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As prompted by Tony over in t'other thread, a look at how I go about developing an upgrade kit from scratch. I'll endeavour to keep the maths out of it, and I'll not be recommending any one product over another.
Firstly, a few thoughts on what we're actually trying to do. Ride and handling is all about controlling weight transfer as the driver fiddles with the controls and the car goes across uneven ground. Weight transfer is an immutable physical law, thanks to Isaac Newton, so you're going to get it anyway. Even if you stop the body from moving around, weight transfer still happens. The difference with a non-moving body is that the reaction to that weight transfer is
a ) taken out in twist of the body, which isn't much but can mess around with your carefully crafted suspension geometry and calibration
b ) is effectively undamped, so can carry on for a long while which really messes around with your cunning engineering and really messes with the drivers brain because you're getting big variations in the contact patch forces and a less consistent feel.
If you watch the ultra slow-motion footage of an F1 car you'll see what I mean - most of the suspension movement is in the sidewalls of the tyres (something that may well disappear next year if Michelin get their way and we get 18" rims for F1 cars) and the bodywork twisting rather than the wheels actually moving up and down relative to the body.
So, I work on the premise that you're going to get weight transfer anyway and its better to have suspension travel which we can control with the dampers rather than over-limiting movement and having the chassis take away some of your control.
That said, some of the weight is transferred directly up the suspension arms into the body, so you can't control that. The amount is a function of the alignment of the various suspension arms and the amount varies as the suspension arms move and the car rolls.
Anyway, back in the room...
Step 1 is always measurement. If you're developing an upgrade kit, you've generally got to work with what the original equipment manufacturer has designed in rather than expecting your end user to fork out for new suspension arms, driveshafts and a whole heap of welding and stiffening to put new hardpoints in. One of my earliest jobs out of university involved a vehicle that used applique plates for bolting the suspension arms to the body (not to mention that it was built out of 75mm thick plate and torsional rigidity wasn't a big issue) but generally you've got to work with what the manufacturer has designed in.
So, it's up on a ramp and out with the tape measure to locate in three dimensions where the suspension arms are relative to the ground, the location of the wheels relative to the outer links, the position of the inner track rod ends and a visit to an alignment rig to find out what the basic alignment values of camber, caster and toe are.
I also measure suspension motion ratios (how much the spring and damper move in relation to the wheel moving), the spring sizes and the anti-roll bar diameters and lever arms.
Once I've got those numbers, then I feed the data into a suspension kinematics program. I use SusProg, mainly because it's cheap, accurate and the developer is the sort of bloke who will customise things just for you. The output of SusProg lets me know how the suspension moves and also what effect changing ride height (and if it's a vehicle like the 5 where the alignment is adjustable by moving inner pickup points around) has on the suspension alignment.
I'm effectively looking at two things:
a ) The roll centre height. It's effectively the point where the load transfer is applied to the body of the car via the suspension and controls how much of the total weight transfer is fed into the suspension and how much is fed directly into the body by the suspension arms
b ) Kinematic changes - things like bump steer (where the toe of the wheel changes as the suspension moves up and down relative to the body), roll steer (where the toe changes as the body rolls) and camber and caster changes.
Sometimes, you get something that is a show stopper for doing sensible things like lowering the car (a lower c of g means less load transfer which is a good thing, but can result in more load transfer into the body at the expense of the suspension which is generally a bad thing). I know of one Teutonic manufacturer where a canny race engineer found large chunks of time by returning the car to stock ride height because the suspension geometry was so duff in its lower position. Similarly sometimes you find that the stock ride height is the best compromise (believe it or not, most R&H engineers working for the OE actually know what they're doing) so you're looking then at optimising one feature of the car's behaviour at the expense of others - for example if you go very extreme with the kit, you may make the car significantly less stable if it carries your weekly shop in the boot.
Step 2: Testing a representative vehicle. It really helps if you know what you're trying to improve, so I endeavour to take the test vehicle to somewhere taxing and measure its handling performance, both objectively and subjectively. In other words, fit a load of data logging equipment to the car and take it to Millbrook Proving Ground. I use Millbrook for several reasons, not least of which is that it's very close to my house. The other main reason is the fact that it has the Outer Handling Circuit. It's a short (about 0.8 mile), narrow (the width of a British B-road) handling circuit designed to expose any frailty in the capabilities of a car (and driver, but that's another matter).
The purpose of testing is to measure the capabilities of the car and its response to the wheel. It's not about setting an outright laptime but actually seeing what happens if you put some very quick changes of direction in of combine a long sweeping bend with a load of camber changes. We're looking at setting a baseline against which we can measure the improvements that the finished kit will bring. One of the key things for most kits is driveability - while we all might like to think we're somewhat more talented than Lewis 'n' Jenson, the fact of the matter is that we're not and while you can engineer a kit with a significantly increased performance envelope, if you need their skills to exploit it without a metal-hedge interface, then it's not an appropriate avenue to explore.
Here's where the subjective stuff comes in. How easy is it to get a 'hooked up' lap? How easy is it to repeat that lap? How easy is it to fix problems created by the wrong speed and line? Are there some nasty behaviours (lift-off oversteer, power understeer and the like) that you might want to try and tune out? There's a whole range of international standard manoeuvres for this sort of thing but you need a subjective assessment as to how well the stock car deals with these things.
Once we've got these things measured, we're ready to start the real work...
Firstly, a few thoughts on what we're actually trying to do. Ride and handling is all about controlling weight transfer as the driver fiddles with the controls and the car goes across uneven ground. Weight transfer is an immutable physical law, thanks to Isaac Newton, so you're going to get it anyway. Even if you stop the body from moving around, weight transfer still happens. The difference with a non-moving body is that the reaction to that weight transfer is
a ) taken out in twist of the body, which isn't much but can mess around with your carefully crafted suspension geometry and calibration
b ) is effectively undamped, so can carry on for a long while which really messes around with your cunning engineering and really messes with the drivers brain because you're getting big variations in the contact patch forces and a less consistent feel.
If you watch the ultra slow-motion footage of an F1 car you'll see what I mean - most of the suspension movement is in the sidewalls of the tyres (something that may well disappear next year if Michelin get their way and we get 18" rims for F1 cars) and the bodywork twisting rather than the wheels actually moving up and down relative to the body.
So, I work on the premise that you're going to get weight transfer anyway and its better to have suspension travel which we can control with the dampers rather than over-limiting movement and having the chassis take away some of your control.
That said, some of the weight is transferred directly up the suspension arms into the body, so you can't control that. The amount is a function of the alignment of the various suspension arms and the amount varies as the suspension arms move and the car rolls.
Anyway, back in the room...
Step 1 is always measurement. If you're developing an upgrade kit, you've generally got to work with what the original equipment manufacturer has designed in rather than expecting your end user to fork out for new suspension arms, driveshafts and a whole heap of welding and stiffening to put new hardpoints in. One of my earliest jobs out of university involved a vehicle that used applique plates for bolting the suspension arms to the body (not to mention that it was built out of 75mm thick plate and torsional rigidity wasn't a big issue) but generally you've got to work with what the manufacturer has designed in.
So, it's up on a ramp and out with the tape measure to locate in three dimensions where the suspension arms are relative to the ground, the location of the wheels relative to the outer links, the position of the inner track rod ends and a visit to an alignment rig to find out what the basic alignment values of camber, caster and toe are.
I also measure suspension motion ratios (how much the spring and damper move in relation to the wheel moving), the spring sizes and the anti-roll bar diameters and lever arms.
Once I've got those numbers, then I feed the data into a suspension kinematics program. I use SusProg, mainly because it's cheap, accurate and the developer is the sort of bloke who will customise things just for you. The output of SusProg lets me know how the suspension moves and also what effect changing ride height (and if it's a vehicle like the 5 where the alignment is adjustable by moving inner pickup points around) has on the suspension alignment.
I'm effectively looking at two things:
a ) The roll centre height. It's effectively the point where the load transfer is applied to the body of the car via the suspension and controls how much of the total weight transfer is fed into the suspension and how much is fed directly into the body by the suspension arms
b ) Kinematic changes - things like bump steer (where the toe of the wheel changes as the suspension moves up and down relative to the body), roll steer (where the toe changes as the body rolls) and camber and caster changes.
Sometimes, you get something that is a show stopper for doing sensible things like lowering the car (a lower c of g means less load transfer which is a good thing, but can result in more load transfer into the body at the expense of the suspension which is generally a bad thing). I know of one Teutonic manufacturer where a canny race engineer found large chunks of time by returning the car to stock ride height because the suspension geometry was so duff in its lower position. Similarly sometimes you find that the stock ride height is the best compromise (believe it or not, most R&H engineers working for the OE actually know what they're doing) so you're looking then at optimising one feature of the car's behaviour at the expense of others - for example if you go very extreme with the kit, you may make the car significantly less stable if it carries your weekly shop in the boot.
Step 2: Testing a representative vehicle. It really helps if you know what you're trying to improve, so I endeavour to take the test vehicle to somewhere taxing and measure its handling performance, both objectively and subjectively. In other words, fit a load of data logging equipment to the car and take it to Millbrook Proving Ground. I use Millbrook for several reasons, not least of which is that it's very close to my house. The other main reason is the fact that it has the Outer Handling Circuit. It's a short (about 0.8 mile), narrow (the width of a British B-road) handling circuit designed to expose any frailty in the capabilities of a car (and driver, but that's another matter).
The purpose of testing is to measure the capabilities of the car and its response to the wheel. It's not about setting an outright laptime but actually seeing what happens if you put some very quick changes of direction in of combine a long sweeping bend with a load of camber changes. We're looking at setting a baseline against which we can measure the improvements that the finished kit will bring. One of the key things for most kits is driveability - while we all might like to think we're somewhat more talented than Lewis 'n' Jenson, the fact of the matter is that we're not and while you can engineer a kit with a significantly increased performance envelope, if you need their skills to exploit it without a metal-hedge interface, then it's not an appropriate avenue to explore.
Here's where the subjective stuff comes in. How easy is it to get a 'hooked up' lap? How easy is it to repeat that lap? How easy is it to fix problems created by the wrong speed and line? Are there some nasty behaviours (lift-off oversteer, power understeer and the like) that you might want to try and tune out? There's a whole range of international standard manoeuvres for this sort of thing but you need a subjective assessment as to how well the stock car deals with these things.
Once we've got these things measured, we're ready to start the real work...
