Sam@TDi

Wow imagine the handling balance now! the S14 chassis is far too front bias even with the little baby SR20 engine mounted mostly behind the front axle let alone with a huge RB26 balanced out front Saying that the guy has removed rear visability and gone for an amp rack instead so I think it's safe to assume that this is just a heavy show queen A hell of alot of work though, all I can assume is some people get much more out of car shows than I do

Blimey i wouldn't of thought it was worth it, one shopping bag weighs more than that!

Now that I can kinda understand, but I guess those iron blocks had a more meaningful mass something like 20-30kg.

Interesting one that, my first reaction would be to say yes. If you need to add ballast then that would be the ideal place to do it. BUT that weight is actually tiny! i'd be amazed if it even weighs one kilo, so I'm gonna guess that Mazda/Ford found something in either testing or simulation that they didn't like and this was a simple band-aid fix. Maybe the cross beem needed a little more mass to effect it's natural frequency and therefore the way it transfers movement or vibration to the bodyshell, what ever it is it's not obvious to me

For what it's worth I don't think Kinematic Toe is an industry term. Kinematics is a huge subject but put very simply is just the scientific study of a mechanics in motion. The science would only normally be applied to a vehicle suspension at design level inside a computer simulation model by a vehicle manufacturer or system supplier. That said in my opinion with the increasing use of multi link suspension designs and large preloaded bushes it's getting more important to recognize and understand how each part influences the net geometry, especially if your a sports driver

DI is the mathematical explanation of the tyres (in axle pairs) ability to influence the actual chassis (i.e. the leverage the tyres actually have upon the chassis weight) this is then considered versus the way in which the chassis presents it’s tyres to the on-coming road during a yaw moment (turn). Antiroll, Springs and Shocks represent a very different chapter in chassis dynamics. The job of these components is to control the vertical load applied to any one tyre at any one time, this function whilst it's related in terms of the finished product these aspects are quite separate from DI and Inertia matching

It’s interesting reading and yep I think we should meet up soon I know what you mean though a lot of the principles and systems that under pin chassis dynamics aren’t at all intuitive. It’s great news that it’s all becoming clearer, and the good news is that there really is no voodoo involved in the subject that can catch you out it really is all just maths & science

Good point Tony, when calculating a dynamic index overall chassis mass is indeed needed in order to factor-in yaw inertia.

The stiffness of the bar is directly connected to the vertical load applied to the tire during a steady straight turn, with 100% extra stiffness on the front axle and 50% extra on the rear it's pretty clear that TRD are trying to make the front tires saturate (or reach their grip limit) before the rear and so giving rise to an under steer or push departure. It's probably been done to counter act a natural oversteer characteristic in the chassis and to give the driver more confidence by being able to find the grip limit on the front axle with plenty of rear axle grip left in hand

Go right ahead

Yeah

Dynamic indexing or Inertia matching as it's sometimes known has been around almost as long as chassis have but it's value has only really ever been appreciated by those we tend to think of as the better chassis designers in the world, for instance both the E36 and E46 Bmw 3 series both have a DI of 1.00 (or as near as damn it) when you add an average weight driver. DI is calculated knowing the overall mass, the distance between the front axle and the centre of gravity and the distance from the rear axle to the centre of gravity. By knowing these lengths you can calculate the chassis "instant centre" and DI is an expression of the length between "the length between the rear axle and the centre of gravity" and "length between the instant centre and the centre of gravity" Please do bare in mind though that whilst having a good DI is really good news for a chassis it's not the be all and end all, you CAN fix a bad DI with enough chassis set-up

A major thorn in the side of a chassis dynamasist is the human element, the driver (even if it happens to be the dynamisist themselves). Often you'll hear people say things like "handling is a very personal thing" it’s true!. But the fact of the matter is that humans are often quite unreliable when it comes to actually assessing a chassis's performance. Often drivers will base there assessment purely on emotion "it felt nervous" or "it doesn't give me confidence" competitive racing cars often feel near on un-drivable and snappy at the limit to an amateur, but does that mean the chassis is bad? The way I understand it is that the idea behind a good drift car is to be as linear as possible on and around the grip limit, to saturate it's rear tires before the front to create an oversteer departure and most importantly to be able to create and decay huge body slip angles without greatly influencing the direction of travel. So with that in mind I'd say that when we talk about the practice of drifting this human feedback problem will be amplified, because whilst we can data-log every other aspect of chassis's dynamic movement in order for us to check up on and/or verify what a driver might be reporting the one thing we can't easily measure is body slip angle. We can guess at it by looking at yaw rate gain vs. wheel speeds vs. steering wheel angle vs. estimated surface grip co-efficient, but we can’t easily measure it. So whilst with the right experience I think you could build a technically brilliant drift chassis on paper purely through hardcore math, making a car which your driver can really exploit and one that they can control instinctively will invariably require some track time, if for no other reason than that there are no mathematical equations that I know of (no matter how long) that can predict human emotional responses

It's very subjective, the lower the Dynamic Index the more agile and lively the chassis tends to feel. It's a very subjective thing but it's powerful, history suggests that drivers emotionally identify cars with DI's between 0.90 and 1.10 as cars that handle well. This is because the car with a DI of 1.00 tends to handle in a linear and predictable fashion, so when at the grip limit tend to behave in a way that’s intuitive to the average driver therefore the required steering corrections or throttle/brake responses seem to come "naturally". The best technical summary I can give is to say that with the chassis at the grip limit, if you were to experience a variance in yaw demand from the front wheels (perhaps encountering a road feature that increases vertical load on the tire) this would "increases rear slip angle" if the DI is lower than 1.00 but the same action "reduces rear slip angle" if the DI is greater than 1.00.... I hope that makes sense Regarding family cars, most tend to be a little higher than 1.00 and tend to get a lot more so as they are loaded with passengers or luggage. You would be amazed how massively far out some cars are. For instance the classic VW beetle which believe it are not has a weight distribution not too far away from 50/50 actually has a DI of 0.48 and I think it's a well know fact that an un-modified one is just straight up dangerous when approaching the grip limit This is usually as a result of a project going to the design house before it goes to the dynamics engineers.

Sam@tdi But believe it or not, it is entirely possible to make a car too snappy by making it too light for its wheelbase. This effect is addressed as part of a dynamic indexing process Sam@tdi The 'indexing', is it actually possible this could form a calculation from all the variables then call this data 'a matter of fact' for the track and dynamics.... in other words in your opinion how accurate do you feel this data is in real terms. Yes dynamic indexing is actually explainable with an equation and it is possible to make a dynamic index calculator that works reliably. The thing to bear in mind is that having a car with a dynamics index of 1.00 (perfect) simply means that you are not forced to follow any particular direction when setting up the many other aspects of the chassis and suspension. Having a good DI gives you choices as to how to approach the set-up

Tony firstly I think drifting is to chassis dynamics, what drag racing is to power tuning! The single most amazing thing I've found whilst studying chassis dynamics is that although much of the subject isn’t naturally intuitive it IS all actually an exact science and it IS all totally provable more over calculatable. The problem as I see it is that few brilliant people who harbour the required knowledge and or talents are busy earning a very good living off of the back of this knowledge and are therefore (understandably) reluctant to share there secrets with up and coming generations of engineers. Can you give me an example of what you mean by "new school Drift command" it's just I fail to see what people are doing in drift cars now that drivers weren’t doing in pre-war F1 cars during the 30's

Imagine shaking the gravel outta all that bodykit The late NSX is a superb chassis, one of my favorite driving cars ever!

could you stretch that average to about 85kg how are these weights attached and what do they use as weights I hope Sam doesn't mind me butting in (and my information is correct) but... With corner balancing you don't add weight unless you've a category minimum to make up to, you just have to make the most of what you've got in the car. On a pure race car you can do things like move the driver around, how the engine is mounted, where the battery is, where the fuel is but all this is a bit extreme for a road car. My understanding is you'll never get 25% of the weight at each corner and rarely 50% of the weight each side or end. The best you can hope for is adjusting the ride height at each corner to adjust that corners load through the tyre onto the road and get the car reasonably well balanced. For idea distribution the left side tyres must have the same front to rear distribution as the whole car, same for the right. IE if the car balance is 60f 40r then the left front should carry 60% of the left hand side weight. I'd say that’s a fair summary But believe it or not, it is entirely possible to make a car too snappy by making it too light for its wheelbase. This effect is addressed as part of a dynamic indexing process

In absolute terms for track precision yes, or at least ballast equivalent to the drivers weight. Bearing in mind the average driver weighs somewhere around 70-80kg you'll find it becomes more important the lighter the chassis is

It's true of almost all engines actually, once you move to air fuel ratio's richer than 14.4:1 any extra fuel particals will find no oxygen to combine with so they go through unburn't... Most modern engines can tolerate stoichiometric ratio (14.4:1) up until around 50-75% load. During the last 50-25% of the throttle pedel engines generally need the air/fuel ratio to richen too approx 12:1 (varys alot from engine to engine) at full load, the additional fuel is added purely as upper cylinder coolant. This V8 supercar phenom of "lift off over fueling" is just an extention on that theme

For what it's worth guys I was with a group of other engine tuners recently and a similar question came up. It turns out it's quite deliberate and actually all about combustion chamber cooling. Bearing in mind that the only reason to run any air fuel ratio's richer than stoichiometric (14.4:1) is to use the excess fuel as a thermal managment media these guys are simply choosing to run a very rich afr during very low intake manifold pressures (only reachable in throttle closed over run) the aim is to cool down the piston crowns and exhaust valves. It's apparently thought to enhance reliabilty over a race distance but some very experienced and highly respected people there that day think it's totally un-founded and a simple case of monkey see monkey do around the V8 supercar paddock

Ok I’ll try and shed some light on the subject, lets concentrate on the process known as corner weighting at the moment. Before we can get into “how” corner weighting is carried out I think it’s important to understand “why”. One of the fundamental aspects of chassis design is inertia matching. It‘s a given that a chassis has mass and the centre of it’s mass is known as the chassis’s centre of gravity. The ideal chassis would have a low centre of gravity, an equal weight distribution on to all 4 of its wheels and it would have a wheelbase that gives the axles the correct amount of leverage upon the centre of gravity (dynamic indexing). The process of corner weighting is to place the chassis on four very accurate scales, one under each tire. This lets us know not only the exact overall weight but also the exact balance of the chassis whilst at rest. Once this information has been gathered it’s possible to make adjustments to the chassis’s mass distribution by either moving heavy components, ballasting, or for finer adjustments it’s possible to adjust the ride height at any one corner. Generally ride height adjustments tend to be more effective at adjusting right to left balance than the fore and aft balance simply due to the lengths involved.

Hi Paul sorry I’ve only just caught up with this thread, ok firstly I think it's entirely possible that there could be more than one problem at play here. I think that with the car being lowered it's likely to be running some "tow out" on the front axle unless it's been checked and corrected recently. This as Tony rightly says will have the effect of dulling the front axle's response to steering inputs and may give rise to a "drifting" feeling. I can't give you exact figures without corner weight results but I would estimate this cars dynamic index at around 1.22 whilst this isn't actually too bad compared to most of rovers creations it would indicate to me that the chassis is a bit of a slug by design so having good front end grip will be absolutely crucial in order to provide good feel & disturbance rejection whilst the vehicle is at speed (you’d feel this effect more as you go faster). The cure for this could be as simple as making sure that you invest in some quality sport rubber for the front axle or even better, all round. PS. I wouldn't assume that the shock absorbers are "good" simply because they passed an mot, the bump test is notoriously un-reliable

Yeah definately now you've mentioned it i'll take a good look at the front of the Civic and see how much movement I can find us. My car is alot lower than stock, the rack is way way too low even in the standard type-r I think it's a legacy of the cars shopping trolley roots I don't know if you'll agree but just reading back over this thread I think it'll be easier for some people to follow if we try to resist the temptation to use abbreviations like COG, ARB, TRE, (on) etc... even if it does make things a little longer

I agree on adding some caster angle, as it happens that is exactly what Honda themselves did when they face lifted the EP3 Civic after almost every motoring journo slated the Type-R's lack of steering feel, i've had a look at doing it in the past but unfortunately it's not going to be straight forward with my current set-up. Regarding the TRE's, the track control arms were running close to 45degrees at normal static ride height. It was purely that the arm was effectively shortening alot during a bump event that was causing the problem. The arm's are now operating at a much more shallow angle now and the problem is all but solved, better than the standard car i'd say