Sam@TDi

It's important to understand that as a driver applies throttle or brakes to the chassis during a turn the chassis will react in an incredibly dynamic way so it's not easy to talk about lift off over steer with sweeping statements or "rules of thumb" as the science of the subject is so massively complex However it's my opinion that having a dynamic index close to 1.00 makes these kinds of control based maneuvers much easier for a driver to initially judge, measure and then control. A good balanced chassis with a DI close to 1.00 is often referred to by drivers as being "very adjustable" at the limit and I think thats a perfect way to describe the effect.

Liftoff over steer is a trait common in almost all chassis designs, it's almost impossible to totally eliminate it from a chassis. It happens when the driver turns the chassis (add's yaw) then as the chassis has loaded up and begun to produce lateral acceleration the driver changes the weight balance of the chassis. Often this is done by lifting throttle suddenly hence the name "lift off over steer".... this action throws the weight distribution forward, this shift of ground pressure to the front removes valuable ground pressure from the rear axle and promotes a spin departure Skilled drivers can learn to manipulate this to great effect, a chassis dynamisist can in turn help by making a chassis's lift off over steer habits as progressive and predictable as possible. Many motorsport drivers lift off at corner entry to help a chassis gain an unnaturally large slip angle, you can see it very obviously in the sports of drifting and rallying The bad news for the uninitiated masses is that often their first taste of car control comes whilst they're having an accident, lifting the throttle tends to be an instinctive reaction to panic in a "normal" driver, learning not to automatically lift the throttle is normally the first thing taught in an advance driving school such as police driver training or motor racing schools

Will do don't remember a Peter specifically but there were 15 of us and I knew only a couple of names

Very interesting subject, had some cracking conversations about this during the lunchtimes at the EFi university course last year which was held at Hertford uni quite a few of the people on the course were in fact lecturers at the uni and had some interesting views as to the way forward with I/C engines

Would make a bit of a mess of the forum if the question happened to be engine based don't you think?

It's unlikely you'll ever get satisfactory results from basic camber bolts on the track, I always use shims on track once the geometry has been decided upon. They can handle the G's normally, but it's the curbs that make them move.

Ooo totally missed this thread, thank you all for your kind words guys I think it's a good idea, the only thing a can't garauntee is how long it'll take me to reply to any particular question. I get on the forum whenever I get a second but work and social life come strictly first in my book, so as long as people can bare with me it sounds fine I don't know everything my knowledge has its limits, I learn new things every day but I'll try to help wherever I can

Welcome to geometry

Tony's right this is a huge topic, especially if you consider dynamic toe effects as the suspension moves or is loaded with forces. But to put it simply... Front axle: Positive toe (toe-in) = Livens the axle up Negative toe (toe-out) = Calms the axle down The exact opposite is true at the rear axle... never toe-out the rear axle!... unless your building a grasstrack car

You are absolutely correct, the ability to influence weight distribution by adjusting ride heights is often quite limited. The only real way to make large adjustments is to move heavy items like the driver, fuel tank, water rad's, fire extinguishers... or in extreme cases engines I use a chassis DI predominantly as information, the moment of rotation must be calculated after ascertaining some critical measurements

It's a brute force way of pushing the roll axis rear ward in the chassis... it strikes me as a typically American approach I'm afraid, thats not to say it won't work reasonably well though ... as long as you run a good sidewall profile at the front with reasonably low pressure

I assume were talking 1000lbs/in springs I would only ever use rates like that in a dedicated circuit racing application, normally where ground effects are demanding that surface seperation be kept totally constant. You should perhaps consider the handling ramifications especially with regard to the limit grip break away characteristics and even straight forward driver physical fatigue. Also for whats it's worth I think 1000 both front and rear could be a bit tricky to balance, we normally stagger the rates on the NSX 1000lbs/in might seem quite stiff but believe it or not I have actually had to use a lot stiffer rates in the past

No offense taken you can call me smart all you like

Can't imagine why these things are as simple as it ever gets

Ok that makes alot of sense, when a system is stiffened it's natural frequency rises. If you drop the spring rates a little the car will need less input

Hi H.I.T the spring rates your running are getting close to the top of the pressure range that I would recommend for that chassis, it must be quite stiff. There is an awful lot of science in damper manufacture, and to make an educated purchasing decision you either need to be a chassis dynamisist or take good advice. As I'm not at all familiar with the nature of the Daiyama shocks I really can't comment about them, good or bad. I think it's vitally important when changing the tune of any car to start with a real problem and then work towards a solution. With this in mind what is the problem that you're hoping to fix?

now thats what I'm talking about!

Ok no problem

It measures EVERYTHING live, including the chassis frame check This friday i'm here but next friday i'll be on my way to the Nurbergring for the weekend

Well yes, it tells you the exact wheel base on each side of the car and from corner to corner... so instantly shows up any difference in front to rear track width or stagger across either front or rear axle. If we know what the cars original wheel base should be we can return it to there and start again. For what it's worth the vehicle data base which snap-on supply on the Arago is unbeleiveable, I doubt we'll be caught out for factory specs too often

It's not totally arbitrary but the problem is that squat and dive and the adjustments there-of cross over the blurred boundary between chassis dynamics and geometry. For instance, in some situations it may be preferable to limit the amount of "squat" during acceleration in order to stop the geometry changing undesirably and limiting available traction... in the same breath limiting the squat will also have a direct effect on the cars dynamic weight distribution during acceleration, so in this respect limiting the squat may cause a lack of weight transfer which could again limit traction during acceleration and totally counter act the gain from the geo side. Whether the gains from the geo side out weigh the losses from the chassis dynamic side (or visa versa) is something that would need to be quantified either by accurate track testing and data logging or alternatively inside a good computer suspension dynamics simulation program. Most people simply make a moderate adjustment and then drive, this method is only as accurate as the drivers feed back... simple as that

Cool glad that made sense. For what it's worth the problem is totally fixable, the Top Fuel regulations frustrate me massively :worried_anim: It's like the rule makers at the NHRA are a bunch of redneck technophobes or something, some of the rules are as follows; Competitors must use a Hemi derivative engine or custom built racing version but it must be to the original hemi design (1950's) No electronic engine management allowed, i.e. Mechanical fuel injection and locked ignition advance at 50degree's No electronic clutch management or launch control, i.e. must use dozens of complicated timed hydraulic actuators and multi lever clutch assembly's Because of these arcane rules the only electronics allowed on the car are for data logging purposes which has now become the single most important area of the entire sport, with each 1/4 mile run costing well over £2000 even if nothing breaks! learning as much as possable from run to run is crucial. Personally I say take the brakes off the development, let the mechanics have their head and the sport will improve. We would see multivalve dohc engines straight away for sure, the electronic engine management would be able to control some injectors for methanol and others for nitro meaning that the nitro percentage could be altered throughout the entire time the engines running - this would seriously improve reliability. The engine management could quite literally cure the problem of hydraulic'ing the motor by monitoring individual cylinder egt's and when it senses a non-fire by the temp drop it could tell the injectors for that cylinder only to miss a beat... I'm not going to even go into the serious benefits that mapped ignition advance would bring

Nitro engines Ok, to be competitive in Top Fuel these days you need to be running over 90% Nitro (that is 90% Nitro &10% Methanol)... One of the reasons Nitromethane is such a powerful fuel is because it's stoichiometric ratio is around 5:1, this means that the chemically perfect (or Lambda) ratio for combining Nitro and atmospheric air is 5 parts air and 1 part pure liquid Nitro, to give you some idea about how rich that is the stoichiometric ratio of normal road unleaded fuel is 14.7:1 If you run internal combustion engines at stoichiometric or lambda 1.00 the lack of any excess fuel in the upper cylinder produces a harsh and hot environment (although the lack of unburnt fuel is great for emissions). In order to keep combustion “controlled†and reduce detonation probability we deliberately over fuel any engine under high load conditions such as full throttle, often in petrol engines looking for 12:1 or 11:1 The same applies to a nitro engine so when running extreme loads, extreme rpm’s, extreme boost pressures and compression ratios the teams need to really richen these engines up in order to prevent the dreaded detonation. This results in Top Fuel engines regularly running afr’s as low as 3:1 or even 2:1… in either case that is an awful lot of liquid Nitro to ignite, especially as the stuff is pretty much inert unless pressurized. The problem comes when the 2 spark plugs and the 2 50amp magneto’s fail to start a fire, the piston has the almost impossible job of trying to expel all of that liquid nitro through one exhaust port. Top Fuel dragsters run ridiculous camshaft duration and what normally happens is that a lot of the liquid nitro stays in the exhaust header then is sucked back into the cylinder through the exhaust port during the valve overlap period for the next induction stroke. This then leaves you with a cylinder totally over full with liquid Nitro for the next compression stroke, the engine will inevitably attempt the compress the mixture and when it does………… Basically the unstoppable force meets the unmovable object!

Well I can't really tell you exactly what that guy was doing, but it is normal engine building practice to apply different types of surface finish to different components, mostly to control or manipulate the speed or severaty of the bedding in proceedure between metal to metal surfaces. Too aggresive with the surface finsh and you reduce component life, too gentle and it's possable for surfaces to "glaze" which is to form a thin ultra hard shell which ultimately won't wear on a microscopic level and therefore will never seal properly. It's common practice when building short life "maximum effort" engines for motorsport to apply very aggresive surface finish's to cylinder bores and alike, this has the effect of reducing the engine running-in time to only a few laps rather than 1000 or so miles required for a normal road engine. The trade off of course is that the involved componants such as piston rings lose maybe a third of there life span during those first "running-in laps" and so will be up for replacement sooner.

Can you elaberate a little on what you mean by scoring? We need to "hone" the cylinder bores so that the surface finish retains oil, but that surface finish is far far removed from a scored surface, we're talking a regular pattern only microns deep We'd actually look for a very smooth surface finish in the combustion chamber it'self to promote fast flame travel and discourage carbon build up and so any resulting hot spots.