep trying even after the apparent death, after all I'm typing this blog one of their PC's that was sold off at the disposal auction.

Darren George
ex-F1 Design Engineer

John Barnard Article in Racecar Engineering

This months edition of Racecar Engineering magazine (http://www.racecar-engineering.com/) has an interesting article about the F1 design innovator John Barnard and his career. Growing up in a racing family and with a desire to become an F1 designer, John was a hero of mine, and the one engineer I desperately wanted to work with and learn from. After losing out on just such a job offer whilst he was at Arrows, I eventually did get my dream job working with him at the age of 25 at B3 Technologies, when he was design consultant for Prost.

It's always interesting to read articles about people that you know ever so well. Have you ever read an article about something or someone you know well? Well if you have you'll know that journalists never seem to catch the person of story correctly, and it's disappointing when the rest of the world then takes that as the gospel just because it's laid down in print.

Well so it's true to a certain degree with articles written about John. I must admit that we fell out in the end, but, I think I have enough respect for him as an engineer, and I have enough self-respect and passion for engineering that I can give a fairer assessment of him as a person than any journalist interviewing him can.

What comes across in the interview is his design genius in how he innovated step changes in F1 technology, which is as you can imagine is slightly far fetched. By the mid-late eighties F1 design teams were expanding and consisted of ever larger numbers of engineers, and by the late nineties when I first got involved there were up to 50 people designing parts in each team. So to say that one person was responsible for the whole idea and for making it work is stretching the truth a bit far. It annoys me today the way that Adrian Newey is lauded as the design for Red Bull, he might have ultimate responsibility but he is really a manager of very many talented individuals, the original ideas for many innovations and developments will have come from a number of sources that you will never hear credited.

The paddle gear change for example I was told was already on the drawing board when John joined Ferrari. If this is the case is it really fair to credit him with the idea? In practicality I believe it is actually fair, because, what noone really stresses about John, is that he is very supportive and has incredible attention to detail. I have no doubt that John made that idea work, even if it wasn't actually his initial idea. He was always prepared to listen to your ideas, work through them with you, see how they'd fit into other ideas and concepts and help you detail the design through to manufacture and realisation. So he is exceptionally supportive in that way and as a very young and inexperienced engineer it was so exciting to have that support and encouragement from an icon like him. Working under him was not easy, extremely long hours including Saturdays and no care that you had a life and family outside of the company. That's what F1 is like, it's total immersion, and I bet everyone is grateful for the regulated August break nowadays.

The contradiction is that he would never credit anyone publicly with any ability. I bet if you were to ask him about the current crop of technical bosses that used to work for him, his opening line will certainly be "when I first employed him, he couldn't draw a milk bottle". F1 is not only competitive on track, but, it's a competitive working environment. You don't get your crack at the top jobs unless you are prepared to stab a few friends in the back, and, I guess maybe this side to him is just a reflection of the competitive environment.

It's true that he knows how to explode and scream and shout, during the first Gulf war his employees termed it "Scudding" after the Iraq missiles. Basically if you did something wrong you could expect him to explode like a Scud missile. These explosive episodes were never fun to be on the receiving end of, but, actually in all fairness he didn't hold grudges and saw the mistakes as interesting problems to be worked through. It was sometimes hard not to laugh, one time he was punching himself in the head in the middle of the design office after being given some bad news, the barer of that bad news, a fabricator had to point out he was "a fucking psyco!". A few minutes after a scudding, he'd likely be your friend again and sat on your shoulder enjoying the challenge of finding a solution to the problem. And this is where you see the passion for engineering that he has, and that I guess even in retirement he hasn't lost. By the time I worked with him, he wasn't bothered about going to the track and races, his passion was in the fine details and in making ever more perfect components. The compound benefits of fine detail improvements was his idea of a significant performance advantage. It upsets me to see some of the current crop of F1 cars, in that some components have still not matched the detail we achieved in the late 90's early 2000's on the Prost!

Another side that doesn't come across in interviews and articles is that he's actually very funny, he's totally un-PC and everyone feels sorry for his long suffering wife. He definitely calls a spade a spade in company he feels comfortable with, he's shy in large groups and new environments, and therefore you only see the real side of him when he's comfortable with you. That's a double edged sword, because only those he's comfortable with will get a full assault scudding, but, also those people are the only one's who get to see the best side of him. He tells a really good story too and as you can imagine with the length of his career he has a lot of stories to tell. If ever you needed a break from an intense design session with him, we all developed little tricks to set him off on story time. He is also colour blind and to keep ourselves amused we'd like to tell him the wrong colour for each line on the CAD screen, so when he next referred to it we could try and confuse him.

At the launch of the Prost AP03 John and I flew out together and the plane had to land at a different airport due to bad fog. Whilst waiting for several hours on the runway to make the short flight back to Barcelona he told me how the deal unfolded with Enzo Ferrari the first time he set up a design office for them. He wouldn't divulge numbers but did say that he was asked how much it would take to get him on board, so he wrote on a piece of paper a number he thought so outrageous Ferrari wouldn't pay it, only for Enzo to agree instantly. That trip we got to our hotel at about 4am and we had to leave for the circuit at 6am, I was up and ready in reception with all the French mechanics who distrusted John and anyone associated with him, and there was no sign of John. I had the reception call him only for him to still be in bed and decide we could stay in bed for another hour or so!

At that test the pit lane was full of gossip mostly spread by Alex Wurtz who was riding up and down pulling tricks on a mountain bike, about one teams technical director who had just been forced to resign over allegations he had a foot fetish. Apparently this guy been fondling the feet of several of the teams female employees under the guise of a secret project. John found it hysterical and joined in the conversation in his normal no nonsense manner.

I think in conclusion it's a shame he wasn't more of a racer, and if he'd committed more to being a traditional technical director and taken full control of the cars performance and stuck with teams and seen through all the developments to their conclusion you'd see a CV with more championships than Adrian Newey. But, John is a real engineers engineer, and it's a shame that the general F1 public can't get a better look at the details of the components and designs he directed. So for young aspiring engineers, try to see through the media's obsession with pinning all the work on one person and forget about the wild fanciful innovations that are going to revolutionise performance and concentrate and learn to love the details, take concepts and push them to the limit by looking at the fine details. Radical innovations may come as a result of your detailed understanding of the problem, but, also you'll only ever get the best out of any idea if you don't focus on the detail. To all young engineers who aren't going to get the benefit of learning from John now, but, hopefully you can find someone like him who is prepared to show you enough respect to nurture and guide you to be a better engineer.

Active Brake Balance Control in F1

Some time ago I designed an active brake balance control system for the Prost F1 car, from memory it was for AP04. The idea was that aerodynamic load builds up differently front to rear with respect to speed and therefore when a driver brakes into a corner and slows the car the load on the tyres and therefore the amount of grip front to rear changes as the car slows. The front wing is far more efficient than the rear, and so as the car slows the brake balance should shift progressively to the front.

Also what we found is that the difference in brake hose length between the front and rear mean't that the rear brakes take fractionally longer to come up to pressure on rapid application of the brake pedal, than the fronts do. So very briefly you have a lot more front bias than you would ideally want.

So our answer was to develop an active brake balance control system. It's hard to know what the other teams were doing at the time, but, we were pretty confident that we were the only ones using it. It never actually got raced because the rules were changed to ban it as soon as we were ready to race it. It seems that 2014's regulation might require this kind of system and that the rules may have been changed to allow it once more.

The heart of any active system is the Moog valve. This is a servo hydraulic control valve that F1 cars use to control the throttles, gear change, and in the early 90's active suspension systems. It's a very sensitive and rapidly responding valve with a built in feedback system that allows you to control the pressure in a system very accurately, and extremely quickly.

The active brake balance system was in essence very simple. All we had to do we 'T' off of the rear brake hose and put in a hydraulic piston. On one side of the piston was the brake fluid and on the other side was the hydraulic fluid controlled by the Moog valve. The hydraulic fluid circuit also included an accumulator and obviously a high pressure pump (the same pump is used for the gear change and throttles). The Moog valve was controlled by software that had the cars speed, front brake pressure and rear brake pressure as inputs. The software did the calculations to compare the front to rear brake pressure split to the nominal selected balance with respect to speed, so in essence we had a 2D map of what brake balance we wanted for each particular speed. The Moog valve then regulated the pressure of the rear brake line increasing or lowering the pressure many thousands of times a second to maintain the optimum balance.

For 2014 with the addition of extra KERS harvesting and therefore variation in the amount of braking that the rear of the car sees during this harvest, this active balance system would be able to reduce rear brake line pressure during harvesting to keep the balance stable.

The simplicity of this system mean't that if there was a failure in the active system the rear brakes would still function as normal because the separator piston had limited travel and if the hydraulic pressure were to fail then the piston would move back against a hard stop allowing the brake master cylinder to build pressure as in a normal system.

F1 cost capping

There's been a lot said recently about the proposal to apply budget restrictions in F1 because a lot of teams can't afford to compete anymore.

I think that's been part of F1 since it's inception and the highly competitive nature of sport will always drive costs up but there must be a limit to how much sponsors will put in before it's no longer cost effective.

From the inside as an engineer the scale of spending is even more apparent and shocking than the spectacle you see each weekend. For example at Prost we spent £15, 000 making two ratchet tools to remove the nose box. Why? Because we could it's as simple as that.  The tools were beautifully designed and made and no consideration to cost was ever given to it. Now that was in a back of grid team that went bust 6 months later,  so imagine the attitude that a top team would be taking.

I don't want to see a slow down in development ir a reduction in staff obviously because that would hurt people like me. I'd like to see a reduction in waste and therefore the cost in that. We made some carbon rear wishbones for Jaguar. 5 sets to a new design proven to be better in the wind tunnel.  They had to be done in a rush to get to the Australian GP. The day we finished them they updated the design because further wind tunnel testing had proven another design change was even better. So all 5 sets were scrapped and we started again to the new design. 

The process for making a carbon wishbone calls for lots of tooling specific to each design. You have to make aluminum patterns,  carbon moulds off if these patterns,  then wishone halves out of these moulds and then bond them and final machine them. The aluminum for the patterns is already many thousands of pounds and machining time is 90 per hour or more and they take days to machine. The waste of 5 sets of wishbones like this is possibly close on £100, 000 today.  And it's pure waste which is just accepted.

So my cost capping rules would first look at finding ways to ensure parts are homologated in such away as to prevent design and manufacture of endless new parts that subsequently don't get used.

Vehicle Dynamics - a layman's introduction

For those with a casual interest in vehicle dynamics but need an introduction that you can understand and doesn't involve huge calculations and derivations I hope you'll find this informative. If you watch motorsport and wish to understand a little more about why commentators bang on about tyres and aerodynamics etc hopefully this will help too.

Tyres

First thing you must know is that the tyres are the only part of the car that can transfer the loads to the ground and therefore are the most important part and limiting factor in a cars performance. So you must understand how they generate these forces and what the limits are to their performance in order to know what the overall limits to your cars performance are.

We can all probably understand that the "grippy" rubber interacts with the ground and the friction between the tyre and the road is what creates the available traction. Newton's equation for friction tells us that the Friction force is equal to the coefficient of friction multiplied by the force that's pushing the two surfaces together (referred to as the normal force, because it's the force normal to (i.e. right angles to) the direction of the friction force. The coefficient of friction is a value that is derived from how "sticky" or "smooth" two surfaces are that are in contact. For most materials this friction coefficient is independent of the normal force, but for a tyre it isn't. More on that later.

So from Newton's friction equation we can see that the more we push the tyre onto the road the more friction we will generate and therefore the more traction we will have for cornering or braking or accelerating.




The above graph shows the relationship between the vertical load pressing the tyre into the road and the amount of traction. Traction for a tyre basically means the amount of force it can generate overall, so you can use this all for cornering, all for braking/accelerating or a combination of both. When you try to go above this force then you have the situation where you lose grip and spin etc.

Slip Angle

The blog link below gives a nice explanation of slip angle. But essentially slip angle is the difference between the direction the wheel is going and the direction where the car is going. Might sound odd at first, as you would hope this is the same, but, to a small degree this is not the case. The wheel during cornering will be at a higher angle than the direction the car is turning. This is because the contact patch of the tyre, is being deflected, the angle difference is referred to as slip angle, and up to a point the greater this angle the more cornering force you can get from the tyre. So on a lot of tyre performance graphs you'll have multiple lines, so you can see the relationship between cornering force and both the slip angle and the vertical load.

http://www.pratperch.com/2011/05/tyre-side-slip-explained/

When you get above the maximum slip angle that the tyre can work at, or that the road conditions will allow then the tyre loses traction. Anyone who drives will likely have experienced this in bad weather conditions, maybe at a roundabout, you turn in and maybe accelerate and the steering feels lighter and less responsive and the car doesn't take the course that you though it would. This is understeer, and it's where you've taken the tyre above it's slip angle limit for those conditions.

Slip angle takes account of speed and steering angle. If you think of a F1 car, it can't take a hair pin bend like the Lowes bend at Monaco at 200 mph, but it can take large radius bends at Silverstone for example pretty much flat out. What will actually happen though is that the slip angle is the same whether it be 30 mph and very tight of 200 mph and very large corner radius. At the tight bend the steering angle will be 20+ degrees but because of the speed of the car the direction the car is taking is close to this steering anlge, and at a high speed corner the steering angle will be much less and the direction of the car also much less but equal as far as the "slip angle" or the tyres contact patch is concerned. So slip angle is important to keep in mind but it allows us to ignore how fast the car is going and the steering angle and equate everything to what the tyre is actually doing.



On a racing tyre like an F1 slick you don't get a lot of warning that you are about to exceed the maximum slip angle of the tyre, and when a driver does go over this limit the tyre's traction rapidly drops off and generally causes a dramatic incident, like a spin. On a road tyre they are much more forgiving and road cars and tyres are designed to give us less competent drivers plenty of warning of impending doom. So the drop off after maximum slip angle is less dramatic. Back to the example of driving a roundabout in wet weather what an inexperienced driver will do is to wind more lock onto the steering in the hope that this will make the car turn more, but, it just makes the situation worse. Big accidents are then caused by the inexperienced driver jumping on the brakes whilst turning more on the steering, and then all control is lost. What should happen is that you wind off some lock so you come back into the usable slip angle range, gently ease off the power until the steering begins to respond again and then you can take back control of the car.

Suspension

So above we have described a little about the performance and limits of the tyres, now the suspension systems job (as far as vehicle performance is concerned) is to keep the vertical load on the tyres consistent. If you were to hit a bump in a very stiffly sprung car the tyre would see a rapid increase in vertical load (and therefore traction) and then the car would bounce on the tyres (because the tyres are very springy) as the tyre oscillates the load will go from very high to very low (low traction) to very high again until after some time the oscillations are damped out and the tyre load goes back to the normal static load from the weight of the car. Obviously if you are cornering, braking or accelerating whilst the tyre is cycling from high traction to low traction the cornering force will cycle from high to low and the cars cornering ability will suffer.

So the job of the suspension is to minimise the effect that bumps etc have on the normal load on the tyre. Just keep this in mind for one moment, whilst I explain about the effect of load transfer as the effect on efficiency is the same.

Load Transfer

When cornering the car will lean (or roll) over to the outside. What happens here is some of the weight of the car stops acting equally side to side on the cars tyres and puts more on the outside tyres and less on the inside tyres. If you were to stand with one foot on one set of bathroom scales and the other on another set, when you stand up straight both sets of scales will read half of your weight. If you then leaned your torso to one side one set of scales will increase and the other decreases by the amount the others increased. Your overall weight hasn't changed just the distribution from one leg to the other has changed. So the same is true with the car, what the outside tyre gains the inside tyre loses.

No problem you would think, we know that the tyres gain traction with increased vertical load, the problem is that it's not a linear relationship. When you look at the first graph above you'll see that as you increase the vertical load, the cornering force goes up, but not as much as it did for the previous increment in load. i.e. tyres are more efficient the less vertical load they have on them. From the first graph at 100 kg's of vertical load we get something like 140 kg's of traction, between 500-600 kg's of vertical load we only add about 50 kg's of traction. So in the case where we are transferring load from one side of the car to another, what happens is we lose more traction on the inside tyre than we gain on the outside tyre and thus overall the amount of traction the cars tyres produce is reduced.

Back to the case where the stiffly sprung car is bouncing on it's tyres and cycling between high and low vertical forces, what we get is less gain in traction at the high load points of the cycle than the loss of traction at the low load points, and therefore overall the tyre is less efficient and less traction is available.

Aerodynamic Load

When you load the tyres with aerodynamic downforce then as above we see that the traction force will increase. With racing slick tyres what you get is tyres that produce more cornering force than the vertical force acting on them. This is where tyres start to defy Newton because Newton says that you can't have a coefficient of friction greater than 1. Whereas racing tyres have a friction coefficient of around 1.5.

'G' we heard talked about a lot on racing commentary and this referred to the number of times heavier an object is whilst cornering or braking than it would be at rest. So a drivers head seems heavier to the driver whilst cornering than it would at rest. As far as the tyres and this blog is concerned "G" refers to the efficiency of the tyres. So a typical Formula Ford on slick tyres and no aerodynamic loads can pull about 1.5 G in the corners. So this means that the cornering force the tyres are generating must be 1.5 times greater than the force of the weight of the car acting on the tyres. Now with an F1 car and it's huge levels of downforce the cars can pull about 4 G in the corners meaning the tyres cornering force is 4 times greater than the normal force caused by the cars weight.

In the last two sentences I've made reference to the vertical force caused by the vehicles weight, because in terms of efficiency and therefore the G pulled during the corner we use the downforce + vehicle weight to determine the tyres cornering force, then divide that by the force caused by the vehicles weight alone, to determine the efficiency and G. So aerodynamic load is free efficiency if you like. I'll totally understand if that's a bit confusing, you might have to just accept it.

Centre of Gravity Height

Weight transfer as mentioned above is not good for a car tyres performance efficiency. The amount of weight transfer you will see is proportional to the cars centre of gravity height (CofG). If you imagine a car has a spot in the middle of it about which the entire cars weight can be considered to act and then when you roll the car over a few degrees this point will move over to outside of the roll. Therefore the weight of the car is now no longer acting perfectly in the middle of the two tyres, and is slightly close to one tyre than the other. Therefore more weight will be acting on that tyre, in proportion to how far this CofG point has moved from the centre point of the tyres.

Now if you lower the CofG, you'll notice when the you roll the car the distance off centre that the CofG moves is reduced, and therefore the amount of weight transfer is reduced.

The pictures above are an extreme view, but, they do clearly illustrate how the position of the centre of gravity moves to one side with roll angle, and how this is reduced the lower the centre of gravity.

There's a lot more to this of course, than I've written above. I'll collect my thoughts together and write more soon on how this relates to suspension geometry, and how CofG relates to other aspects of suspension geometry and vehicle dynamics.